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

Background: The optimal target for partial pressure of arterial carbon dioxide (PaCO₂) remains uncertain in patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO) following 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 non-traumatic adult OHCA patients on VA-ECMO with PaCO₂ levels measured within six hours of initiation (initial PaCO₂ set) and at 18-30 hours post-initiation (24-hour PaCO₂ set). PaCO₂ levels were categorized into five groups: hypocapnia (<30 mmHg), low normocapnia (30-<40 mmHg), high normocapnia (40-<50 mmHg), mild hypercapnia (50-<60 mmHg), and moderate to severe hypercapnia (≥60 mmHg). The primary outcome was the favorable functional outcome at 30 days, analyzed using 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 to high normocapnia, low normocapnia was associated with worse functional outcomes in both initial and 24-hour PaCO₂ analyses, with adjusted odds ratios 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 the favorable functional outcome than those ending in low normocapnia, regardless of initial PaCO₂ levels.

Interpretation: In non-traumatic adult OHCA patients on 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 on VA-ECMO after OHCA.