Immediate effects of hyperbaric oxygenation on blood pressure, acid-base and blood gas status and parameters of oxidative stress in healthy male rats

Hyperbaric oxygenation (HBO) is the medical use of pure oxygen at a level higher than atmospheric pressure. There are different protocols of HBO being used for research purposes ; however, data on the changes in blood pressure, oxidative stress and acid-base and gas status induced by some of the possible oxygenation patterns/protocols are scarce and conflicting. In this work we aimed to investigate the immediate influence of oxygenation at a pressure of 2 bar during 2 hours on blood pressure, acid- base and blood gas status and parameters of oxidative stress in healthy rats. Healthy male 12-15 week old Sprague-Dawley rats were anesthetized with ketamine (75 mg/kg) and midazolam (2.5 mg/kg) i.p. Femoral artery was cannulated for blood pressure measurements (AP) and blood sampling prior and immediately after single time hyperbaric oxygenation (HBO) in a hyperbaric oxygen chamber (100% oxygen at a pressure of 2 bar for 2 hours, with additional 15 minutes for compression and decompression). Arterial blood samples were collected to analyze acid-base and blood gas status and to determine Ferric reducing ability of plasma (FRAP) and Thiobarbituric Acid Reactive Substances (TBARS ; based on reaction of malonilaldehyde (MDA) with thiobarbituric acid). Paired t-test for AP, blood gases and acid-base status (N of rats = 12) and t- test for FRAP and TBARs (N of rats = 12) were used ; p< ; 0.05 was considered significant. Data are expressed as mean± SD. The study was approved by Ethical Committee of Faculty of Medicine University of Osijek. After HBO there was significant decrease in systolic and diastolic AP (control 138± 14/ 103± 13 vs. 113± 12/ 72± 16 kPa after HBO), although in normal AP range. pH significantly decreased after HBO (control 7.34± 0.05 vs. 7.28± 0.05 after HBO). After HBO, pCO2 was significantly decreased (7.07± 0.89 vs. 5.76± 0.50 kPa) and pO2 significantly increased (12.48± 0.88 vs. 13.68± 2.4 kPa). Plasma bicarbonate significantly decreased (control 27.04± 3.25, vs. 20.52± 3.02 after HBO). Exposure to HBO significantly increased MDA concentration (from 0.173± 0.092 to 21.79± 1.05 microM/MDA), while FRAP was significantly decreased compared to control condition (0.152± 0.035 to 0.117± 0.013 mM/L TE). Control values are in agreement with previously published data on anesthetized rats (1). Acute exposure to HBO had significant effects on all observed parameters. Acidosis may be contributed to prolonged anesthesia (2). However, there is immediate improvement in pCO2 and pO2, although with increase in oxidative stress products and acute decrease in plasma antioxidative capacity, after single time HBO exposure (3).