The Ability of Shock Index In Detecting Postpartum Haemorrhage: A Retrospective Case-Control Study

Abstract

Background: shock index (SI), calculated as the ratio of heart rate (HR) to systolic blood pressure (SBP), is used to measure the degree of hypovolemia in shock states. Little literature reported on the role of SI in detecting postpartum haemorrhage (PPH) in obstetrics. This study aimed to determine whether SI was superior to clinical criteria to identify PPH, to identify independent risk factors of surgical intervention and blood transfusion.Materials and Methods: Records were retrospectively examined for patients who experienced PPH (n=305) or not (n=305). HR and SBP were recorded at five different time points from admission to postpartum 24 h. The performance of vital signs based on area under the receiver operating characteristic curve (AUROC) was used to evaluate the ability among peak SI, HR, SBP for estimating PPH. Two formulas using the fitted curve in a scatter plot (maximum SI and blood loss postpartum 24 h based on draps weighing method against blood loss postpartum 24 h with hemoglobinometry, respectively) were provided to determine the ability between SI and draps weighing method in detecting PPH. Univariate and logistic regression analyses were used to determine predictors of surgical intervention and blood transfusion. The sensitivity and specificity of SI for predicting transfusion were calculated. Results: SI had the highest AUROC of 0.646 [95% confidence interval (CI), 0.590-0.700] and 0.665 (95% CI, 0.582-0.748) for PPH of ≥1,000 and ≥1,500 ml. SI was inferior to drapes weighing method (coefficient of correlation, 0.351 vs 0.759) in estimating PPH. Caesarean delivery, placenta previa were independent risk factors for surgical interventions and transfusion. Body mass index(BMI) and peak SI ≥1 were also independent risk factors for transfusion. The SI ≥ 1 predicted transfusion with a specificity of 0.81, negative predictive value 82% but sensitivity of only 0.39. Conclusions: The peak SI may be superior to HR or SBP for detecting PPH. However, due to the low correlation with blood loss, the severity of PPH needs to be judged accompanied with other signs and symptoms. SI < 1 may indicate no blood transfusion needed.