The AccuFlow Sensor: A Novel Tool to Assess Intrapartum Blood Loss

Abstract

To 1) assess patient comfort with a wireless, cellular-capable heat flux sensor, the AccuFlow Sensor, during scheduled cesarean delivery, and 2) determine the most appropriate site at which to use the sensor to measure vasoconstriction as a proxy for intrapartum blood loss. Patients with a BMI of < 35kg/mˆ2 and hemoglobin ≥10.0g/dL undergoing scheduled cesarean were enrolled. Perfusion sensors were applied to the wrist, forearm, bicep, and chest prior to spinal anesthesia. Postoperatively, patients rated the tolerability of the sensors and standard anesthesia monitoring equipment on a validated comfort rating scale for wearable computers (CRS). Blood loss was estimated by the surgical team and also calculated by change in hematocrit adjusted for weight and height. Wilcoxon signed ranks tests were used to compare CRS scores. Correlations between calculated blood loss and surgical team estimates, and between calculated blood loss and sensor readings, were compared using Fisher’s R-to-z transformation. 25 patients were enrolled; none requested sensor removal. CRS scores were similar for the sensor and the standard anesthesia equipment (Table). Change in blood flow at all sites on the arm correlated with blood loss. Change in perfusion at the wrist was most strongly correlated with blood loss (R=-0.41, Figure). The sensor performed better than the surgical team at estimating blood loss (R=-0.41 vs R=0.087, p=0.043). In isolation, wrist perfusion at cesarean conclusion also correlated with blood loss (R=0.22), indicating that the device detects decreased perfusion in the absence of pre-hemorrhage measurements. The AccuFlow Sensor was well-tolerated, may estimate surgical blood loss more accurately than the surgical team, and shows promise to detect decreased perfusion in the absence of pre-hemorrhage readings. A larger trial is needed to assess the sensor’s ability to predict clinically important outcomes such as need for blood transfusion.View Large Image Figure ViewerDownload Hi-res image Download (PPT)