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The association of Shock Index (SI) and non-invasive Hemoglobin (SpHb) variation with blood loss after vaginal deliveries: A prospective cohort study
Abstract Number: GM-02
Abstract Type: Original Research
Postpartum hemorrhage (PPH) is one of the leading causes of death during childbirth . Substantial variation exists in the onset of clinical signs of PPH . Shock Index (SI) (heart rate/systolic blood pressure [BP]) and continuous non-invasive hemoglobin monitoring (SpHb) (Masimo©, US) have both been proposed for the timely diagnosis of PPH. The objective of this study was to determine the association of SI and SpHb variation with blood loss after vaginal delivery. We hypothesized that both assessment tools are early indicators of PPH.
We conducted a prospective observational study in women ≥37 wks gestation undergoing vaginal deliveries. SpHb and heart rate were recorded continuously and non-invasive BP recorded every 10 min for 2 hrs after delivery. Actual blood loss (ABL) was measured at 30, 60 and 120 min postpartum by using calibrated drapes and weighing soiled pads. The primary outcome was the cumulative ABL during the study period. Linear mixed models were used to determine the association of SI and SpHb with ABL. Logistic regression was used to determine the area under the receiver operator curve (AUROC) and the optimal cut off-point for detecting ABL ≥1L.
We recruited 67 women to the study. Both SI and SpHb demonstrated downward trend over time (p=0.04, p<0.01). However, the slope of this trend was not associated with ABL (SI p=0.65; SpHb p=0.32). Mean (SD) SI was higher in women with ABL ≥1L compared to those with ABL <1L (0.91 [0.17] vs. 0.80 [0.14], p = 0.009). Change in SpHb (g/dL) from baseline was not different in women with or without ABL ≥1L (-7.08 (8.98) vs. -3.83 (7.84), p=0.18). Maximum SI within the first hr of delivery was significantly correlated with ABL (r=0.45, p <0.001) and was a predictor of ABL ≥1L (p=0.004, AUROC 0.760) with a value of SI ≥0.9 demonstrating 91% sensitivity and 54% specificity (Fig 1). Maximum change in SpHb from baseline was not correlated with ABL (r=0.23, p=0.057) and was not a predictor of ABL ≥1L (p=0.14).
Higher SI values are associated with more blood loss after vaginal delivery and an SI ≥ 0.9 within the first hr after delivery may be a clinically useful tool for the early detection of PPH. SpHb variation does not accurately predict blood loss after delivery.
2. BMJ 2017;358:j3875