Hemoglobin measurement patterns during noninvasive diffuse optical spectroscopy monitoring of hypovolemic shock and fluid replacement.

The purpose of this study is to demonstrate the feasibility of broadband diffuse optical spectroscopy (DOS) for noninvasive optical monitoring of differentiating patterns of total tissue hemoglobin (THC), oxy- (OxyHb), and deoxyhemoglobin (DeOxyHb) concentrations during hypovolemic shock and subsequent fluid replacement with saline and whole blood. The goal of this DOS application is to determine the efficacy of resuscitation efforts at the tissue level rather than currently available indirect and invasive measurements of hemodynamic parameters. 16 New Zealand white rabbits are hemorrhaged 20% of their total blood volume. In resuscitated animals, shed blood volume is replaced with equal volume of crystalloid or whole blood (five animals each). Physiological variables (cardiac output, mean arterial pressure, systemic vascular resistance, hematocrit) are measured invasively, while (OxyHb) and (DeOxyHb) are measured during the interventions using broadband DOS. During the pure hypovolemic hemorrhages, the decrease in THC is mainly due to the decrease in (OxyHb), since the decrease in THC due to blood loss results in decreased tissue perfusion, with a resultant increased tissue extraction of oxygen. The hemorrhage with the whole blood resuscitation model shows significant changes in (OxyHb) during resuscitation phases due to the higher oxygen carrying capacity of whole blood, as opposed to the limited volume replacement effects and the decreased tissue oxygen content from the euvolemic anemia of the saline resuscitation. Broadband DOS noninvasive optical monitoring reveals distinct patterns of total tissue hemoglobin, oxy-, and deoxyhemoglobin during hemorrhage. Further studies are needed to confirm potential clinical utility and accuracy under more complex clinical conditions in animal models and patients.