Background Three different protocols tested the hypothesis that hind limb muscle tissue O2 saturation (StO2), measured noninvasively with near-infrared spectroscopy (NIRS), is as reliable as invasive systemic oxygenation indices to guide fluid resuscitation. Methods In series 1, swine (n=30) were hemorrhaged, then received either no fluid, a fixed volume of colloid (15 mL/kg), or shed blood plus lactated Ringer's (LR) titrated to MAP >60 mm Hg. In series 2, swine (n=16) received a penetrating femur injury, a 47% to 55% hemorrhage to determine a median lethal dose (LD50) then shed blood plus LR titrated to MAP >60 mm Hg. In series 3, swine (n=5) received the femur injury plus LD50 hemorrhage, and were resuscitated with LR titrated to StO2 >50%. Results In series 1, StO 2 tracked mixed venous O2 saturation (SvO2), but discriminated between 3 survivor groups better than SvO2, arterial lactate, or arterial base excess. In series 2, StO2 tracked SvO2 but discriminated between 2 survivor groups better than SvO 2, arterial lactate, or arterial base excess. In series 3, animals survived to extubation when resuscitated to an StO2 target. Conclusions Noninvasive muscle StO2 determined by NIRS was more reliable than invasive oxygenation variables as an index of shock. Because muscle StO2 can be easily monitored in emergency situations, it may represent an improved method to gauge the severity of shock or the adequacy of fluid resuscitation after trauma.
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