Traditionally, postpartum hemorrhage is defined as the loss of ::500 mL of blood after completion of the third stage of labor. This is problematic because almost half of all women delivered vaginally shed that amount of blood or more when losses are carefully measured (Pritchard, 1962). These results are depicted in Figure 41-1 and show further that approximately 5 percent of women delivering vaginally lose more than 1000 mL of blood. According to the American College of Obstetricians and Gynecologists (2017d), postpartum hemorrhage is deined as cumulative blood lossr> 1000 mL accompanied by signs and symptoms ofhypovolemia. And, almost a third of women undergoing cesarean delivery have blood loss that exceeds 1000 mL. These studies show that estimated blood loss is commony ony approximatey hafthe actual loss. Because of this, estimated blood loss in excess of "average" should alert the obstetrician to possible excessive bleeding. Whether quantiication of blood loss improves accuracy is controversial (Hamm, 2017; Toledo, 2007).
TABLE 41 -1. Calculation of Maternal Total Blood Volume next week or so. Whenever thepospartum hematocrit is lower than one obtained on admission or deivery, blood loss can be estimated as the sum of the calculated pregnancy-added volume plus 500 mL or each 3 volume percent decline ofthe hematocrit.
Excessive blood loss has been estimated by several methods. Sosa and colleagues (2009) used specially constructed drapes and reported that 10.8 percent of women had hemorrhage in excess of 500 mL with vaginal delivery, whereas 1.9 percent lost > 1000 mL. Compared with the indings of Figure 41-1, these estimates likely are too low. Tita and associates (2012) used a 6-volume percent drop in the postpartum hematocrit to define clinically signiicant blood loss with vaginal delivery. This decline easily signifies a > 1000-mL blood loss in the averaged-sized woman. hey documented this amount in a fourth ofwomen, which agrees with Figure 41-1.
Another marker used to estimate hemorrhage incidence is the transfusion rate. In the study by Tita just cited, more than 6 percent of women who delivered vaginally underwent blood transfusions. In a study of more than 66,000 women delivered at Parkland Hospital, 2.3 percent overall were given
Nonpregnant blood volumea: [Height (inches) x 50J + [Weight (pounds) x 25J = Blood volume (mL)
Pregnancy blood volume:
Average increase is 30 to 60 percent of calculated nonpregnant Increases across gestational age and plateaus at approximately 34 weeks
Usually larger with low normal-range hematocrit (-30) and smaller with high normal-range hematocrit (-40) Average increase is 40 to 80 percent with multifetal gestation
Average increase is less with preeclampsia-volumes vary inversely with severity
Postpartum blood volume with serious hemorrhage:
Assume acute return to nonpregnant total volume after fluid resuscitation Pregnancy hypervolemia cannot be restored postpartum aFormula arrived at by measuring blood volume and blood loss in more than 100 women using 51Cr-labeled erythrocytes. Data from Hernandez, 201n2.
blood transfusions for hypovolemia (Hernandez, 2012). Half 25 of these women had undergone cesarean delivery. Importantly, for those transfused, these investigators calculated blood loss to E average approximately 3500 mLl Finally, Green and coworkers (2016) reported that the incidence of massive tranfusion for
From the foregoing, it is apparent that significant blood loss � t postpartum hemorrhage was 23 per 100,000 births.