Postpartum hemorrhage is one of the most common emergencies faced by obstetricians, complicating 1 in 20 to 1 in 100 deliveries.1 Not only is it a leading cause of maternal morbidity, but it also remains one of the top three causes of maternal mortality throughout the world.2,3 In order to manage postpartum hemorrhage effectively, the obstetrician must have a thorough understanding of normal delivery-related blood loss, physiological adaptation to hemorrhage, the most common etiologies of postpartum hemorrhage, and appropriate therapeutic interventions.
NORMAL DELIVERY-RELATED BLOOD LOSS
Normal delivery-related blood loss depends on mode of delivery. The average blood loss for a vaginal delivery, cesarean delivery, and cesarean hysterectomy has been estimated at 500, 1000, and 1500 mL, respectively. While recent data based upon objective quantification supports these values, clinicians often underestimate blood loss and its clinical implications due to the significant blood volume expansion that accompanies pregnancy.4,5
Postpartum hemorrhage has been variably defined in published literature.4-6 Definitions have included subjective assessments greater than the standard norms, a 10% decline in hematocrit, and need for blood transfusion. For practical purposes, postpartum hemorrhage is best defined as excessive bleeding that causes the patient to be hemodynamically symptomatic and/or hypovolemic.
PHYSIOLOGICAL ADAPTATION TO HEMORRHAGE
The obstetric patient can adapt to hemorrhage more effectively than her nonpregnant counterpart due to five primary hemodynamic changes that accompany pregnancy. These changes include: (1) increased red cell mass, (2) increased plasma volume, (3) increased cardiac output, (4) decreased systemic vascular resistance, and (5) increased procoagulant blood factors. In the early phases of hemorrhage, the body compensates by raising systemic vascular resistance to maintain blood pressure and perfusion to vital organs. However, as bleeding continues, further vasoconstriction is impossible, resulting in reduced blood pressure, cardiac output, and end-organ perfusion.7,8 Table 3-1 classifies the physiological adaptation that occurs with various stages of hemorrhage. It is important for the obstetrician to recognize these responses since the quantity of blood loss that occurs during a postpartum hemorrhage is often underestimated as stated previously.
TABLE 3-1Hemorrhage Classification and Physiological Adaptation ||Download (.pdf) TABLE 3-1 Hemorrhage Classification and Physiological Adaptation
|Hemorrhage class ||Acute blood loss (mL) ||Lost (%) ||Physiological adaptation |
|1 ||1000 ||10-15 ||Dizziness, palpitations, minimal blood pressure change |
|2 ||1500 ||20-25 ||Tachycardia, tachypnea, sweating, weakness, narrowed pulse pressure |
|3 ||2000 ||30-35 ||Significant tachycardia and tachypnea, restlessness, pallor, cool extremities, hypotension |
|4 ||≥2500 ||≥40 ||Cardiogenic shock, air hunger, oliguria or anuria |
ETIOLOGIES OF POSTPARTUM HEMORRHAGE
There are two categories of postpartum hemorrhage etiologies. Primary (or early) causes are those that occur within 24 hours of delivery; whereas, secondary ...