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

Abstract

Objective To test the hypothesis that a fractional inspired oxygen (F IO 2) 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. Methods Thirty rats underwent: HS for 75 min, during which 3.0 mL/100 g of blood was withdrawn, followed by FR for 75 min, during which 1.0 mL/100 g of shed blood and 3.0 mL/100 g of crystalloid solution were infused.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 F IO 2 (0.21 vs. 0.4 vs. 1.0) groups, and observed for survival until 72 h in each group. Hemodynamics, liver tissue PO 2 (P TO 2), and, plasma antioxidants levels were also monitored. Results Oxygen inhalation increased mean arterial pressure (MAP) and decreased heart rate (HR) during HS and FR. Liver P TO 2 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 F IO 2 0.21 ( P < 0.01). MAP, HR, and P TO 2 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 F IO 2 0.21 survived up to 72 h (NS). Conclusions Supplemental oxygen does not mitigate tissue dysoxia during HS, but does reduce tissue dysoxia without enhancing oxidative stress during subsequent FR. Increased F IO 2 appears to prolong survival. These beneficial effects of supplemental oxygen do not differ between an F IO 2 of 0.4 and 1.0.