Shock Index and Postpartum Hemorrhage in Vaginal Deliveries: A Multicenter Retrospective Study

INTRODUCTION: Shock index (SI), calculated by dividing heart rate by systolic blood pressure, is used to detect hemodynamic instability and hypovolemia. In obstetric practice, limited evidence is available regarding its usefulness in detecting postpartum hemorrhage (PPH). We aimed to evaluate the usefulness of SI in detecting PPH in vaginal deliveries using clinical data from 12 primary maternity care units in Japan. MATERIAL AND METHODS: In this multicenter retrospective study, a total of 30,820 women who delivered vaginally at term at 12 primary maternity care units from January 2012 to December 2018 were included. Systolic and diastolic blood pressures and heart rate were measured at five different time points from admission to postpartum 2 h, and postpartum blood loss was measured. We evaluated the trend of average SI and the performance of each vital sign for detection of PPH. RESULTS: The trend of average SI during labor and the immediate postpartum period was approximately 0.7 in women with blood loss of <500 mL. SI from the time of delivery of the placenta increased with an increase in blood loss. SI had the highest area under the receiver operating characteristic curve of 0.699 [95% confidence interval (CI), 0.682-0.716] and 0.758 (95% CI, 0.729-0.788) for PPH of ≥1,000 and ≥1,500 mL, respectively. However, both sensitivity of SI (1.0) for PPH (≥1,000 mL; 29.9%, and ≥1,500 mL; 40.5%, respectively) and correlation between maximum SI and blood loss (coefficient of correlation, 0.263) were low. CONCLUSIONS: SI is a better parameter for PPH detection in vaginal deliveries than other vital signs. However, clinical judgment must incorporate other vital signs and symptoms associated with hypovolemic shock due to the low sensitivity of SI.