Clinicians face the challenge of not only accurately measuring blood loss but also understanding its clinical significance for each expectant mother. A crucial piece of information is knowing a patient's peripartum circulating blood volume, as it enables us to interpret hemorrhage severity correctly and provide appropriate resuscitation.

In cases of obesity, greater body weight can lead to an overestimation of blood volume, which, in turn, may set overly high thresholds for blood product transfusions and cause treatment delays. The current linear calculations employed to estimate circulating blood volumes based solely on patients' weights may contribute to this issue. This is because blood volume doesn't increase proportionally to body composition.

Of note, these calculations don't account for variations in circulating blood volume related to factors such as maternal age, ethnicity, multiple pregnancies, pre-existing medical conditions, or fetal size.

Disclosure: The calculator is not recommended for a BMI > 50.

References

Kennedy H, Haynes SL, Shelton CL. Maternal body weight and estimated circulating blood volume: a review and practical nonlinear approach. Br J Anaesth. 2022 Nov;129(5):716-725. doi: 10.1016/j.bja.2022.08.011. Epub 2022 Sep 24. PMID: 36167682.

Contributed by

Todd Nelson, M.D.

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