Simultaneous multi-depth assessment of tissue oxygen saturation in thenar and forearm using near-infrared spectroscopy during a simple cardiovascular challenge

INTRODUCTION: Hypovolemia and hypovolemic shock are life-threatening conditions that occur in numerous clinical scenarios. Near-infrared spectroscopy (NIRS) has been widely explored, successfully and unsuccessfully, in an attempt to use it as an early detector of hypovolemia by measuring tissue oxygen saturation (StO(2)). In order to investigate the measurement site dependence and probe dependence of NIRS in response to hemodynamic changes, such as hypovolemia, we applied a simple cardiovascular challenge: a posture change from supine to upright, causing a decrease in stroke volume (as in hypovolemia) and a heart rate increase in combination with peripheral vasoconstriction to maintain adequate blood pressure. METHODS: Multi-depth NIRS was used in nine healthy volunteers to assess changes in StO(2 )in the thenar and forearm in response to the hemodynamic changes associated with a posture change from supine to upright. RESULTS: A posture change from supine to upright resulted in a significant increase (P < 0.001) in heart rate. Thenar StO(2 )did not respond to the hemodynamic changes following the posture change, whereas forearm StO(2 )did. Forearm StO(2 )was significantly lower (P < 0.001) in the upright position compared to supine for all probing depths. CONCLUSIONS: The primary findings in this study were that forearm StO(2 )is a more sensitive parameter to hemodynamic changes than thenar StO(2 )and that the depth at which StO(2 )is measured is of minor influence. Our data support the use of forearm StO(2 )as a sensitive parameter for the detection of central hypovolemia and hypovolemic shock in (trauma) patients.