Vital Sign Prediction of Adverse Maternal Outcomes in Women with Hypovolemic Shock: The Role of Shock Index

Abstract

ObjectiveTo determine the optimal vital sign predictor of adverse maternal outcomes in women with hypovolemic shock secondary to obstetric hemorrhage and to develop thresholds for referral/intensive monitoring and need for urgent intervention to inform a vital sign alert device for low-resource settings.Study DesignWe conducted secondary analyses of a dataset of pregnant/postpartum women with hypovolemic shock in low-resource settings (n = 958). Using receiver-operating curve analysis, we evaluated the predictive ability of pulse, systolic blood pressure, diastolic blood pressure, shock index, mean arterial pressure, and pulse pressure for three adverse maternal outcomes: (1) death, (2) severe maternal outcome (death or severe end organ dysfunction morbidity); and (3) a combined severe maternal and critical interventions outcome comprising death, severe end organ dysfunction morbidity, intensive care admission, blood transfusion ≥ 5 units, or emergency hysterectomy. Two threshold parameters with optimal rule-in and rule-out characteristics were selected based on sensitivities, specificities, and positive and negative predictive values.ResultsShock index was consistently among the top two predictors across adverse maternal outcomes. Its discriminatory ability was significantly better than pulse and pulse pressure for maternal death (p<0.05 and p<0.01, respectively), diastolic blood pressure and pulse pressure for severe maternal outcome (p<0.01), and systolic and diastolic blood pressure, mean arterial pressure and pulse pressure for severe maternal outcome and critical interventions (p<0.01). A shock index threshold of ≥ 0.9 maintained high sensitivity (100.0) with clinical practicality, ≥ 1.4 balanced specificity (range 70.0–74.8) with negative predictive value (range 93.2–99.2), and ≥ 1.7 further improved specificity (range 80.7–90.8) without compromising negative predictive value (range 88.8–98.5).ConclusionsFor women with hypovolemic shock from obstetric hemorrhage, shock index was consistently a strong predictor of all adverse outcomes. In lower-level facilities in low resource settings, we recommend a shock index threshold of ≥ 0.9 indicating need for referral, ≥ 1.4 indicating urgent need for intervention in tertiary facilities and ≥ 1.7 indicating high chance of adverse outcome. The vital sign alert device incorporated values 0.9 and 1.7; however, all thresholds will be prospectively validated and clinical pathways for action appropriate to setting established prior to clinical implementation.

Case–control study of shock index among women who did and did not receive blood transfusions due to postpartum hemorrhage

“…A study of 233 postpartum women with PPH and blood loss greater than 1500 mL found that an SI value of 0.9 or higher more accurately identified women who required ICU admission after delivery and those who received more than four units of blood products. This threshold for SI (0.9) has also been identified as an important cutoff for predicting adverse maternal outcome . After delivery, values of SI greater than 0.9 had 100%, 95.2%, and 94% sensitivity in predicting maternal death, severe maternal outcomes (death or severe end‐organ failure maternal morbidity), and critical intervention (ICU admission, blood transfusion >5 units, or emergency hysterectomy), respectively …”

“…This threshold for SI (0.9) has also been identified as an important cutoff for predicting adverse maternal outcome . After delivery, values of SI greater than 0.9 had 100%, 95.2%, and 94% sensitivity in predicting maternal death, severe maternal outcomes (death or severe end‐organ failure maternal morbidity), and critical intervention (ICU admission, blood transfusion >5 units, or emergency hysterectomy), respectively …”

“…This threshold for SI (0.9) has also been identified as an important cutoff for predicting adverse maternal outcome. 14…”

“…The SI might be an important tool applicable to the early diagnosis of PPH. An increase in SI has been related to severe maternal outcomes and maternal death, requirement for massive transfusion, massive PPH, low fibrinogen levels, and transfusion of blood volume and fresh frozen plasma . In most studies, a cutoff point of 0.9 for the SI value has been found to be associated with PPH and increased risk of maternal death, end‐organ failure, maternal morbidity, and critical interventions such as intensive care unit (ICU) admission and massive transfusion …”

“…17 In most studies, a cutoff point of 0.9 for the SI value has been found to be associated with PPH and increased risk of maternal death, end-organ failure, maternal morbidity, and critical interventions such as intensive care unit (ICU) admission and massive transfusion. 13,14,16 The aim of the present study was to assess whether SI values vary significantly between women who require blood transfusion in the postpartum period and those who do not require transfusion, and to identify factors associated with the need for blood transfusion due to PPH.…”