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Chapter: Clinical Anesthesiology: Anesthetic Management: Obstetric Anesthesia

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Anesthesia for Cesarean Section: Regional Anesthesia

Cesarean section requires that dermatomes up to and including T4 be anesthetized.

REGIONAL ANESTHESIA

 

Cesarean section requires that dermatomes up to and including T4 be anesthetized. Because of the associ-ated sympathetic blockade, patients should receive an appropriate intravenous bolus of crystalloid such as lactated Ringer’s (typically 1000–1500 mL) or col-loid (typically 250–500 mL) solution at the time of neural blockade. Such boluses will not consistently prevent hypotension but can virtually eliminate preexisting hypovolemia. After the local anesthetic injection, phenylephrine may be titrated to maintain blood pressure within 20% of baseline. An approxi-mate 10% decrease in blood pressure is expected. Administration of ephedrine (5–10 mg) may be necessary in the hypotensive patient with reduced heart rate. Some studies suggest that phenyleph-rine produces less neonatal acidosis compared with ephedrine.

 

After spinal anesthetic injection, the patient is placed supine with left uterine displacement; supple-mental oxygen (40–50%) is given; and blood pres-sure is measured every 1–2 min until it stabilizes. Hypotension following epidural anesthesia typically has a slower onset. Slight Trendelenburg positioning facilitates achieving a T4 sensory level and may also help prevent severe hypotension. Extreme degrees of Trendelenburg may interfere with pulmonary gas exchange.

Spinal Anesthesia

The patient is usually placed in the lateral decubi-tus or sitting position, and a hyperbaric solution of lidocaine (50–60 mg) or bupivacaine (10–15 mg) is injected. Bupivacaine should be chosen if the obstetrician will not likely complete the surgery in minutes. Use of a 22-gauge or smaller, pencil-point spinal needle (Whitacre, Sprotte, or Gertie Marx) decreases the incidence of PDPH. Adding 10–25 mcg of fentanyl or 5–10 mcg of sufentanil to the local anesthetic solution enhances the inten-sity of the block and prolongs its duration without adversely affecting neonatal outcome. Addition of preservative-free morphine (0.1–0.3 mg) can prolong postoperative analgesia up to 24 h, but requires monitoring for delayed postoperative respiratory depression. Regardless of the anesthetic agents used, considerable variability in the maxi-mal dermatomal extent of anesthesia should be expected . In obese patients, a stan-dard 3.5-in. (9-cm) spinal needle may not be long enough to reach the subarachnoid space. In these cases, longer spinal needles of 4.75 in. (12 cm) to 6 in. (15.2 cm) may be required. To prevent these longer needles from bending, some anesthesiolo-gists prefer larger diameter needles, such as the 22-gauge Sprotte needle. Alternatively, a 2.5-in. (6.3-cm) 20-gauge Quincke type spinal needle can be used as a long introducer and guide for a 25-gauge pencil-point spinal needle.

 

Continuous spinal anesthesia is also a reason-able option, especially for obese patients, follow-ing unintentional dural puncture sustained while attempting to place an epidural catheter for cesar-ean section. After the catheter is advanced 2–2.5 cm into the lumbar subarachnoid space and secured, it can be used to inject anesthetic agents; more-over, it allows later supplementation of anesthesia if necessary.

Epidural Anesthesia

 

Epidural anesthesia for cesarean section is typically performed using a catheter, which allows supplemen-tation of anesthesia if necessary and provides an excellent route for postoperative opioid admin-istration. Aft er negative aspiration and a negative test dose, a total of 15–25 mL of local anesthetic is injected slowly in 5-mL increments in order to minimize the risk of systemic local anesthetic toxic-ity. Lidocaine 2% (typically with 1:200,000 epineph-rine) or chloroprocaine 3% are most commonly used in the United States. The addition of fentanyl, 50–100 mcg, or sufentanil, 10–20 mcg, greatly enhances the intensity of the analgesia and prolongs its duration without adversely affecting neonatal out-come. Some practitioners also add sodium bicarbon-ate (7.5% or 8.4% solution) to local anesthetic solutions (1 mEq/10 mL of lidocaine) to increase the concentration of the nonionized free base and pro-duce a faster onset and more rapid spread of epidural anesthesia. If pain develops as the sensory level recedes, additional local anesthetic is administered in 5-mL increments to maintain a T4 sensory level. “Patchy” anesthesia prior to delivery of the baby can be treated with 10–20 mg of intravenous ketamine in combination with 1–2 mg of midazolam or 30% nitrous oxide. After delivery, intravenous opioid sup-plementation may also be used, provided excessive sedation and loss of consciousness are avoided. Pain that remains intolerable in spite of a seemingly ade-quate sensory level and that proves unresponsive to these measures necessitates general anesthesia with endotracheal intubation. Nausea can be treated intra-venously with a 5-HT3-receptor antagonist such as ondansetron, 4 mg.

 

Epidural morphine (5 mg) at the end of surgery provides good to excellent pain relief postopera-tively for 6–24 h. An increased incidence (3.5–30%) of recurrent herpes simplex labialis infection has been reported 2–5 days following epidural mor-phine administration in some studies. Postoperative analgesia can also be provided by continuous epi-dural infusions of fentanyl, 25–75 mcg/h, or sufent-anil, 5–10 mcg/h, at a volume rate of approximately 10 mL/h. Epidural butorphanol, 2 mg, can also pro-vide effective postoperative pain relief, but marked somnolence is often a side effect.

CSE Anesthesia

 

The technique for CSE is described in the earlier section on Combined Spinal & Epidural Analgesia for labor and vaginal delivery. For cesarean section, it combines the benefit of rapid, reliable, intense blockade of spinal anesthesia with the flexibility of an epidural catheter. The catheter also allows supple-mentation of anesthesia and can be used for post-operative analgesia. As mentioned previously, drugs given epidurally should be administered and titrated carefully because the dural hole created by the spinal needle may facilitate movement of epidural drugs into CSF and enhance their effects.

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