Subcutaneous tissue oxygen and carbon dioxide tensions during hyperbaric oxygenation: An experimental study in rats

Objective: To investigate the response of subcutaneous tissue oxygen (O-2) and carbon dioxide (CO2) tensions to hyperbaric oxygenation. Design: Experimental study. Setting: University hospital, Finland. Subjects: 10 Wistar rats. Intervention: Subcutaneous tissue PO2 and PCO2 were directly measured with an implanted Silastic tube tonometer and capillary sampling technique while breathing air and exposed to hyperbaric oxygen (HBO) at 2.5 or 2.8 ATA pre ssure. Hyperbaric exposures were carried out in a large multiplace chamber pressurised with air. Main outcome measures: Subcutaneous tissue PO2 and PCO2. Results: The mean subcutaneous PO2 rose from the baseline of 8 kPa (60 mmHg ) to 16 kPa (112 mmHg) when rats breathed room air during pressurisation to 2.8 atm. When the rats breathed oxygen at 2.5 ATA the maximal mean tissue PO2 was four times higher than the mean starting value. During the HBO trea tment at 2.8 ATA the tissue PO2 rose to a value about five times above base line. The tissue PCO2 values almost doubled during the exposure to HBO at 2 .5 ATA, probably because elimination of carbon dioxide was impaired. Conclusion: Measurements of tissue PO2 and PCO2 with an implanted Silastic tonometer and a capillary sampling technique can successfully be adapted to hyperbaric conditions. The method yielded reproducible results and is appl icable to clinical use in hyperbaric medicine.