Effects of various concentrations of inhaled oxygen on tissue dysoxia, oxidative stress, and survival in a rat hemorrhagic shock model

ObjectiveTo test the hypothesis that a fractional inspired oxygen (FIO2) of 1.0 compared to 0.4 during hemorrhagic shock (HS) and fluid resuscitation (FR): mitigates tissue dysoxia; however, enhances the oxidative stress; therefore, offsets the benefit on survival.MethodsThirty rats underwent: HS for 75 min, during which 3.0 mL/100 g of blood was withdrawn, followed by FR for 75 min, during which 1.0 mL/100 g of shed blood and 3.0 mL/100 g of crystalloid solution were infused. Ten rats were randomized into one of three FIO2 (0.21 vs. 0.4 vs. 1.0) groups, and observed for survival until 72 h in each group. Hemodynamics, liver tissue PO2 (PTO2), and, plasma antioxidants levels were also monitored.ResultsOxygen inhalation increased mean arterial pressure (MAP) and decreased heart rate (HR) during HS and FR. Liver PTO2 was less than 10 Torr in all groups throughout HS; while it increased to average 26–35 Torr in oxygen groups during FR, it remained at 10 Torr with FIO2 0.21 (P < 0.01). MAP, HR, and PTO2 did not differ significantly between oxygen groups. Plasma antioxidants levels did not differ among the three groups. All rats treated with oxygen, but eight of 10 rats with FIO2 0.21 survived up to 72 h (NS).ConclusionsSupplemental oxygen does not mitigate tissue dysoxia during HS, but does reduce tissue dysoxia without enhancing oxidative stress during subsequent FR. Increased FIO2 appears to prolong survival. These beneficial effects of supplemental oxygen do not differ between an FIO2 of 0.4 and 1.0.