Use of near-infrared spectroscopy in early determination of irreversible hemorrhagic shock

Background: In field situations, patient triage may require early determination 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. 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 expired during resuscitation (unresuscitatable) and animals that survived all resuscitative steps (resuscitatable). Results: Neither global oxygen delivery, oxygen consumption, nor lactate distinguished resuscitatable from unresuscitatable animals. Invasive measurements of SvO₂ 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 ²=0.45) (p = 0.005). Conclusions: Non-invasive NIRS monitoring of leg and stomach StO₂ differentiates resuscitatable from unresuscitatable animals after the initial resuscitative bolus. Use of this non-invasive tool may guide appropriate use of resuscitative fluids and has possible point-of-care applications.