Surface pH of the medial gastrocnemius and soleus muscles during hemorrhagic shock and ischemia.

Surface pH (SpH) responses of muscles of different fiber type composition were determined in sodium pentobarbital-anesthetized rabbits by comparison of the medical gastrocnemius (MG) and soleus (S) muscles. With hemorrhagic shock, S SpH decreased to 7.24 +/- 0.04 (mean +/- SD, P much less than 0.001) and MG SpH to 7.05 +/- 0.13 (P much less than 0.001). The mean of paired difference in SpH decrease (PDD) was 0.20 +/- 0.14 (P less than 0.002). With 1 hour of arterial ischemia, S SpH increased 0.02 +/- 0.03 (P less than 0.06) initially; overall, it decreased 0.17 +/- 0.07 (P much less than 0.001) to 7.24 +/- 0.09. The MG SpH decreased 0.49 +/- 0.24 (P much less than 0.001) to 6.90 +/- 0.23. The mean PDD was 0.32 +/- 0.22 (P less than 0.001). With 2 hours of arterial ischemia, S SpH increased 0.03 +/- 0.04 (P less than 0.05) initially; overall, it decreased 0.46 +/- 0.18 (P much less than 0.001) to 6.95 +/- 0.17. The MG SpH decreased 0.74 +/- 0.23 (P much less than 0.001) to 6.66 +/- 0.23. The mean PDD was 0.28 +/- 0.14 (P less than 0.001). Four of the 10 MG responses in the 2-hour arterial ischemia group were irreversible. SpH responses correlated with fiber type compositions. Initial increases in S SpH demonstrate that SpH does not invariably decrease during ischemia (as formerly assumed) and represent a potentially false negative clinical response. The large decrease in MG SpH shows that a highly glycolytic muscle will give the most sensitive indicator of reduced perfusion. Assessment of reperfusion may be problematic because of irreversible changes in SpH after prolonged ischemia. Conversely, SpH measurements may help identify regions of irreversibly damaged skeletal muscle, particularly those with mainly glycolytic fibers.