Background: Near infrared (NIR) spectrometry offers a noninvasive monitor of tissue hemoglobin O2 saturation and has been developed to report a quantitative clinical variable, StO2 [= HbO2/(HbO2 + Hb)]. In this study, a prototype NIR oximeter was used to investigate the hypothesis that changes in systemic O2 delivery index (DO2I) would be reflected by changes in StO2 in skeletal muscle, subcutaneous tissue, or both, as reperfusion occurs during shock resuscitation. StO2 was also compared with other indices of severity of shock or adequacy of resuscitation, including arterial base deficit, lactate, gastric mucosal PCO2 (PgCO2), and mixed venous hemoglobin O2 saturation (SvO2).
Methods: Skeletal muscle and subcutaneous tissue StO2 were monitored simultaneously in eight severely injured trauma patients (88% blunt mechanism; age, 42 ± 6 years; Injury Severity Score, 27 ± 3) during standardized shock resuscitation in the intensive care unit with the primary goal of DO2I ≥ 600 mL O2/min/m2 for 24 hours, and for an additional 12 hours during transition from resuscitation to standard intensive care unit care.
Results: Skeletal muscle StO2 increased significantly from 15 ± 2% (mean ± SEM) at the start of resuscitation to 49 ± 14% at 24 hours, and to ∼55% from 25 to 36 hours. Subcutaneous tissue StO2 ∼ 82% and was significantly greater than skeletal muscle StO2 throughout. DO2I increased significantly from 372 ± 54 to 718 ± 47 mL O2/min/m2 during resuscitation. Over 36 hours, mean DO2I and skeletal muscle StO2 were highly correlated (r = 0.95). Neither DO2I-PgCO2 nor DO2I-SvO2 were significantly correlated; neither SvO2 nor subcutaneous tissue StO2 changed significantly.
Conclusion: Hemoglobin O2 saturation was monitored noninvasively and simultaneously in skeletal muscle and subcutaneous tissues as StO2 (%) by using a prototype NIR oximeter. Skeletal muscle StO2 tracked systemic O2 delivery during and after resuscitation. As a rapidly deployable, noninvasive monitor of peripheral tissue oxygenation and O2 delivery, skeletal muscle StO2 obtained using NIR spectrometry would be useful to guide resuscitation in the intensive care unit, to monitor resuscitation status in the operating room, and, potentially, in combination with indicators such as base deficit and lactate, to detect shock during initial assessment of the severe trauma patient in the emergency department.
Shock adversely affects the outcome of severely injured patients, and adequate resuscitation is an important early priority. Whereas volume loading of patients in shock before or on arrival in the emergency room is controversial, after surgical bleeding has been controlled, optimizing systemic O2 delivery (DO2) is the current clinical standard for shock resuscitation of high-risk patients. A monitor of tissue oxygenation that reflects DO2, particularly one that is noninvasive, would be an important triage tool in the initial emergency department evaluation of the patient with multiple system injuries to diagnose unrecognized shock, for evaluation of response to resuscitation as the patient progresses through diagnostic imaging and/or surgical intervention, and to guide resuscitation in the intensive care unit (ICU).
Near infrared (NIR) spectrometry offers a method of monitoring hemoglobin O2 saturation in tissue (StO2) noninvasively, and has been developed extensively during the 1990s. In this study, we used a prototype NIR spectrometer to noninvasively monitor skeletal muscle StO2 and subcutaneous tissue StO2 during and after a standardized shock resuscitation protocol. The patients monitored had sustained major torso trauma and were at known risk for multiple organ failure (MOF). The protocol-directed resuscitation optimizes O2 delivery index (DO2I) for 24 hours. Based on previous experience with NIR monitoring 1 and recent publication of animal study results, 2 our study hypothesis was that changes in DO2I would be indicated by changes in skeletal muscle StO2, subcutaneous tissue StO2, or both. This study also compared StO2 with other commonly used indices of the adequacy of shock resuscitation, including arterial base deficit (BD), serum lactate concentration (lactate), partial pressure of gastric mucosal interstitial CO2 (PgCO2), and mixed venous hemoglobin O2 saturation (SvO2).