Shock index in the first trimester of pregnancy and its relationship to ruptured ectopic pregnancy

The shock index (SI), the ratio of heart rate to systolic blood pressure, has been reported to be a useful tool in the evaluation of trauma patients presenting to the emergency department (ED).

To determine the range of values for SI seen in first-trimester patients presenting to the ED, and to estimate the ability of the SI to predict ruptured ectopic pregnancy (EP).

This was a prospective cohort study enrolling all patients in the first trimester of pregnancy presenting to the ED with abdominal pain and/or vaginal bleeding. Patients had a SI calculated based on their presenting vital signs, and were followed longitudinally to determine a final diagnosis. Ectopic pregnancies were categorized based on surgical pathology. Mean levels for SI were determined for each group, and ruptured EPs were compared with all other pregnancies using a receiver operating characteristic (ROC) curve.

The study enrolled 280 patients, 24 ruptured EPs, 28 unruptured EPs, and 228 non-EPs. The means for SI were 0.67 (95% CI = 0.65 to 0.68) for non-EPs, 0.64 (95% CI = 0.61 to 0.67) for unruptured EPs, and 0.84 (95% CI = 0.77 to 0.9) for ruptured EPs. The ROC curve for SI, heart rate, mean arterial pressure, and systolic blood pressure demonstrated areas under the curve (AUCs) of 0.84 (95% CI = 0.78 to 0.88), 0.74 (95% CI = 0.67 to 0.79), 0.63 (95% CI = 0.67 to 0.79), and 0.70 (95% CI = 0.64 to 0.77), respectively.

The range of values for SI for patients being evaluated for pain and/or vaginal bleeding within the first trimester of pregnancy, who do not have a ruptured EP, are within the previously reported range of 0.5-0.7 for nonpregnant patients. A SI > 0.85 made the diagnosis of ruptured EP 15.0 (95% CI = 5.6 to 40.4) times more likely. This study suggests that SI could impact directly on the diagnostic and therapeutic course of the patient.