Early exposure to hyperoxia after resuscitation from cardiac arrest may lead to poor neurological function at hospital discharge
An association with poor neurological outcome starting from PaO2 (partial pressure of oxygen) 300 mm Hg and above after resuscitation from cardiac arrest has been reported by Roberts BW et al  in Circulation. It was a multi centre prospective cohort study and included adult patients who were ventilated after cardiac arrest and received targeted temperature management. Cardiac arrest due to trauma and sepsis were excluded from the study. PaO2 was measured at 1 hour and 6 hours after return of spontaneous circulation (ROSC). Hyperoxia was defined as PaO2 >300 mm Hg during the initial six hours after ROSC. Poor neurological outcome was defined as modified Rankin score (mRS) above 3. Thirty eight percent of the 280 patients had exposure to hyperoxia. Poor neurological outcome at hospital discharge was noted in 77% of those who had exposure to hyperoxia and 65% in those who did not have exposure to hyperoxia. One hour longer exposure to hyperoxia was associated with 3% increase in risk of poor neurological outcome as per the study. They also noted that SaO2 (arterial oxygen saturation) and FiO2 are not reliable indicators of hyperoxia, mandating frequent arterial blood gas (ABG) estimation to exclude hyperoxia.
Though oxygenation is good for the hypoxic brain, more is not better in this scenario!
Exposure to hyperoxia (supranormal PaO2) caused by high fractional inspired oxgyen (FiO2) after resuscitation can amplify the production of oxygen free radicals leading to neuronal injury and death as result of failure of cellular metabolism and apoptosis (programmed cell death). Current guidelines recommend titration of FiO2 to avoid prolonged exposure to hyperoxia. If SaO2 is more than 98% in the early period after ROSC, FiO2 should be titrated down, but cautiously with regular observation.
- Roberts BW, Kilgannon JH, Hunter BR, Puskarich MA, Pierce L, Donnino M, Leary M, Kline JA, Jones AE, Shapiro NI, Abella BS, Trzeciak S. Association Between Early Hyperoxia Exposure After Resuscitation From Cardiac Arrest and Neurological Disability: Prospective Multicenter Protocol-Directed Cohort Study. Circulation. 2018 May 15;137(20):2114-2124.