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Visual Estimation and Calculated Blood Loss After Delivery
Abstract & Commentary
By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.
Synopsis: These researchers propose new methods for calculating blood loss during delivery.
Source: Stafford I, et al. Visually estimated and calculated blood loss and vaginal and cesarean delivery. Am J Obstet Gynecol 2008;199:519.e1-519.e7.
A few studies have suggested that we tend to underestimate blood loss during deliveries and cesarean sections. A group from Louisiana State University has addressed this issue again in a very clever way.
Between Jan. 1, 2005, and Sept. 2, 2005, when hurricane Katrina cut the study short, complete data were available on 671 women, none having a blood transfusion. Two hundred and thirty one (34%) mothers had cesarean sections, 421 had spontaneous deliveries (62.2%), and 25 patients (3.7%) had operative vaginal deliveries. Each patient had a subjective clinical estimation of blood loss during and after her delivery, which was paired with the calculated blood volume loss by an accepted set of formulas. First, the maternal blood volume was calculated in the following way: 0.75 × [(maternal height in inches × 50) + (maternal weight in pounds × 25)]. Then the blood loss was computed by multiplying the maternal blood volume by the percent of blood volume lost, the latter being quantified by the equation: [(pre-delivery Hct - post-delivery Hct)/pre-delivery Hct]. (I have included these formulas for those wanting to more accurately determine blood loss in their patients.)
The median estimated blood loss (EBL) by visual assessment was 250 cc, 300 cc, and 800 cc for normal spontaneous delivery, operative delivery, and cesarean delivery, respectively. The same median figures for calculated blood loss were 575 cc, 728 cc, and 818 cc. The median difference between the two methods was 306 cc for normal spontaneous delivery, 469 cc for operative delivery, and 75 cc (a surprise) for cesarean sections. However, when blood loss during cesarean section exceeded 1000 cc, then there was a significant underestimation by the visual method. Last, as expected, there was an impressive increase in blood loss with each successive degree of perineal laceration. For example, the calculated blood loss (by the above formulas) was 519 cc, 604 cc, 764 cc, and 932 cc for no laceration, first degree, second degree, and third/fourth degree lacerations, respectively. The visual estimations undershot the calculated value in each category by 200-580 cc.
This study shows we are not very good at ballparking blood loss. Perhaps wishful thinking plays a role in our estimates, but it seems that in every category there was a major underestimation of true blood loss. Review of records of pregnancies ending in maternal mortality (13 per 100,000) or severe maternal morbidity has shown a tendency to miscalculate the seriousness of these patients' clinical conditions. Since maternal hemorrhage plays a major role in most of these complications, early blood replacement could be extremely important in preventing the rapid deterioration of these patients' conditions.
This tendency to underestimate blood loss by a factor of two might possibly be something that happens only in New Orleans, but I seriously doubt it. It might be useful for us to try the above formula ourselves on a few patients to see how close we come to the EBL. However, reading this may well bias our subjective estimates.