There are three anesthetic choices for cesarean delivery. Selection of one over the others depends on the patient's desires, medical status, and the urgency of the operation. Regional anesthesia is strongly preferred in the United States ( Table 3.4).
TABLE 3.4. Types of cesarean anesthesia provided by size of hospital in three time periods
Epidural Anesthesia
Epidural anesthesia accounts for approximately 40% of anesthetics used for cesarean section. It offers the advantages of unlimited duration, minimizing the risks of airway management, and providing a route for postoperative pain management.
To carry out a cesarean delivery, a sensory dermatome level of at least T-4 is required. Anesthesia to this level eliminates proprioception from the respiratory muscles of the chest wall, and the parturient may experience a subjective sensation of dyspnea. Reassurance will usually allay this fear. The patient should be placed on the operating table with the uterus displaced laterally through elevation of the right hip or by tilting of the operating table, to prevent aortocaval compression.
A vascular preload of 1000 to 1500 mL of a non–glucose-containing crystalloid solution should be administered before dosing of the epidural needle or catheter with the anesthetizing solution. A surgical concentration of a local anesthetic (often 2% lidocaine) with or without added opioid is administered through the catheter in 3- to 5-mL increments. The patient should be given oxygen by nasal cannula or by mask. One study failed to reveal any differences in the clinical condition of neonates, as
assessed by Apgar scores and blood gas analyses, when oxygen administration by these two modalities was compared.
Epidural opioids have been useful for relieving pain of visceral origin, which affects as many as one-third of the women who have cesarean sections under epidural anesthesia. Visceral pain occurs primarily during bladder retraction, exteriorization of the uterus, and suturing of the peritoneum. The addition of fentanyl or sufentanil to the local anesthetic reduces the time of onset of analgesia, decreases the incidence of nausea, and increases the quality of analgesia without depressing the
neurobehavioral status of the newborn.
Studies of fentanyl concentrations in neonates demonstrate that fentanyl crosses the placenta. Even high maternal doses (e.g., 100 µg) of fentanyl yield safe levels in the newborn. Morphine 2 to 4 mg is often administered through the epidural catheter after delivery to provide 12 to 24 hours of postoperative analgesia, although the incidence of associated pruritus and nausea can be high. Use of epidural morphine may reactivate herpetic labialis (herpes simplex virus-1) infections ( 30).
There are several advantages to using epidural analgesia for cesarean section delivery:
if an epidural catheter is already in place, it can be used expeditiously for the cesarean section delivery.
maternal hypotension may be less pronounced and slower in onset with epidural than with spinal anesthesia.
headache is usually avoided, unless the patient sustains an accidental dural puncture.
the length of anesthesia is controllable in case surgery is prolonged.
the technique is adaptable for postoperative pain relief.
The disadvantages include:
the slower onset of analgesia
the requirement for a larger amount of anesthetic solution with its attendant increased risk of systemic toxicity the lower success rate than that experienced with subarachnoid block.
An unexpectedly high level of anesthetic block may be achieved with epidural or spinal anesthesia and, as a result, this should be monitored. The likelihood of
inadvertent spinal anesthesia while attempting epidural block can be minimized through gentle aspiration of the catheter combined with using a test dose of sufficiently small volume that it is unlikely to produce a high block. A total spinal block generally occurs within 90 seconds after injection, but it may be delayed for as long as 20 minutes. Dyspnea, hypotension, unconsciousness, and apnea are signs and symptoms of total spinal block. Treatment includes ventilation through an endotracheal tube and, if needed, circulatory support.
Subarachnoid or Spinal Anesthesia
A subarachnoid block provides excellent anesthesia for cesarean section delivery. Over 50% of cesarean deliveries are performed using this technique (see Table 3.4).
Prehydration is administered with 1500 to 2000 mL of a non–glucose-containing crystalloid solution. A 22- to 27-gauge pencil-point spinal needle is inserted into the subarachnoid space, which is identified by the characteristic feel of the needle penetrating the dura and observing CSF in the needle. Bupivacaine 0.75%, 10 to 12 mg, with dextrose, is most commonly used. Analgesia of shorter duration is obtained with the use of lidocaine 5% in 7.5% dextrose.
Opioids may also be administered intrathecally to improve quality of analgesia, decrease nausea, and improve cardiovascular stability by allowing a lower dose of local anesthetic. Spinal (as well as epidural) narcotics are associated with a high incidence of pruritus, as well as the rare but real potential for delayed respiratory
depression. Fentanyl may be administered to improve intraoperative analgesia while the addition of morphine can provide postoperative analgesia that may last for 18 to 24 hours.
Contraindications to spinal anesthesia are the same as for epidural anesthesia and include patient refusal, septicemia, infection of the puncture site, acute or chronic hypovolemia, and abnormal clotting parameters. Spinal anesthesia is usually avoided in pregnant women with acute CNS disease.
The most common complication of spinal anesthesia is hypotension. This should be treated promptly with fluid administration and intravenous ephedrine (5- to 10-mg bolus). Oxygen should be given, and the parturient's oxygen saturation should be monitored with a pulse oximeter. In the event of a high spinal block which
compromises ventilation or airway control, cricoid pressure should be applied and endotracheal intubation performed to prevent aspiration of gastric contents.
With the increasing use of spinal and epidural narcotics, pruritus is becoming a commonplace adverse effect. Its incidence approaches 60% when spinal or epidural morphine is employed. The cause seems to be related to stimulation of opioid receptors rather than to release of histamine. Naloxone can be used to control pruritus, but the dose must be titrated carefully to avoid antagonism of analgesia. Nalbuphine may also be used and is less likely to antagonize analgesia.
Approximately 23% of women experience shivering during normal labor and delivery, and the rate increases to approximately 68% with epidural analgesia. Shivering can be diminished or abolished through epidural injection of opioids (e.g., fentanyl 100 µg) or small intravenous doses of meperidine (e.g., 12.5 mg).
General Anesthesia
General anesthesia is used for cesarean delivery when the patient refuses regional analgesia or has a contraindication to regional analgesia, or when a need exists for rapid delivery because of fetal distress, cord prolapse, shoulder dystocia, or maternal hemorrhage.
The American College of Obstetricians and Gynecologists in the fifth edition of Guidelines for Perinatal Care, cites the risk factors for failed intubation and urges obstetricians to be alert to the presence of the factors that place parturients at increased risk for complications from emergency general anesthesia. Among these are marked obesity, severe facial and neck edema, extremely short stature, short neck, difficulty opening the mouth, a small mandible, protuberant teeth, arthritis of the neck, anatomic abnormalities of the face or mouth, a large thyroid gland, asthma, serious medical or obstetric complications, and a history of problems with
anesthetics. If any of these factors is identified, a member of the anesthesia team should be consulted to prepare for the unexpected need to induce general anesthesia. If the anesthesiologist has concerns about his or her ability to intubate the patient, early placement of a regional anesthetic should be planned or arrangements for an awake intubation should be made.
Pneumonitis resulting from aspiration of gastric contents has long been feared as a complication of general anesthesia for obstetrics, but is extremely rare. One review compared the incidence of aspiration in obstetric and gynecological patients ( 31). The incidence of clinically significant aspiration was 0.11% in women undergoing cesarean delivery compared to 0.01% in gynecology inpatients. No patient died, but morbidity was significant. The prudent anesthetist administers a nonparticulate oral antacid, such as sodium citrate, given prophylactically to increase the gastric pH. If time allows, an H 2-blocker (e.g., ranitidine 50 mg intravenously) should be
administered. Intravenous metoclopramide, 10 mg, hastens gastric emptying, increases gastroesophageal sphincter tone, and may decrease nausea.
Before induction of anesthesia, the patient should be preoxygenated with 100% oxygen by mask for at least 3 minutes. Induction is commonly carried out using
thiopental (3–4 mg per kg i.v.). Propofol (Diprivan) has also been used. Propofol is associated with a blunted hypertensive response to endotracheal intubation and has yielded similar and satisfactory Apgar scores, neurologic and adaptive capacity scores, and umbilical cord blood gas analyses. If propofol infusion is used for
maintenance of anesthesia for a prolonged time before delivery, neonatal blood levels are high, and neurologic and adaptive capacity scores may be impaired. If the patient is hemodynamically unstable, ketamine 1 mg per kg or etomidate 0.3 mg per kg may be used.
Intubation is facilitated by use of succinylcholine. Cricoid pressure is maintained during induction of anesthesia until the endotracheal tube is in place, the cuff has been inflated, respirations have been auscultated, and end-tidal carbon dioxide has been seen. After successful intubation, a mixture of equal parts of nitrous oxide and oxygen may be administered, and a low dose of an inhalational agent, such as desflurane 3%, sevoflurane 1% or isoflurane 0.75%, is administered to optimize maternal analgesia and amnesia. These low concentrations have minimal effects on uterine contractility and are not associated with postpartum hemorrhage. After delivery of the infant, the nitrous oxide concentration may be increased to 70%, and narcotics may be given intravenously to supplement the anesthesia. Midazolam may be used to decrease the risk of maternal recall.
The advantages of general anesthesia include:
If the cords are poorly visualized during laryngoscopy, no more than three attempts at endotracheal intubation should be made before beginning a failed intubation drill ( 32). The initial maneuver in the failed intubation drill depends on the obstetric indication for cesarean section. If the operation is not emergent, the patient should be awakened and an epidural or spinal block performed. If a regional anesthetic cannot be accomplished, an awake fiberoptic intubation should be considered. In an obstetric emergency where surgery must proceed, the patient must be ventilated with bag and mask or laryngeal mask airway, and anesthesia may be maintained with inhalational or intravenous agents throughout the remainder of the cesarean section. The continuation of cricoid pressure is important to reduce the maternal risk of aspiration. If it should prove impossible to ventilate the patient with bag and mask, an emergency maneuver such as cricothyroidotomy must be performed. Use of an esophageal gastric tube airway (Combitube) or laryngeal mask may enable adequate ventilation.
Inability to intubate has been estimated to occur seven times more commonly in the obstetric patient than in the general operating room, and continues to contribute significantly to anesthetic causes of maternal mortality ( 33). Anticipation of a difficult intubation allows the anesthesia team to be prepared to avoid general anesthesia or plan an awake intubation.
Analgesia after Cesarean Section
Considerable advances have been made in the management of pain after cesarean section. The availability of spinal and epidural narcotics has enabled the anesthesia team to provide the postsurgical patient with effective, long-term analgesia. Morphine is the most commonly used neuraxial opioid because of its long duration and lack of motor block compared to local anesthetic infusions. The most feared complication is respiratory depression. The rate of analgesia-related
respiratory depression is approximately 0.09%. Because this complication is rare, patients receiving postoperative neuraxial opioid analgesia may be safely nursed on the general ward, if the nurses are appropriately educated in monitoring the degree of somnolence and the respiratory rates of their patients. Patients who did not receive regional anesthesia may receive intravenous PCA. Combining narcotics and nonsteroidal antiinflammatory medications such as ketorolac or ibuprofen improves the quality of analgesia and allows reduced doses of narcotics. Naloxone should be readily available to antagonize respiratory depression.
SUMMARY POINTS
Pain management is an important part of modern obstetric care. Most women will request some form of analgesia during childbirth.
Parenteral narcotics for labor analgesia may be administered by intermittent injection or patient-controlled intravenous infusion. There are advantages and disadvantages of all opioids.
High systemic blood levels of local anesthetic caused by intravascular injection or excessive absorption may lead to convulsions and cardiac arrest.
Resuscitation equipment must be immediately available whenever regional blocks are used.
Modern techniques of regional analgesia for labor (dilute concentrations of epidural local anesthetics, combined spinal–epidural analgesia and
patient-controlled epidural infusions) emphasize pain relief with minimal motor block. Studies indicate these techniques do not impact progress of labor.
Although modern anesthetic care for cesarean delivery is extremely safe (anesthesia-related maternal mortality = 1.1 per million live births), general anesthesia complications are more common than regional anesthetic complications because of difficulties with airway management.
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Chapter 4 Early Pregnancy Loss
Danforth’s Obstetrics and Gynecology
Chapter 4
D. Ware Branch and James R. Scott