Postpartum hemorrhage is the most common cause of clinically significant blood loss in obstetrics practice and is the leading cause of maternal and fetal morbidity and mortality globally. It is defined as any bleeding occurring within 6 weeks following delivery. However, serious blood loss most frequently occurs during the immediate postpartum period or within 1–2 hours following delivery. Blood loss of greater than 500 mL for vaginal delivery or greater than 1000 mL for caesarian section are values commonly included in guidelines for the diagnosis of postpartum hemorrhage. A decrease of 10% of hematocrit from admission to the postpartum period can also signify significant blood loss. It should be noted that many studies have shown postpartum blood loss to be significantly underestimated by clinicians.
Because uterine blood flow is approximately 600–700 mL/min, postpartum hemorrhage can result in the loss of large quantities of blood very quickly. In the event of significant bleeding, large-bore intravenous (IV) access must be established expeditiously and aggressive volume resuscitation initiated. Anesthesiologists and obstetricians must review the full differential diagnosis collaboratively, identify the likely etiology, and initiate the appropriate therapy as quickly as possible. The potential for a hysterectomy must be considered and appropriate preparations made.
Uterine atony occurs in 2%–5% of deliveries and is the cause of greater than 90% of cases of postpartum hemorrhage. It is the result of the failure of the uterus to contract following delivery, which results in continued blood flow through the placental intervillous spaces. There are multiple conditions associated with an increased risk of atony (Table 168-1). Because many of these conditions lead to caesarian section, there is a higher occurrence in patients receiving caesarian section compared to vaginal births. In addition to the use of uterotonic agents, first-line interventions include uterine massage, oxygen supplementation, and aggressive fluid resuscitation. In cases of refractory hemorrhage, an attempt may be made to ligate or embolize the uterine arteries. Operative interventions such as obstetric hysterectomy or uterine compression sutures may be required. The use of red blood cell salvage can be considered.
TABLE 168-1Conditions Associated with Increased Risk of Uterine Atony ||Download (.pdf) TABLE 168-1 Conditions Associated with Increased Risk of Uterine Atony
Prolonged labor (augmentation with oxytocin)
Abnormalities in placentation
Retained placental tissue
Poor perfusion of uterine myometrium
There are three classes of uterotonic agents used to manage uterine atony.
The initial therapy for uterine atony is IV oxytocin, which promotes uterine contraction by interacting with specific oxytocin receptors in the uterine myometrium. The endogenous hormone is produced in the posterior pituitary while the exogenous form is a ...