The choice of anesthesia is often influenced by the urgency of the operative procedure and the condition of the fetus. Most patients undergoing cesarean delivery in the United States do so under spinal or epidural anesthesia.
- Neuraxial Anesthesia.Blockade to theT4
dermatome is necessary to perform cesarean delivery. The most common complication is hypotension and the attendant risk of uteroplacental perfusion (left uterine displacement, intravenous fluid administration, liberal use of vasopressors). It is common to administer a nonparticulate antacid before induction of anesthesia. Blood pressure should be measured frequently for the first 20 minutes after initiation of anesthesia. Although supplemental oxygen is frequently administered, there is no evidence of benefit to the mother or fetus. Intrathecal morphine provides superior and longer lasting analgesic compared with bilateral transversus abdominis place block.
- Spinal anesthesia is provided most often with 1.6 to 1.8 mL of hyperbaric bupivacaine 0.75% lasting approximately 120 to 180 minutes. Improved perioperative analgesia can be provided by addition of fentanyl (6.25 µg) or preservative-free morphine (100 µg) to the local anesthetic solution. It is probably not necessary to adjust the dose of local anesthetic based on the parturient's height.
- Despite a block extending to T4, parturients often experience visceral discomfort, particularly with exteriorization of the uterus and traction on abdominal viscera (25 µg of fentanyl IV may be useful).
- Oxygen should be routinely administered by face mask to optimize maternal and fetal oxygenation.
- Lumbar Epidural Anesthesia. Compared with spinal anesthesia, lumbar epidural anesthesia requires more time and drug to establish an adequate sensory level, but there is a lower risk of postdural puncture headache, and the level of anesthesia can be adjusted by titration of local anesthetic solution injected through the indwelling catheter.
- Adequate anesthesia is usually achieved with injection through the lumbar epidural catheter of 15 to 25 mL of local anesthetic solution (Table 40-5: Epidural Anesthesia for Cesarean Section).
- Addition of morphine (3–5 mg) to the local anesthetic solution provides postoperative analgesia.
- Combined spinal–epidural anesthesia for cesarean delivery provides a rapid onset of a dense block with a low anesthetic dose and the ability to extend the duration of anesthesia and perhaps to provide continuous postoperative analgesia.
- General anesthesia may be necessary when contraindications exist to regional anesthesia or when time precludes central neuraxial blockade. Situations in which uterine relaxation facilitates delivery (multiple gestations, breech position) are most often managed with general anesthesia (Table 40-6: General Anesthesia for Cesarean Section).
- A newborn's condition after cesarean section with general anesthesia is comparable to that when regional techniques are used. The uterine incision to delivery time (<180 seconds) is more important to fetal outcome than is the anesthetic technique.
- The usual amount of blood loss during cesarean section is 750 to 1,000 mL, and transfusion is rarely necessary.
- When tracheal intubation is unexpectedly difficult, it may be prudent to permit the parturient to awaken and then to pursue alternative approaches (awake fiberoptic tracheal intubation, regional anesthesia) rather than to persist with repeated unsuccessful and traumatic attempts at tracheal intubation (Fig. 40-1: Management of a difficult airway in pregnancy).