Blood Loss as a Function of Body Surface Area: Redefining Parameters of Obstetric Blood Loss

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We read the article by Burtch et al1 with great interest. The study identifies the average blood loss volume encountered in deliveries based on body surface area. Authors speculated that obstetric hemorrhage should be defined based on one of the trauma shock classifications for clinical relevance. Using the same rationale, we had previously performed a clinical study.2 We would like to share a few concerns related to the methodologic steps followed in the current study.
The authors tried to identify the volume of blood loss that exceeds 15% of total blood volume to develop the features of at least class II shock. For this, a formula was used to calculate total blood volume that was developed based on 150 women and men aged 46 years on average. Pregnancy brings physiologic changes such as increased blood volume, red cell mass, cardiac output, and stroke volume,3 along with its own adaptation mechanisms to blood loss. So the total blood volume could have been better calculated based on a formula developed specifically for an obstetric population, such as the formula by Milosevic et al.4 The authors estimated the expected blood loss by the subjective pictorial view report, which can be inaccurate owing to the misleading effects of placental volume, hemorrhage, and amniotic fluid. Estimating blood loss based on two inappropriate calculations of total blood volume and expected blood loss could be misleading. The patient selection should have been more meticulous, rather than including a wide gestational age range of 24–42 weeks, which may influence blood loss owing to uterine and placental size. Term deliveries, for example, could have been included. The clinical confounding factors of obstetric hemorrhage should also be more delicately excluded in addition to excluding multiple gestations. We were also surprised not to encounter any comparisons between patients in need of transfusion or not. However, there were no patients with transfusion. We appreciate the efforts of the authors but are afraid that their methods could be misleading and should be reconsidered.
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