(113) Characterizing Shock Index in Pregnant Patients Undergoing Massive Transfusion for Obstetric Hemorrhage

Objective:
Whole blood (WB) is widely used in trauma resuscitation but remains underutilized in obstetrics. In 2019, our institution incorporated low-titer O+ whole blood (LTOWB) into its massive transfusion protocol (MTP) for obstetric hemorrhage. Shock index (SI), calculated as heart rate divided by systolic blood pressure, has been proposed as an early marker of hemodynamic compromise, with values >0.9 associated with increased mortality. We aimed to evaluate the physiologic response to LTOWB by assessing time to SI normalization in obstetric patients undergoing massive transfusion.

Study Design:
We conducted a retrospective observational study of obstetric patients (n = 47) who received LTOWB at a single tertiary care center from 2020 to 2024. We assessed time from transfusion initiation to SI normalization (SI < 0.9), along with the proportion of patients normalizing SI at 5, 15, 30, 60, 90, and 120 minutes. Additional analyses included time to peak SI and associations between time to normalization and estimated blood loss, total transfusion volume, hemorrhage etiology, and mode of delivery.

Results:
Median SI at transfusion initiation was 1.0 (IQR 0.78–1.16), peaking at 1.18 (1.03–1.36) before improving. SI normalization was achieved by 60 minutes (median SI 0.85 [0.72–1.0]) and sustained through 120 minutes (0.80 [0.68–0.94]). Among 27 patients with abnormal SI at initiation, median time to normalization was 76 minutes, with nearly two-thirds normalizing within 30 minutes. Neither estimated blood loss (HR 1.00, 95% CI 1.00–1.00, p > 0.9) nor total transfusion volume (HR 1.01, 95% CI 0.98–1.04, p = 0.7) was significantly associated with time to normalization. ICU admission occurred in 63.8%, hysterectomy in 76.6%, and DIC in 14.9%.

Conclusion:
Among obstetric patients undergoing massive transfusion, LTOWB was associated with rapid improvement in SI, with most patients normalizing within 30 minutes. These findings support the physiologic benefit of early transfusion in obstetric hemorrhage and highlight the need to identify additional predictors of hemodynamic recovery.