Predictive performance of Shock Index for postpartum hemorrhage during cesarean delivery

•Shock Index is a useful indicator to detect postpartum hemorrhage in vaginal delivery.•Shock Index peaks at 10–15 min after delivery during cesarean delivery.•Spinal anesthesia and various medications affect Shock Index during cesarean delivery.•Shock Index does not correlate with total blood loss.•Shock Index has poor ability to detect postpartum hemorrhage during cesarean delivery. The Shock Index (SI), defined as heart rate divided by systolic blood pressure, is reportedly an early surrogate indicator for postpartum hemorrhage (PPH). However, most previous studies have used clinical data of women who delivered vaginally. Therefore, we aimed to evaluate the SI pattern during cesarean delivery and determine its usefulness in detecting PPH. This was a single-center retrospective study using the clinical data of women (n = 331) who underwent cesarean delivery under spinal anesthesia at term between 2018 and 2021. We assessed the SI pattern stratified by total blood loss and evaluated the predictive performance of each vital sign in detecting PPH (total blood loss ≥1000 mL) based on the area under the receiver operating characteristic curve (AUROC). At 10–15 min after delivery, the mean SI peaked between 0.84 and 0.90 and then decreased to a level between 0.72 and 0.77, which was similar to that upon entering the operating room. Among 331 women, 91 (27.5%) were diagnosed with PPH. There was no correlation between SI and total blood loss (rs = 0.02). The SI had low ability to detect PPH (AUROC 0.54, 95% confidence interval 0.47 to 0.61), which was similar to other vital signs (AUROCs 0.53–0.56). We determined the pattern of SI during cesarean delivery. We found no correlation between SI and total blood loss. Unlike in vaginal delivery, the prognostic accuracy of SI for PPH detection in cesarean delivery was low.