High Normocapnia and Better Functional Outcome in Patients Undergoing Venoarterial Extracorporeal Membrane Oxygenation After Out-of-Hospital Cardiac Arrest.

Abstract

Background: The optimal target for Paco₂ remains uncertain in patients undergoing venoarterial extracorporeal membrane oxygenation (VA-ECMO) after out-of-hospital cardiac arrest (OHCA).

Research question: Are Paco₂ levels associated with functional outcomes in patients receiving VA-ECMO after OHCA?

Study design and methods: This multicenter, registry-based observational study, conducted from 2014 to 2020, included adult patients with nontraumatic injury with OHCA and receiving VA-ECMO with Paco₂ levels measured within 6 hours of initiation (initial Paco₂ set) and 18 to 30 hours after initiation (24-hour Paco₂ set). Paco₂ levels were categorized into 5 groups: hypocapnia (< 30 mm Hg), low normocapnia (30 to < 40 mm Hg), high normocapnia (40 to < 50 mm Hg), mild hypercapnia (50 to < 60 mm Hg), and moderate to severe hypercapnia (≥ 60 mm Hg). The primary outcome was a favorable functional outcome at 30 days, analyzed by multivariable logistic regression. Paco₂ trajectories from initial to 24-hour levels were also explored.

Results: A total of 1,454 and 572 patients were analyzed in the initial and 24-hour Paco₂ sets, respectively. Compared with high normocapnia, low normocapnia was associated with worse functional outcomes in both initial and 24-hour Paco₂ analyses, with adjusted ORs of 0.59 (95% CI, 0.38-0.89) for initial low normocapnia and 0.56 (95% CI, 0.33-0.95) for 24-hour low normocapnia. Other categories were similarly associated with worse functional outcomes in both Paco₂ analyses. In exploratory analyses, trajectories ending in high normocapnia demonstrated higher proportions of favorable functional outcome than those ending in low normocapnia, regardless of initial Paco₂ levels.

Interpretation: In adult patients with nontraumatic injury with OHCA and receiving VA-ECMO, high normocapnia was associated with better functional outcomes than low normocapnia in both initial and 24-hour Paco₂ analyses. These findings suggest a hypothesis that maintaining high normocapnia levels, irrespective of initial Paco₂, may improve functional outcomes for patients undergoing VA-ECMO after OHCA.