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 medial gastrocnemius (MG) and soleus (S) muscles. With hemorrhagic shock, S SpH decreased to 7.24 ± 0.04 (mean ± SD, P <<0.001) and MG SpH to 7.05 ± 0.13 (P<<0.001). The mean of paired difference in SpH decrease (PDD) was 0.20 ± 0.14 (P<0.002). With 1 hour of arterial ischemia, S SpH increased 0.02 ± 0.03 (P<0.06) initially; overall, it decreased 0.17 ± 0.07 (P<<0.001) to 7.24 ± 0.09. The MG SpH decreased 0.49 ± 0.24 (P<<0.001) to 6.90 ± 0.23. The mean PDD was 0.32 ± 0.22 (P<0.001) to 6.90 ± 0.23. The mean PDD was 0.32 ± 0.22 (P<0.001). With 2 hours of arterial ischemia, S SpH increased 0.03 ± 0.04 (P<0.05) initially; overall, it decreased 0.46 ± 0.18 (P<<0.001) to 6.95 ± 0.17. The MG SpH decreased 0.74 ± 0.23 (P<<0.001) to 6.66 ± 0.23. The mean PDD was 0.28 ± 0.14 (P<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.