P082: ALLOWABLE BLOOD LOSS CALCULATION: A POTENTIAL TOOL FOR TRANSFUSION MANAGEMENT IN OBSTETRICS
Giselle De La Rua, BS; Anthony Rios, BS; Brian Tran, MD; Michelle Fletcher; Yanyun Wu, MD, PhD; Paloma Toledo, MD, MPH
University of Miami Miller School of Medicine
Introduction: The incidence of severe maternal morbidity (SMM) and mortality has been increasing. Postpartum hemorrhage (PPH) continues as a leading contributor to both. Blood transfusions, although now excluded from SMM indicators, previously accounted for nearly half of SMM. Transfusions are not benign, the incidence of transfusion reactions among pregnant patients is double that of non-pregnant patients; hence identifying strategies to reduce transfusions is necessary.
For patients without cardiac disease, a transfusion threshold of hemoglobin < 7 g/dL is recommended. Use of a restrictive transfusion threshold has not been shown to be inferior to liberal transfusion in anemic women who experienced severe PPH. Yet, despite well-established guidelines, clinicians often base the decision to transfuse on clinical judgement leading to significant variation in clinical practice. The concept of allowable blood loss (ABL) calculates the amount of blood which could be lost before necessitating transfusion. We hypothesize that inclusion of ABL in pre-procedural time out would reduce the rate of transfusions among patients undergoing a cesarean delivery at a single institution.
Methods: In this Institutional Review Board approved study (IRB: 20220290), electronic medical record data were abstracted for women who underwent cesarean delivery at Jackson Memorial Hospital. Implementation of ABL in pre-procedural time out began in July 2024, thus data were collected comparing two 6-month periods one year apart (7/1/23 – 12/31/23; 7/1/24 – 12/31/24). Women with preoperative Hgb < 7 g/dL or who received only cell salvaged blood were excluded. Data extracted for transfused patients included starting hemoglobin, weight, hemorrhage risk, intraoperative blood loss, and transfusion data.
ABL was calculated using the following formula:
ABL = Allowable blood loss (mL)
Hgbinitial = Initial hemoglobin
EBV = Estimated blood volume
The EBV was calculated using pregnancy-adjusted blood volume and the patient’s weight. For patients whose body mass index (BMI) was > 30 kg/m2, 65 kg was used instead of true weight.
BW = Body weight (kg)
The primary outcome was transfusion rate defined as administration of one or more units of packed red blood cells intraoperatively. Normal distribution of continuous variables evaluated with the Shapiro-Wilk test. Categorical data evaluated using chi-squared test and continuous data evaluated with Kruskall-Wallis test. P < .05 was considered significant.
Results: A total of 2204 women met inclusion criteria (1052 pre-intervention and 1152 post-intervention). Results summarized in Table 1. Transfusion rate pre-intervention was 27 (2.57%) compared to 11 (0.95%) in the post-intervention group (P = .01). The calculated PPH risk did not differ between the two cohorts, but admission hemoglobin levels, ABL values, and intraoperative blood loss values were lower in the post-intervention period.
Discussion: This study demonstrates that the introduction of calculated ABL in pre-procedural time out significantly decreased transfusion rate. Announcing ABL during time out ensured that surgeons, nurses, and anesthesiologists were aware of how much blood loss could occur prior to transfusion. Avoiding unnecessary transfusions minimizes risk of transfusion-related adverse events, associated costs, and conserves scarce blood resources. Furthermore, ABL could be useful for preoperative hemoglobin optimization and be beneficial when applied to other high-risk surgeries.
