Use of Near-Infrared Spectroscopy in Early Determination of Irreversible Hemorrhagic Shock

BACKGROUND:In field situations, patient triage may require early identification of patients progressing to irreversible shock. We investigated the utility of near-infrared spectroscopy (NIRS) in early detection of irreversible hemorrhagic shock. METHODS:Twenty instrumented pigs were treated with a protocol involving 35% blood volume hemorrhage, 90 minutes of shock, and stepwise resuscitation with lactated Ringer’s solution. Hemodynamics and NIRS measurements of skeletal muscle (leg), stomach, and liver tissue oxyhemoglobin saturation (Sto2) were measured at baseline, every 30 minutes during shock, and after each resuscitative step. Measurements were compared between animals that died during resuscitation (unresuscitatable) and animals that survived all resuscitative steps (resuscitatable). RESULTS:Neither global oxygen delivery nor oxygen consumption or lactate distinguished resuscitatable from unresuscitatable animals. Invasive measurements of venous oxygen saturation did distinguish resuscitatable from unresuscitatable animals. After the first fluid bolus, both stomach and leg Sto2 differed significantly between resuscitatable and unresuscitatable animals. Regression analysis revealed skeletal muscle (leg) Sto2 obtained after the first resuscitative step was a significant mortality predictor despite resuscitation (r = 0.45, p = 0.005). CONCLUSION:Noninvasive NIRS monitoring of leg and stomach Sto2 differentiates resuscitatable from unresuscitatable animals after the initial resuscitative bolus. Use of this noninvasive tool may guide appropriate use of resuscitative fluids and has possible point-of-care applications.