Extracorporeal Life Support: What Should We Be Targeting?*

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Extracorporeal life support (ECLS) or, more commonly, extracorporeal membrane oxygenation (ECMO), is a rapidly growing, high-impact technology used to support cardiorespiratory failure in the ICU. In the United States alone, the use of ECMO increased by 433% between 2006 and 2011 (1), largely driven by increased use in adult respiratory support (2). Although randomized controlled studies comparing outcomes on ECMO support are limited (3–5), outcomes in matched pairs studies, particularly in H1N1 influenza, have suggested benefit (6–8). As the use of mechanical support of organ failure in the ICU becomes more commonplace, the need for data to support informed patient management decisions has become more urgent. In this issue of Critical Care Medicine, Munshi et al (9) have taken on the important question of goals of oxygenation support during ECLS.
The topic is clinically relevant, as, once ECLS is initiated, the intensive care team has considerable latitude in controlling previously uncontrollable oxygenation. Adjustment of pump blood flow allows titration of oxygen delivery to vary systemic oxygenation along the important ranges of the oxygen-hemoglobin saturation curve. With this latitude comes the question of “what is the most appropriate PaO2 target?.” This is not clearly established, and definition of appropriate goals of therapy on ECLS would clearly enhance current practice.
From a more general ICU perspective, we know that this answer is not simple; higher oxygen targets are not necessarily better. In the original acute respiratory distress syndrome Network ARMA tidal volume study, the 12 mL/kg group had earlier reversal of hypoxemia, yet also had higher overall mortality (10). In contrast, mortality and long-term cognitive outcomes may be adversely affected by hypoxemia in the ICU (11, 12). A 2014 Cochrane systematic review identified no randomized trials meeting criteria for evaluating hypoxemia versus normoxemia in critically ill patients (13). Internationally, several randomized trials to evaluate oxygenation targets in the ICU are in progress or in the planning stages (ICU-ROX [Australian and New Zealand Intensive Care Society, Australian New Zealand Clinical Trials Registry Number 12615000957594], O2-ICU [NCT02321072], HOT-ICU [NCT03174002], LOCO2 [NCT02713451]).
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