Study into changes in case mix for adult hospital admission in a medical specialties’ in Colchester 1991 and 1995: Using Severity of Disease Measurement. by Gregory A. Benn-Ohikuare Department of Public Health and Epidemiology The University of Birmingham Medical School Dissertation Submitted to the Faculty of Medicine of the University of Birmingham for part of the Master in Public Health and Epidemiology; (M.P.H)
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Case Mix in specialist adult hospital admission using APACHE score, (1997). Master in Public Health & Epidemiology (MPH), University of Birmingham Medical School
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Study into changes in case mix for adult hospitaladmission in a medical specialties’ in Colchester 1991 and 1995:Using Severity of Disease Measurement.
b y
Gregory A. Benn-Ohikuare
Department of Public Health andEpidemiology The University ofBirmingham Medical School
Dissertation Submitted to the Faculty of Medicine of the University of Birmingham for part of the
Master in Public Health and Epidemiology; (M.P.H)
June 1997
33
CONTENTS
ABSTRACT ..................................3
BACKGROUND AND INTRODUCTION ................7LITERATURE REVIEW ..........................15
Case Mix and Measurement of case mix severity ...............................15What are the variables that goes into case mix ....................................16What are the benefits of case mix 17What are the different measures of case mix........................................17What causes variation in case mix .....25What are case mix limitations 26 Studies conducted on case mix and theirimplications 27
Study which looked at how case mix could be analysed using different types ofmeasurement methodology .........27 Study which examines case mix variationsusing disease andseverity ofillnessmeasurementtechniques 29 Study which examines case mix differencesbetween teaching and non-teachinghospitals 30
SUMMARY OF THE LITERATURE, HYPOTHESIS AND PUBLICHEALTH IMPORTANCEMETHOD 35
Patients and Method ...................35Selection of study cases and Data collection 35
Sampling Methods 36How the pilot study was conducted 38
Variables that measures the severity of disease
at admission ...................42 Measurement of case mix severity of
patients illness .................43
RESULT ..................................... 44The distribution of patients admission by genderin 1991/92 and 1995/96 44The distribution of patients sample cases by year ................................46The distribution of patient case notes for analyses ...............................47Case note analyses findings ...........47
DISCUSSION ..................................52Main Findings 52The implications of the results 52The limitation of the study ...........54 Explanation of the result by evaluating therole ofchance, bias, and confounding in the study ........................................55Criticism of laboratory investigation effect on study.. 60Comparison with previous study .........61
CONCLUSION 64Implication to Public Health ..........65Lessons learnt 67Recommendation for future work .........68
BIBLIOGRAPHY ...............................69
APPENDIX ...................................71Appendix 1 ............................71Definition of sickness at admission variables 71Appendix 2 ............................73Statistical calculation formula used ...73Appendix 3 ............................ 77
The ten individual diagnostic categoriesused in the study derived from one primaryorgan system .....................77
Appendix 4 .......................... 78 Characteristics of severity measurement
system 78Appendix 5 ........................... 79
Data scoring form 79Appendix 6 ........................... 83Data recording form ..................83Appendix? ............................ 87Method applied for the calculation of the
mean difference for APACHE II score andcomponent parts………………………………………… . …… .87Appendix 8............................. 89
Documents, letters and Excel Spreadsheets...................... 89
3
ABSTRACT
Objectives
1. To analyse the Severity of illness in 1991 and 1995.
2. To compare the differences between 1991 and 1995.3. To compare differences between 1991 and 1995
with previous study in 1985 and 1990.
4. To describe the trend in severity of illness over 10year period 1985 and 1995.
Design
Retrospective cross-sectional case note study of admissions to a medical speciality in Colchester General Hospital in 1991 and 1995.
Setting
Emergency admissions to an acute medical bed in Colchester General Hospital in 1991 and 1995.
4
Subject
2500 admissions of patients suffering from acute chest disease, who are 65 years old or more, whose admission and discharge diagnosis was recorded strictly as pneumonia; asthma; or bronchitis.
1991: Pneumonia, asthma and bronchitis : ICD 9 codes 480 to 4961995: Pneumonia : ICD 10 codes J18.0 to J18.9
Bronchitis : ICD 10 codes 120.0 to J20.9Asthma : ICD 10 codes J45.0 to J45.0
Method
Case mix severity was measured using Acute Physiology and Chronic Health Evaluation (APACHE11). 3
Results
The findings from the result was that mean APACHE II score rose from 15.63 (SE 0.54) in 1991 to 16.33 , standard error (SE 0.54) in 1995. The difference in the distribution of APACHE II scores by Two-Sample t-Test was found to be statistically not significant (P<0.10).
The mean age difference in 1995 was 1.27 higher thanin 1991. This was found to be statisticallysignificant (P<0.01).
The mean difference of the acute physiology score was 0.61 higher in 1995 than in 1991. This was found to bestatistically not significant (P<0.10) .
The mean difference of the History of Chronic status scorewas 0.11 higher in 1995 than in 1991. This was found to benot significant by the Two-Sample t-Test (P<0.10)
Discussion
The main finding from this study was that case mix severity of illness at admission, using APACHE II score, was slightly higher in 1995 than in 1991 and the mean difference was statistically not significant (P<0.10). However, when this is compared to previous study in 1985 and 1990 result, differences found in the mean APACHE score was much higher in 1985 and 1990 than in 1991 and 1995.
In view of the fact that the age category of the patientsinvestigated in this study were elderly, the cause of themean difference in the overall APACHE II score could be associated with several factors such as gender
differences, age, varying hospitals admission policy, increase threshold in admission, patient presenting illness too late and or increase in the incidence of severe illness in the community.
However, it is difficult to link any of the above causal suggestions to my result without setting out the design of the study in such a way to incorporate these attributes for measurement.
6
Whatever the reason, my study has provided a reasonable follow-up investigation to support the continuing concernsfrom the GPs (General Practitioners) and the hospital Physicians that admission of patients into acute medical bed is becoming difficult, emergency is going up and case mix is in the increase. However, the increase in the case mix has to be weighted against the fact that, the observeddifference in the mean APACHE 11 score was found to be statistically not significant (p<0.10).
Conclusion
Despite the increase in the APACHE II score in the measurement of case mix severity of illness at admission for acute respiratory condition, the difference in the score was statistically not significant (P< 0.10) . This meant that one cannot reject the hypothesis that there isno difference between 1991 and 1995.
7
BACKGROUND & INTRODUCTION
Population change :
Essex Rivers Health care (NHS) Trust catchment area of which Colchester is one includes Tendring and part of Braintree. Colchester is the fourth largest district inEssex. The mid-1993 population estimate for the Boroughstands at 149,100 representing 9.6% of the county's population. Only Southend-on-Sea, Basildon and Chelmsford are larger (10.7%, and 10.0% of the county'spopulation resceptively).
Between 1992 and 1993, the population grew by 500. Although this is a comparatively small increase, over theperiod 1991 to 1993 as a whole Colchester was nevertheless the second fastest growing district in Essex, with 3,200 more people than in 1991, an increase of 22%.The Borough is one of only a handful of district in the South East region whose population grew at more than double the regional rate between 1991 and 1993 (0.8%).59.4% of the increase in population 1991 - 1993, or1,900 people, was due to migration (more people moving into the Borough to live than moving out). This is the third highest gain due to migration in Essex after Southend-on-Sea and Tendring (5,200 and 3,200 people respectively).
There are now almost 11,000 more people in Colchester than there were in 1981, an increase of 7.8%. Only Chelmsford and Tendring have experience bigger population increase than this (16,000 and 14,000 peoplerespectively) 1.
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Population Structure
The 20-24 years age group is the largest in the Borough, at 13,100 persons in 1993. This is followed bythe 25-29 years age group, at 12,500. Over one-sixth ofthe Borough's population falls into these two age groups (17.2%).
There are 37,700 children and young people aged under 20in the Borough, over a quarter of the population (25.3%). Over a fifth are aged 30-44 (31,600, 21.3%), a further 29,400 (19.7%) are aged between 45 and personable age, and 25,100 (16.8%) are pensioners over the age of 65 years.
Although the numbers of men and women are quite evenly balanced in the population asa whole, this differs with age. Up to age 44, there are more men than women in the population, particularly amongst 20-29 years old. However, this changes from age 45, with women making up 53.8% of the population overall.The population of women continues to rise through the older age groups.
Colchester's population is 'ageing'. In 1981, the 15-19 years group was the largest at 12,100 persons, and in all, almost a third of the population were aged under 20(29.9%, 41,300 persons). Since then the numbers of
children and teenagers have fallen by 3,600 (8.7%), witha larger fall of 21.5% in the numbers of 15-19 years old. This has been accompanied by significant increases in the older age groups. 1
l1 /,
North Essex Health Authority Geographical location
Population Structure of Colchester Borough 1993 (Mid - Yearestimates) :
10
Elderly Population
There are 25,100 people of pension-able age (women from
age 60, men from age 65) in the Borough, with over a third of these aged 75 and over (9,700 people). This
figure is 2,500 higher than in 1981, an increase of 11.1%.
The size of the pension population is increasing faster than the size of the population as a whole. Between 1981 and 1993, the total population increased by 7.9%, 3.2 percentage points lower than the increase in the pensioner population. Between 1992 and 1993, there was anincrease of 200 (0.8%) in the population of pension age, almost three times the increase in the population as a whole (0.3%).
There are marked differences within this broad age group.There has been little change in the 65-69 years age group, while the 80 and over age groups have increased consistently both over the longer period and more recently. Between 1981 and 1993, the 80-84 years age group increased by 39.1%, whiles the 85 and over group increased even more dramatically by 60.0%. The increase in the 85 and over group was the largest percentage increase in the Borough between 1981 and 1993.
Between 1981 and 1993, the size of the total population aged 75 and over increased by 27.6% (2,100 people). Thisis a higher percentage increase than that experienced byEngland and Wales as a whole since 1981 (22.7%).
Since 1991, the 80-84 and 85 and over age groups have increased by 6.7% and 9.1% respectively. The 75-79 yearsgroup, although increasing by 7.9% over the longer period, has fallen back recently, decreasing in size by 8.9% between 1991 and 1993.
11
Almost two-thirds (64.9%) of the population of pension age are women. This percentage increases with age until at age 85 and over three-quarters of the population are women. 1
Implications
For the future, the continuing increase in the Borough's population and changes in age structure is bound to have a major implication for housing and other services, and local economic expansion. In addition to a general demandfor housing, infrastructure and employment provision, keychanges in population structure and distribution will have specific implications in particular to the health needs of the growing numbers of elderly people
The stimulus to my interest in the severity of illness at admission was given in a previous study which looked at providing an objective evidence to refute or support the anecdotal evidence from hospital physicians and GP's (General Practitioners) that , to gain admission to a hospital bed, a patient in 1990 would have to be more severely ill than in say 1985. Having looked at the evidence by using APACHE II classification system to scorethe severity of sickness at admission to Colchester Hospital for patients age 65 years old and over in 1985 and 1990 , they found that the mean APACHE II score for
1990 was statistically significantly higher than in 1985. 2
12
Although, they found that there was a statistical significance between the mean difference between 1985 and 1990, they concluded that this result does not confirm that there is a link between the level of severity of sickness at admission and the difficulty in gaining admission into hospital beds in 1985 or in 1990 but that, they have been able to provide an objective data for the concerns raised by the GP's and hospital admission Physicians.
My interest, therefore, is to conduct a follow-up study tolook at whether there is a continuing anecdotal evidence of case mix severity of illness at admission in ColchesterHospital in 1991 and 1995 and also whether the APACHE 11 score methodology could be used to provide the evidence.
Measuring how sick a patient is at the time of hospitaladmission is a prerequisite for such studies. In this study report, I present the result of measuring the severity of illness at admission for three illnesses: pneumonia, asthma, and bronchitis, using APACHE II score classification system.
13
My choice of conditions for this problem has been based onthe previous study conducted by Irwin D, et al (1993), which stated their rationale for the choice of those conditions as follows “the effect of a squeeze on medical beds could be to increase the threshold for a decision to admit. For some conditions (e.g. Coma or haematemesis ) there is little option but to admit, for other conditions particularly chest problems the GP and admitting doctor have to make a judgment about whether the patient is ill enough to need inpatient care, and these judgment will be affected by the number of beds in the hospital". 2
The other stimulus was due to the perception held by the hospital physicians that emergency admissions is onthe increase, and that admission of acute patients intomedical bed is becoming difficult and case mix is on the increase and that there is the possibilities, that GP's (General Practitioners) are sending patients frequently to hospital for admission. If this is the case, the threshold for admission into acute medical beds for severely ill patients will be low.
14
Against this back drop, I was intrigued by the APACHE II system, although designed to stratify and predict severity of illness in intensive care unit (ICU) patientsin terms of their likelihood of death. 3 It has been foundto perform well in other 34 diseases categories in a study which included 5815 patients in 13 hospitals in U.S.A. The APACHE II system makes use of laboratory, physiologic, chronic health data, age and the Glasgow Coma scale. The more abnormal the values, the more weightascribed to the abnormality. The APACHE II system has been shown to predict reliably ICU mortality. Thus, it isa physiologic severity measure that was appropriately validated using a physiologic end point death for ICU patients ' 4
Therefore, the aim of my retrospective cross-sectional case note study is to examine the Null hypothesis that there is no difference between 1991 and 1995 in the severity of illness at admission of patient with acute chest conditions into Colchester General Hospital by using APACHE H classification scoring system .
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LITERATURE REVIEW
Case Mix and Measurement of Case
Mix Severity
What is Case Mix :There are various definitions of case mix and different types of ways of measuring case mix complexity. Case mix is sometimes defined as thevector of illness characteristics and consequentcare requirements of a single patient or group of patients seeking treatment. Concepts such as diagnostics and severity, type of indicated treatment, socio-economic status, physical dependence and age may all be regarded as part of
case mix. 5
Case mix systems are assumed to be entirely exogenous, that is they measure patient characteristics that are independent of the place of treatment.
But in practice, this assumption is not always justified. Recorded diagnostic data give an incomplete picture of the need for care and we usually have to assume treatmentrequirements from actual treatment given. Where 'actual treatment differs from' appropriate treatment measured case mix
will differ from true case mix. When the definition of case mix is based on primary diagnosis, primary diagnosis is recorded using coding schemes. These coding schemes provide a classification of conditions of morbidity and mortality for statistical reporting purposes as well as information retrieval.
16
Other definitions of Case mix is that they are a means of constructing and applying classificationscheme which comprises subgroups of patients possessing similar clinical attributes and outpututilisation patterns. 6
What are the variables that goes into Case mix:
The variables that goes into case mix falls
into two broad groups: indirect or proxy variables and direct patient-related
variables.
Indirect or proxy variables includes such things as hospital bed size, assets per bed, number of facilities, services offered in terms of hours of nursing care, medications and laboratory tests, other hospital characteristics such as surgical complexity and extent of surgery performed.
This involves relating the demographic, diagnosticand therapeutic characteristics of patients to theoutput they are provided so that cases are differentiated by only those variables related to the conditions of the patient (e.g., age, primary diagnosis) and treatment process (e.g., operations) that affect their utilisation of the hospital's facilities. 7
Direct case mix variables is typically based on diagnostic classifications of hospitalised patients.
17
What are the benefits of Case mix:
The partitioning of patients into groups on economic grounds, for certain applications in patient care monitoring, budgeting, cost control reimbursement andplanning is seen as a benefit. Whilst partitioning into groups based on diagnosis or ranges of diagnosesalone, has benefits in terms of uniform reporting of descriptive statistics about a population. It is not sufficient for defining cases with respect to output utilization only. Other variables such as surgical procedures and age of patient in conjunction with diagnosis are necessary to describe adequately sets of patients with similar utilisation patterns of inpatient facilities. 6
What are the different measures of Case mix :
There are several different methods used for quantifying case mix. They fall into two major sections. Firstly, there are methods which are based on diagnosis classification system. Secondly, there are methods which are single dimensional measures.
Diagnosis Classification Systems:
These provides alternative methods of defining and classifying the
multiple types of cases treated by the hospital. Theyare created by aweighted aggregation of individual cases. Their importance is based on the fact that diagnosis is a hypothesis regarding the nature of the patient's illness, which contains four elements: aetiology, location, manifestation, and severity
18
In view of the fact that diagnosis is such a focal point in the physician's interaction with the patient, diagnosis classification system provides the means of establishing the relevant technology ofcare and, hence, the types and levels of resources required to treat the illness. For this reason, diagnosis classification system was developed to measure hospital output in such a way that it is used to group patients according to similarities anddifferences in their diseases.
The diagnosis classification systems used for measuring case mix are ICD's (International Classification of Disease) currently up to
version 10; Disease staging; Diagnostic Related Groups (DRG's); Hospital Resources Group (HRG's); OPCS 4 Procedure Codes; Read codes; Patient Management Categories (PMC); and Patient Severity index (PSI). 8
ICD's (International Classification System): Many versions of the International Classification of Disease (ICD) have been produced over the past years. The most recent version of the classification system is the ICD-10, which was published in 1993.
ICD-9-CM, which was a modification of ICD-9 version (1977); was published in 1978 and stayed in existence until 1993, when it was replaced by ICD-10.
19
ICD-9-CM has similar characteristics in most areas to other previously published ICD's. It was produced for clinical modification. However, it hasmore codes and more precision than those needed only for statistical groupings and trend analysis. It was a classification system for disease, injuries, impairments, symptoms and causes of death, It was developed to classify morbidity and mortality information for statistical purposes and to index hospital records by disease and operation for quality assessment purposes. Therefore ICD-9-CMis better suited to the purpose of case mix measurement than previous nosological systems.
ICD-9-CM contains 17 broad classifications that represent aetiology, timing, and location of disease, as well as symptoms, signs, and ill-defined conditions. Each of these classifications is broken down into specific clinical entities, plus residual groups. The scheme includes 10,171 categories. Although, ICD-9-CM classification system is extremely finely divided and its specificity offers a great deal of flexibility, there are problems with it in terms of inconsistentcoding criteria. Other problems associated with theapplication of ICD-9-CM to case mix measurement is that it includes both symptoms and diagnoses which are in-fact different in terms of clinical
characterisation of the patient and should not be considered.
20
The implication of this is that successful treatmentof a symptom does not distinguish between symptomatic relief and cure of the underlying cause of the symptom. Whereas, on the other hand, successful treatment of a disease, implies a greatercontribution to the patient's welfare than just symptomatic relief. The fact is that, a case mix measurement scheme which is not sensitive to the distinction between symptoms and disease would not discriminate between two hospitals differing in diagnostic acumen. 8
Disease Staging system:
The purpose of disease staging is to provide a more completespecification of the patient's illness so that any application requiring a case mix measure will not confound differences in the patient's condition withdifferences in the therapeutic response.
Staging refers to the measurement of the severity of the patient’s condition at any given point Information on severity is important because it relates to the patient's prognosis (the expected outcome of illness episode) as well as to his use of medical resources, admission to the hospital, length of stay and the use of ancillary
services. Disease staging system has been found to be well suited to application for large scale case mix measurement purposes, and can provide a more detail clinical assessment of the type of cases being treated in the hospital. 8
21
Diagnostic Related Group (DRGs) System :
Diagnostic Related Group (DRGs) was developed to relate the demographic, diagnostic, and therapeuticcharacteristics of patients to the output they are provided so that patients are differentiated by only those variables related to the condition of the patient (e.g., age, primary diagnosis) and treatment process (e.g., operations) that affect the utilisation of hospital facilities. The developers of DRG's reject patient groups defined on the basis of primary diagnosis alone because they felt that such groups do not show sufficientlyhomogeneous utilisation patterns.
One of the most important draw-back to DRG's is that the system did not define "clinical meaningfulness". Rather, clinical meaningfulness and the appropriate degree of variance reduction were judged by the physician consultants, which meant that another group of physicians might define DRG's differently.
22
Patient Management Categories (PMC) system:
Patient Management Categories (PMC) was designed to address three problems. (1) inconsistencies in the classification and coding of disease arising out of dependence on the International Classification of Disease and its variation; (2) inadequate attention to the diversity of appropriate types of h hospital stays with diagnostic categories; and (3) lack of prior clinical input in defining appropriate management of homogenous groups of hospitalised patients. 8
Patient Severity Index system :
The purpose of the Patient Severity Index (PSI) system is to measure the severity of the patient's illness, so that the performance of the physicians with respect to prescribing appropriate length of stay could be improved.
The PSI is based on clinical data contained in themedical record and has seven component : (1) stageof disease, from pre-clinical to life-threatening;(2) severity of complications ; (3) concurrent interacting conditions which are likely to affect the hospital course of the illness; (4) level of nursing care required; (5) performance of
procedures outside of the operating room, from non-invasive diagnostic procedures to emergency life-sustaining procedures performed in the emergency room; (6) rate of response to therapy; and (7) completeness of response to therapy. 8
23
Single Dimensional Measures :
Single dimensional measures consist of the following Scalar case-mix index, Information theory index and the Acute Physiology Chronic Health Evaluation (APACHE) II. 8
Scalar case-mix index :
Scalar case-mix index is characterised by three components: a diagnostic classification scheme for grouping the patients treated by the hospital, a weighting scheme for valuing the manygroups relative to a single characteristic. 8
Information Theory index :
The purpose of the information theory case mix is to describe the inequality of the distribution of the mix of cases either within the hospital system, or within the hospital itself. 8
24
Acute Physiology Chronic Health Evaluation (APACHE) II :
APACHE II is a severity of disease classification system. APACHE II uses a point score based upon initial value of 12 routine physiologic measurements, age, and pervious health status to provide a general measure of severity of disease. APACHE II scoring index can be used to evaluate the use of hospital resources and compare the efficacy of intensive care in different hospitals or overtime.
APACHE H system provides weightings for 34 potential physiologicmeasures, the sum of which yields an acute physiology score (APS).
This weighting system is based on a scale of 0 to 4, as illustrated by the following weights assigned to variations in serum pH. 9
Weighted Score pH Range
+4 <7.15
+3 7.15 - 7.24
+2 7.25 - 7.32
0 7.33 - 7.49
+1 7.50 - 7.59
+3 7.60 -
+4 7.7 or >
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The APS is determined from the most deranged (worst) physiologic value, e.g., the lowest BP (blood pressure) or the highest respiratory rate, during the initial 24 hr's after ICU admission. The 24hrs time period ensures that all pertinent physiological values are available, and clinical judgement ensures that each value is legitimate.
APACHE II is said to be reliable and useful meansof classifying ICU patient's and for comparing the success of different treatment programs. 9
What causes variation in Case Mix :
Several factors have been found to contribute to the variation in case mix in hospitals. Factors that may influence cross sectional hospital case mix complexity and variations include the extent to which illnesses are diagnosed and treated, whether treatment occurs in hospitals or in other health care settings, and modes of hospital treatment ( e.g., surgical versus non-surgical). In addition, the distribution of cases among hospitals may be influenced by inter-community patient border-crossing and by the extent and types of competing hospital and other health care providers within communities. 7
26
Other factors identified which causes variation in case mix are listed as follows: resource need; hospitals with an approved residency program ;hospitals with medical school affiliation ; hospitals who aremembers of the council of teaching hospitals; hospitals with funded research ; hospitals who areprivately owned ; occupancy proportion ; outpatient visits per admission ; proportions of patients covered by health care insurance ; proportion of patients by hospital medical specialities; health district per capital income ;number of short term beds per 1000 population in district general hospital ; and the proportion of general practitioners in the health district area.7
What are Case mix limitations :
The limitation of case mix is centered aroundseveral factors. Firstly, case mix measurement is dependent on the adequate classifications,which allows homogeneous case mix grouping of patients. The ability to obtain homogeneous case mix groups of patients is dependent on several factors, some of which are reliant on patient’s characteristics and also some of which
relies on hospital characteristics. The ability to bring all this various dependent variables together successfully is difficult.
Case mix are measured using different methods and these different methods have been developed to answer some of the questions been asked by the developers of these methods.
27
In certain situations, where some of the measurement methods try to answer all the questions affecting patients both from clinical point of view and economic point of view, they have not been successful in maintaining credible coding system.
Other limitations of case mix are concerned with availability ofinformation. Information on patient diagnostic characteristics isroutinely collected but not consistent from hospitalto hospital. Also when research on case mix is basedon hospital data, these data's are usually based on small samples.
The disparity in the inter-ratter reliability among case mix measurement methodologies is a major limiting factor.
Studies conducted on Case Mix and their Implications:
Study which looked at how case mix could be analysed using different types of measurement methodology :
Case mix complexity measurements are essential to determine health care efficiency and
effectiveness. Measures of patient care processes and outcomes must be adjusted for case mix before valid comparison can be made and since a key variable for hospital classification is case mix, methodologies which measures case mix must be robust enough to be able to effectively quantify case mix differences and complexity.
28
Horn SD et al (1979) conducted a study which looked at how case mixcomplexity could be analysed using information theory and diagnostic related grouping. 10
Their approach was based on information theoreticapproach which defines information theory measures of case mix complexity using the following variables : the number of hospitals in the district area, the number of cases of diagnostic types in all hospitals in the state orarea, the number of cases of all types in all state or area hospital.
They found that in general , Information theory approach using Diagnostic Related Group's gave a good picture of the complexity of the diagnosis. However, the methodology was unable to show the disparity between certain characteristics of patients and hospital but noticed that Information theory approach do have advantages such as its computational ability and sensitivity to some hospital characteristics.
The implication of this information theory approach to case mixmeasurement is the inconsistency and specificity of the method in capturing the required case mix
variables across all patients and hospital characteristics.
29
Study which examines Case Mix variations using disease and severity of illness measurement techniques :
Rowan KM et al (1993) conducted a study which looked at the extent of variation in case mix ofadult admissions to general intensive care
units in Britain and Ireland and the impact of suchvariation on outcome using APACHE 11 method to evaluate the history of chronic conditions; surgical status; diagnosis; and severity of illness.11
The study was a prospective cohort study of consecutive admissions to intensive care units. Their outcome measures were death or survival at discharge before and after adjustment of case mix. The case mix were collected under six main headingsnamely: socio-demographic factors (age, sex, race);a history of chronic conditions; surgical status; diagnosis; other active problems; and severity of illness (acute physiological state). They found that mortality in hospital increased significantly with increasing age, mortality in hospital was the same for both male and female, mortality in hospital was similar between race, mortality in hospital was significantly lower for surgical patients than for non-surgical patients. Patients who had emergency surgery had significantly
higher mortality in hospital than had patients who underwent elective surgery. Finally, they found that mortality in hospital increased highly significantly with increasing acute physiology and APACHE II scores. However, they noted that the collection of data on case mix needs to be standardised and differences in case mix adjusted for when comparing outcome between different intensive care units.
30
The implication of this study is that APACHE H system is a good method to show case mix variationacross different units, hospitals or places where patients are cared for. Also, case mix data need to be standardised and case mix need to be adjusted when comparing different health care institutions.
Study which examines Case Mix differences between teaching and Non-teaching hospitals
Goldfard MG et al (1987), conducted a study which isolates case mix attributes to given patient populations from that attributed to hospital treatment standards using Disease Staging and diagnosis related groups (DRG) measurement technique. 12 The data they collected were on diagnosis, procedures, length of stay, and dischargestatus of their sample population. They found that in the mortality - weighted case mix indices, there are no significant differences between non-medical schools based (non-MBS) teaching hospitals and non-teaching hospitals, regardless of whether the classification system is based on DGRs or Disease Staging. The medical school based (MSB) hospitals, however, do have a significantly more serious case
mix than do both non-teaching and non-MSB teaching hospital when the weighting systems is DRGs.
31
When the classification system used is Disease Staging, MSB or university hospitals are significantly different from non-teaching hospitals,but from other teaching hospitals. The result changewhen the weight in the case mix definition includes measures of resources use such as length of stay, cost weights and probabilities of admitting case types that were candidate for surgery are analysed and the classification system is DRGs, hospitals with any teaching program (that is, one or more approved residency programs) have significantly higher case mix values than do non-teaching hospitals.
If however, the classification system is changed from DRGs to Disease Staging, there are no statistically significant differences in case mix weighted either by length of stay-or by cost among any of the hospital categories. They also found that on average the presence of at least one approval residency program is sufficient to generate a significantly more surgery prone case mix than for strictly non-teaching hospitals. Theyfound that the presence of one or more teaching programs raises the length of stay, holding the case mix constant, by more than a day whether illness is measured by DRGs or by Disease Staging.The presence of more intensive commitment to
teaching ( as measured in medical school) does notraise the case mix adjusted relative value scores significantly. Non-medical school hospitals somewhat reports higher case mix adjusted death rates than do non-teaching hospitals under DRGs, but not under Disease Staging.
33
The implication of this study is that when case mix variability are to be measured and resource variables are to be assessed, Disease staging method is not as good as DRG's in identifying case mix differences between institutions with different status.
The other implication of this study is identifying that, hospital status do have impacton case mix variability
SUMMARY OF THE LITERATURE, HYPOTHESIS AND PUBLIC HEALTH IMPORTANCE
In Summary, there is some direct evidence that severity scales are useful in evaluating diagnostic efficiency of physicians, refining measures of prognostic, therapeutic effectiveness, and utilisation of health care services, designing clinical trials, and developing systems for controlling resources based on the diagnosis of their patient's conditions. In the area of health care evaluation, severity scales enables more accurate measurement of health status before, during, and after medical intervention and comparisons among physicians, hospitals, and health insurance programs as to the type of patients being treated 12.
34
My review of the literature suggest that case mix measurement canrelate to different aspects of hospital behaviour. As the proportions of a hospital's patients are combined by differing weighting schemes and classification systems, the concept of the case mixmeasure changes. For example, if mortality rates for specific diseases over all hospitals are used as weights, the severity of hospital's case mix in terms of likelihood of death is measured. Consequently, this makes it difficult to find a single classification system which can measure all the variables that underpins case mix satisfactory and completely between patients and across institutions where patients are cared for.
One question of interest that can be addressed with the measurement of patients case mix severity which will be of health importance from the Public Health perspective is who are the patients who tend to havemore severe cases of a particular disease ?. Also important to Public Health using this method in evaluating case mix complexity is highlighting the appropriateness of the hospital system in meeting the demands of patients who presents themselves for hospitalisation.
Furthermore, what is also important to Public health when case mix complexity of patients are measured, is that it provides the sort of information required for the development of Public health policy ; enhances administrative arrangements between health care providers and Public health departments and provides the necessary impetus for further research and development.
METHOD
Patients and Method:
My study was carried out in a 355 bed district generalhospital in the town of Colchester, County of Essex. Nearly 40,000 patients are admitted to the hospital each year of which between nearly 2500 patients suffering from acute infection are admitted each year (5% of the total admission).
Selection of Study Cases and Data Collection:
A listing was obtained from the hospital activity database of all admissions to Colchester General Hospital between 1st April to 31st March 1991/92 and1995/96, where the admission is the first admission in that year.
Inclusion criteria :
The case definition was an emergency admission in 1991and 1995 to Colchester General Hospital for an acute chest problem, where the primary diagnosis at admission and discharge are the same.
In 1991/92, Pneumonia, asthma, and bronchitis are ICD 9 codes 480 to 497 and in 1995/96, Pneumonia is ICD10 codes J18.0 to 118.9; Bronchitis is ICD10 codes J20.0 to J20.9; and Asthma is ICD10 codes 145.0 to 145.9.
Patients must be 65 year of age or more.
36
Exclusion criteria :
From the listing, patients were excluded (a) if they had been admitted for administrative reasons (that is, they were not admitted as emergency and acute patients) ; (b) if their primary reason for admission was acute chest problem but their discharge diagnosis was something different ; (c) if they were admitted in the first instances to other medical institutions such as Community hospitals or Day Care centers in the county and then latertransferred to Colchester General Hospital ; (d) if they were under 65 year old; (e) if their primary reason for admission was some other medical problems ( for example fracture neck of femur) and the secondary diagnosis was acute chest problem (for example pneumonia, asthma and bronchitis) and then discharged on their secondary diagnosis.
Sampling method:
The selection criteria I used had been obtained from previous study on the same subject conducted by Irwin D, et al (1993) but had to be improved so that I can obtain a more homogenous patient group.From the hospital listing of patients name, admission number, age, date of first admission, date of discharge,length of stay and 1CD (International Classification of
Disease) codes; I obtained a systematic random sample of106 patient admissions in
1991/92 and 1995/96.
37
How Systematic random sample was obtained :
The Systematic random sampling method was obtained by firstly, examining that the list from which the source population is taken from is not arranged in any sort of periodic order. Secondly, a total of 942 patients from the study population which satisfies the age study criteria of 65 year old or over were listed. The total of942 was divided by 106 which had been calculated from thepilot study as the number of patients required for the main study. This gave a value of 8 as the required numberto maintain a systematic gap between the numbers of the sampling number. Thirdly, the starting point for the first sample was determined at random between one and eight. After the first number had been obtained, the second and subsequent sample numbers were obtained by adding the eight to each new sample number such that if 2 was the first number, the second, third, fourth, fifth and so on number would be 2, 10, 18, 26, 34 and so on until the total number of patients amounting to one hundred and six patients is obtained.
The selection was actually performed by a staff member of the Medical Record Manager on my behalf.A pilot study was conducted in order to establish the standard deviation (SD) to obtain the required sample size for the main study.
38
How the Pilot Study was Conducted:
From the hospital listing which had the list of all patients who were admitted as emergency to the acute medical bed in 1991 and 1995, as their first admission ,whose diagnosis at admission and discharge were strictlypneumonia, asthma or brochitis, I extracted a listing of2,500 patient's.
From this listing, I obtained a second listing of all patients age 65 years old or more because this was one ofthe main criteria of the study design. The total number of patients who met these criteria for both years was 942(408 in 1991 and 534 in 1995).
In order to be able to estimate the SD from the source population and also to calculate the required sample sizewhich will allow me to detect a difference in the population for 1991 and 1995, if it exist, I did the following :
From the patient population of 942 (408 in 1991 and 534 in 1995) who satisfied the study criteria of age (65 years of age or more), I took a sample of 10% of 408 from 1991 and 10% of 534 from 1995 at random, using a systematic random sampling approach. This amounted to 94patients overall for years, 1991 and 1995.
From the overall 94 patients, 76.5% (72 out of 94) were excluded because they did not meet the study criteria of diagnosis at admission and discharge which must strictly be pneumonia, asthma or bronchitis. Overall, only 22 out of 94 patients, (12 out of 41(29.3%) in 1991) and (10 outof 53 (18.9%) in 1995 met the study criteria.
The acute physiologic data, the age data and history of chronic status data were extracted from the medical record case notes of the patients. These data's were scored using APACHE II scoring method.
The mean APACHE II score was 14.53 for 1991 and 15.01 in
1995, standard deviation for the APACHE II score was calculated as 4.73 for 1991 and 4.75 for 1995.
How the Sample Size was obtained:
Firstly, I calculated the standard deviation of the source population from the pilot study.
The difference I wanted to be able to detect, if it exists was obtained from the previous study conducted by Irwin A et al (1993) on the Severity of Sickness at admission to hospital in Colchester in 1985 and 1990.2 In which they found a statistical significance difference in the mean APACHE II score between 1985 and 1990. The mean difference that they found was 2.1 higher in 1990 than in 1985. I
therefore, decided to design my study to detect as a minimum difference of 2.1 mean, if it exists, as my base.
I then used a formula for the required sample size (N) when the primary statistical test significance will be an unpaired t- or z-test and the comparison of interest is a comparison of two group means.
The formula used is as follows:
n (Sample size in each group) = 2 [ Z¢ + zB ^2 * sDA2 DA2
where; ZO = 1.96 (2 -sided type 1 error of 5% )ZB = 1.28 (type 2 error of 10% - B isalways one- sided) SD = Is the standard deviation of the source population, which was estimated from the pilot study as 4.73 for 1991 and 4.75 for 1995. To be conservative, I have used the 4.73 SD for 1991.
D = Is the smallest difference I wanted to be able toIdentify, if it exists. The difference, I decided to use in my study was obtained from the previous study, which found that the mean difference of APACHE II score between 1998 and 1990 was 2.1higher in 1990 than in 1985.
Sample size calculation
By putting the above values into the formula, the samplesize for the study was obtained as follows:
For the collection of data, I constructed my own data abstraction and recording form as advised in the study conducted by Knaus WA et al (1985).9 My data abstraction and recording form is shown in appendix six.
The Medical record files for all patients who met the study criteria were retrieved by Mrs Jane Morgan (Medical Record Manager), the Medical Record staffs andby Mrs Anita Bryan (Secretary to the Clinical Audit department).
The examination, extraction, recording and review of case notes were performed by me over a period of seven
days. Of the seven days, I used two days to conduct the Pilot study and five days to conduct the main study.
All medical record files were retrieved from three different hospital locations within the borough, at EssexRivers Health care Trust Hospital, Colchester General Hospital and Severalls Medical Record Storage Department.Most of the medical record files were retrieved ready before my arrival for the extraction of data. However, I helped to retrieve some of the patient’s medical record files in some cases.
The extraction of data was performed for each year systematically. The files for 1991/92patient’s were examined first before 1995/96.
41
Within each patient medical record file, I extracted the data for the acute physiologic status from their laboratory investigation result card which were in most cases attached to the front cover of their medical recordfile or sometimes embedded in the file. All recorded laboratory data related to the investigation result givenat the first date of admission or in some cases second orthird day results.
The date of birth for the age data were mostly extracted from the Hospital database listings and cross checked with the date of birth in the medical record file.
The history of chronic health status data were extracted from the physician notes made at the day of admission or two days after in some cases and cross checked with Nursing notes taken during the period of hospitalisation.
Each data extracted were immediately recorded for each patient onto the recording form prepared for the study. Ialways extracted the first available data. If the patienthad missing data on day one, I accepted data from day two, because day two values may represent the admission status of patients who were admitted late at night.
42
When all the data's were extracted completely for allpatients in the study sample for both years, each patients data recording forms were scored on to a scoring form prepared for the study.
All patient data scores for each year were entered on a computer spreadsheet using Excel spreadsheet software application programme. Each spreadsheet were saved separately in the computer.
Variable that Measures the Severity of Disease at admission :
I obtained the variable that measures severity of disease at admission, using a previously published studyby Knaus WA et al (1985) which looked into the APACHE II: A Severity of disease classification System,10 usingthe variables (acute physiologic status, age status, andhistory of chronic health status) to determine the validity and reliability of using methodology in the classification of disease severity at admission.
The instrument I used (The APACHE II: A Severity of disease classification System) had been validated in U.S.A, using 14,000 plus patients to measure severity ofillness of medicare patients for prospective payment system. 9
43
Measurement of Case Mix Severity of Patients illness :
APACHE H Method :
The precise definitions for the variables used in the APACHE If classification system and its modifications in Britain and Ireland are listed in appendix one. I obtained the modified definitions from a study conducted by Rowan, KM et al (1993). 11
For each patient up to two possible values ( highest and lowest) were recorded for each of the 12 physiological variables constituting the acute physiologic score. All values were extracted and recorded as raw data.
Missing physiological values were assumed to be normal andassigned zero points. The acute physiology score was calculated as the sum of the points for the 12 variables. The APACHE IT score was calculated as the sum of the acutephysiology score plus the points for age and history of chronic conditions as shown in appendix two. 11
Ten individual categories for use in this study were derived from one primary organ systems as shown in appendix three.11 Patients were assigned to one of thesecategories according to the principal reason for admission.
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Result
The Distribution of Patient Admission by gender 1991/92 & 1995/96
The distribution of patient admissions between 1991 and 1995 by gender are as follows: Of the 2500 patients admitted for acute medical problems, in 1991/92 and 1995/96, overall only 942 (37.7%) were 65 years old and over. Of this,408 (43.3%) in 1991 and 534 (56.7%) in 1995.
Males were 198 (48%) and females were 210 (51.5%) in 1991, whereas 216 (40.4%) were male and 318 (59.5%) were female in 1995.
Of the 942 admitted for acute medical condition,only 212 (22.5%) were admitted into the sample population; 53 (50%) were male, 52 (50%) were female in 1991/92 and 58 (54.7%) were male and 48 (45.3%) were female in 1995/96.
Amongst the 212 patients admitted into the sample study population, only 89 (42%) met the study criteria of which 21 (48.8%) were male and22 (51.2%) were female in 1991 and 22 (47.8%) were male, 24 (52.1%) were female in 1995.
DescriptionAge Grou
Total number of admission in study Population
65-74>75
65-74>75
65-74>75
TOTAL
Number of admission in sample populationTOTAL
Number of admission who met the study criteriaTOTAL
1991/92
MaleNo %
FemaleNo %
Total No %
8520.8 77 18.9
162 39.711327.7 133 32,
6246 60.3
198 485 210 51.5
408 100
2826.4 22 20. 50 47.22523.6 31 29.
256 52.8
53 50 52 50 106 100
920.9 9 20. LB 41.91227.9 13 30.
325 58.1
2148.8 22 51.2
43 100
1995196
MaleNo %
FemaleNo %
TotalNo %
30 5.6 115 21.5 145 27.2186 34.
8203 38 389 72,
8216 40. 318 59.5 5,34 100
19 17. 8 7.6 27 25.539 36.
840 37.7 79 74.5
58 54.7
48 45.3 106 100
6 13. 3 6.5 9 19.616 34.
721 45.6 37 80.4
22 47. 24 52.1 46 100
Female & Male
1995/96 Female &
Male 1995/96
Female & Male -
1991/92 Female &
Male - 1991/92
4 5
DISTRTTIBUTION OF PATIENT ADMISSION INTO ACUTE MEDICAL BED BY GENGER IN 1991 AND 1995
Graphical representation of the Proportion of Admission who met the study Criteria by Gender
1991/92 Number of Patients admitted into the study by Gender •
Female
Male
Female
Male
Female
Male
Female
Male
1995196 Number of Patients admittedintothe study by Gender
*75
65-74
0 0 20 30
1991/92 and1995/96 Number of Patients admitted intothe.study by Gender
Study StudyDefinition DefinitionMet Not Met
No % No %63 59.4 43 40.660 56.6 46 43.4
123 58.0 89 42.0
TotalNo %106 50.0106 50.0
212 100.0
Year1991/921995/96
TOTAL
Study Definition I ]Not Met
Study Definit
10 20 40 60 80
1995/
96
1991/
92
1995/9
46
DISTRIBUTION OF SAMPLE CASES BY YEAR
GRAPHICAL REPRESENTATION OF THE DISTRIBUTION SAMPLE CASES BY YEAR,
47
The Distribution of Patient case notes for analyses
When the case notes were analysed, 59 %, and53% (63 out of 106 for 1991/92 and 60 out of106 in 1995) did not meet the studydefinition.
The main reason for the exclusion were admission and discharge diagnosis differences for 27 in 1991 and 29 in 1995; for non-emergency admissions, there were 10 in 1991 and8 in 1995. For those who met the case definition, there were 43 in 1991 and 46 in 1995.
Case Note analyses findings
The APACHE Score Analysis :
The mean APACHE II score was 15.63 , standarderror (SE) 0.54, standard deviation (SD) 3.53,and the confidence interval (CI) was 14.56 to16.69 in 1991/92. Whereas, in 1995/96, the meanAPACHE II score was 16.33, (SE) 0.54, (SD) 3.65,and the (CI) was 15.26 to 17.39
The mean difference for the APACHE II score between 1991/92 and 1995/96, using the Two-Sample t-Test was found to be statistically notsignificant (P<0.10). Which means that, despite, the observed difference between 1991/92 and 1995/96, the Null hypothesis cannotbe rejected.
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The Mean Age at Admission Analysis :
The mean age at admission was 76.21, (SE) 1.13, (SD) 7.33 (CI) 73.99 to 78.43 in 1991/92 and in 1995/96 the mean age was 80.48, (SE) 1.22, (SD) 8.16, (CI) 78.09 to 82.86.
The statistical significance of the mean difference in age between 1991/92 and 1995/96, using the Two-Sample t-Test was P<0.01 This shows that the age difference was statistically significant.
The Acute Physiology Score Analysis :
The acute physiology element of the score showsa mean of 9.0, (SE) 0.47, (SD) 3.03, (CI) 8.08 to 9.91 in 1991/92, whereas in 1995/96, the mean was 9.61, (SE) 0.46 , (SD) 3.09, (CI) 8.71to 10.51.
The mean difference of the score between 1991/92and 1995/96, using the Two-Sample t-Test was found to be statistically not significant (P<0.10) .
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The History of Chronic Status Analysis :
The history of chronic condition element of thescore shows a mean of 1.07, (SE) 0.25, (SD) 1.64, (CI) 0.57 to 1.57 in 1991/92 but in 1995/96, the mean was 0.96, (SE) 0.24, (SD) 1.60, (CI) 0.49 to 1.43.
The mean difference between the score for 1991/92and 1995/96, using the Two-Sample t-Test was found to be statistically not significant (P<0.10)
Within the acute physiologic element of APACHE H score, Serum Albumin were recorded frequentlyin 1991 but were hardly recorded in 1995. The very low recording of Serum Albumin in 1995 made me to exclude the data item from the finalanalysis of the physiology score component.
All the statistical analysis calculation were done using Excell Spreadsheet Software as shown in appendix two and seven.
bar X SE SD CI.
36.48 0.35 2.24 35.8 to 37.1591.86 2.2714.69 87.42 to 96.3124.74 0.74 4.81 23.29 to 26.2138.95 0.66 4.31 137.65 to 140.26
4.4 0.1 0.53 4.21 to 4.591.22 0.06 0.39 1.1 to 1.34
44.16 0.42 2.75 43.33 to 44.9912.65 0.85 5.46 10.99 to 14.3126.09 0.58 3.75 24.96 to 27.23132.37 4.2727.66 .
124.01to 140.74
8.63 0.64 4.14 7.33 to 9.88
Parameters
bar X I SE SD CI
Mean (bar X), Standard Deviation (SD), Standard Error (SE), Confidence Interval (CI) for the values of the variables in 1991/92 .
StandardError,ConfidenceIntervalfor the APACHEIIscore and its components1995/96
1995/96 Table
APACHE II score components
Components
bar XI SE I SD1 CI
Acute Physiologic scoreAge scoreHistory of Chronic Health Condition
APACHE II score
16.33 0.54 3.65 15.26 to 17.39
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DISCUSSION
Main Findings:
In this comparison of patients severity of illness at admission into acute beds in 1991/92 and 1995/96, the main finding from this study was that, the case mix severity of illness at admission using APACHE II score measurement, was slightly higher in 1995/96 than in 1991/92. However, the observed mean difference between the two years 1995/96 and 1991/92 was found to be statistically not significant (P<0.10)
The Implication of the Result:
The implication of the result is that, there has been a continuing increase in the case mix severity of illness of patients admitted to Colchester General Hospital between 1991 and 1995. However, it is important to emphasize, that despite the observed differences between 1991 and 1995, the mean difference in the APACHE II scorewas found to be statistically not significant (P<0.10)
There may be various reasons for the increase. It may becaused by reduced number of bed, more managementinvolvement in case mix, reluctance of patientspresenting their cases early, improvement in the
recording of medical information, and or increase in theage of patients presenting themselves for admission.
It may be true that the threshold for the decision to admit has actually gone up as explained in the previousstudy conducted by Irwin et al (1993) on the same issue, in which they tried to put objective evidence against the concerns raised by GP's and hospital admission doctors.
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The implication of the possibility of the rise in the threshold to admit acute patient to medical beds is that,it is by nature possible, that the kind of patient group that has been investigated in this study and which may have been exposed to this sort of admission difficulties,would respond to such hospital behaviour cowardly, and thereby presenting their ill health late to the hospital.
Other likely reasons for the increase in the case mix severity of illness at admission as observed in this studycould be due to effect of change management. When organizations are going through a change circle, the recipients of the services are likely to experience some change themselves. For example, could the recent introduction of internal market into the National Health Service (NHS) which brought about a change in the hospitalstatus of most health care providers such as Colchester General Hospital be a factor in the changes to the hospital system such as admission policy.
It is difficult to ignore the fact that the introduction of the internal market into health care provision brought with the need for hospitals to respond to the demand and raised expectation of patients, or the inability of the hospitals to respond to patients demand due to over demandor increased frequency of the demand and lack of the capacity to code with the demand , and the added pressure on the hospital system in trying to meet National
directives, Policy changes both local and National are bound to have direct impact on patients attitude, health belief and be behaviour.
After all, in my literature review, there was evidence shown by some of the studies that a change in hospital status, and a change in resource need of hospitals do have impact on patient's case mix severity.
Or could the increase be due to some unknown factors inthe community causing an increase in patient case mix severity at admission.
The Limitations of the Study:
The limitation of the study could be associated with the fact that the study was a retrospective study, which limits the scope of the other variables that could have been investigated in order to mitre at a wider more robust result. A prospective study would have given me the opportunity to redress these information constraints.
It also follows that because the study was a retrospectivestudy, the integrity of the data collected had to be dependent on what has already been collected. Which meant
that, in a situation where some data were not re-coded consistently among patients would not have arisen if the study was a prospective study. One such example observed in my study was the recording of Serum Albumin, which was recorded consistently in 1991/92 and hardly recorded in 1995/96. This may have had an impact on the outcome of theresult obtained for the acute physiology score.
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Explanation of the result by evaluating the role of chance, bias, and Confounding:
Could the Result be due to Chance :Despite the fact that the study showed that the APACHE H score was statistically not significant.(P<0.10).It is unlikely that the result obtained from my study wasdue to chance in view of the fact that the sampling was done by a different observer; the methodology and approach for the collection of the samples were consistently applied throughout the groups in the study. Although, I started with a larger sample but ended up with a rather smaller sample after the imposition of the study criteria, this in my view, could not have by itselfbe a cause for the likelihood of chance to be an explanation.
Could the Result be due to Bias:
Firstly, more than half of the initial random sample of cases obtained from the hospital activity listing failed to meet the case criteria. This obviously raises two questions: was the study sample biased? and could the sample have been drawn more efficiently or was the study inclusion criteria too strict? thereby, limiting potentialpatients who could have been included in the study.
Sampling Efficiency :
Taking efficiency first, it is worth noting that the commonest reason for exclusion was a discrepancy between discharge diagnosis (recorded on the hospital activity database) and admission diagnosis (the study criteria). The listing included many patients who died of pneumonia as a complication of their initial reason for admission. It might have been possible to use secondary diagnosis to screen out some admissions in this category, but I was determined to keep the study criteria tight irrespective of the implication this might have on the final sample size. Also, I was unsure how sensitive and specific such ascreening procedure would be to the study aims and objective.
Another common reason for exclusion was that the hospitaldatabase listing contains patients who were admitted intoother health institutions such as Community hospitals in the first instance and then later transferred to the general hospital.
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Selection Bias in the Study
Selection bias could not have been a problem in my studybecause, the criteria for the selection of the study population was defined before the hospital database listing was produced. The criteria's were also the same for both years. The selection of the samples was conducted by a different observer and a systematic random method was used to collect the samples and was applied the same way.
Although, in principle, selection bias is said to be a particular problem in a retrospective study, like my study, due to both exposure and outcome occurring at the same time. But in my study, the period of exposure and the outcome is unknown which consequently reduces or eliminates the possibility of a selection bias.
Information Bias in the study
I noticed that the standard of completeness and accuracy of admission and discharge coding in Colchester hospital is very high: over 98% of admission and discharge notes were medically coded and neatly typed by the administrators. Although, accuracy has not been formally studied, the very fact that the admission and discharge notes were neatly typed and signed by a medical officer, gives validity, reliability and credibility to the
coding process and the information inherent in the notes.Therefore medical coding was found to be no problem to the study.
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Investigation bias :
Although this study is not a blind study, it was not possible to make data abstraction blind either as to thehypothesis, or as to the year (1991 or 1995) of the case.There may be little room for observation error in the abstraction of case notes in the recording of pulse rate or systolic blood pressure, some of these data items are buried deep in the files in 1991 than 1995 and in certainsituations the admitting doctor's notes differ slightly from the Nursing notes (which were sometimes used as a secondary source of information). However, according to APACHE II rule, the most abnormal reading by a doctor or Nurse is to be taken.
Despite all these, it is difficult to assess the likelihood or extent of investigation bias, but it would have been a practical impossibility to organise a blind study.
Could the Result be due to Confounding:
Age was found to be the only factor within the APACHE II score that had a mean difference that is statistically significant after APACHE II score itself. Other variable which made up of APACHE H score ( such as acute physiology, and history of chronic status ) was not significant.
59
Therefore, could age be a confounder in this study. It is very difficult to conclude that this is the case without testing the nature and strength of the relation between age and APACHE H score. However, it is my view that age isprobably not a confounder. If it is the effect of age as aconfounder should have been adjusted for in the design stage of the study or in the analysis stage of the study.
Gender could be a probably confounder in this study because the proportion of men and women in the study population in 1991 is different from that of 1995.
It is my view that, it is possible that gender and age been an independent risk factor for the case mix severityof illness at admission. Therefore, there is a probability that an association between age, gender and APACHE II score exist.
However, it was difficult for me to control the effect of age and gender at the design stage by using randomisation,restriction, or stratification methods because age was oneof the component part of the case mix variables being measured using APACHE II classification system.
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Criticism of Laboratory investigation :
One of the other problems which I consider to have an impact on APACHE II score was the inconsistencies in the laboratory investigation for these group of patients. The need to standardise laboratory investigation for patients of a particular grouping would have an enhanced validity on the use and outcome of APACHE II classification system as a measurement instrument. In this study about 95% of Serum Albumin was investigated in 1991/92 whereas only about 2% was investigated in 1995/96. The conservative approach of excluding Serum Albumin score from both 1991/92 and 1995/96 samples still showed an increased score, although with a probability of 5% that this was dueto chance. While the probability of human error cannot be excluded, I feel that the consistencies of the other result make this unlikely.APACHE H score assumes that if results are not recordedit is regarded as being normal. 14 The fact that APACHE II score was specially developed to measure particularly ICU patients makes the assumption in the application to other illnesses a bit suspicious
61
Comparison with Previous Studies:
When the result of my study is compared with previous study in 1985 and 1990, the mean APACHE II score was much higher in 1985 and 1990 than in 1990 and 1995 as shown in the table below.
The Possible reasons for the higher mean APACHE II score in 1985/90 than in 1991/95
Firstly, The study in 1985/90 could have produced a higher APACHE II score due to the fact that , the investigators did not calculated the sample size used. Their sample size figure was based on an arbitrary figurewhich may a cause for a possible effect of chance.
Other possible explanation may be due to the fact that the study criteria I have imposed in my study is more stricter than the previous study. In the previous study, they have allowed patients admitted in other health care institutions into their study, whilst, my study was strictly based only on patients who were admitted into Colchester General Hospital.
Other possible explanation is that case note file anddata contained in the file's which were extracted forthe purpose of the study, were much more carefully written in 1991/95 than in 1985/1990
62
Why should it be different:
There are various possible reasons why the results obtained in 1985/90 is higher than in 1991/95. Firstly, the study design efficient of the studies is likely to bea possible consideration. The hospital characteristics (such admission policy), the patient’s characteristics (such as patients presenting their illness late, the resource implications which were at the height of the agenda in 1985/90 but has probably receded in 1991/95 arepossible explanation.
What are the implications:
The implications for having a reduced APACHE H score as evidence of case mix severity of illness at admission isthat, although my study had shown a continuing increase in the APACHE II score, some of the assumptions of the causes of the increase in APACHE II score, made in the study in 1985/90 has probably been reduced. Or could it have been that the factors which have been used in the studies for both period, needed to be expanded to include other variable which may have a direct impact onthe outcome of future investigations.
Definitely, a future investigation on this issue should be conducted prospectively to allow for the opportunity
of better design criteria to be imposed and more variable used in the study.
Description of the trend in severity of illness over 10 year period as measure by using APACHE 11 score : 1985 and 1995
According to the table above, in 1985 the score was 11.6 (SE 0.47), 1990 13.7 (SE 0.57), 1991 15.6 (SE 0.54) and in 1995 16.3 (SE 1.54).
This means that, in comparing the circular trend in thedistribution of APACHE II score between 1991, 1995 and1985, and 1990, that the mean APACHE H score has goneup over the ten year period , although notsubstantially.
CONCLUSION
Despite the reason given in the previous studies which led to an investigation into the severity of sickness atadmission at Colchester hospital five years ago by usingthe APACHE II score. My follow-up study in 1991 and 1995did not confirm any substantial increase in the case mixseverity of illness at admission as measured by APACHE II score but has confirmed that there is statistically no significance in the difference in the APACHE II scoreover the two years.
Also like the previous study, my study does not confirm that admission was too easy in 1991 nor too difficult in 1995, or whether the change observed in APACHE II score is an indication of a change in the case mix severity of illness, nor whether the change is due to a reduction in the hospital resources, increase in the population of people of Colchester or an increase incidence of severityof illness in the community.
Whatever the reason, my study has provided a reasonable objective follow-up data on this subject and has achieved its aims and objective.
It confirms clinical perception that they are seeing increasingly severely ill patients in hospital and therefore, if the intensity of severity did hold, factors in terms of staffing will need to be considered.However, it also, probably disapproves the perception that, severity in emergency admission is due to lowered threshold of GP's sending patient's for admission more frequently,
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Implications to Public Health
One question that can be addressed with the measurement of patient case mix severity which will be of health importance from public health perspective are who are thepatient who tend to have more severe cases of a particular disease ? or how often do people get a particular severe case and where do this people come from.
In other to answer these questions a fully rigorous epidemiological investigation should be under taken. However, it seems possible that such large investigation will require a great deal of time and resources and in view of resource constraints facing the health services, the justification of such an investigation has to be backed up with the appropriate cost and benefit implication.
According to Charlson PP, et al (1991), stratifying patients on the basis of specificcharacteristics determined at the time of admission will be useful in studies of patientoutcomes and resource utilisation, that illness severitystudies of patients in which mortality, morbidity and functional status are being measured as outcomes must take appropriate risk adjustments based on illness severity. In addition, studies of health care delivery, resource utilisation and the organisation and
measurement of health care systems also require accuratemeasures of case mix.15
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Other implications that could affect the practice of public health functions is the need for the public healthdirectorates to keep track of how the hospital system is performing for his or her residents, particularly at a time of resource constraints both in terms of finance, human resources, and structures and to be able to predictthe effect of changing patterns of practice and health service organisation, and factors important in influencing trends in work load. Clearly, if this factorswere to be achieved, there is a need for information thatallows say comparison of costs and prices, but still takes into account differences in patient populations andtherapies administered, that is, differences in case mix.
Planning for patient care is one of the most demanding and important obligations ofhealth care providers today. Planners such as the publichealth administrators and practitioners need valid and reliable tools to determine patient need and to allocateresources. Identifying levels of resource requirements for patient care is an application of classification theory, which is concerned with arranging patients into groups to presumed "similar" relationships.
The problem with using case mix severity measurement isthat there are several instruments and methodologies developed to measure illness severity based on information extracted from medical record and
these measures were developed for differing reasons, and therefore vary considerably in the domains they measure. Therefore, caution must be taken in the use ofthe instruments: The characteristics of severity measurement systems are shown in appendix 4
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Lessons Learnt
The investigation of this type which involves the use of patients hospital case notes needed to be planned well in advance, with the full co-operation of all parties who makeuse of the files, control, and manages the custody of the notes including (Hospital Physicians, Nurses, Administrators and Secretaries). My experienced was that having left the decision of my final study topic too late, I was fortunate to be able to get the necessary approval just in time mainly with the goodwill of all people
concerned.
I learnt about how medical records are organised and about system of retrieval of medical files
I have also been able to put into practice some of the skills of project management. This meant that at the later stage of my project, I was able to control the whole project with very little concern. This has made meto appreciate that in future if I was to do another study, I would institute a much more rigorous application of project management.
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Recommendation for future work
In view of my study being a follow-up of a previous studyconducted on the same subject, I am confident that the instrument of measurement used in this study could be used in future studies to investigate issues relating to severity of illness measurement.
However, it is my view that the design methodology for future work in this area of study could be conducted from a prospective perspective in order to determine theutilisation of hospital services from any of the case mix focus (economy, physiology, functional and psychology).
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APPENDIX 1
Definition of Sickness at Admission Variables :
1. Rectal temperature : Measurements of temperature from sitesother than the rectum (oesophagus, tympanic membrane, nasopharynx, and pulmonary artery) were considered to be core temperatures. To temperature measurements at the oral sites half a degree was added and to temperature measurement atperipheral sites (axilla and groin) one degree was added before points were assigned.
2. Mean blood pressure : Mean arterial pressure was calculated as the sum of twice the diastolic value plus the systolic value divided by three.
3. Oxygenation : When the oxygen concentration was greater than or equal to 50% points were assigned to the alveolar to arterial oxygen tension difference. Thiswas calculated as (percentage oxygen concentration x713)- arterial oxygen tension (mm Hg) - arterial carbon dioxide tension (mmHg). When the oxygen concentration was less than 50% points were assignedto the lowest arterial oxygen tension.
4. Arterial pH : was measured in the same blood sample used to measure oxygenation. Concentrations of hydrogen ions were converted to pH values by taking the
negative logarithm of the concentration of hydrogenions.
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5. Serum Creatinine : Measurements in tuno1/1 were converted to mg/100 ml by dividing by 88.4. Points for serum creatinine value of greater than 1.4 mg/100 during the previous 24-48 hours associated with oliguria. Oliguria was defined as a urine output of less than 135m1 over eight consecutive hours that was not caused by absence or obstruction of a urinary catheter or by incontinence.
6. Haematocrit :When haemotocrit values not availablepoints were assigned to the haemoglobinconcentration multiplied by three.
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APPENDIX 2
Statistical Calculation
1. Calculation of Standard Deviation :
The Standard Deviation usually denoted by (s) was calculated using the following formula:
S = Square root of [sum XA2 ( sum X )A2 / N]/ (N -1)where N = is the number of sampleobservation
X = is the individual sample values.(sumx)A2 NSumA2 - = Sum of squares of differences from
mean.N - 1 = degree of freedom
2. Calculation of standard error of the sample mean
The Standard Error of the sample mean denoted by (SE) was calculated using the following formula :
SE = Square root of: 212N
where S = is the standard deviation
N = is the number of sample observation
3. Calculation of Confidence interval (CI)
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Confidence interval was derived by using the following Formula : I began by constructing the critical ration for t :
(bar X - p ) / SESince t can be either positive or negative,depending on whether bar X > p or p > bar X, and since the t-table list is only positive values :the formula then becomes p = bar X ± t * SEwhere p here represents the population mean.also here bar X ± t * SE is the confidence for the population value.
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4. Calculation for the "Statistical Significance" of an observed
difference in the outcome means of two study group : Using the Two-Sample t -Test.
In order to draw an inference based on the difference between two independent sample means, I decided to use Two-Sample t Test, because my assumption was that the sample sizes did not grossly violated the assumption requirement of the central limittheorem.
Also I stated in the introduction of the report that my researchhypothesis : is that there is no difference in APACHE II score between 1991 and 1995.
The following formulas were used :
Firstly, the pooled sample variance using the formula : SA 2p = (ni _1)*sA21 (n"2 _1)* 5/%22 (ni 41-12 -2)
I solved for t using the formula:t = (bar Xi - barX2) / square root of [SA2p ( 1 / n1 +1 / n2)]
After obtaining the value of t, then thisvalue is looked up in the t - table for a two-sided P-value at the required degrees offreedom.
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The interpretation of the p-value will be shown with an inequality sign (P< value) or (P> value) due to the fact that, the calculation is done using t-table which does not and cannot give the exact p-value. If a statistical package such as SPSS , SAS, or Epi-Info was used for the calculation of the t -test, then, the p-value would have been given as P=value.
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APPENDIX 3
The Ten individual diagnostic categories used inthis study derived from the one primary organ system :
Past Medical History in notes or discharge letter:Congestive Heart Failure [1]Arrhythmias [2]Swallowing disorder [2]Ng (nasogastric) tube [3]Hospital admission in the past 1 month [2]Thoracic or abdomina surgery in the past month
[2]Disease of thorax [3]Multiple Myeloma [2]Splenectomy [2]Dementia [2]
Current Problems Recorded in notes or discharge letter :Smoking [2]
Alcoholism [2]Obesity [2]Hypoalbuminaemia/Malnourishment [3]immunocompromised State [2]
TOTAL APACHE II SCORE Calculation_
A = APS ( APACHE Physiological point score )________Age point
Chronic Health Status point
Total APACHE II = Sum of [A] + [B] + [C]
Appendix 6DATA RECORDING FORMStudy Ref. :Name:Date of Admission :Date of Discharge :
/ / Length of Stay :
Sex : Male [Female [
Discharge Status : Dead [Alive [
ICD 9 Code from discharge letter: [[
ICD 10 Code from discharge letter: ] 1
[Diagnosis :
Surgical,Status : NonePresent :
Elective surgical patientEmergency surgical or non-surgical patient
one = (dt) degree of freedomSDA21 is the standard deviation of the first group value squared. (n2-1) is the number of observation inthe second group minus
one (df) isthe degree of freedom.SDA22 is the standard devbiation in the second group squared.
T--testformula used :
t=bar xlbar x2divided by the squareroot of thePooled variance multiplied by (I/n1 +11n2).
where :bar X1is themean of thefirst group.bar X 2 is the mean of the second group. (1/n1 +1/n2) is one divided by the number of obersations in the first group plus one divided by the number of observation in the second group.
Data from the study used
Acute) History ofYears APACHE H Physiology I Age Chronic status
score score value1991/92 bar xl 15.62 9.00 76.211995/96 bar x2 16.33 9.61 80.48
5 ammo WNW 0.67193, 36571114 8.5739225 8.00711346360565117
45 11421264 0.7009031 8.014251
Caraway. Interval
0.7088049610.6107883
C o n d o n e . I n f e r r e
5. 63 48 32 46 3 .8 88 87 88 7
C a r d e n a s l i t e r a l0,4.73.9921.42545358
C a r d o n a . i n t o w a l
1 5 . 2 5 0 8 5 0 9 1 7 . 3 9 1 2 8 3
AP67C0,91.393212132 pm2718197
126Heart Rate 9 12 11 111 82
18 18 18 30 16 28
4.1 5.83.9 3.3 4.44.6Serum Potassium mMol/L
1
I,
32
44 44 48 45 41 48
26 292 19 2429
8.6 3.9 4.6 23.6 9.7 12.0
APS VAL U E.595phy12:27 pm27/8/97
SEVERITY OF ILLNESS AT ADMISSION STATISTICAL CALCULATION ON OVERALL DATA YEAR : 1ST APRIL 1995 - 31ST MARCH 1996
Mean Value Deviation from Mean Squared DeviationRespiratoryRate Mean Value Deviation from Mean Squared DeviationOxygenation A-aDo2 orPao2 :a. if Fio2>0.5 (A-aDo2)b. if Fio2<0.5Serum Sodium mMol/L Mean ValueDeviation from
Mean Value = Deviation from Mean = Squared Deviation =Respiratory RateMean Value = Deviation from Mean = Squared Deviation =Oxygenation A-aDo2 orPao2 :a. if Pio2>0.5 (A-aDo2)Arterial pHSerum Sodium mMol/LMean Value = Deviation from Mean = Squared Deviation =
Mr. G. A. Benn-ohikuare, MSc, DipHE, MHSM, MIAPTalltrees10 Hastings Place,BrightlingseaColchesterEssex C07 OAP
Dear Mr. Benn-ohikuare,
Georkey Carroll has passed on to lila yourhiril regarding our wish to do your dissertation in North Essex. We would be delighted to assist you in your project and as you suggest, thereare various opportunities which we could explore further. Perhapswe should arrange to meet each other when we could discuss the various options that are available to you. Please ring my secretary Sandy on 01206 851257 ext. 234 to make an appointment at your convenience.
Yours sincerely,
Dr. Sushi! athannaConsultant in Public Health Medicine and Clinical Policy.
Chairman: Alec `-z' :on Head Office: C eleplione 01376 5165 I 5 F.: "..5.3Y. 6
Chief Exectnive: Mid Essex Office: I 37..i ,I e515 iWest Essex Off cc: ; CH2',1. I DR, l clepherie 01271 .11 (,309
n _North East Essex Office: 111itl. r Raid, C:olcho,iQr, C.0,15'JF( I riephole 01206 951257 01.
Date 20th March 1997Our reference PED/pmg/EthicsYour reference
Department Medical Personnel, Postgraduate Medical Centre
Direct Line: 01206 832147Fax No: 01206 851231
Mr Gregory A Benn-Ohikuare2 Sparrow HouseStation RoadBrightlingseaCOLCHESTEREssexCO7 ODT
Dear Mr Benn-Ohijuare
APPROVAL FOR ACCESS TO THE MEDICAL RECORDS OF PATIENTS TO FACILITATE PROPOSED STUDY INTO CHANGES IN CASE MIX FOR ACUTE HOSPITAL ADMISSION IN A MEDICAL SPECIALTY IN COLCHESTER 1991 AND1995
Thank you for your letter. We do need to know the number of the sample size. Your letter also quotes that you will be looking specifically on anecdotal evidence from hospital physicians and consultants in the Public Health Department but you do not state whether these are local Essex Rivers Healthcare Trust consultants.
would be grateful if you could forward to me this information.