Mechanical ventilation in cardiac arrest: association between hyperoxia, hypercarbia and positive end-expiratory pressure with mortality

Abstract

Background Optimization of mechanical ventilation (MV) in patients with cardiac arrest (CA) may help improve outcomes in these patients. We sought to investigate the association between hyperoxia, PCO2, and positive end-expiratory pressure (PEEP) with mortality in patients with CA. Methods Patients admitted to our medical center CICU from 2001 through 2012 (MIMIC-III database) who received MV with available information on MV parameters and had arterial blood gases sampling were included. Hyperoxia was defined as time-weighted mean of PaO2 >120 mmHg and non-hyperoxia as PaO2 ≤120 mmHg, while Hypercarbia was defined as PCO2 >35 mmHg during CICU admission. The primary outcome was in-hospital mortality. Multivariable logistic regression was used to assess the association between hyperoxia and in-hospital mortality adjusted for age, female sex, Oxford Acute Severity of Illness Score, creatinine, lactate, pH, PaO2/FiO2 ratio, PCO2, PEEP, and time spent on PEEP. Results Among 136 patients, PaO2 = 139±55 mmHg, PCO2 = 39±10 mmHg, and PEEP = 6.4±2.2cmH2O. Unadjusted mortality was higher in the hyperoxic group (51.4%) compared to the non-hyperoxic group (29.0%) (long rank test p=0.0034, figure). In multivariable analysis, hyperoxia was independently associated with higher in-hospital mortality (OR 4.046, 95% CI: 1.501–10.907, p=0.0057). Additionally, there was no association between the presence of hypercarbia and in-hospital mortality (OR 0.896, 95% CI: 0.319 to 2.521, p=0.836) nor when PCO2 was analyzed as a continuous variable (OR 1.063 per 1 mmHg increase in CO2, 95% CI: 0.111–10.145, p=0.957). Similarly, there was no assocation between PEEP and in-hospital mortality (OR 1.012 per 1cmH2O increase, 95% CI: 0.807 to 1.270, p=0.917). Post-hoc analysis with PaO2 as a continuous variable was consistent with the primary analysis (OR 1.214 per 10 mmHg increase in PaO2, 95% CI: 1.059–1.391, p=0.005). Conclusions In patients with CA, hyperoxia was associated with increased mortality, while PCO2 and PEEP levels were not. Optimal MV parameters are important in the management of patients with CA. Further research is warranted to confirm this association and explore the mechanisms behind these observations. These studies can help establish the best MV strategies for patients with CA. Funding Acknowledgement Type of funding source: None