Hyperoxia-Induced Secondary Respiratory Failure in a Systemic Ischaemia-Reperfusion Injury

Recent studies revealed that excessive supplemental oxygen, such as inhaled 100% O₂, damages various organ functions in post-cardiac arrest (CA) patients. Optimal indicators of supplemental oxygen are therefore important to prevent hyperoxic organ injuries. In this study, we evaluated a hyperoxic pulmonary injury and assessed the association between alveolar-arterial oxygen difference (AaDO₂) and a degree of lung oedema. In this study, we focused on the hyperoxia-induced lung injury and its association with changes of gas-exchange parameters in post-CA rats. Rats were resuscitated from 10 min of asphyxial CA and stratified into two groups: those with inhaled 100% O₂ (CA-FiO₂ 1.0) and those with 30% O₂ (CA-FiO₂ 0.3). We prepared a sham surgery group for comparison (sham-FiO₂ 0.3). After 2 h, animals were sacrificed, and the lung wet-to-dry (W/D) weight ratio was measured. We collected blood gas results and measured the ratio of partial pressure arterial oxygen and fraction of inspired oxygen (p/f ratio), and calculated AaDO₂. The lung W/D ratio in the CA-FiO₂ 1.0 group (5.8 ± 0.26) was higher than in the CA-FiO₂ 0.3 (4.6 ± 0.42) and sham-FiO₂ 0.3 groups (4.6 ± 0.38, p < 0.01). There was a significant difference in AaDO₂ between CA-FiO₂ 1.0 (215 ± 49.3) and, CA-FiO₂ 0.3 (36.8 ± 32.3), and sham-FiO₂ 0.3 groups (49.0 ± 20.5, p < 0.01). There were also significant changes in pH and blood lactate levels in the early phase among the three groups. AaDO₂ showed the strongest correlation with W/D ratio (r = 0.9415, p < 0.0001), followed by pH (r = -0.5131, p = 0.0294) and p/f ratio (r = -0.3861, p = 0.1135). Hyperoxic injury might cause the pulmonary oedema after CA. Measuring respiratory quotient (RQ) in rodents enabled an accurate calculation for AaDO₂ at a variety level of inhaled O₂. Given that AaDO₂ measurement is non-invasive, we therefore consider AaDO₂ to be a potentially optimal indicator of post-CA hyperoxic pulmonary injury.