Non-Invasive Hemoglobin Monitoring during Hemorrhage and Hypovolemic Shock

Background: Serial blood draws for the assessment of a trauma patient’s hemoglobin (sHgb) and hematocrit (sHct) is standard practice. In the event of multiple casualties this process can be time consuming and lead to the inefficient use of valuable resources. A device that would allow for continuous real-time, non-invasive monitoring of hemoglobin and tissue perfusion would not only improve the utilization of scarce and valuable resources but would also improve triage efforts. Purpose: We developed a device utilizing the technology of Diffuse Optical Spectroscopy (DOS) to obtain non-invasive measurements of tissue hemoglobin concentration (THC) and oxygen consumption in an animal model of hypovolemic shock induced by successive blood withdrawals. Measured DOS results were compared against invasive systemic physiological measurements to demonstrate that DOS provides a reliable non-invasive measurement of tissue THC, and also quantifies various degrees of hemorrhage induced systemic hypovolemia and subsequent tissue perfusion decreases. Methods: Intubated New Zealand White rabbits (N=16) were hemorrhaged via a femoral arterial line every 10 minutes until a 20% blood loss (10-15 cc/kg) was achieved to attain hypovolemia. A DOS probe was placed on the inner thigh to measure muscle concentrations of oxygenated-Hgb (Hb-O2) and deoxygenatedHgb (Hb-R), during bloodletting. THC and tissue hemoglobin saturation (STO2) were calculated using oxygenated and deoxygenated hemoglobin concentrations. DOS-measured values were compared against traditional invasive measurements, systemic hemoglobin (sHgb), arterial oxygen saturation (SAO2), and venous oxygen saturation (SVO2) drawn from arterial and central venous blood. Systemic blood pressure (mAP), heart rate (HR) and SAO2, were monitored throughout the entire experiment. Results: DOS and traditional invasive measurements versus blood loss were closely correlated (R=0.98 and R=0.97, respectively) showing a decline in both. STO2 and Hb-O2 followed similar trends with hemorrhage whereas an increase in Hb-R was observed. Conclusion: DOS provides a potential platform for reliable non-invasive measurements of tissue oxygenated and deoxygenated hemoglobin and may accurately reflect the degree of systemic hypovolemia and compromised tissue perfusion.