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To test fiber-optic PO2, PCO2, and pH sensors placed in skeletal muscle as monitors of hemorrhage, shock, and resuscitation, compared with mean arterial blood pressure, cardiac output, and blood gas variables.Observational study in physiology laboratory, using a canine controlled hemorrhagic shock model.Mongrel dogs (20-35 kg; n = 10) were monitored with arterial, venous, and pulmonary artery catheters. A probe (0.5 mm in diameter) with fiber-optic PO2, PCO2, and pH sensors was placed percutaneously in the adductor muscle of the right medial thigh. Mean arterial blood pressure of 45 to 50 mm Hg was maintained for 1 hour with controlled hemorrhage, after which shed blood was reinfused. The animals were monitored for 4 hours after reinfusion.Skeletal muscle PO2 (PmO2) decreased from 31 +/- 9 to 5 +/- 4 mm Hg during shock and recovered with reinfusion. Skeletal muscle pH (pHm) decreased from 7.24 +/- 0.10 to 6.94 +/- 0.12 during shock, to 6.90 +/- 0.13 with reinfusion, and recovered to near baseline 2 hours after reinfusion. PmCO2 increased from 48 +/- 14 to 134 +/- 86 mm Hg during shock, to 138 +/- 92 mm Hg with a time course inverse to pHm, and recovered to near baseline 30 minutes after reinfusion. On average, skeletal muscle PCO2 (PmCO2) and pHm did not recover to baseline, possibly indicating persistent anaerobic metabolic effects. O2 delivery, mixed venous PO2, mixed venous O2 saturation and PmO sub 2 responded with similar time courses.PmO2, PmCO2, and pHm can be monitored simultaneously for several hours with fiber-optic sensors in a single, small probe. PmO2 may provide information comparable to O2 delivery. PmCO2 may reflect adequacy of perfusion. pHm may indicate success of resuscitation. This technology may offer new insight into the extent of injury and refinement of shock resuscitation and monitoring.