According to an investigation in JAMA, individuals who developed respiratory failure after being infected with severe 2009 H1N1 influenza, and who received treatment with a system that adds oxygen to their blood, had a lower rate of dying in hospital compared to those who did not receive the treatment.

The investigation is being published early online to accompany its presentation at the European Society of Intensive Care Medicine meeting being held in Berlin.

Extracorporeal membrane oxygenation (ECMO) is an extracorporeal method that provides both cardiac and respiratory support oxygen to individuals whose heart and lungs have stopped functioning. The researchers explain: "ECMO may be used either as a rescue intervention or to minimize ventilator-associated lung injury and its associated multiple organ dysfunction, both crucial determinants of survival for patients with acute respiratory distress syndrome [ARDS; a lung condition that leads to respiratory failure due to the rapid accumulation of fluid in the lungs]." A prior investigation discovered that if individuals with severe ARDS were transferred to a single ECMO center, the outcomes were more favorable. "Moreover, ECMO doubled hospital costs compared with conventional care. Hence, the role of ECMO in adults with severe ARDS remains controversial.''

Moronke A. Noah, M.R.C.S., of the Heartlink ECMO Centre, Glenfield Hospital, Leicester, England, and team carried out an investigation to analyze the mortality of individuals with influenza A (H1N1)-related ARDS who, following a referral and being accepted, had been transferred to one of four adult ECMO centers in the UK during winter 2009-2010.

Using data from a longitudinal cohort investigation (Swine Flu Triage Study) of those critically ill with suspected or verified H1N1, the researchers matched individuals who were referred for EMCO with non-ECMO-referred individuals. Researchers used detailed physiological, comorbidity and demographic data in three different matching methods (propensity score, GenMatch, and individual).

80 individuals who had been referred, and accepted, were transferred to one of the four ECMO centers in the UK, 69 of whom received ECMO (86.3%). Out of a group that consisted of 1,765 individuals, they identified 75 matched pairs using propensity score matching, 75 matched pairs using GenMatch matching, and 59 matched pairs of ECMO-referred patients and non-ECMO-referred patients using individual matching.

22 individuals (27.5%) transferred to the ECMO centers died. They discovered that hospital mortality was roughly two fold for matched non-ECMO-referred individuals compared to those who were referred. The researchers explain:

"The hospital mortality was 23.7 percent for ECMO-referred patients vs. 52.5 percent for non-ECMO-referred patients when individual matching was used; 24.0 percent vs. 46.7 percent, respectively when propensity score matching was used; and 24.0 percent vs. 50.7 percent, respectively when GenMatch matching was used. The survival curves indicate a considerable number of early deaths among the non-ECMO-referred patients. The benefit of ECMO persisted after repeating the survival analysis and excluding the matched pairs in which either the ECMO-referred patient or the non-ECMO-referred patient died during the first 48 hours."

The researchers explain that the unique value of the investigation lies in the matching techniques used and the homogeneity of the individuals.

"The role of ECMO in ARDS is debated. Several reports and our study demonstrate that ECMO can be undertaken without the prohibitive morbidity and adverse events seen in the 1970s."

William Checkley, M.D., Ph.D., of Johns Hopkins University, Baltimore, writes in an associated report that:

"the study by Noah et al involving critically ill patients with H1N1 joins other recent investigations that have revitalized interest in the use of ECNO as a treatment strategy for ARDS. While underlying risk factors may be different, severe respiratory failure from H1N1 infection presents a clinical challenge similar to that involving ARDS from other causes. Despite several decades of investigation into potential treatment strategies, use of low tidal volumes [volume of air that is drawn in or expelled] remains the only proven therapy to decrease mortality in ARDS. In light of the large observed differences in mortality with and without ECMO, large consortia of trialists may be enticed to consider ECMO as a potential target for a randomized controlled trial early in the course of severe ARDS from all causes."

Written by Grace Rattue