When a young otherwise healthy individual develops severe acute respiratory distress syndrome (ARDS), rescue therapies are often employed to improve oxygenation, with extra-corporeal membrane oxygenation (ECMO) used as the last resort. While sporadic use of this modality occurs, the advent of the pandemic H1N1 influenza virus prompted its use on a larger scale, despite questions of benefit. During the pandemic, one major study illustrated that transfer to an ECMO-capable center was associated with a reduction in mortality, but in that study, not all patients received ECMO, so the benefits of the therapy itself could not be fully evaluated.¹ More recently, Pham and colleagues have published the results of their study of the largest cohort of H1N1 patients treated with ECMO, providing more evidence by which to judge the efficacy of this rescue therapy,² but not enough to resolve the clinical dilemma that attends use of ECMO.

Pham´s study used an H1N1 registry that collected prospective data on H1N1-infected patients admitted to 114 French intensive care units between July 2009 and May 2011. Patients receiving ECMO were matched according to propensity scores to patients not receiving ECMO. The propensity score was the probability that a patient would receive ECMO based upon individual characteristics. In all, 123 patients receiving ECMO were included in the study. Their mean age was 42 years, 50% were male, 40% were obese, and 15% were pregnant or post-partum. All received antiviral therapy.

ECMO was initiated a median of 2 days after intubation. Other rescue therapies were used in 75% prior to ECMO initiation, with 72% receiving inhaled nitric oxide and 45% receiving prone positioning. The mean P/F ratio was 63. The mortality rate was 36%. Factors associated with death on ECMO included increasing age, higher ventilator plateau pressure, and higher lactate level.

In the matched analysis, 52 patients who received ECMO within the first week of mechanical ventilation were compared with propensity-matched patients who did not receive ECMO but had similar characteristics. The ICU mortality rates of the ECMO and non-ECMO groups--50% and 40% respectively--were not statistically different.

Of note, 51 patients, who received ECMO within week 1 of mechanical ventilation, could not be matched adequately. These unmatchable patients were younger, more obese, and more frequently pregnant. They also had lower PF ratios, oxygen saturations, and higher plateau pressures. However, their mortality was only 22%, as compared with the 50% mortality rate in matched ECMO patients. Quantifying the relative contribution of age to this lowered mortality rate is an important question that was not able to be addressed in this study.

This new study highlights the clinical dilemma faced when considering the use of ECMO in patients with severe ARDS: It is not at all clear who will benefit from this invasive and cumbersome technology. Although some patients did not seem to benefit from ECMO, the younger, more severely ill patients did seem to benefit. This result suggests that ECMO can be life-saving in patients with specific characteristics, but identifying them early enough and getting them transported to ECMO-capable centers will remain a challenge for pandemic response planning and for those providing inter-pandemic care of patients with severe ARDS.³

1. Noah MA, Peek GJ, Finney SJ, et al. Referral to an extracorporeal membrane oxygenation center and mortality among patients with severe 2009 influenza A (H1N1). JAMA. 2011;306:1659-1668.
2. Pham T, Combes A, Roze H, et al. Extracorporeal membrane oxygenation for pandemic influenza A (H1N1)-induced acute respiratory distress syndrome: a cohort study and propensity-matched analysis. Am J Respir Crit Care Med. 2013;187:276-285.
3. Adalja AA, Watson M, Waldhorn RE, Toner ES. A conceptual approach to improving care in pandemics and beyond: severe lung injury centers. J Crit Care. 2012. Corrected proof. http://www.sciencedirect.com/science/article/pii/S0883944112003267. Accessed March 4, 2013.