Gastric and Colonic Oxygen Tension Measured with a Vacuum-Fixed Oxygen Electrode

Abstract

A new electrode system for determination of visceral oxygen tension is presented. The system consists of a transcutaneous oxygen electrode (E5242 Radiometer A/S, Copenhagen), which is screwed into a suction ring and fixed to the organ by applying a vacuum. The electrode membrane is then in contact with the organ surface via a fluid layer with a thickness of a few micrometres, without interference from atmospheric air and without mechanical disturbance of the membrane. The electrode system was tested on the gastric and colonic wall in six pigs. As reference, a silicone tonometer was placed subserously beneath the vacuum-fixed electrode. The silicone tonometer was connected to a second transcutaneous oxygen electrode. The tissue oxygen tension was changed by subjecting the animals to various inspiratory concentrations of oxygen and to hypovolaemia. The oxygen tension measured by the vacuum-fixed electrode (Po₂vac) was compared with the oxygen tension measured by the tonometer (Po₂tono). A good correlation was demonstrated between Po₂vac and Po₂tono, the correlation coefficient being 0.8619, confirming that the suction-fixed oxygen electrode measures tissue oxygen. The lowest possible vacuum to hold the electrode unit in place was between 4.0 and 6.7 kPa. Provided the measuring time did not exceed 3 min, vacuum had only slight influence on the measured oxygen values. The mean change in Po₂vac induced by varying the vacuum from 7 to 26kPa, and 26 to 7 kPa, was only +0.23 kPa(-1.2 to+ 1.9) and +0.19 kPa (-0.3 to +1.3), respectively. The mean stabilization time, defined as the time from electrode application until achieving 95% of the equilibration value, was 66 sec (SEM, 3.4 sec) and 57 sec (SEM, 3.0 sec) on the gastric and colonic wall, respectively. The measured values of Po₂vac varied significantly between different areas on the gastric wall (p < 0.001). When several surface measurements were performed throughout the investigated area, the mean oxygen tension approached the oxygen tension measured by the tonometer. It is concluded that the vacuum-fixed electrode constitutes a reliable, easy and, non-invasive method for measurements of the oxygen tension in the gastric and colonic tissue.

Key Words:

• Colonic surgery
• gastric surgery
• oximetry
• oxygen tension
• tonometry