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Anesthesia and
Obese Patients
Abdullah Halawani, MBChB, FRCPC.Department of Anesthesiology
KFSH & RC , Riyadh
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Obesity is a relatively common condition,
that can have a profound impact on
morbidity/mortality and anesthesia.
Physiological derangements, difficult
airway management, and alterations in
pharmacokinetics & dose/response
relationships can all be part of thepicture.
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Twenty Years of Increasing Obesity
30.5%
22.9%
15%14.5%13.4%
0%
10%
20%
30%
40%
1960 1974 1980 1994 2000
%O
bes
ity
Source NCHS -- JAMA 2002:14:1723-27.
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All-cause mortality versus
BMI for each sex in the
range 15 to 50 kg/m2
(excluding the first fiveyears of follow-up)
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Dr. Tushar Chokshi 5
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Definitions
- Overweight is defined as weight abovethe normal range.- Obesity is defined as an abnormally high
percentage of body weight as fat.- Body mass index (BMI) is used todistinguish between the two terms andalso determines the degree of excess
weight
BMI = body weight (in kg) height (in meters) squared
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Classification of BMI
* Underweight BMI
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Equations
Ideal body weight in Kg (IBW)
(Brocas Index)
Height in centimeters - 100 for men Height in centimeters - 105 for women
-----------------------------------------------------
Body mass index (BMI) weight in Kg / height (m) 2
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Causes of Obesity
Complex and multifactorial Genetic predisposition
Socialization
Age
Sex
Race
Economic status
Psychological
Cultural
Emotional
Environmental factors
Cessation of smoking
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Diseases Linked to Obesity
Diabetes Coronary Heart Disease
High Blood Pressure ( Hypertension is about 6 timesmore frequent in obese subjects than in lean men and
women ) Stroke
Arthritis
Gastroesophageal reflux
Cancer
High cholesterol
Endocrine disease
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Diseases Linked to Obesity
Hypertrophic Cardiomyopathy Infertility
Depression
Obstructive sleep apnea
Gallstones
Fatty liver
Stress incontinence
Venous ulcers end-stage kidney failure
Sudden death
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Physical Complications of Obesity
Heart disease Type II diabetes mellitus
Hypertension
Stroke
Cancer (endometrial, breast, prostrate, colon)
Gallbladder disease
Sleep apnea
Osteoarthritis Reduced fertility
increased risk of morbidity and mortality as wellas reduced life expectancy
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9.2prevalence is2Diabetes Mellitus Type
times higher in the obese than in non-obesefor those 20-75 years of age.
hasCardiovascular diseasesMorbidity due tobeen reported to be almost 90 % in those withsevere obesity.
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Psychological Complications
of Obesity
Emotional distress
Discrimination
Social stigmatization
Anxiety, Fear, Hostility and Insecurity
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PathophysiologyCardiovascular
in Obesity
Excess body mass
metabolic demand CO
For every 13.5 kg of fat gained: 25 miles of neovascularization occurs
Increased CO of 0.1 L/min for each kg of fat.
workload
LVH
pulmonary blood flow and HPV
Pulmonary HTN cor pulmonale right heart
failure
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PathophysiologyCardiovascular
in Obesity
Stroke volume index and stroke work indexare the same as non-obese
SV and SW must
Proportion to body weight
SV and SW
LVH dilatation
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PathophysiologyCardiovascular
Risk of arrhythmias
Hypertrophy
Hypoxemia Fatty infiltration of cardiac conduction system
Catecholamines
Sleep apnea Dyslipidemia
Glucose intolerance
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Cardiac Evaluation:
Assess For
Prior MI
HTN
Angina
PVD
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Cardiac Evaluation
Indications of LV dysfunction
Limitations in exercise tolerance
History of orthopnea
Paroxysmal nocturnal dyspnea
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Cardiac Evaluation: ECG
Determination of
resting rate
Rhythm
Ventricular hypertrophy or strain
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ECG Changes That May Occur in Obese Individuals
Heart rate
PR interval
QRS interval
or QRS voltage
QTc interval
QT dispersion
SAECG (late potentials)
ST-T abnormalities
ST depression
Left-axis deviation
Flattening of the T wave (inferolateral leads)
Left atrial abnormalities
False-positive criteria for inferior myocardialinfarction
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Cardiac Evaluation: ECG
Investigate ischemic changes or evidence
of coronary artery disease
Low voltage ECG
Excess overlying tissue
Underestimate LVH
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Cardiac Evaluation: ECG
Axis deviation and atrial tachyarrhythmias
Sudden cardiac death is more prevalent
with
LVH
Ventricular ectopy
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Vascular Access
Challenging at best
Excessive fat obscures blood vessels
Central line placement
Vessels impeded by distortions of the
underlying anatomy by adipose tissue
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Volume Replacement
Adult total body water percentage is 60%to 65%.
Severely obese total body water is 40%.
Estimated blood volume in obese patient is45 to 55 mL/kg actual body weight
70 mL/kg for the non-obese
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Volume Replacement
Avoid rapid rehydration
Lessen cardiopulmonary compromise.
Administer Hetastarch at recommended
volumes per kilogram of IBW 20 mL/kg
Albumin 5% and 25% used as indicated
Support circulatory volume and oncoticpressure.
Replace blood loss with crystalloid
3:1 ratio
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PathophysiologyRespiratory
There is a clear association between dyspnea andobesity. Obesity increases the work of breathingbecause of the reductions in both chest wall
compliance and respiratory muscle strength
Excess metabolically active adipose + workload onsupportive respiratory muscle
CO2 production
Hypercarbia
O2 consumption
Hypoxia
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Time to desaturation
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FRC.FRC..FRC..FRC. F RC
Obesity in anaesthesia and intensive care
J. P. Adams and P. G. Murphy British Journal of Anaesthesia, 2000, Vol. 85, No. 1 91-108
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PathophysiologyRespiratory
Restrictive lung disease
Decreased chest wall compliance
Diaphragm forced cephalad Decreased lung volumes
Accentuated by supine and Trendelenbergpositions
FRC may fall below closing capacity Alveolar collapse
Ventilation / perfusion mismatch
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Changes in Pulmonary
Volumes and Function Tests Tidal volume
Normal or decreased
Inspiratory reserve volume
Decreased
Expiratory reserve volume
Greatly decreased
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Changes in Pulmonary
Volumes and Function Tests
FRC
Greatly decreased
Direct inverse relationship between BMI
and FRC
FEV1
Normal or slightly decreased
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PathophysiologyRespiratory Relatively hypoxemic
Occasionally hypercapnic
Obesity-hypoventilation (Pickwickian syndrome)
Obesity usually extreme
Hypercapnia
Cyanotic / hypoxemia
Polycythemia
Pulmonary HTN
Biventricular failure
Somnolence
Obstructive sleep apnea syndrome (OSAS)
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Obesity alters upper airway anatomy
Increased fat deposition in pharyngeal
tissues increases the likelihood of
pharyngeal wall collapse, which can
complicate the performance of rapidsequence intubation
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OSAS
Definition
10 seconds or more of total cessation of
airflow despite respiratory efforts
Clinically relevant
5 episodes per hour
30 episodes per night
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OSAS
Snoring
Dry mouth and short arousal during sleep
Partners report apnea pauses during sleep
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OSAS
More vulnerable to airway obstruction
Opioids
Sedatives
More vulnerable in supine or Trendelenberg
position
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Detecting OSAS
Nocturnal polysomnography
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PathophysiologyGI
incidence
Gastroesophageal reflux
Hiatal hernia
abdominal pressure
Severe risk of aspiration
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PathophysiologyGI
After 8 hour fast
85 90% of morbidly obese patients
have
Gastric volumes > 25 ml
Gastric pH < 2.5
A th ti C id ti
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Anesthetic Considerations:
Preoperative
risk for aspiration pneumonitis if reflux history
Consider H2 antagonist ( pre, intra and post )
Metoclopramide, Ranitidine or Ondansetron
Sleep apnea, asthma, smoking
Avoid unnecessary respiratory depressants
BHT (breath holding time)
Assess for
Cardiopulmonary reserve
ECG & X-ray Chest, if necessary echocardiography
LFT & RFT
ABG
PFTs
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Anesthetic Considerations:
Preoperative
BP with appropriate size cuff
Plan / examine for venous / arterial
access Possible regional anesthesia
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AIRWAY ASSESSMENT
Obesity and airway difficulty
The goal of airway assessment is to identifyclinical features that predict difficulty in any
of the following areas of emergency airway
management:- Ventilation with bag-mask or extraglottic
device
- Laryngoscopy and endotracheal intubation
- Surgical airway performance
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Anesthetic Considerations:
Preoperative Airway Assessment
Limited TM joint mobility
Limited atlanto-occipital mobility
Narrow upper airway
Small space between mandible and sternal
fat pads
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The Mallampati classification fordifficult laryngoscopy and intubation
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Neck Circumference
Normal neck circumference in cm is
weight in kg / 2
Normal neck cir. at 7o kg is 35 cm
If it increase by 13 % then difficultintubation is counted
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Bag-mask ventilation
Obesity makes bag-mask ventilation more difficult Redundant upper airway soft tissue coupled with
increased body mass results in increased airwayresistance
Higher pressures are required to ventilateeffectively, and this can lead to difficulty
maintaining a mask seal
The MOANS mnemonic for difficult bag
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The MOANS mnemonic for difficult bag
mask ventilation
Mask seal
Obesity/obstruction
Aged (over 55 years)
No teeth
Stiff lungs
d h l b
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Endotracheal intubation
Studies assessing emergency airway management in obese patients are
scarce. Nevertheless, multiple studies performed in the operating roomhave found an association between obesity and difficult laryngoscopy andendotracheal intubation :
19 Lundstrm, LH, Mller, AM, Rosenstock, C, et al. High body mass indexis a weak predictor for difficult and failed tracheal intubation: a cohort
study of 91,332 consecutive patients scheduled for direct laryngoscopyregistered in the Danish Anesthesia Database. Anesthesiology 2009;110:266.
20 Juvin, P, Lavaut, E, Dupont, H, et al. Difficult tracheal intubation is morecommon in obese than in lean patients. Anesth Analg 2003; 97:595.
21 Lavi, R, Segal, D, Ziser, A. Predicting difficult airways using theintubation difficulty scale: a study comparing obese and non-obesepatients. J Clin Anesth 2009; 21:264.
22 Brodsky, JB, Lemmens, HJ, Brock-Utne, JG, et al. Morbid obesity andtracheal intubation. Anesth Analg 2002; 94:732
The LEMON mnemonic for predicting the
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The LEMON mnemonic for predicting the
difficult emergency airway
Look externally
Evaluate 3-3-2
Mallampati
Obstruction/Obesity
Neck mobility
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Endotracheal Intubation
Position
Preoxygenation
Equipments
Backup plan
Help
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RAMP position
A) In the supine patient,access to the airway isobstructed.
B) With the patient
propped on linens in theRAMP position, access tothe airway is improved. Inthis position, an imaginary
horizontal line can bedrawn from the externalauditory meatus to the
sternal notch.
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Airway
Airtraq optical laryngoscope
Endotracheal tube introducer ("bougie")
video laryngoscope
The laryngeal mask airway (LMA) allows flexible
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The laryngeal mask airway (LMA) allows flexiblebronchoscopy and ventilation to be performedunder general anesthesia. The device can also
serve as an excellent rescue airway.
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Surgical airway
Excessive soft tissue in the anterior necklimits access to the cricothyroid
membrane and makes it difficult to
identify the anatomic landmarks neededto perform a cricothyrotomy
The SHORT mnemonic for assessing
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g
difficult cricothyrotomy
Surgery (or other airway disruption)
Hematoma (or infection or abscess)
Obesity (or other access problem)
Radiation (or other tissue deformity)
Tumor
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Induction Airway Equipment
Light Stylet
Gum elastic bougie
Oral airway, Nasopharyngeal Airway
LMAs
ETT with stylet
Anesthetic Considerations:
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Anesthetic Considerations:
Induction
Consider awake intubation
Avoids airway collapse
Minimal to no sedation LMA is good alternative for temporary
mechanical ventilation in grossly and morbidobese patient
Consider tracheotomy kit and surgeon
standing by
Anesthetic Considerations:
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Anesthetic Considerations:
Intraoperative
Awake fiberoptic intubation if difficult airwaysuspected
Breath sounds distant
ETCO2 more important
Relatively high FIO2 may be needed in:
Lithotomy
Trendelenberg Prone
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VENTILATION
In morbidly obese patients, the best strategy forventilation is to deliver TV according to IBW (8-10ml/kg )
Apply 5 cm H2O PEEP in order to decrease theincidence of atelectasis.
Minute ventilation and ETCO2 need to be monitored
closely Usually use pressure control ventilation
The metabolism and pharmacokinetics
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The metabolism and pharmacokinetics
of Drugs
Lipophilic drugs have a larger volume of distribution (Vd),since the Vd is dependent upon the amount of adiposetissue
Obese patients are known to have higher glomerular
filtration rates, and renally excreted drugs may haveshorter half-lives since their elimination is directlyproportional to creatinine clearance
Obesity does not generally affect the clearance of drugs
that are metabolized by the liver
Because of the complexity of obesity-relatedpharmacokinetic changes and because detailed data arelacking for many drugs, individual drug dosing for obese
patients remains controversial
Obesity: Pharmacology
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Obesity: Pharmacology
Overdosing of pre medication and anesthesia drugsin obese patient is very common
doses should be calculated on predicted lean
body weight Lean body weight = body weight - fat weight
Avoid IM injection due to unpredictableabsorption
If possible, avoid narcotics and sedation in obesepatient
Obesity: Pharmacology
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Obesity: Pharmacology
Propofol at TBW
Thiopental at IBW
Midazolam at IBW
Scolene at TBW Vcuronium at IBW
Atracurium at TBW
Rocuronium at IBW
Fentanyl & Sufentanyl at TBW
Remifentanil at IBW
Ideal body weight and approximate lean
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y g pp
body weight in obesity (adult)
Height (in) Height (cm) IBW* (kg)ApproximateLBW in classIII obesity
(kg)
Female(adult)
60 152 46 52
65 165 57 60
70 178 68 70
75 191 80 80
Male (adult)
60 152 50 63
65 165 62 73
70 177 76 85
75 191 89 97
80 203 103 112
Anesthetic Considerations:
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Anesthetic Considerations:
Intraoperative
Morbidly obese patient should never lie flat
Semi-Fowlers position
Upper body elevated 30 40
Semi-recumbent position
Best position during post-operative
period
PositionTrendelenburgReverse
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g
RTP is bestintraoperative position
Can amelioratedeleterious effects ofsupine position
RTP is 30 degree head upposition
RTP
pulmonarycompliance
FRC
Returned P(A-a)O2 tobaseline
RTP may be a bettersolution than
Large TV and PEEP
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monitoring
ECG
Pulse Oxymeter
Blood pressure
Temperature
Inspired oxygen concentrationCapnography
Arterial catheter to continuously measure BPand blood gases ( if medically indicated )
CVP catheter
Urinary catheter
Advance monitoring according to Surgery
Anesthetic Considerations:
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Anesthetic Considerations:
Intraoperative
Regional anesthesia
Technically more difficult
Require 20 25% less LA for Spinal or Epiduralanesthesia because of
(Epidural fat and distended epidural veins)
Combined epidural/general(GA) preferred to
decrease GA requirement Epidural anesthesia may postoperative
respiratory complications
Anesthetic Considerations:
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Anesthetic Considerations:
Intraoperative
Pulmonary compliance and FRC Worsened by GETA and high intraabdominal
pressure
Opening the abdomen or lifting thepanniculus FRC
Improves oxygenation
G l f f h
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Goals for Maintenance of Anesthesia
Strict maintenance of airway Adequate skeletal muscle relaxation
Optimum oxygenation
Maintenance of anesthesia with inhalation andintravenous agents
Avoid residual effects of muscle relaxants
Appropriate intraoperative and postoperative tidal
volume
Effective postoperative analgesia.
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Anesthetic Considerations:
Postoperative Respiratory failure risk increased by
Preoperative hypoxia
Thoracic or upper abdominal surgery Vertical incision
Delayed extubation until Complete reversal of muscle relaxation
Patient fully awake
Follows commands
Anesthetic Considerations:
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Anesthetic Considerations:
Postoperative
Supplemental O2 after extubation
Transport from OR to Recovery room
45 degree head up position
Unload diaphragm
Improves oxygenation
Improves ventilation
CPAP and BiPAP should available
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Anesthetic Considerations:
Postoperative PCA
Can provide good pain relief
Dose based on IBW
NSAIDs, Local anesthetic infiltration
Epidural route is preferred
Administration of smaller dose than IV
route
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The first intubation attempt should be by the most experiencedintubator
If the first best attempt determines difficult or impossiblelaryngoscopy or intubation, change to either Rescue Airway plan (ifpatient condition is critical), or earlyFiberoptic Intubation beforeairway trauma worsens the situation
Large breasts may get in the way of the laryngoscope handle (half-size handles are available).
Response to induction agents is less predictable for intubation
Confirmation of endotracheal intubation should be by three ormore methods including either capnometry or capnography
Obese patients will desaturate oxygen rapidly
All obese patients with airway problems or impending intubationshould have 100% oxygen
In failed Intubation by all methods, in emergency Percutaneouscricothyrotomy or surgical tracheostomy
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Message
The anesthetic management of the clinicallysevere obese patient requires meticulouspreoperative, perioperative and postoperativecare. Careful planning is essential before taking
the patient in the operating room. To haveexcellent outcome, a multidisciplinary approach,including the primary care physician,anesthesiologist, surgeon, nursing staff andsocial worker is necessary.
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L f A h i Th E i l
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Laws of Anesthesia: The Essentials
Air goes in and out. Blood goes round and round.
Numb is good.
Numb and hemodynamically stable is better.
Numb, hemodynamically stable and amnestic isbest.
Numb, hemodynamically stable, amnestic andwarm is better yet.
Dead meat dont beat.
Evidence-based medicine and the critically
ll b
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ill bariatric patient
Subject Study Weight exclusion criteria
Early goal-directed thrapyin patients with sepsis
Rivers, 2001 N/A
Low tidal volumes in ARDS ARDSnet, 2000Excluded if weight >1kg/cm of height
Low-dose corticosteroidsfor refractory shock
Annane, 2002 N/A
Intensive insulin therapy van den Berghe, 2001N/A; mean body massindex = 26
Activated protein C Bernard, 2001 Excluded if weight >135 kg
Daily dialysis in renalfailure
Schiffl, 2002 N/A
Effect of PA catheterSandham, 2003 N/A
Richard, 2003 N/A
Clinical and laboratory data for the evaluation
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y
of overweight patients