Noninvasive muscle oxygenation to guide fluid resuscitation after traumatic shock

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.