Extracorporeal Membrane Oxygenation Therapy for Community-Acquired Pneumonia: Are We Moving the Dial?*
In this issue of Critical Care Medicine, Kollengode et al (5) utilized the ELSO registry to identify risk factors associated with mortality in adults diagnosed with community-acquired pneumonia (CAP) who received ECMO. Including all patients more than 18 years old, they found 1,055 patients diagnosed with pneumonia based on International Classification of Diseases, 9th Edition (ICD-9) coding between 2002 and 2012 with complete data. To homogenize the dataset, patients with an ICD-9 code of aspiration pneumonia were excluded. Their primary outcome was in-hospital mortality. The group then analyzed available variables in the registry including patient demographics, pre-ECMO ventilation variables, need for supportive, and adjunctive therapy such as inotropic requirements and use of inhaled pulmonary vasodilators and neuromuscular blockade. The authors performed a univariate analysis to find potential associations between survival and risk factors followed by a multiple logistic regression model for nonsurvivors to identify risk factors associated with mortality.
The authors found that over time, the number of patients diagnosed with pneumonia and treated with ECMO increased. Additionally, mortality increased until 2006 at 50% before decreasing to 34% in 2012. Not surprisingly, ECMO use increased after 2009, which is consistent with the reports out of several countries suggesting its use as a supportive therapy during the 2009 H1N1 influenza pandemic (1–3, 6). In this dataset, 66.3% of patients survived to hospital discharge after a median of 197 hours or 8.2 days on ECMO. Median days from mechanical ventilation to ECMO use was 2.38 days. Perhaps surprisingly, only 49% of patients were reported to have received neuromuscular blockade. Not all pneumonias were of bacterial origin and fungal pneumonia was diagnosed in 40 patients who had a higher mortality than those diagnosed with bacterial or viral pneumonias. Similar to prior reports, the authors also found a higher mortality with increased age, duration of ECMO use, and whether venoarterial ECMO was required (7). These authors found that mortality was significantly higher if ECMO was initiated more than 6 days on mechanical ventilation prior to ECMO support possibly reflecting a patient who is not responsive to therapy or inadequate treatment of the offending organism (8). Additionally, those on high-frequency oscillatory ventilation and pre-ECMO acidosis also had higher mortality likely reflecting increased severity of illness. This publication reflects the clinical changes that occurred after the 2009 H1N1 pandemic with ECMO being used in patients with increased age, allowance for longer ECMO runs, and initiation of ECMO in patients with higher PaO2/FIO2 ratios. Not surprisingly, patients with more ECMO-related complications had a higher risk of death, although it is notable that 50% of patients with four or more complications survived.