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Oxygenating System Reduced H1N1 Mortality
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Referral for extracorporeal membrane oxygenation cut mortality approximately in half for 2009 H1N1 patients with severe respiratory distress, a study finds.
Patients with severe respiratory distress due to the 2009 H1N1 flu were approximately twice as likely to survive hospitalization if referred for extracorporeal membrane oxygenation (ECMO) compared with those limited to conventional treatment, a new study finds. The study, which used data from the UK Swine Flu Triage (SwiFT) study, was published online Wednesday in JAMA.
ECMO involves circulating the patient’s blood through an artificial lung, which removes carbon dioxide and adds oxygen. It is generally thought to be less damaging than mechanical ventilation, which can cause lung injury and associated multiple organ dysfunction. Indeed, studies have found that ECMO produces significantly higher survival rates than conventional treatment for patients with acute respiratory distress syndrome (ARDS), in which accumulation of fluid in the lungs leads to respiratory failure. However, ECMO costs approximately twice as much as conventional care, so its use remains controversial.
To further investigate the procedure’s performance, researchers took advantage of local variation in referral of H1N1 patients with ARDS for ECMO in the UK. Drawing on the SwiFT data, from a prospective cohort of H1N1 patients who required critical care, they compared the mortality of patients who were referred for ECMO for H1N1-related ARDS with that of carefully matched patients who were not referred for ECMO. Patient characteristics used in the matching included: age, degree of hypoxemia, organ dysfunction, pregnancy status, obesity, and use of alternative ventilator strategies.
The SwiFT data included 80 patients who were referred, accepted, and transferred to one of four UK ECMO centers, 69 of whom went on to receive. ECMO. 59 of the ECMO-referred patients were matched with 59 patients who were not referred for ECMO. Of all those referred for ECMO, 27.5% died before being discharged from the hospital. In the matched groups, the mortality rate prior to hospital discharge for the ECMO-referred patients was 23.7% compared with 52.5% for the non-ECMO-referred patients. The mortality rates were 24.0% and 46.7% when propensity score matching was used, and 24.0% and 50.7% when GenMatch matching was used.
Shortcomings of the study include the possibility that some of those not referred for ECMO were determined too sick for the procedure; although the researchers attempted to account for this possibility through the matching criteria, they were limited by the information available from the SwiFT study.
In addition, the researchers note that those referred for ECMO were not representative of all H1N1 patients. They were “younger, more likely to be currently or recently pregnant, had received longer durations of mechanical ventilation including use of alternative ventilation strategies, and had worse respiratory physiological characteristics compared with eligible non—ECMO-referred patients.” The ECMO-referred patients may also have benefitted from other advantages offered by the four specialized centers providing ECMO.
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