Brochard, Laurent

Jonkman, Annemijn

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of increasing PEEP in this setting. Increasing PEEP increasesintrathoracic pressure and leads to challenge the cardiac performance,which may result in a drop in cardiac output (3, 4). Despite observingan increase in SaO2 during incremental PEEP, the drop in cardiacoutput may eventually induce a decrease in oxygen delivery(Figure 1). This effect has been notably reported in patients withCOVID-19 (5, 6). Calculation of oxygen delivery requires thedetermination of cardiac output, hemoglobin concentration, andSaO2, which can be obtained easily at the bedside. Unfortunately,arterial pressure monitoring is not accurate to assess changes incardiac output, which can be noninvasively measured withechocardiography. Therefore, assessing the impact of PEEP onhemodynamics and its influence on oxygen delivery to determine theoptimal PEEP for patients with ARDS could complement the methodproposed by Jonkman and colleagues. It would provide a morecomprehensive understanding of the effects of PEEP and helpoptimize ventilatory strategies for patients with ARDS.Author disclosures are available with the text of this letter atwww.atsjournals.org.Correspondence and requests for reprints should be addressed to MartinDres, M.D., Ph.D., Service de Medecine Intensive – Reanimation(Departement “R3S”), Assistance Publique–Hôpitaux de Paris, SorbonneUniversite, Hôpital Pitie-Salpêtriere, 47-83 Boulevard de l’Hôpital, 75013Paris, France. Email: martin.dres@aphp.fr.References1. Jonkman AH, Alcala GC, Pavlovsky B, Roca O, Spadaro S, Scaramuzzo G,et al.; Pleural Pleasure Working Group (PLUG). Lung RecruitmentAssessed by Electrical Impedance Tomography (RECRUIT): amulticenter study of COVID-19 acute respiratory distress syndrome.Am J Respir Crit Care Med 2023;208:25–38.2. Sahetya SK, Goligher EC, Brower RG. Fifty years of research in ARDS.Setting positive end-expiratory pressure in acute respiratory distresssyndrome. Am J Respir Crit Care Med 2017;195:1429–1438.3. Jardin F, Farcot JC, Boisante L, Curien N, Margairaz A, Bourdarias JP.Influence of positive end-expiratory pressure on left ventricularperformance. N Engl J Med 1981;304:387–392.4. Jardin F, Vieillard-Baron A. Right ventricular function and positive pressureventilation in clinical practice: from hemodynamic subsets to respiratorsettings. Intensive Care Med 2003;29:1426–1434.5. Bonny V, Janiak V, Spadaro S, Pinna A, Demoule A, Dres M. Correctionto: Effect of PEEP decremental on respiratory mechanics, gasexchange, pulmonary regional ventilation, and hemodynamics inpatients with SARS-Cov-2-associated acute respiratory distresssyndrome. Crit Care 2020;24:675.6. Barthelemy R, Beaucote V, Bordier R, Collet M, Le Gall A, Hong A, et al.Haemodynamic impact of positive end-expiratory pressure in SARS-CoV-2 acute respiratory distress syndrome: oxygenation versus oxygendelivery. Br J Anaesth 2021;126:e70–e72.Copyright © 2023 by the American Thoracic SocietyReply to Jimenez and Hyzy and to Le Stang and DresAnnemijn Jonkman1,2 and Laurent Brochard2,3*; on behalf of all theauthors1Department of Intensive CareMedicine, Erasmus Medical Center,Rotterdam, the Netherlands; 2Keenan Research Centre, Li Ka ShingKnowledge Institute, St. Michael’s Hospital, Unity Health Toronto, Toronto,Canada; and 3Interdepartmental Division of Critical CareMedicine,University of Toronto, Toronto, Ontario, CanadaFrom the Authors:We thank Jimenez and Hyzy as well as Le Stang and Dres forcarefully reading our article “Lung RecruitmEnt assessed byeleCtRical Impedance Tomography (RECRUIT): AMulticenterStudy of COVID-19 ARDS” (1). The authors of both lettersacknowledged the importance of our work and the relevance of ourfindings, in particular, the discrepancy that we report between theelectrical impedance tomography (EIT)–based optimal positiveend-expiratory pressure (PEEP) level where overdistention andcollapse are jointly minimized (EIT crossing point) and the PEEPrelated to the highest respiratory system compliance. This stressesthe complex relationship between recruitment and compliance andthe potential benefit of EIT for assessing regional effects of PEEPon the lungs. Furthermore, both letters mentioned the importance ofthe negative correlation between oxygenation and overdistention athigher PEEP levels that we found (1), possibly specific to coronavirusdisease (COVID-19) pathology. This could trigger a vicious circle ofincreasing levels of PEEP and increasing overdistention; such harmfuleffects may, indeed, occur with conventional PEEP approaches(PEEP-FIO2 tables), as also mentioned by Jimenez and Hyzy. Le Stangand Dres further stressed the importance of assessing the effects ofPEEP on hemodynamics in addition to the impact on the lungs, andFigure 1. Determinants of oxygen delivery. EELV=end-expiratorylung volume; EIT=electrical impedance tomography; PEEP=positiveend-expiratory pressure; SaO2 =oxygen arterial saturation.This article is open access and distributed under the terms of theCreative Commons Attribution Non-Commercial No DerivativesLicense 4.0. For commercial usage and reprints, please e-mailDiane Gern (dgern@thoracic.org).Supported in part by Timpel (Sao Paulo, Brazil) and Dr€ager MedicalGmbH (L€ubeck, Germany). The funders played no role in the designand conduct of the study; interpretation of the data; preparation,review, or approval of the manuscript; or the decision to submit themanuscript for publication. The opinions, results, and conclusionsreported in this paper are those of the authors.Originally Published in Press as DOI: 10.1164/rccm.202306-0987LEon June 30, 2023638 American Journal of Respiratory and Critical Care Medicine Volume 208 Number 5 | September 1 2023CORRESPONDENCE we agree with these authors that this important component shouldnot be neglected. However, performing cardiac output measurementsat different PEEP steps would have added a great deal of complexityto the protocol. Of note, performing cardiac ultrasound couldinfluence the reliability of the EITmonitoring (primarily, EIT signaldisturbances related to positioning of the probe on the thorax), andsuch measurements should ideally be performed consecutively.Measurement of regional ventilation/perfusion by contrast-enhancedEIT (saline bolus)—a feature that has recently been developed—and/orperforming volumetric capnography would also be an interestingapproach to studying the effects of increasing levels of PEEP onmacro- andmicrocirculation. We are lacking now a preciseguidance on how these two complex approaches could bedirectly used.Jimenez and Hyzy mentioned that the EIT-based PEEP level didnot differ from the highest compliance approach in nonrecruitablepatients. To clarify, in the high-recruitability patients, this differencewas nonsignificant, as indicated in Figure 5 of our article (1). Overall,the EIT crossing point yielded a slightly higher PEEP level thanwith the compliance approach, but large individual variability wasfound.We agree that differences in recruitability likely explain thedifferences in optimal PEEP level by means of any PEEP settingapproach (conventional or EIT based) in earlier ARDS studies, andthat assessing lung recruitability should be part of a personalizedmechanical ventilation strategy. EIT application is a feasible andpromising technique for assessing lung recruitability at the bedside.One could imagine starting with the recruitment-to-inflation ratio (2)and then using EIT if the lung is found to be recruitable.Individualization of PEEP setting using EIT to improve outcomes is atopic of ongoing research (including a randomized clinical trial:ClinicalTrials.gov identifier NCT 05307913), and we look forward tofurther investigating the role of EIT to optimize personalizedmechanical ventilation.Author disclosures are available with the text of this letter atwww.atsjournals.org.Correspondence and requests for reprints should be addressed toLaurent Brochard, M.D., Li Ka Shing Knowledge Institute,209 Victoria Street, Room 4-08, Toronto, ON, M5B 1T8 Canada.Email: laurent.brochard@unityhealth.to.*L.B. is Deputy Editor of AJRCCM. His participation complies withAmerican Thoracic Society requirements for recusal from review anddecisions for authored work.References1. Jonkman AH, Alcala GC, Pavlovsky B, Roca O, Spadaro S, Scaramuzzo G,et al.; Pleural Pressure Working Group (PLUG). Lung RecruitmEntAssessed by EleCtRical Impedance Tomography (RECRUIT):a multicenter study of COVID-19 acute respiratory distress syndrome.Am J Respir Crit Care Med 2023;208:25–38.2. Chen L, Del Sorbo L, Grieco DL, Junhasavasdikul D, Rittayamai N,Soliman I, et al. Potential for lung recruitment estimated by therecruitment-to-inflation ratio in acute respiratory distress syndrome.A clinical trial. Am J Respir Crit Care Med 2020;201:178–187.Copyright © 2023 by the American Thoracic SocietyRenal Replacement Therapy in a World ofConstraints: Lessons from the COVID-19 PandemicStephane Gaudry1,2,3, Khalil Chaïbi1,2,3, and Didier Dreyfuss2,4,51Service de Reanimation Medico-Chirurgicale, AssistancePublique–Hôpitaux de Paris, Hôpital Avicenne, Bobigny, France;2French National Institute of Health andMedical Research, UMR_S1155,CORAKID, Hôpital Tenon, Paris, France; 3UFR SMBH, UniversiteSorbonne Paris Nord, Bobigny, France; 4Service deMedecine IntensiveReanimation, Hôpital Louis Mourier, Assistance Publique–Hôpitaux deParis, Colombes, France; and 5Universite Paris Cite, Paris, FranceORCID ID: 0000-0002-1105-6785 (S.G.).To the Editor:We read with interest the insightful article byMekontso Dessap andcoworkers titled “Technical Innovation in Critical Care in aWorld ofConstraints: Lessons from the COVID-19 Pandemic” (1).Critical care services worldwide have had to cope withconstrained conditions during the coronavirus disease (COVID-19)pandemic, particularly because of the limited availability oflife-sustaining devices. Mekontso Dessap and colleagues (1) dealtonly with the obvious major problems of respiratory failure andmechanical ventilation. However, COVID-19 also causes an excessnumber of other organ failures, particularly acute kidney injury(AKI), requiring renal replacement therapy (RRT).Among critically ill patients with COVID-19, 56–76% developedAKI (2), and 14–36% of these patients required RRT (2). This ledsome teams to face RRT shortages, leading to significant challengesin RRT delivery during the first wave (3). Acute peritoneal dialysis,a modality seldom used in high-income countries, regained interestin this context (4), resulting in outcomes that were similar to thoseamong patients who received extracorporeal RRT (5).Besides recourse to peritoneal dialysis, a more rational useof extracorporeal RRT can help in coping with such constrainedsituations. Recent evidence demonstrates that RRT initiation can besafely deferred in many patients with AKI, allowing a major reductionin the number who actually need this treatment (6). In addition toa better selection of patients who need RRT initiation, wiser use ofavailable techniques may allow a substantial increase in the numberof patients who can be treated on the same day. Indeed, intermittenthemodialysis may allow the daily treatment of three to four patientswith only one machine, in contrast to continuous RRT techniques.This is not the place to compare the relative merits of each techniquein normal situations, even if current evidence does not provide anydefinite clue as to the superiority of one over the other technique forany patient-centered outcome (6). Catastrophic conditions, such asthose recently encountered, do not allow subtle discussions on thepossible minor advantages of any technique.A frugal approach to critical care should not be limited tomechanical ventilation. The rationalization of RRT delivery is anotherThis article is open access and distributed under the terms of theCreative Commons Attribution Non-Commercial No DerivativesLicense 4.0. For commercial usage and reprints, please e-mailDiane Gern (dgern@thoracic.org).Originally Published in Press as DOI: 10.1164/rccm.202305-0926LEon July 12, 2023Correspondence 639CORRESPONDENCE 

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