Insufficient oxygen inhalation during cardiopulmonary resuscitation induces early changes in hemodynamics followed by late and unfavorable systemic responses in post‐cardiac arrest rats

<jats:title>Abstract</jats:title> <jats:p> Cardiac arrest (CA) and concomitant post‐CA syndrome lead to a lethal condition characterized by systemic ischemia–reperfusion injury. Oxygen (O <jats:sub>2</jats:sub> ) supply during cardiopulmonary resuscitation (CPR) is the key to success in resuscitation, but sustained hyperoxia can produce toxic effects post CA. However, only few studies have investigated the optimal duration and dosage of O <jats:sub>2</jats:sub> administration. Herein, we aimed to determine whether high concentrations of O <jats:sub>2</jats:sub> at resuscitation are beneficial or harmful. After rats were resuscitated from the 10‐min asphyxia, mechanical ventilation was restarted at an FIO <jats:sub>2</jats:sub> of 1.0 or 0.3. From 10 min after initiating CPR, FIO <jats:sub>2</jats:sub> of both groups were maintained at 0.3. Bio‐physiological parameters including O <jats:sub>2</jats:sub> consumption (VO <jats:sub>2</jats:sub> ) and mRNA gene expression in multiple organs were evaluated. The FIO <jats:sub>2</jats:sub> 0.3 group decreased VO <jats:sub>2</jats:sub> , delayed the time required to achieve peak MAP, lowered ejection fraction (75.1 ± 3.3% and 59.0 ± 5.7% with FIO <jats:sub>2</jats:sub> 1.0 and 0.3, respectively; <jats:italic>p</jats:italic>  < .05), and increased blood lactate levels (4.9 ± 0.2 mmol/L and 5.6 ± 0.2 mmol/L, respectively; <jats:italic>p</jats:italic>  < .05) at 10 min after CPR. FIO <jats:sub>2</jats:sub> 0.3 group had significant increases in hypoxia‐inducible factor, inflammatory, and apoptosis‐related mRNA gene expression in the brain. Likewise, significant upregulations of hypoxia‐inducible factor and apoptosis‐related gene expression were observed in the FIO <jats:sub>2</jats:sub> 0.3 group in the heart and lungs. Insufficient O <jats:sub>2</jats:sub> supplementation in the first 10 min of resuscitation could prolong ischemia, and may result in unfavorable biological responses 2 h after CA. Faster recovery from the impairment of O <jats:sub>2</jats:sub> metabolism might contribute to the improvement of hemodynamics during the early post‐resuscitation phase; therefore, it may be reasonable to provide the maximum feasible O <jats:sub>2</jats:sub> concentrations during CPR. </jats:p>