Intensive Care Medicine An Introduction · Intensive Care Medicine An Introduction ... critical...
Transcript of Intensive Care Medicine An Introduction · Intensive Care Medicine An Introduction ... critical...
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