Unconventional Volume-Outcome Associations in Adult Extracorporeal Membrane Oxygenation in the United States

Abstract

Background The aim of this study was to evaluate institutional volume-outcome relationships in extracorporeal membrane oxygenation (ECMO) with subanalyses of ECMO in patients with a primary diagnosis of respiratory failure. Methods All institutions with adult ECMO discharges in the Nationwide Inpatient Sample from 2002 to 2011 were evaluated. International Classification of Diseases (ninth revision) codes were used to identify ECMO-treated patients, indications, and concurrent procedures. Patients who were treated with ECMO after cardiotomy were excluded. Annual institutional and national volume of ECMO hospitalizations varied widely, hence the number of ECMO cases performed at an institution was calculated for each year independently. Institutions were grouped into high-, medium-, and low-volume terciles by year. Statistical analysis included hierarchical, multivariable logistic regression. Results The in-hospital mortality rates for ECMO admissions at low-, medium-, and high-volume ECMO centers were 48% (n =467), 60% (n =285), and 57% (n = 445), respectively (p = 0.001). In post hoc pairwise comparisons, patients in low-volume hospitals were more likely to survive to discharge compared with patients in medium-volume (p = 0.001) and high-volume (p = 0.005) hospitals. There was no significant difference in survival between medium-volume and high-volume hospitals (p = 0.81). In a subanalysis of patients with respiratory failure, low-volume ECMO centers maintained the lowest rates of in-hospital mortality (47%), versus 61% in medium-volume institutions (p = 0.045) and 56% in high-volume institutions (p = 0.15). Multivariable logistical regression produced similar results in the entire study sample and in patients with respiratory failure. Conclusions ECMO outcomes in the Nationwide Inpatient Sample do not follow a traditional volume-outcome relationship, and these results suggest that, in properly selected patients, ECMO can be performed with acceptable results in U.S. centers that do not perform a high volume of ECMO.

Venovenous extracorporeal membrane oxygenation treatment in a low‐volume and geographically isolated cardiothoracic centre

“…Additionally, patients transferred to high‐volume centres and subsequently placed on ECMO had both increased mortality compared to index admissions, and increased costs to the accepting medical institution . The authors did report limitations of the database, one being the lack of relevant clinical information such as whether VA‐ or VV‐ECMO was applied …”

“…Currently, ELSO guidelines recommend a minimum of six ECMO cases per year . Controversially, recent studies from USA found that outcomes in the Nationwide Inpatient Sample did not follow the traditional volume‐outcome relationship as low‐volume ECMO centres had the lowest rates of in‐hospital mortality . Additionally, patients transferred to high‐volume centres and subsequently placed on ECMO had both increased mortality compared to index admissions, and increased costs to the accepting medical institution .…”

“…However, adult VV‐ECMO from 2008‐2013 proved to be an exception in this study as there was no statistically significant association between centre volume and patient survival . The traditional volume‐outcome relationship has furthermore been challenged in recent years, with studies from the United States showing that ECMO mortality rates in low‐volume centres was lower or no different than in medium‐ and high‐volume centres . Additionally, a study on paediatric ECMO cases from 2003‐2014 showed that centre volume was not independently predictive of mortality for older infants and children …”

Commentary: Patient selection is key to improving postcardiotomy extracorporeal membrane oxygenation outcomes

“…Of note, the results of this study contradict previous findings that ECMO outcomes are not directly related to the total number of cases performed. 11,12 In addition, this study failed to report on the effect of iatrogenic, intraoperative complications on the outcomes of ECMO. Issues such as surgical misadventure or suboptimal myocardial protection can be significant drivers of mortality, and ECMO therapy often cannot salvage the situation.…”

The ICM research agenda on extracorporeal life support

“…However, experience with directing ECMO cases to high-volume centers is limited, and has not been scientifically proven superior as a strategy. A recent study even suggested that lowvolume centers have better ECMO in-hospital mortality than high-volume centers [44], questioning the existence of a positive volume-outcome relationship in this population. Another unresolved issue is the nurse-to-patient ratio for ECMO patients [45].…”