Intensive Care Medicine An Introduction · Intensive Care Medicine An Introduction ... critical care beds throughout a hospital. These levels of care will give you an idea of the

IntensiveCareMedicine

AnIntroduction

Dr.R.BaylissandDr.S.P.Holbrook

(Email:[email protected];[email protected])

Theaimofthisdocumentistohelpprepareyouforyourtimeinintensivecareas

partofthefourthyearanaesthesiamodule.WalkingontoanIntensiveCareUnit

(ICU)forthefirsttimemayfeelprettydaunting.Staffinthisenvironmentcarefor

themostcriticallyillandclinicallychallengingpatientsinthehospital.Notonly

willyouexperiencethesepatientsfirsthand,butalsoyouwillencounterthevast

arrayofinterventionsutilisedtosupportthem.Hospitalintensivecareservices

havebecomeincreasinglycomplex.Wehopethatthisintroductionwillhelp

improveyourunderstandingofthetechnologyandequipmentthatyoumay

comeacross.

CriticallyIllPatients‐LevelsofCare

In the modern hospital environment clinical staffing and resources should be provided to meet the

patient’sneedse.g.patient’srequiringintensivecarewillhaveanursetopatientratioof1:1,whereas

eachnurseonanormalwardmaybelookingafter10ormorepatients.ThefollowingdescribestheUK

classificationofcriticalcarebedsthroughoutahospital.Theselevelsofcarewillgiveyouanideaofthe

patientsyoumightexpecttofindincriticalcarewards.

Level0 Patientswhoseneedscanbemetthroughnormalwardcaree.g.

observations>4hourly

Level1 Patientsatriskoftheirconditiondeterioratingorrecentlydischarged

fromahigherlevelofcare

Patientsneedingadditionalmonitoring(includingminimum4hourly

observations),clinicalinterventions,inputoradvicefromthecriticalcare

outreachsupportteam(seebelow)

Level2 Patientsneedingpre‐operativeoptimisationORneedingextended

postoperativecare(e.g.aftermajorelectiveoremergencysurgeryin

highriskpatients)ORpatientssteppingdownfromLevel3care

Patientsreceivingsingleorgansupport:

• Basicrespiratorysupporte.g.>50%oxygenviafacemask,non‐

invasiveventilation

• Basiccardiovascularsupporte.g.centralvenouspressure

monitoring,singleintravenousvasoactivedruguse

• Advancedcardiovascularsupporte.g.multipleintravenous

vasoactivedruguse,cardiacoutputmonitoring

• Renalsupporte.g.renalreplacementtherapy

• Neurologicalsupporte.g.intra‐cranialpressuremonitoring

• Dermatologicalsupporte.g.majorburnscare

Level3 Patientsrequiringadvancedrespiratorysupportalone(e.g.invasive

mechanicalventilation)ORpatientsrequiringaminimumof2organs

supportede.g.basicrespiratoryandrenalsupport

Traditionally the levels of care provided identified critical carewards i.e. Level 2 = High Dependency

Unit,Level3=IntensiveCareUnit.Ideally,patientlocationshouldnotdeterminetheirlevelofcare.The

creation of critical care outreach teams (CCOT) has permitted the provision of critical care skills to

patients in normal wards (“critical care without walls”). Find outmore about the CCOT: explore the

literatureoroneofthetextsinthebibliography;evenbetter,trytospendtimewiththeCCOTonyour

assignedICUtogainsomeinsightintotheirworkandhowtheysupportstaffonnormalwards.

TheIntensiveCareBedSpace

Figure1.A‘typical’intensivecarebedspace

Intensivecarebedspacesaredesignedspecificallytoprovidethecomplexcarethatpatientsrequire.

Suction

Monitor:providingareal‐

timedisplayofthe

patient’sphysiological

variablese.g.ECG,oxygen

saturation(SpO2),

respiratoryrate,arterial

bloodpressure,central

venouspressure.

MechanicalVentilator

Oxygenandmedicalair

supply

Drug/fluidinfusionpumps

Pressurerelievingmattress

AirwaySupport

Many patients on the intensive care unit require invasive ventilatory support. Invasive ventilation

requiresadefinitiveairwaydevicetoprotecttheairwayfromaspirationofgastriccontents.Themost

commonlyuseddevicesareoralendotrachealtubes(ETTs)ortracheostomytubes.

Endotrachealintubation

The oral ETT (Figure 2) consists of a tube that is passed down the pharynx and larynx that permits

deliveryofpositivepressureventilation.ThetipoftheETTispositionedinthetracheaabovethecarina.

Ithasacuff, inflatedwithair,whichsitsjustbelowthevocalcords.Theintubatedpatientisunableto

speakasthereisnoairflowoverthevocalcords.Complicationsassociatedwithendotrachealintubation

are shown in Figure 3.Most complications can beminimised through operator skill and experience.

However,aspirationmayoccur inanemergencysituation,as thepatient isunlikely tohaveanempty

stomach.

Traumatoanysectionof theairway

includingmouth,teeth,trachea

Aspirationofstomachcontents

Tubemalposition

AirwayObstruction

EarlyComplications:

Hypoxiafromprolongedattempts

Infection

Mucosal damage to mouth or

trachea(fromcuffpressure)

Injurytovocalcords

Latecomplications:

Trachealstenosis

Figure3.Complicationsofendotrachealintubation

Tracheostomy

Atracheostomytube(Figure4) isapercutaneousairwaydeviceusedforpatientsrequiringprolonged

airway or ventilatory support. Patients tolerate them better than oral ETTs as they provide a more

comfortable airway: this may permit withdrawal of sedation and aid weaning from mechanical

ventilation. Tracheostomies may avoid some of the complications associated with long‐term oral

endotrachealintubation,buttheyhaverisksoftheirown(Figure5).Thetracheostomytubeisinserted

throughanincisionmadeintheanteriorneckbetweenthetrachealcartilaginousrings.Thecuffisthen

inflated to forma seal against the trachealwall providing a definitive airway. The insertion is usually

observedbyasecondoperatorusingabronchoscopetoensurecorrectstomaandtubeplacement.

Figure2.Cuffedoral

endotrachealtube

1.Vocalcords

2.Thyroidcartilage

3.Cricoidcartilage

4.Trachealcartilage

5.Ballooncuff

Figure4.Atracheostomyinsitu Figure5.Complicationsoftracheostomy

Haemorrhage

Pneumothorax

Tubemisplacement

Surgicalemphysema

Blockagewithsecretions

Stomalinfection

EarlyComplications:

Mucosalulceration&

perforation;tracheo‐

oesophagealfistula

Late haemorrhage (erosion

intoinnominateartery)

Trachealgranulomata

Trachealstenosis

Scarring,persistentsinus

LateComplications:

Trachealnecrosis

Breathing(OxygenationandVentilation)

Oxygenationissimplytheprovisionofoxygentothetissues.Ventilationisthedeliveryofoxygentothe

lungsandtheremovalofcarbondioxide.Therearevariousartificialmeanstofacilitatethese.

Oxygentherapy

Increasingapatient’sinspiredoxygenconcentrationallowsbetteroxygendeliverytothetissues.Itisthe

simplestformofrespiratorysupportandwillbediscussedindepthintherespiratoryphysiologytutorial.

In intensivecare,oxygen isdeliveredusingdevices thatdelivera fixedconcentrationofoxygenwhilst

warming and humidifying the oxygen to improve patient comfort and reduce complications such as

mucusplugging.Oxygentherapyisnotwithoutitsrisksandhighconcentrationsofinspiredoxygenfora

longperiodoftime(e.g.>60%for>48hours)mayresultinpulmonaryinjury.

Non‐invasiverespiratorysupport

Two commonly used techniques are continuous positive airway pressure (CPAP) and non‐invasive

ventilation(NIV).CPAPisusedtosupportpatientsinacutehypoxicrespiratoryfailureortoassistwith

weaningfrominvasiveventilation.Itprovidesaconstantpressureduringinspirationandexpiration.NIV

incorporatesCPAPinadditiontoanincreasedpressuretriggeredbythepatient’sinspiration.Thisassists

the patient’s own breathing, reducing the amount they have to ‘work’, and helping the patient to

eliminateor‘blowoff’carbondioxide.NIViscommonlyavailableinrespiratorycareunitsandhasbeen

demonstratedinclinicaltrialstopreventtheneedforinvasiveventilationinpatientswithCOPD.Non‐

invasivetechniquesrequirethepatienttobealertandco‐operative:theymustbeabletocough,make

their own respiratory effort and protect their airway. They typically use a tight fittingmask over the

noseandmouth,althoughtheymaybedeliveredviaahoodthatfitsovertheentirehead(Figure6).A

highflowblowerunitoraventilatorprovidespositivepressure.

Figure6.CPAP/NIVdeliveryviafacemaskandhelmet

Patients often find it difficult to tolerate the tight fitting mask and the alternative helmets are

disorientating,noisyandunwieldy.Howeverbothmayberemovedforshortperiodstoalloweatingand

drinkingandreappliedlater.

IntermittentPositivePressureVentilation(IPPV)

During normal breathing the inspiratory muscles contract

increasingthethoracicvolume.Thiscreatesnegativepressure

within the thorax and causes inflow of air. Expiration is

passive. During IPPV the ventilator creates positive pressure

within the endotracheal tube driving air into the lungs.

Ventilatorsmay be set to deliver a specific concentration of

oxygen, number of breaths per minute, and tidal volume

whichmaybealteredtooptimisethepatient’sventilationand

oxygenation. More sophisticated ventilators (Figure 7), like

those used in the ICU, are also capable of sensingwhen the

patientistryingtobreatheandsynchronisingthedeliveryofa

“breath”tosupportthepatient’sownbreathing.Thesemodes

are especially useful in assisting patients in weaning from

ventilation.

Themain advantage of IPPV is that oxygenation and ventilation can be achievedwithout the patient

makinganyrespiratoryeffort,howeveritisnotwithoutitscomplications.

• Ventilator‐associatedpneumonia(VAP)

• Ventilator‐associatedlunginjury

• Barotraumae.g.pneumothorax

• Haemodynamicinstability

VAPiscommon;inadditionitincreaseslengthofhospitalstayanddoubleshospitalmortality.However,

thesetopicswillnotbeexploredanyfurtherhere.Mechanicalventilationisapostgraduatesubject,but

feelfreetoexploretheliteratureorquestionthecliniciansontheICUifyouareinterested.

Figure7.Exampleofanintensivecare

invasiveventilator

Circulation

Interventions used to support the circulation in intensive care patients are used to prevent

complications relating to hypoperfusion of vital organs, especially the kidneys. Hypotension may be

relatedtosepsis,hypovolaemia,cardiacdysfunction,anaphylaxis,oranumberofotherpathologies.

Fluids

Themostcommonlyusedandeffectiveinterventiontosupportthecirculationisinfusionofintravenous

fluids. This topicdiscussed indepth inboth theCardiovascularPhysiologyTutorial and the lectureon

FluidManagement. Fluid resuscitation should begin on the normalwards butwill continue in critical

careareasalongwithmoresophisticatedinterventions.

Vasoactivedrugs

A patient must always be adequately fluid resuscitated before considering vasoactive drugs.

Cardiovasculardrugsusedinintensivecareinclude:

• Inotropes Increasethecontractileforceofthecardiacmuscleincreasingstroke

volume

• Chronotropes Increasetheheartrate

• Vasopressors Constrictthearterialtreeincreasingthesystemicvascularresistance

The majority of the drugs used have more than one of these effects. Most of these drugs require

administration intoacentralveinbecauseoftheriskoftissue ischaemiasecondarytoextravasation if

giventhroughperipheralveins.Theyaregivenasacontinuousinfusionallowingcarefultitrationofthe

dose.ThemostcommonagentsusedareshowninFigure8.

Drug ReceptorsAffected Inotrope Chronotrope Vasopressor

Adrenaline α1β1β2 Yes Yes Yes

Dobutamine β1β2 Yes Yes No

Noradrenaline α1β1 Yes No Yes

Phenylephrine α1 No No Yes

Figure8.Effectsofcommonvasoactivedrugs

Apart from dobutamine all these drugs increase vascular tone. This increases systemic vascular

resistance, raising arterial blood pressure and thus improving vital organ perfusion. It must be

remembered that the use of these drugs is not devoid of risk: patients should always be receiving

invasive haemodynamic monitoring (via arterial and central venous catheters) and care from

appropriatelytrainedmedicalandnursingstaff.Otherdrugs,whichmayyoumayseeused,includeanti‐

diuretichormone(vasopressin)anddopamine.

Figure9.Anexampleofa

machineforcontinuousveno‐

venoushaemofiltration.

RenalReplacementTherapy

Acute kidney injury is common in critical care patients. It is most

commonly a secondaryeffect causedbyproblems suchas shockor

sepsisratherthanaprimaryproblemwiththekidneys.Acutekidney

injury is demonstrated by a falling urine output to less than

0.5ml/kg/houroranacutedeteriorationinglomerularfiltrationrate,

manifestedbyrisingserumcreatinineandurea.Forthis reasonsick

patientswhoneedcriticalcarearecatheterisedearlytoenableurine

output monitoring. Untreated acute kidney injury may result in

hyperkalaemia,acidosis,fluidoverloadanduraemia.

The techniques available to treat a patient with failing kidneys

include intermittent haemodialysis (as used in patients with end‐

stage renal failure) or a variety of continuous renal replacement

therapies.Patients incriticalcareareasare lessabletotoleratethe

largefluidchangesassociatedwithintermittentdialysis.Continuous

techniquesareconsideredmorephysiologicalasfluidandelectrolyte

changes occur continuously at a slower rate. The most commonly

used technique in intensive care is continuous veno‐venous

haemofiltration(Figure9)whichiscarriedoutviaalargedoublelumencatheterinsertedintoacentral

vein.

5‐10%ofpreviouslynormalpatientsrequiringrenalreplacementtherapyforacutekidneyinjurywillgo

ontorequirelongtermrenalreplacementtherapy.

Sedation,AnalgesiaandMuscleRelaxation

Sedation is administered to aid tolerance of ETTs and to reduce patient pain and anxiety. It typically

consists of an infusion of an analgesic, most often an opioid, and a sedative agent. Ideally both

analgesics and sedatives should act quickly but have a short half‐life allowing sedation to wear off

quickly. Synthetic opioids such as alfentanil or remifentanil are commonly used analgesics. Themost

frequentlyused sedative ispropofol, an intravenousanaesthetic inductionagent: it canbegivenasa

continuousintravenousinfusionforsedation.

Sedation is alsoused to facilitate ventilationand in somecircumstancesmaybe required formedical

reasonse.g.treatmentofstatusepilepticusorreducingthemetabolicdemandofthebrainaftersevere

headinjury.Sedativesshouldbeusedassparinglyaspossibleandstoppedattheearliestopportunity.

Insufficient sedation can lead to poor ventilation or agitation but prolonged sedation is linked with

increased risk of chest infection, neuropathies and venous thromboembolism. At least once a day

patientsshouldhavea“sedationhold”.Duringthistimeallsedationisstoppedtopreventaccumulation

ofsedativedrugs,allowingassessmentofneurologicalfunctionandreducingtheriskofcomplications.

Patients who have a prolonged need for ventilation will often have their sedation stopped after a

tracheostomy has been performed to allow physiotherapy, interactionwith clinical staff and visitors,

andultimatelytopermittheresumptionofactivitiesofdailyliving.

Musclerelaxantsareadministeredtoaidinitialintubationbutcontinuousinfusionsarerarelyrequired.

SpecialistUnits

Cardiac intensivecare ispredominantlyusedbypatientsrecoveringaftercardiacsurgeryandprovides

specialist care such as intra‐aortic balloon pumps. Neurosurgical intensive care unitsmainly care for

patientswith acuteneurosurgical problems such as subarachnoid haemorrhageormajor head injury.

Theyprovidespecialistcaresuchasintracranialpressuremonitoring.

Conclusion

Thisinformationhasbeendevelopedtosupplementyourtimeintheintensivecaredepartmentandis

not intendedasan indepthreview.Feel freetoexplorethetopicsthroughadditionalreadingbutthe

informationisnotcoreknowledgethatyouwillbeexaminedon.However,abasicunderstandingofthe

treatmentsdescribedwillhelpyougetthemostoutofyourplacement.Pleasequestionthecriticalcare

nursingandmedicalstaffonyourplacementifyouwishtolearnmore:this isanidealopportunityfor

youtaptheirknowledgeandexperience.

BibliographyandFurtherReading

Oh’s Intensive CareManual. 6th Edition. 2009. Eds. Berston AD and Soni N. Butterworth, Heineman,

Elsevier.

IntensiveCare.2010.WhiteleySM,BodenhamA,BellamyMC.ChurchillLivingstone.

ABCofIntensiveCare.ArticleseriesinBMJ.1999.Availablefromwww.bmj.com

RespiratorySupportinIntensiveCare.2ndEdition.1999.Eds.SykesKandYoungJD.BMJBooks.

www.ics.ac.uk An excellent resource for Intensivists, UK trainees and patients. Plenty for medical

studentstogettheirteethintoo.HereisthelinkforLevelsofCriticalCare.

http://www.ics.ac.uk/intensive_care_professional/standards_and_guidelines/levels_of_critical_care_for

_adult_patients