Maternal hemorrhage is one of the most com-mon severe morbidities complicating obstetricanesthesia. Causes include uterine atony, placenta previa, abruptio placentae, and uterine rupture.
A placenta previa is present if the placenta implants in advance of the fetal presenting part. The incidence of placenta previa is 0.5% of pregnancies. Placenta previa often occurs in patients who have had a previ-ous cesarean section or uterine myomectomy; other risk factors include multiparity, advanced maternal age, and a large placenta. An anterior-lying placenta previa increases the risk of excessive bleeding for cesarean section.
Placenta previa usually presents as painless vaginal bleeding. Although the bleeding often stops spontaneously, severe hemorrhage can occur at any time. When the gestation is less than 37 weeks in duration and the bleeding is mild to moderate, the patient is usually treated with bed rest and obser-vation. After 37 weeks of gestation, delivery is usu-ally accomplished via cesarean section. Patients with low-lying placenta may rarely be allowed to deliver vaginally if the bleeding is mild.
Active bleeding or an unstable patient requires immediate cesarean section under general anesthe-sia. The patient should have two large-bore intrave-nous catheters in place; intravascular volume deficits must be replaced, and blood must be available for transfusion. The bleeding can continue after delivery because the placental implantation site in the lower uterine segment often does not contract well (as does the rest of the uterus).
A history of a previous placenta previa or cesarean section increases the risk of abnormal placentation.
Premature separation of a normal placenta com-plicates approximately 1–2% of pregnancies. Most abruptions are mild (grade I), but up to 25% are severe (grade III). Risk factors include hypertension, trauma, a short umbilical cord, multiparity, pro-longed premature rupture of membranes, alcohol abuse, cocaine use, and an abnormal uterus. Patients usually experience painful vaginal bleeding with uterine contraction and tenderness. An abdominal ultrasound can help in the diagnosis. The choice between regional and general anesthesia must factor in the urgency for delivery, maternal hemodynamic stability, and any coagulopathy. The bleeding may remain concealed inside the uterus and cause under-estimation of blood loss. Severe abruptio placen-tae can cause coagulopathy, particularly following fetal demise. Fibrinogen levels are mildly reduced (150–250 mg/dL) with moderate abruptions but are typically less than 150 mg/dL with fetal demise. The coagulopathy is thought to be due to activation of circulating plasminogen (fibrinolysis) and the release of tissue thromboplastins that precipitate disseminated intravascular coagulation (DIC). Platelet count and factors V and VIII are low, and fibrin split products are elevated. Severe abruption is a life-threatening emergency that necessitates an emergency cesarean section. Massive blood transfu-sion, including replacement of coagulation factors and platelets, may be anticipated.
Uterine rupture is relatively uncommon (1:1000– 3000 deliveries) but can occur during labor as a result of (1) dehiscence of a scar from a previous (usually classic) cesarean section (VBAC), extensive myo-mectomy, or uterine reconstruction; (2) intrauter-ine manipulations or use of forceps (iatrogenic); orspontaneous rupture following prolonged labor in patients with hypertonic contractions (particularly with oxytocin infusions), fetopelvic disproportion, or a very large, thin, and weakened uterus. Uterine rup-ture can present as frank hemorrhage, fetal distress, loss of uterine tone, or hypotension with occult bleed-ing into the abdomen. Even when epidural anesthesia is employed for labor, uterine rupture is often her-alded by the abrupt onset of continuous abdominal pain and hypotension. Treatment requires volume resuscitation and immediate laparotomy, typically under general anesthesia. Ligation of the internal iliac (hypogastric) arteries, with or without hysterectomy, may be necessary to control intraoperative bleeding.