Changes in End Tidal CO2 and Arterial Blood Gas Levels After Release of Tourniquet

We studied nine healthy adult patients having orthopedic surgical procedures requiring the use of a tourniquet under general anesthesia with controlled mechanical ventilation to determine changes in end tidal CO2 (EtCO2) and arterial blood gas values after tourniquet deflation. After deflation of the tourniquet, EtCO2 and PaCO2 increased maximally within one minute; EtCO2 returned to baseline at a mean time of 13 minutes 7 seconds +/- 5 minutes 17 seconds, while PaCO2 was still above baseline when the study was terminated. The pH level decreased significantly, with the maximal fall occurring within four minutes; it remained below baseline when the study was terminated. The PaO2 level decreased and the bicarbonate level increased, though neither change was statistically significant. After tourniquet release, hyperventilation may be indicated to facilitate the return of PaCO2 and pH levels to baseline; in patients whose acid-base status is compromised by preexisting disease, PaCO2 and pH should be monitored closely. The PaCO2 level could be predicted by monitoring the EtCO2 level.