Favorable Neurocognitive Outcome with Low Tidal Volume Ventilation after Cardiac Arrest

Rationale: Neurocognitive outcome after out-of-hospital cardiac arrest (OHCA) is often poor, even when initial resuscitation succeeds. Lower tidal volumes (VTs) attenuate extrapulmonary organ injury in other disease states and are neuroprotective in preclinical models of critical illness. Objective: To evaluate the association between V-T and neurocognitive outcome after OHCA. Methods: We performed a propensity-adjusted analysis of a twocenter retrospective cohort of patients experiencing OHCA who received mechanical ventilation for at least the first 48 hours of hospitalization. VT was calculated as the time-weighted average over the first 48 hours, in milliliters per kilogram of predicted body weight (PBW). The primary endpoint was favorable neurocognitive outcome (cerebral performance category of 1 or 2) at discharge. Measurements and Main Results: Of 256 included patients, 38% received time-weighted average V-T greater than 8 ml/kg PBW during the first 48 hours. Lower V-T was independently associated with favorable neurocognitive outcome in propensityadjusted analysis (odds ratio, 1.61; 95% confidence interval [CI], 1.13-2.28 per 1-ml/kg PBW decrease in V-T; P = 0.008). This finding was robust to several sensitivity analyses. Lower VT also was associated with more ventilator-free days (beta = 1.78; 95% CI, 0.39-3.16 per 1-ml/kg PBW decrease; P = 0.012) and shockfree days (beta = 1.31; 95% CI, 0.10-2.51; P = 0.034). VT was not associated with hypercapnia (P = 1.00). Although the propensity score incorporated several biologically relevant covariates, only height, weight, and admitting hospital were independent predictors of V-T less than or equal to 8 ml/kg PBW. Conclusions: Lower V-T after OHCA is independently associated with favorable neurocognitive outcome, more ventilator-free days, and more shock-free days. These findings suggest a role for low-V-T ventilation after cardiac arrest.