Fig. 4

Assessment of dynamic microvascular reactivity and nitric oxide bioavailability during major gynecological abdominal tumor surgery. Dynamic microvascular reactivity was assessed before beginning of and every 30 min during surgery by measuring tissue oxygenation by near-infrared spectroscopy (NIRS) combined with an arterial vascular occlusion maneuver (VOT). a Image illustrates general setup of assessment. A NIRS sensor is placed on the left forearm and connected to the NIRS monitor. A blood pressure cuff is placed around the ipsilateral upper arm. For VOT maneuver, the cuff is inflated to 50 mmHg above the systolic arterial blood pressure, and the pressure is maintained for 4 min before the cuff is rapidly and completely deflated. b Muscle tissue oxygen saturation (S_tO₂) during VOT maneuver. The following parameters can be derived from the VOT curve: baseline S_tO₂ before VOT maneuver (PreVOT), slope of tissue desaturation during VOT maneuver (DesatVOT), time to recover to baseline S_tO₂ following deflation of the cuff (RecovVOT), and size of reactive hyperemic area following VOT (HyperemicVOT). c Changes of VOT parameters over time during major gynecological abdominal tumor surgery. Values were compared with the respective baseline using the Friedman test in case of complete data sets from all included patients. In case of missing values at various time points, Friedman test is inappropriate and Wilcoxon signed-rank test was used instead