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

Abstract

To test the hypothesis that a fractional inspired oxygen (F(I)O(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. Thirty rats underwent: HS for 75min, during which 3.0mL/100g of blood was withdrawn, followed by FR for 75min, during which 1.0mL/100g of shed blood and 3.0mL/100g of crystalloid solution were infused. Ten rats were randomized into one of three F(I)O(2) (0.21 vs. 0.4 vs. 1.0) groups, and observed for survival until 72h in each group. Hemodynamics, liver tissue PO(2) (P(T)O(2)), and, plasma antioxidants levels were also monitored. Oxygen inhalation increased mean arterial pressure (MAP) and decreased heart rate (HR) during HS and FR. Liver P(T)O(2) was less than 10Torr in all groups throughout HS; while it increased to average 26-35Torr in oxygen groups during FR, it remained at 10Torr with F(I)O(2) 0.21 (P<0.01). MAP, HR, and P(T)O(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(I)O(2) 0.21 survived up to 72h (NS). Supplemental oxygen does not mitigate tissue dysoxia during HS, but does reduce tissue dysoxia without enhancing oxidative stress during subsequent FR. Increased F(I)O(2) appears to prolong survival. These beneficial effects of supplemental oxygen do not differ between an F(I)O(2) of 0.4 and 1.0.