The acute effects of tourniquet ischemia on tissue and blood gas tensions in the primate limb.

Tourniquet ischemia results in tissue hypoxia which has been measured indirectly by blood gas analysis. The Medspect mass spectrometer allows direct measurement of gas tension in different tissues and may provide more useful information regarding safe tourniquet times. Calibrated Teflon catheters were inserted into the subcutaneous tissue (11 animals), tibial medullary cavities (bone) (nine animals), and tibialis anterior muscles (10 animals) in both lower extremities of anesthetized stumptail monkeys. Tourniquet ischemia was maintained for 1 hour at 400 mm Hg. Tissue and venous blood gas tensions were recorded from both limbs for 1 1/2 hours. Comparisons between gas tensions in each tissue group were made on the basis of their percentage change from control values. In the ischemic limb within 5 minutes muscle PO2 fell 42 +/- 4% (p is less than 0.001), whereas bone and subcutaneous PO2 dropped 25 +/- 4% (p is less than 0.05). Blood PO2 fell 29 +/- 3% and differed only from that of muscle (p is less than 0.01). One hour after tourniquet inflation, blood PO2 levels has fallen 90 +/- 5% (p is less than 0.001) from their control. Changes in tissue PCO2 were less dramatic and did not vary significantly from those recorded in venous blood. After deflation, blood PO2 exceeded its control by 20 +/- 6% (p is less than 0.005) in 5 minutes, but tissue tensions remained 50 +/- 6% below their control values. These studies indicate that tissue gas tensions are a more sensitive indicator of tourniquet hypoxia than are blood gases within the ischemic extremity.