Article
Reference
Treating hypoxemic patients with SARS-COV-2 pneumonia: Back to applied physiology
BENDJELID, Karim, GIRAUD, Raphaël
BENDJELID, Karim, GIRAUD, Raphaël. Treating hypoxemic patients with SARS-COV-2
pneumonia: Back to applied physiology. Anaesthesia Critical Care & Pain Medicine , 2020, vol. 39, no. 3, p. 389-390
DOI : 10.1016/j.accpm.2020.04.003 PMID : 32305591
Available at:
http://archive-ouverte.unige.ch/unige:143204
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Editorial
Treating hypoxemic patients with SARS-COV-2 pneumonia:
Back to applied physiology
Asmedicaldoctors,wearefacingterribleandunprecedented challengesin theprovisionofmedical caretopatients infected withSARS-CoV-2pneumonia(severeacuterespiratorysyndrome coronavirus2).IntensiveCareUnitsaroundtheworldarestraining as demand for intubation and mechanical ventilation (MV) continuesits ever-upward curve.In this regard,as intensivists, wewouldliketosharesomethoughtsonhowappliedphysiology mightrelatetoSARS-CoV-2pneumonia(pneumonitis).
Wewilldescribeourexperienceindealingwithpatientswho wereintubatedandventilatedwithpositivepressureMV.Upto thisday,wehaveadmitted89patientsintoourcriticalcareunitof which92%neededinvasiveMV(uptothisday26patientshave been discharged). During the first two days of mechanical ventilation,themajoritysurprisinglyexhibitedgoodlungcompli- ance with preserved lung mechanics and diffuse and bilateral groundglassareasonComputedTomographyandcoalescentB2 linesonbedsidelungultrasound[1].Itappearsthatattheinitial stage, SARS-CoV-2 pneumonia induces high permeability-type pulmonaryoedema witha large capillaryleaksyndrome and a significant venous admixture (poorly aerated-perfused lung regions) concomitant with a loss of hypoxic vasoconstriction (Euler-Liljestrandmechanism)[2].Thus,theobservedbenefitafter intubationandpositivepressureMV,attheearlystageofSARS- CoV-2 pneumonia, does not seem to be related to the usual recruitmentoflungvolumebutmainlytoa decreasein venous return,rightventricularoutput,transpulmonarybloodflowand finallyintrapulmonaryshunt[3,4].Thepositiveimpactofreverse TrendelenburgpositioningonSaO2values,inselectedpatients,can bespectacular.
However,somepatientswithahistoryoflungdisease,and/or latebacterialsuperinfection,orfollowing48hoursofMVthereby inducingheterogeneousmechanicalstress,willpresentatypical inflammatory ARDS phenotype with large consolidations pre- dominatingindependentlowerlobes[5].Thepresentcondition
generates large areas of true pulmonary shunt (non-aerated/
perfusedlungregions),thatfurtherworsenoxygenation,decrease respiratory complianceandmayrequireahigherPEEP,a lower tidalvolume,prone positioning, neuromuscularblockingagents and,fortheworstcases,VV-ECMO.Obviously,thissecondpheno- type,moretypicalofclassicalARDS,willneedalongerMVperiod.
Interestingly, the initial, high permeability-type pulmonary oedema phenotype that characterises SARS-CoV-2 pneumonia with apparently preserved lung mechanics, while undergoing positivepressureMV,mayshifttothetypicalARDSphenotypein absenceoftimelyweaningMV.
Acloserlookatthepathophysiologyofthishypoxemicalveolar state reveals that a decrease in venous admixture induced by decreasing in transpulmonary blood flow may be obtained mechanically (PPV), chemically (nitroglycerin in cardiogenic pulmonary oedema), by body posture (reverse Trendelenburg positioning)oracombinationofthese.However,whencapillary hydrostatic pressure is low or normal as observed in high permeability-typepulmonaryoedema,amedicationlikealmitrine bismesylate,that promoteshypoxic pulmonaryvasoconstriction [6],mayimprovehypoxemiaresultingfromSARS-CoV-2pneumo- nia. Indeed, there are several studies indicating that upon intravenousadministration,almitrineiseffectiveinhumanARDS byincreasingarterialPO2iftheriseinpulmonaryarterypressureis adequately supported bytherightventricle and cardiacoutput does not fall [7]. Unfortunately, almitrine is not available in Switzerland.
ItisnotablethatpatientswithsevereSARS-Cov-2pneumonia tendtobeelderlyand/orhavelimitedorgansfunctionalreserve.In thisregard,wemaythinkthatitisunfortunatetobeforcedtotreat selected clinically stable patients with temporary hypoxemia (silent hypoxemia) using invasive MV to decrease their initial venousadmixture,wheninsteadwecouldpotentiallytreatthem bydecreasingtranspulmonarybloodflow(almitrine,continuous positiveairwaypressure[CPAP],reverseTrendelenburgposition- ing,fluiddepletion...).Indeed,in-hospitalmortalityreportedfrom Wuhan was very high among patients requiring invasive mechanicalventilation,ofwhombetween62%and97%ofpatients died[8].
Thepresentmessagehighlightsthatthemortalityisveryhigh among patients with severe SRAS-CoV-2 pneumonia who are underorrequiringMV[8].Thus,anytherapyandproceduresthat could prevent intubation and MV, or enhance MV weaning, withoutfurtherdeteriorationofthepatient’sparlousstatewould AnaesthCritCarePainMedxxx(2020)xxx–xxx
ARTICLE INFO
Keywords:
Hypoxemia Venousadmixture Shunt
SARS-CoV-2pneumonia GModel
ACCPM-649;No.ofPages2
Pleasecitethisarticleinpressas:Bendjelid K,Raphae¨ G.TreatinghypoxemicpatientswithSARS-COV-2pneumonia:Backtoapplied physiology.AnaesthCritCarePainMed(2020),https://doi.org/10.1016/j.accpm.2020.04.003
https://doi.org/10.1016/j.accpm.2020.04.003
2352-5568/C 2020Socie´te´ franc¸aised’anesthe´sieetdere´animation(Sfar).PublishedbyElsevierMassonSAS.Allrightsreserved.
bewelcome.Thepresentapproachseemsrationalinasituation wherewearefacingterriblechallengesintheprovisionofICUbeds andventilators[9].Allproceduresseemjustifiedaslongastheydo notobscureclinicaldetectionoftheneedfor MVanddoes not increase the transmission dynamics of COVID-19 by aerosol- generating procedures (in absenceof protective equipment for healthcareprofessionals).
AsincerethanksyoutoDrJohnVogel,ConsultantinIntensive CareandAnaesthesiaatEalingHospitalNHSTrustforhisdiligent proofreadingofthepresentmanuscript.
Disclosureofinterest
Theauthordeclaresthathehasnocompetinginterest.
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KarimBendjelida,b,c,*,GiraudRaphae¨a,b,c
aIntensivecaredivision,universityhospitals,Geneva,Switzerland
bGenevahaemodynamicresearchgroup,Geneva,Switzerland
cFacultyofmedicine,Geneva,Switzerland
*Correspondingauthorat:Intensivecaredivision,university hospitals,Geneva,Switzerland E-mailaddress:karim.bendjelid@hcuge.ch(K.Bendjelid).
Availableonlinexxx Editorial/AnaesthCritCarePainMedxxx(2020)xxx–xxx
2 GModel
ACCPM-649;No.ofPages2
Pleasecitethisarticleinpressas:Bendjelid K,Raphae¨ G.TreatinghypoxemicpatientswithSARS-COV-2pneumonia:Backtoapplied physiology.AnaesthCritCarePainMed(2020),https://doi.org/10.1016/j.accpm.2020.04.003
