COVID-19, ECMO, and lymphopenia: a word of caution
Authors: Brandon Michael Henry
Journal: The Lancet Respiratory Medicine (2020)

Extracorporeal membrane oxygenation (ECMO) can serve as life-saving rescue therapy for refractory respiratory failure in the setting of acute respiratory distress syndrome, such as that induced by coronavirus disease 2019 (COVID-19). In the study by Yang and colleagues,1Yang X Yu Y Xu J et al.Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study.Lancet Respir Med. 2020; (published online Feb 24.)https://doi.org/10.1016/S2213-2600(20)30079-5Summary Full Text Full Text PDF Scopus (6969) Google Scholar who compared clinical characteristics and outcomes in patients with severe COVID-19, five (83%) of six patients receiving ECMO died. Although this sample was small, and specific baseline characteristics and disease courses were almost unknown, it raises concerns about potential harms of ECMO therapy for COVID-19. Lymphocyte count has been associated with increased disease severity in COVID-19.1Yang X Yu Y Xu J et al.Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study.Lancet Respir Med. 2020; (published online Feb 24.)https://doi.org/10.1016/S2213-2600(20)30079-5Summary Full Text Full Text PDF Scopus (6969) Google Scholar, 2Ruan Q Yang K Wang W Jiang L Song J Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China.Intensive Care Med. 2020; (published March 3.)DOI:10.1007/s00134-020-05991-xCrossref PubMed Scopus (3388) Google Scholar Patients who died from COVID-19 are reported to have had significantly lower lymphocyte counts than survivors.2Ruan Q Yang K Wang W Jiang L Song J Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China.Intensive Care Med. 2020; (published March 3.)DOI:10.1007/s00134-020-05991-xCrossref PubMed Scopus (3388) Google Scholar As such, we need to consider the potential compounding immunological insults involved with initiation of an extracorporeal circuit in these patients. During ECMO, substantial decreases in the number and function of some populations of lymphocytes is commonplace.3Bizzarro MJ Conrad SA Kaufman DA Rycus P Infections acquired during extracorporeal membrane oxygenation in neonates, children, and adults.Pediatr Crit Care Med. 2011; 12: 277-281Crossref PubMed Scopus (246) Google Scholar As it might be hypothesised that repletion of lymphocytes could be key to recovery from COVID-19, lymphocyte count should be closely monitored in these patients receiving ECMO. Ruan and colleagues2Ruan Q Yang K Wang W Jiang L Song J Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China.Intensive Care Med. 2020; (published March 3.)DOI:10.1007/s00134-020-05991-xCrossref PubMed Scopus (3388) Google Scholar also showed that interleukin-6 (IL-6) concentrations differed significantly between survivors and non-survivors of COVID-19, with non-survivors having up to 1·7-times higher values. During ECMO, IL-6 concentrations are consistently elevated and inversely correlated with survival in children and adults.4Risnes I Wagner K Ueland T Mollnes T Aukrust P Svennevig J Interleukin-6 may predict survival in extracorporeal membrane oxygenation treatment.Perfusion. 2008; 23: 173-178Crossref PubMed Scopus (53) Google Scholar Those that survived ECMO were able to normalise their IL-6 concentrations, whereas those that died had persistently elevated values. Moreover, elevated IL-6 concentrations in lung induced by initiation of ECMO have been convincingly shown to be associated with parenchymal damage in animal models of venovenous ECMO.5Shi J Chen Q Yu W et al.Continuous renal replacement therapy reduces the systemic and pulmonary inflammation induced by venovenous extracorporeal membrane oxygenation in a porcine model.Artif Organs. 2014; 38: 215-223Crossref PubMed Scopus (35) Google Scholar While not to discourage the use of ECMO, based on the abovementioned observations, the immunological status of patients should be considered when selecting candidates for ECMO. More reports are needed to understand the potential benefits or harms of extracorporeal life support in severe COVID-19 and future authors should be encouraged to provide more data for this subset of patients. Lastly, clinicians should consider tracking both lymphocyte count and IL-6 during ECMO to monitor patient status and prognosis. I declare no competing interests. Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational studyThe mortality of critically ill patients with SARS-CoV-2 pneumonia is considerable. The survival time of the non-survivors is likely to be within 1–2 weeks after ICU admission. Older patients (>65 years) with comorbidities and ARDS are at increased risk of death. The severity of SARS-CoV-2 pneumonia poses great strain on critical care resources in hospitals, especially if they are not adequately staffed or resourced. Full-Text PDF