SPONTANEOUS HYPOCAPNIA AFTER CARDIAC ARREST IS ASSOCIATED WITH 60-DAY MORTALITY

Abstract

Background: Hypocapnia exposure after successful resuscitation from cardiac arrest has been previously demonstrated to be associated with poor clinical outcomes. During mechanical ventilation after return of spontaneous circulation (ROSC) it is unclear if spontaneous hyperventilation, as opposed high prescribed minute ventilation, is a common cause of hypocapnia. The objectives of this study were to determine the incidence of hypocapnia induced by spontaneous hyperventilation (spontaneous hypocapnia) among patients successfully resuscitated from cardiac arrest and to test if spontaneous hypocapnia is independently associated with 60-day mortality. Methods: Pre-planned analysis of a prospective multi-center cohort. We included adult, cardiac arrest patients who were mechanically ventilated and received targeted temperature management after return of spontaneous circulation (ROSC). We excluded patients with cardiac arrest due to trauma or sepsis. Per protocol, partial pressure of arterial carbon dioxide (PaCO2) was measured at one and six hours after ROSC. Hypocapnia was defined as a PaCO2 < 35 mmHg. We defined spontaneous hypocapnia as hypocapnia plus a measured actual respiratory rate greater than the prescribed respiratory rate and induced hypocapnia as hypocapnia plus an actual respiratory rate not higher than the prescribed respiratory rate during the initial six hours after ROSC. The primary outcome was 60-day mortality. A multivariable Cox proportional hazards model was used to test the associations between spontaneous hypocapnia and 60-day mortality compared to induced hypocapnia and no hypocapnia exposure. Results: Of the 280 patients included, 112 (40%) had exposure to hypocapnia; 89 vs. 23 spontaneous and induced hypocapnia, respectively. Sixty-day mortality occurred among 55% of patients in the entire cohort, and 47%, 57%, and 70% among patients with no, induced, and spontaneous hypocapnia respectively. Spontaneous hypocapnia was independently associated with 60-day mortality, hazards ratios 1.64 (95% CI 1.43-1.87) compared to no hypocapnia exposure and 1.44 (95% CI 1.10-1.88) compared to induced hypocapnia. Conclusion: Spontaneous hypocapnia is common during the initial six hours after return of spontaneous circulation and is independently associated with 60-day mortality.