Post-cardiac arrest hyperoxia and mitochondrial function

Rapid post-ischemic re-oxygenation is necessary to minimize ischemic injury, but itself can induce further reperfusion injury through the induction of reactive oxygen species. Utilization of oxygen within the cell primarily occurs in the mitochondria. The objective of this study was to determine heart mitochondrial function after 1 h of controlled arterial oxygenation following cardiac arrest and restoration of spontaneous circulation (ROSC). We hypothesized that arterial hyper-oxygenation following ROSC would result in greater impairment of heart mitochondrial function.

KCl cardiac arrest was induced in anesthetized rats. Following 6.5 min of cardiac arrest, animals were resuscitated with standard thumper CPR, ventilation and epinephrine. Following ROSC, all animals were ventilated for 60 min with either 100% O(2) or 40% O(2) titrated to achieve normoxia utilizing pulse oximetry. At the end of 1 h, heart mitochondria were isolated and mitochondrial respiratory function was measured.

Post-ROSC arterial PaO2 was 280 ± 40 in the 100% O2 group and 105 ± 10 in the 40% O2 group. One hour after ROSC, heart mitochondrial state 3 respirations and respiration control ratio (state 3/4 respiration) were significantly reduced from baseline in animals ventilated with 100% O(2), but not with 40% O(2).

Post-ROSC arterial hyperoxia after a short cardiac arrest exacerbates impaired mitochondrial function. The overall clinical significance of these findings is unclear and requires additional work to better understand the role of post-arrest hyperoxia on cardiac and mitochondrial function.