CHAPTER 25: Obstetrical Analgesia and Anesthesia

As cited by Williams, anesthetic techniques were a most welcome addition to obstetrics. That said, obstetrical anesthesia presents unique challenges. Labor begins without warning, and anesthesia may be required within minutes of a full meal. Vomiting with potential aspiration of the gastric contents is a constant threat due to delayed gastric emptying during pregnancy. Disorders of pregnancy such as preeclampsia, placental abruption, or sepsis further compound provision of obstetrical anesthesia.

Of all anesthesia-related deaths in the United States from 1995 to 2005, 3.6 percent were in pregnant women (Li, 2009). Creanga and colleagues (2017) analyzed deaths of women during or within 1 year of pregnancy in the United States from 2011 through 2013. Of these deaths, they found that 3 of 2009 (0.2 percent) were attributable to anesthesia complications. As shown in Table 25-1, between 1979 and 2002, anesthesia-related maternal mortality rates decreased nearly 60 percent, and currently approximately five deaths per million live births are attributed to anesthesia complications.

About two thirds of deaths associated with general anesthesia are caused by intubation failure or induction problems during cesarean delivery. Deaths associated with regional analgesia are caused by high spinal or epidural blocks—26 percent; respiratory failure—19 percent; and drug reaction—19 percent. The improved case-fatality rate for general anesthesia is especially notable considering that such anesthesia is now used for the highest-risk patients and the most hurried emergencies, that is, decision-to-incision intervals <15 minutes (Bloom, 2005).

The most significant factor linked to lower maternal mortality rates is the greater use of regional analgesia (Hawkins, 2011). In-house anesthesia coverage that is available around the clock is certainly another contributing factor. Logically, with increased use of regional analgesia, there are now reports of complications with these techniques. Indeed, compared to pre-1990 data, post-1990 obstetrical anesthesia was associated with more legal claims involving regional analgesia (Davies, 2009). In a recent analysis of 466,442 obstetrical hospital discharges, complications associated with regional analgesia accounted for 81 percent of anesthesia-related adverse events (Guglielminotti, 2015).

For the fetus, recent human studies suggest that single, relatively short exposure to general anesthetic and sedation is unlikely to have negative effects on subsequent behavior or learning. This evidence is presented in Chapter 46 (Medications and Surgeries). That said, in 2016, the Food and Drug Administration (FDA) warned that repeated or lengthy use of general anesthetic and sedation drugs in pregnant women during their third trimester may affect fetal brain development. Listed drugs include inhalation agents used in general anesthesia as well as lorazepam, ketamine, propofol, and midazolam. Notably, the American College of Obstetricians and Gynecologists (2016a) and the Society for Obstetric Anesthesia and Perinatology (2017) have voiced concerns with this statement and cited the lack of significant human data, especially in pregnant women, to underpin this warning.

Obstetrical Anesthesia Services

The American College of Obstetricians and Gynecologists (2017a) recognizes that a woman’s request for labor pain relief is sufficient medical indication for its provision. Identification of any of the risk factors shown in Table 25-2 should prompt consultation with anesthesia personnel to permit a joint management plan. This plan should include strategies to minimize the need for emergency anesthesia.

Goals for optimizing obstetrical anesthesia services have been established by the American College of Obstetricians and Gynecologists (2017a) and the American Society of Anesthesiologists (2016) and include:

1. Availability of a licensed practitioner who is credentialed to administer an appropriate anesthetic whenever necessary and to maintain support of vital functions in an obstetrical emergency.

2. Availability of anesthesia personnel to permit the start of a cesarean delivery within 30 minutes of the decision to perform the procedure.

3. Anesthesia personnel immediately available to perform an emergency cesarean delivery during the active labor of a woman attempting vaginal birth after cesarean (Chap. 31, Labor and Delivery Considerations).

4. Appointment of a qualified anesthesiologist to be responsible for all anesthetics administered.

5. Availability of a qualified physician with obstetrical privileges to perform operative vaginal or cesarean delivery during administration of anesthesia.

6. Availability of equipment, facilities, and support personnel equal to that provided in any surgical suite.

7. Immediate availability of personnel, other than the surgical team, to assume responsibility for resuscitation of a depressed newborn (Chap. 32, Transition to Air Breathing).

To meet these goals, 24-hour, in-house anesthesia coverage is usually necessary. Providing such service in smaller facilities is more challenging—a problem underscored by the fact that approximately a third of all hospitals providing obstetrical care perform fewer than 500 deliveries per year. The financial burden incurred to provide 24/7 obstetrical anesthesia coverage may result in cost deficits (Bell, 2000). Compounding this burden, some third-party payers have denied reimbursement for epidural analgesia in the absence of a specific medical indication—an approach repudiated by the American College of Obstetricians and Gynecologists (2017a).

Regarding obstetricians, they should be proficient in local and pudendal analgesia. These may be administered in appropriately selected circumstances described in Central Nervous System Toxicity.

Pain Relief Principles

Hawkins (2010) emphasized that labor pain is a highly individual response to variable stimuli that are uniquely received and interpreted (Fig. 25-1). These stimuli are modified by emotional, motivational, cognitive, social, and cultural circumstances. Labor pain caused by uterine contractions and cervical dilation is transmitted through visceral afferent sympathetic nerves entering the spinal cord from T₁₀ through L₁. Later in labor, perineal stretching transmits painful stimuli through the pudendal nerve and sacral nerves S₂ through S₄. Cortical responses to pain and anxiety during labor are complex and may be influenced by maternal expectations for childbirth, her age, preparation through education, emotional support, and other factors. Pain perception is heightened by fear and the need to move into various positions. A woman may be motivated to have a certain type of birthing experience, and these opinions will influence her judgment regarding pain management.

Maternal physiological responses to labor pain can influence maternal and fetal well-being and labor progress. For example, hyperventilation may induce hypocarbia. A greater metabolic rate augments oxygen consumption. Increases in cardiac output and vascular resistance may raise maternal blood pressure. Pain, stress, and anxiety trigger release of stress hormones such as cortisol and β-endorphins. The sympathetic nervous system response to pain leads to a marked elevation in circulating catecholamines that can adversely affect uterine activity and uteroplacental blood flow. Effective analgesia attenuates or eliminates these responses.

If uterine contractions and cervical dilatation cause discomfort, pain relief is offered. If neuraxial analgesia is contraindicated or unavailable or is declined, a narcotic from Table 25-3 plus one of the tranquilizer-antiemetic drugs such as promethazine (Phenergan) is usually appropriate. With a successful program of analgesia and sedation, the mother ideally rests quietly between contractions. In this circumstance, discomfort usually is felt at the acme of an effective uterine contraction.

Parenteral Agents

Meperidine and Promethazine

Meperidine, 50 to 100 mg, with promethazine, 25 mg, may be administered intramuscularly at intervals of 2 to 4 hours. A more rapid effect is achieved by giving meperidine intravenously in doses of 25 to 50 mg every 1 to 2 hours. Whereas analgesia is maximal 30 to 45 minutes after an intramuscular injection, it develops almost immediately following intravenous administration. Meperidine readily crosses the placenta and can have a prolonged half-life in the newborn (American College of Obstetricians and Gynecologists, 2017a). Its depressant effect in the fetus follows closely behind the peak maternal analgesic effect.

According to Bricker and Lavender (2002), meperidine is the most common opioid used worldwide for pain relief during labor. In one randomized study at Parkland Hospital, patient-controlled intravenous analgesia with meperidine was found to be an inexpensive and reasonably effective method for labor analgesia (Sharma, 1997). Women randomized to self-administered analgesia were given a 50-mg meperidine plus 25-mg promethazine dose intravenously as an initial bolus. Thereafter, an infusion pump was set to deliver 15 mg of meperidine every 10 minutes as needed until delivery. Neonatal sedation, as measured by the need for naloxone treatment in the delivery room, was identified in 3 percent of newborns. Both meperidine and its metabolite, normeperidine, are lipophilic and readily cross the placenta. Analgesia with meperidine was associated with lower Apgar scores in comparison to epidural analgesia (Sharma, 2004). Normeperidine is a strong respiratory depressant that has a significantly longer half-life than meperidine and is likely responsible for the fetal side effects of meperidine.

Butorphanol

This synthetic opioid receptor agonist–antagonist analgesic, given in 1- to 2-mg intravenous doses, compares favorably with 40 to 60 mg of meperidine. Its major side effects are somnolence, dizziness, and dysphoria. Neonatal respiratory depression is reported to be less than with meperidine. Importantly, the two drugs are not given contiguously because butorphanol antagonizes the narcotic effects of meperidine. Butorphanol has been associated with transient sinusoidal fetal heart rate patterns (Hatjis, 1986).

Nalbuphine

This is another mixed opioid receptor agonist–antagonist analgesic. It can be given intramuscularly, intravenously, or subcutaneously. The usual dose is 10 to 20 mg, administered every 4 to 6 hours irrespective of the route of administration. Small doses of nalbuphine may also be used to treat pruritus associated with neuraxial opioids.

Fentanyl

This short-acting and potent synthetic opioid may be given in doses of 50 to 100 μg intravenously every hour. Its main disadvantage is its short duration of action, which requires frequent dosing or use of a patient-controlled intravenous infusion pump.

Remifentanil

This is a synthetic opioid with an extremely rapid onset of action. It is hydrolyzed rapidly, resulting in a half-life of 3.5 minutes (Ohashi, 2016). Although it readily crosses the placenta, it is quickly metabolized or redistributed within the fetus (Kan, 1998). Various dosing regimens have been studied, and single boluses appear to mirror the periodic uterine contraction pattern. Infusions, on the other hand, have been reported to cause maternal apnea (Waring, 2007). Due to the aforementioned risks, only trained personnel should administer it, and only under strictly controlled circumstances.

Efficacy and Safety of Parenteral Agents

Hawkins and colleagues (1997) reported that four of 129 maternal anesthetic-related deaths were from parenteral sedation—one from aspiration, two from inadequate ventilation, and one from overdosage. Opioids used during labor may cause newborn respiratory depression. Naloxone is a narcotic antagonist capable of reversing this respiratory depression. It acts by displacing the narcotic from specific receptors in the central nervous system. Withdrawal symptoms may be precipitated in recipients who are physically dependent on narcotics. For this reason, naloxone is contraindicated in a newborn of a narcotic-addicted mother.

Nitrous Oxide

Inhaled nitrous oxide has a rapid onset and offset that provides analgesia during episodic contractions. It can be self-administered as a mixture of 50-percent nitrous oxide and 50-percent oxygen premixed in a single cylinder (Entonox) or using a blender that mixes the two gases from separate tanks (Nitronox). The gases are connected to a breathing circuit through a one-way valve that opens only during inspiration. The use of intermittent nitrous oxide for labor pain is generally regarded as safe for the mother and newborn, but pain control is less effective than epidural analgesia (Barbieri, 2014; Likis, 2014). In many cases, nitrous oxide simply serves to delay more definitive neuraxial analgesia. For maximal efficacy, nitrous oxide is inhaled 30 seconds prior to the start of a contraction, although this prevents adequate rest for the mother. Nitrous oxide is also associated with nausea and vomiting. The environmental and health risk of its use without proper scavenging remains to be carefully evaluated (King, 2014).

Various nerve blocks have been developed over the years to provide pain relief during labor and/or delivery. These include pudendal, paracervical, and neuraxial blocks such as spinal, epidural, and combined spinal-epidural techniques.

Anesthetic Agents

Some of the more commonly used nerve block anesthetics, along with their usual concentrations, doses, and durations of action, are summarized in Table 25-4. The dose of each agent varies widely and is dependent on the particular nerve block and physical status of the woman. The onset, duration, and quality of analgesia can be enhanced by raising the volume and/or concentration. This can be done safely only by incrementally administering small-volume boluses of the agent and by carefully monitoring early warning signs of toxicity. Administration of these agents must be followed by appropriate monitoring for adverse reactions. Equipment and personnel to manage these reactions must be immediately available.

Most often, serious toxicity follows inadvertent intravenous injection. Systemic toxicity from local anesthetics typically manifests in the central nervous and cardiovascular systems. For this reason, when epidural analgesia is initiated, dilute epinephrine is sometimes added and given as a test dose. A sudden significant rise in the maternal heart rate or blood pressure immediately after administration suggests intravenous catheter placement. This should halt further injection and should prompt catheter repositioning. Local anesthetic agents are manufactured in more than one concentration and ampule size, which raises the potential for dosing errors.

Central Nervous System Toxicity

Early symptoms are those of stimulation, but as serum levels rise, depression follows. Symptoms may include light-headedness, dizziness, tinnitus, metallic taste, and numbness of the tongue and mouth. Patients may show bizarre behavior, slurred speech, muscle fasciculation and excitation, and ultimately, generalized convulsions, followed by loss of consciousness.

Cardiovascular Toxicity

These manifestations generally develop later than those of cerebral toxicity. Moreover, no symptoms may develop because signs are usually induced by higher serum drug levels. The notable exception is bupivacaine, which is associated with neurotoxicity and cardiotoxicity at virtually identical levels (Mulroy, 2002). Because of its toxicity risk, use of a 0.75-percent solution of bupivacaine for epidural injection has been proscribed by the FDA. Similar to neurotoxicity, cardiovascular toxicity is characterized first by stimulation and then by depression. Accordingly, hypertension and tachycardia are soon followed by hypotension, cardiac arrhythmias, and impaired uteroplacental perfusion.

Management of Local Anesthetic Systemic Toxicity

Seizures and severe ventricular arrhythmias can follow large doses of local anesthetics that are given inadvertently. Labor and delivery units should be stocked with a 20-percent lipid emulsion solution (Intralipid). It is administered as a rapid intravenous bolus followed by an infusion upon the first sign of local anesthetic systemic toxicity (Neal, 2012). Controlling seizures and securing the airway are essential to prevent aspiration and hypoxemia. Benzodiazepines, such as midazolam or lorazepam, may be used to help control seizures, particularly if lipid emulsions are not available. Magnesium sulfate also controls convulsions (Chap 40, Management of Eclampsia). Abnormal fetal heart rate patterns that include late decelerations or bradycardia can follow and stem from maternal hypoxia. With proper management, including supportive measures, the fetus usually recovers. Therefore, it is best for the fetus and mother to delay delivery until the mother is stabilized.

With proper treatment of local anesthetic systemic toxicity (LAST) with lipid emulsions, vital signs usually return to normal. The woman, however, should be monitored, placed in the lateral decubitus position to avoid aortocaval compression, and provided continued supportive care. Vasopressors can be used to support blood pressure. With cardiac arrest, emergency cesarean delivery is considered if maternal vital signs have not been restored within 5 minutes (Chap, 47, Cardiopulmonary Resuscitation). As with convulsions, however, the fetus is likely to recover more quickly in utero once maternal cardiac output is reestablished.

Pudendal Block

Pain with vaginal delivery arises from stimuli from the lower genital tract. These are transmitted primarily through the pudendal nerve, the peripheral branches of which provide sensory innervation to the perineum, anus, vulva, and clitoris. The pudendal nerve passes beneath the sacrospinous ligament just as the ligament attaches to the ischial spine. Sensory nerve fibers of the pudendal nerve are derived from ventral branches of the S₂ through S₄ nerves.

The pudendal nerve block is a relatively safe and simple method of providing analgesia for spontaneous delivery. As shown in Figure 25-2, a tubular introducer is used to sheathe and guide a 15-cm-long 22-gauge needle into position near the pudendal nerve. The end of the introducer is placed against the vaginal mucosa just beneath the tip of the ischial spine. The introducer allows 1.0 to 1.5 cm of needle to protrude beyond its tip, and the needle is pushed beyond the introducer tip into the mucosa. A mucosal wheal is made with 1 mL of 1-percent lidocaine solution or an equivalent dose of another local anesthetic (see Table 25-4). To guard against intravascular infusion, aspiration is attempted before this and all subsequent injections. The needle is then advanced until it touches the sacrospinous ligament, which is infiltrated with 3 mL of lidocaine. The needle is advanced farther through the ligament. As the needle pierces the loose areolar tissue behind the ligament, resistance against the plunger drops. Another 3 mL of solution is injected in this region. Next, the needle is withdrawn into the introducer, which is moved to a point just above the ischial spine. The needle is inserted through the mucosa and a final 3 mL is deposited. The procedure is then repeated on the other side.

Within 3 to 4 minutes of injection, a successful pudendal block will allow pinching of the lower vagina and posterior vulva bilaterally without pain. If delivery occurs before the pudendal block becomes effective and an episiotomy is indicated, then the fourchette, perineum, and adjacent vagina can be infiltrated with 5 to 10 mL of 1-percent lidocaine solution directly at the planned episiotomy site. By the time of repair, the pudendal block usually has become effective.

Pudendal block usually does not provide adequate analgesia when delivery requires extensive obstetrical manipulation. Moreover, such analgesia is usually inadequate for women in whom complete visualization of the cervix and upper vagina or manual exploration of the uterine cavity is indicated.

Infrequently, complications may follow this block. As previously described, intravascular injection of a local anesthetic agent may cause serious systemic toxicity. Hematoma formation from perforation of a blood vessel is most likely when there is a coagulopathy (Lee, 2004). Rarely, severe infection may originate at the injection site. The infection may spread posteriorly to the hip joint, into the gluteal musculature, or into the retropsoas space (Svancarek, 1977).

Paracervical Block

This block usually provides satisfactory pain relief during first-stage labor. However, because the pudendal nerves are not blocked during paracervical blockade, additional analgesia is required for delivery. For paracervical blockade, usually 5 to 10 mL of lidocaine (1 to 2 percent) or chloroprocaine (3 percent) is injected into the cervix laterally at 3 and 9 o’clock. Because these anesthetics are relatively short acting, this block may have to be repeated during labor.

Fetal bradycardia is a worrisome complication that occurs with approximately 15 percent of paracervical blocks (Rosen, 2002). Bradycardia usually develops within 10 minutes and may last up to 30 minutes. Doppler studies have shown a rise in the pulsatility index of the uterine arteries following paracervical blockade. These observations support the hypothesis of drug-induced arterial vasospasm as a cause of fetal bradycardia (Manninen, 2000). For these reasons, paracervical block is not used in situations of potential fetal compromise.

Epidural, spinal, or combined spinal-epidural techniques are the most common methods used for pain relief during labor and delivery. In the United States in 2008, epidural analgesia was used in nearly 70 percent of mothers during labor and had a success rate of 98.8 percent. Neuraxial analgesia was used even more often in operative vaginal deliveries and supported 84 percent of forceps deliveries and 77 percent of vacuum extractions (Osterman, 2011).

Spinal (Subarachnoid) Block

Anesthetic in this block can be given as a single dose, can be partnered with an epidural catheter as combined spinal-epidural analgesia, or can be administered as a continuous infusion. Injection of a local anesthetic into the subarachnoid space to effect analgesia has long been used for delivery. Advantages include rapid analgesia onset, short duration of action, and high success rate. The subarachnoid space during pregnancy is smaller, which likely results from internal vertebral venous plexus engorgement. Thus, in parturients, the same amount of anesthetic agent in the same volume of solution produces a much higher blockade than in nonpregnant women.

Vaginal Delivery

The first stage of labor requires a sensory block to the level of the umbilicus (T₁₀). During the second stage of labor and for operative vaginal delivery, a sensory block of S₂ through S₄ is usually adequate to cover pain from perineal stretching and/or instrumentation. Analgesic options include continuous lumbar epidural analgesia, combined spinal-epidural, continuous spinal analgesia, and other blocks such as pudendal and paracervical blocks.

Local anesthetic agents are usually given to establish a sensory block to the desired dermatome level. They are almost exclusively used in conjunction with neuraxial opioids. The mechanism of action is a function of the administration route and lipid solubility. Analgesia is induced by absorption into the vascular system (supraspinal), actions on the dorsal horns, and direct spread in the cerebrospinal fluid to the brainstem. Highly-soluble lipid opioids such as fentanyl and sufentanil have a rapid onset of action. But, because they are absorbed into lipid membranes and the epidural vasculature, their duration of action is short. Hydrophilic solutions such as morphine, on the other hand, provide extended analgesia (Lavoie, 2013). The major advantages of using such a combination are the rapid onset of pain relief, a decrease in shivering, and less dense motor blockade. Side effects are common and include pruritus and urinary retention. Nalbuphine, 2.5 to 5 mg intravenously, can be used to treat pruritis without diminishing the analgesic effect.

Cesarean Delivery

A level of sensory blockade extending to the T₄ dermatome is desired for cesarean delivery. Depending on maternal size, 10 to 12 mg of bupivacaine in a hyperbaric solution or 50 to 75 mg of lidocaine hyperbaric solution is administered. The addition of opioid increases the rapidity of blockade onset, reduces shivering, and minimizes referred pain and other symptoms such as nausea and vomiting. The addition of a preservative-free morphine (Duramorph or Astramorph), 0.1 to 0.3 mg intrathecal or 2 to 4 mg epidural, provides pain control up to 24 hours postoperatively.

Complications

Hypotension

Shown in Table 25-5 are some of the more common adverse events associated with neuraxial analgesia. Importantly, obese women have significantly impaired ventilation, and thus close clinical monitoring is imperative (Vricella, 2011).

Hypotension is a common complication that may develop soon after injection of the local anesthetic agent. It is the consequence of vasodilatation from sympathetic blockade and is compounded by obstructed venous return due to uterine compression of the great vessels. In the supine position, even in the absence of maternal hypotension measured in the brachial artery, placental blood flow may still be significantly reduced. Treatment includes uterine displacement by left lateral patient positioning, intravenous crystalloid hydration, and intravenous bolus injections of ephedrine or phenylephrine.

Ephedrine is a sympathomimetic drug that binds to α- and β-receptors but also indirectly enhances norepinephrine release. It raises blood pressure by raising heart rate and cardiac output and by variably elevating peripheral vascular resistance. In early animal studies, ephedrine preserved uteroplacental blood flow during pregnancy compared with α₁-receptor agonists. Accordingly, it had been the preferred vasopressor for obstetrical use. Phenylephrine is a pure α-agonist and elevates blood pressure solely through vasoconstriction. A metaanalysis of seven randomized trials by Lee (2002a) suggests that the safety profiles of ephedrine and phenylephrine are comparable. Following their systematic review of 14 reports, Lee (2002b) questioned whether routine prophylactic ephedrine is needed for elective cesarean delivery. Although fetal acidemia has been reported with prophylactic ephedrine use, this was not observed with prophylactic phenylephrine use (Ngan Kee, 2004).

High or Total Spinal Blockade

Most often, high or total spinal blockade follows administration of an excessive dose of local anesthetic or inadvertent injection into the subdural or subarachnoid space. Subdural injection manifests as a high but patchy block even with a small dose of local anesthetic agent, whereas subarachnoid injection typically leads to complete spinal blockade with hypotension and apnea. These conditions must be immediately treated to prevent cardiac arrest. In the undelivered woman: (1) the uterus is immediately displaced laterally to minimize aortocaval compression; (2) effective ventilation is established, preferably with tracheal intubation; and (3) intravenous fluids and vasopressors are given to correct hypotension. If chest compressions are to be performed, the woman is placed in the left-lateral position to allow left uterine displacement.

Postdural Puncture Headache

Leakage of cerebrospinal fluid (CSF) from the dura mater puncture site can lead to postdural puncture or “spinal headache.” Presumably, when the woman sits or stands, the diminished CSF volume creates traction on pain-sensitive central nervous system structures. Another mechanism may be the compensatory cerebral vasodilation in response to the loss of CSF—the Monro-Kellie doctrine (Mokri, 2001).

Rates of this complication can be reduced by using a small-gauge spinal needle and avoiding multiple punctures. In a prospective, randomized study of five different spinal needles, Vallejo and associates (2000) concluded that Sprotte and Whitacre needles had the lowest risks of postdural puncture headaches. Sprigge and Harper (2008) reported that the incidence of postdural puncture headache was 1 percent in more than 5000 women undergoing spinal analgesia. Postdural puncture headaches are much less frequent with epidural blockade because the dura mater is not intentionally punctured. The incidence of inadvertent dural puncture with epidural analgesia approximates 0.2 percent (Introna, 2012; Katircioglu, 2008). There is no good evidence that placing a woman absolutely flat on her back for several hours is effective in preventing this headache.

Once headache develops, it is managed aggressively, as expectant management increases hospital-stay lengths and subsequent emergency-room visits (Angle, 2005). Conservative management, such as fluid administration and bed rest, is largely ineffective. If not effectively treated, postdural puncture headache can persist as a chronic headache (Webb, 2012).

Epidural blood patch is considered the gold standard for treatment. Typically, 10 to 20 mL of autologous blood obtained aseptically by venipuncture is injected into the epidural space. Further CSF leakage is halted by either mass effect or coagulation. Relief is almost always immediate, and complications are uncommon. The initial success rate of an epidural blood patch ranges from 61 to 73 percent (Paech, 2011). Performing a “prophylactic” blood patch is debatable and is thought not to be as effective as if performed after the headache develops (Scavone, 2004, 2015).

If a headache does not have the pathognomonic postural characteristics or persists despite treatment with a blood patch, other diagnoses are considered. Chisholm and Campbell (2001) described a case of superior sagittal sinus thrombosis that manifested as a postdural headache. Smarkusky and colleagues (2006) described pneumocephalus, which caused immediate cephalgia. Finally, intracranial and intraspinal subarachnoid hematomas have developed after spinal analgesia (Dawley, 2009; Liu, 2008).

Convulsions

In rare instances, postdural puncture cephalgia is associated with temporary blindness and convulsions. Shearer and associates (1995) described eight such cases associated with 19,000 regional analgesic procedures done at Parkland Hospital. It is presumed that these too are caused by CSF hypotension. Immediate treatment of seizures and a blood patch were usually effective in these cases.

Bladder Dysfunction

With neuraxial analgesia, bladder sensation is likely to be obtunded and bladder emptying impaired for several hours after delivery. As a consequence, bladder distention is a frequent postpartum complication, especially if appreciable volumes of intravenous fluid are given. Millet and colleagues (2012) randomized 146 women with neuraxial analgesia to either intermittent or continuous bladder catheterizations and found that the intermittent method was associated with significantly higher rates of bacteriuria. That said, we do not recommend routine postpartum use of indwelling catheters following uncomplicated vaginal delivery.

Arachnoiditis and Meningitis

Local anesthetics are no longer preserved in alcohol, formalin, or other toxic solutes, and disposable equipment is usually used. These practices, coupled with aseptic technique, have made meningitis and arachnoiditis rare (Centers for Disease Control and Prevention, 2010).

Contraindications to Neuraxial Analgesia

Shown in Table 25-6 are absolute contraindications. Obstetrical complications that are associated with maternal hypovolemia and hypotension—for example, severe hemorrhage—are contraindications (Kennedy, 1968).

Disorders of coagulation and defective hemostasis also preclude neuraxial analgesia use. Although no randomized studies guide the management of anticoagulation at the time of delivery, consensus opinion suggests that women given subcutaneous unfractionated heparin or low-molecular-weight heparin should be instructed to stop therapy when labor begins (Krivak, 2007). Subarachnoid puncture is also contraindicated if cellulitis involves the planned needle entry site. Many consider neurological disorders to be a contraindication, if for no other reason than that exacerbation of the neurological disease might be erroneously attributed to the anesthetic agent. Other maternal conditions, such as aortic stenosis or pulmonary hypertension, are also relative contraindications (Chap. 49, Physiological Considerations in Pregnancy).

Severe preeclampsia is another comorbid condition in which markedly decreased blood pressure can be predicted when neuraxial analgesia is used. Wallace and associates (1995) randomly assigned 80 women with severe preeclampsia undergoing cesarean delivery at Parkland Hospital to receive general anesthesia or either epidural or combined spinal-epidural analgesia. Maternal and neonatal outcomes did not differ. Still, 30 percent of women given epidural analgesia and 22 percent of those given spinal-epidural blockade developed hypotension. The average reduction in mean arterial pressure ranges between 15 and 25 percent.

Epidural Analgesia

Relief of labor and childbirth pain, including cesarean delivery, can be accomplished by injection of a local anesthetic agent into the epidural or peridural space (Fig. 25-3). This potential space contains areolar tissue, fat, lymphatics, and the internal vertebral venous plexus. This plexus becomes engorged during pregnancy such that the volume of the epidural space is appreciably reduced. Entry for obstetrical analgesia is usually through a lumbar intervertebral space. Although only one injection may be elected, usually an indwelling catheter is placed for subsequent agent boluses or infusion via a volumetric pump. The American College of Obstetricians and Gynecologists (2017a) concludes that under appropriate physician supervision, labor and delivery nursing personnel who have been specifically trained in the management of epidural infusions should be able to adjust dosage and also discontinue infusions.

Continuous Lumbar Epidural Block

Complete analgesia for the pain of labor and vaginal delivery necessitates a block from the T₁₀ to the S₅ dermatomes (see Fig. 25-1). For cesarean delivery, a block extending from the T₄ to the S₁ dermatomes is desired. The effective spread of anesthetic depends on the catheter tip location; the dose, concentration, and volume of anesthetic agent used; and whether the mother is head-down, horizontal, or head-up (Setayesh, 2001). Individual variations in anatomy or presence of synechiae may preclude a completely satisfactory block. Finally, the catheter tip may migrate from its original location during labor.

Technique

One example of the sequential steps and techniques for performance of epidural analgesia is detailed in Table 25-7. Before injection of the local anesthetic therapeutic dose, a test dose is given. The woman is observed for features of toxicity from intravascular injection and for signs of high or total blockade from subdural or subarachnoid injection. If these are absent, only then is a full dose given. Analgesia is maintained by intermittent boluses of similar volume or by small volumes delivered continuously by infusion pump (Halpern, 2009). Current pumps used for epidural analgesia offer a programmed intermittent epidural bolus (PIEB) mode, which reduces the required concentration of local anesthetics, the degree of lower extremity motor blockade, and rates of operative vaginal delivery (Capogna, 2011). The addition of small doses of a short-acting narcotic—fentanyl or sufentanil—has been shown to improve analgesic efficacy while avoiding motor blockade (Chestnut, 1988). As with spinal blockade, close monitoring, including the level of analgesia, is imperative and must be performed by trained personnel. Appropriate resuscitation equipment and drugs must be available during administration of epidural analgesia.

Complications

Higher or Total Spinal Blockade

In general, complications with epidural analgesia are similar to those with spinal analgesia (see Table 25-5). Dural puncture with inadvertent subarachnoid injection may cause total spinal blockade. Sprigge and Harper (2008) cited an incidence of 0.91 percent recognized accidental dural punctures at the time of epidural analgesia in more than 18,000 women. Personnel and facilities must be immediately available to manage this complication as described earlier (Cesarean Delivery). In other aspects, however, complications are unique and inherent to epidural analgesia use.

Ineffective Analgesia

Using currently popular continuous epidural infusion regimens such as 0.125-percent bupivacaine with 2-μg/mL fentanyl, 90 percent of women rate their pain relief as good to excellent (Sharma, 1997). Alternatively, a few women find epidural analgesia to be inadequate for labor. In a study of almost 2000 parturients, Hess and associates (2001) found that approximately 12 percent complained of three or more episodes of pain or pressure. Risk factors for such breakthrough pain included nulliparity and heavier fetal weights. Dresner and colleagues (2006) also reported that epidural analgesia was more likely to fail as body mass index increased. If epidural analgesia is allowed to dissipate before another injection of anesthetic drug, subsequent pain relief may be delayed, incomplete, or both.

In some women, epidural analgesia is insufficient for cesarean delivery. For example, in a Maternal Fetal Medicine Units (MFMU) Network study, 4 percent of women initially given epidural analgesia required a general anesthetic for cesarean delivery (Bloom, 2005). Also at times, perineal analgesia for delivery is difficult to obtain, especially with the lumbar epidural technique. When this situation is encountered, pudendal block or systemic analgesia or rarely general anesthesia may be added.

Hypotension

Sympathetic blockade from epidurally injected analgesic agents can cause hypotension and decreased cardiac output. Despite precautions, hypotension is the most frequent side effect and is severe enough to require treatment in a third of women (Sharma, 1997). According to Miller and coworkers (2013), hypotension is more common—20 percent—in women with an admission pulse pressure <45 mm Hg, compared with 6 percent in those whose pulse pressure is >45 mm Hg. In normal gravidas, hypotension induced by epidural analgesia usually can be prevented by rapid infusion of 500 to 1000 mL of crystalloid solution as described for spinal analgesia. Maintaining a lateral position also minimizes hypotension.

Maternal Fever

Fusi and colleagues (1989) observed that the mean temperature rose in laboring women given epidural analgesia. Subsequently, several randomized and retrospective cohort studies have confirmed that some women develop intrapartum fever following this procedure. Many studies are limited by inability to control for other risk factors such as labor length, duration of ruptured membranes, and number of vaginal examinations. With this in mind, the frequency of intrapartum fever associated with epidural analgesia was found by Lieberman and O’Donoghue (2002) to be 10 to 15 percent above the baseline rate.

The two general theories concerning the etiology of maternal hyperthermia are maternal-fetal infection or dysregulation of body temperature. Dashe and coworkers (1999) studied placental histopathology in laboring women given epidural analgesia and identified intrapartum fever only when there was placental inflammation. This suggests that fever is due to infection. The other proposed mechanisms include alteration of the hypothalamic thermoregulatory set point; impairment of peripheral thermoreceptor input to the central nervous system, with selective blockage of warm stimuli; or imbalance between heat production and heat loss. Sharma (2014) randomized 400 nulliparas with labor epidural analgesia to receive cefoxitin 2 g prophylactically versus placebo. It was hypothesized that epidural-related fever was due to infection and that prophylactic antimicrobial use should significantly reduce the rate of fever. Approximately equal proportions—about 40 percent—of women developed fever >38°C during labor. This suggests that infection is unlikely to be the cause of fever.

Back Pain

An association between epidural analgesia and subsequent back pain has been reported by some but not all. In a prospective cohort study, Butler and Fuller (1998) reported that back pain after delivery was common with epidural analgesia, however, persistent pain was uncommon. Based on their systematic review, Lieberman and O’Donoghue (2002) concluded that available data do not support an association between epidural analgesia and development of de novo, long-term backache.

Miscellaneous Complications

A spinal or epidural hematoma is a rare complication of an epidural catheter (Grant, 2007). Epidural abscesses are equally infrequent (Darouiche, 2006). And uncommonly, the plastic epidural catheter can be sheared off (Noblett, 2007).

Effects on Labor

Most studies, including the five from Parkland Hospital, report that epidural analgesia prolongs labor and increases the use of oxytocin stimulation (Table 25-8). Alexander and associates (2002) examined the effects of epidural analgesia on the Friedman (1955) labor curve described in Chapter 22 (First Stage of Labor). Compared with original Friedman criteria, epidural analgesia prolonged the active phase of labor by 1 hour. As further shown in Table 25-8, epidural analgesia also increased the need for operative vaginal delivery because of prolonged second-stage labor. But importantly, this led to no greater rates of adverse neonatal effects.

This association among epidural analgesia and prolonged second-stage labor and operative vaginal delivery has been attributed to anesthesia-induced motor blockade and resultant impaired maternal expulsive efforts. Craig and colleagues (2015) randomized 310 nulliparous women with labor epidural analgesia to bupivacaine plus fentanyl or fentanyl alone during second-stage labor. Epidural bupivacaine analgesia did cause motor blockade during the second stage, however, the duration of the second stage was not increased.

Fetal Heart Rate

Hill and associates (2003) examined the effects of epidural analgesia with 0.25-percent bupivacaine on fetal heart rate patterns. Compared with intravenous meperidine, no deleterious effects were identified. Reduced beat-to-beat variability and fewer accelerations were more frequent sequelae in fetuses whose mothers received meperidine (Chap. 24, Cardiac Arrhythmia). Based on their systematic review, Reynolds and coworkers (2002) reported that epidural analgesia was associated with improved neonatal acid-base status compared with meperidine.

Cesarean Delivery Rates

A contentious issue in the past was whether epidural analgesia increased the risk for cesarean delivery. Supporting evidence for this view came from the era when dense blocks of local anesthetic agents were used that impaired motor function and therefore likely did contribute to higher cesarean delivery rates. As techniques were refined, however, many investigators came to believe that epidural administration of dilute anesthetic solutions did not increase cesarean delivery rates.

Several studies conducted at Parkland Hospital were designed to answer this and related questions. From 1995 to 2002, a total of 2703 nulliparas at term and in spontaneous labor were enrolled in five trials to evaluate epidural analgesia techniques compared with methods of intravenous meperidine administration. The results from these are summarized in Figure 25-4 and show that epidural analgesia does not significantly raise cesarean delivery rates.

Timing of Epidural Placement

In several retrospective studies, epidural placement in early labor was linked to an increased risk of cesarean delivery (Lieberman, 1996; Rogers, 1999; Seyb, 1999). These observations prompted at least five randomized trials, which showed that timing of epidural placement has no effect on the risk of cesarean birth, forceps delivery, or fetal malposition (Chestnut, 1994a,b; Ohel, 2006; Wong, 2005, 2009). Thus, withholding epidural placement until some arbitrary cervical dilation has been attained is unsupportable and serves only to deny women maximal labor pain relief.

Safety

The relative safety of epidural analgesia is reflected by the extraordinary earlier experiences reported by Crawford (1985) from the Birmingham Maternity Hospital in England. Similarly, there were no anesthesia-related maternal deaths among nearly 20,000 women who received epidural analgesia in the MFMU Network study cited earlier (Bloom, 2005). And, Ruppen and associates (2006) reviewed data from 27 studies involving 1.4 million pregnant women who received epidural analgesia. They calculated risks of 1:145,000 for deep epidural infection, 1:168,000 for epidural hematoma, and 1:240,000 for persistent neurological injury.

Contraindications

Thrombocytopenia

For epidural analgesia, contraindications are similar to those with spinal analgesia (see Table 25-6). Although low platelet counts are intuitively worrisome, the level at which epidural bleeding might develop is unknown according to the American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2016). Epidural hematomas are rare, and incidence of nerve damage from a hematoma is estimated to be 1 in 150,000 (Grant, 2007). The American College of Obstetricians and Gynecologists (2016b) has concluded that selected women with platelet counts of 80,000 to 100,000/μL may be candidates for regional analgesia. Caveats include a stable platelet count, no acquired or congenital coagulopathy, normal platelet function, no antiplatelet-specific drugs, and anticoagulation parameters, described next, that are met. Counts between 50,000 and 80,000 require an individualized decision on risks and benefits (van Veen, 2010). Single-shot spinal anesthesia with a 25-gauge needle is less traumatic than epidural or combined spinal-epidural anesthesia with a 17- or 18-gauge epidural needle and thus may be safer for patients with platelets in this range.

Anticoagulation

Women receiving anticoagulation therapy who are given regional analgesia are at increased risk for spinal cord hematoma and subsequent cord compression (Chap. 52, Labor and Delivery). Our practice pattern includes the following:

1. Women receiving unfractionated heparin therapy should be able to receive regional analgesia if they have a normal activated partial thromboplastin time (aPTT).

2. Women receiving prophylactic doses of unfractionated heparin or low-dose aspirin are not at increased risk and can be offered regional analgesia.

3. For women receiving once-daily, low-dose low-molecular-weight heparin, regional analgesia should not be placed until 12 hours after the last injection.

4. Low-molecular-weight heparin should be withheld for at least 2 hours after epidural catheter removal.

5. The safety of regional analgesia in women receiving twice-daily low-molecular-weight heparin has not been studied sufficiently. It is not known whether delaying regional analgesia for 24 hours after the last injection is adequate.

Severe Preeclampsia-Eclampsia

Potential concerns with epidural analgesia in women with severe preeclampsia include hypotension as well as hypertension from pressor agents given to correct hypotension. Additionally, pulmonary edema following infusion of large volumes of crystalloid is a potential risk. These are outweighed by disadvantages of general anesthesia. Tracheal intubation may be difficult because of upper airway edema. Moreover, general anesthesia can lead to severe, sudden hypertension that can cause pulmonary or cerebral edema or intracranial hemorrhage.

With improved techniques for infusion of dilute local anesthetics into the epidural space, most obstetricians and obstetrical anesthesiologists have come to favor epidural blockade for labor and delivery in women with severe preeclampsia. There seems to be no argument that epidural analgesia for women with severe preeclampsia-eclampsia can be safely used when implemented by trained anesthesiologists and obstetricians (Lucas, 2001).

Women with severe preeclampsia have remarkably diminished intravascular volumes compared with unaffected gravidas (Zeeman, 2009). Conversely, extravascular volume is increased because of the capillary leak caused by endothelial cell activation (Chap. 40, Pathophysiology). This imbalance is manifested as pathological peripheral edema, proteinuria, ascites, and total lung water. For all of these reasons, aggressive volume replacement increases the risk for pulmonary edema, especially in the first 72 hours postpartum. In one study, Hogg and associates (1999) reported that 3.5 percent of women with severe preeclampsia developed pulmonary edema when preloaded without a protocol limitation to volume. Importantly, this risk can be reduced or obviated with judicious prehydration—usually with 500 to 1000 mL of crystalloid solution. Specifically, in the study by Lucas and colleagues (2001), there were no instances of pulmonary edema among the women in whom the crystalloid preload was limited to 500 mL. Moreover, vasodilation produced by epidural blockade is less abrupt if the analgesia level is achieved slowly with dilute solutions of local anesthetic agents. This allows maintenance of blood pressure while simultaneously avoiding infusion of large crystalloid volumes.

Combined Spinal–Epidural Analgesia

The combination of spinal and epidural techniques has increased in popularity and may provide rapid and effective analgesia for labor and for cesarean delivery. An introducer needle is first placed in the epidural space. A small-gauge spinal needle is then introduced through the epidural needle into the subarachnoid space—this is called the needle-through-needle technique (see Fig. 25-3). A single bolus of an opioid, sometimes in combination with a local anesthetic, is injected into the subarachnoid space. The spinal needle is withdrawn, and an epidural catheter is then placed through the introducer needle. A subarachnoid opioid bolus results in the rapid onset of profound pain relief with virtually no motor blockade. The epidural catheter permits repeated analgesia dosing. Miro and associates (2008) compared epidural analgesia with combined spinal-epidural analgesia for labor in 6497 women and found the overall outcomes and complications to be similar for the two techniques. In a randomized comparison, however, Abrão and colleagues (2009) reported that combined spinal-epidural analgesia was associated with a greater incidence of fetal heart rate abnormalities related to uterine hypertonus. Beamon and coworkers (2014) reported similar results.

Continuous Spinal Analgesia During Labor

There is emerging interest in continuous spinal analgesia for relief of labor pain. Arkoosh (2008) randomized 429 laboring women to either continuous spinal or conventional epidural analgesia. Complication rates between these two neuraxial techniques did not differ. Tao and colleagues (2015) reported their experiences with 113 women. With a dilute bupivacaine solution for analgesia, they found no cases of peripheral nerve injury and a headache rate of 2.6 percent. The utility of continuous spinal analgesia in labor and delivery remains to be further studied.

A local block is occasionally useful to augment an inadequate or “patchy” regional block that was given emergently. Rarely, local infiltration may be needed to perform an emergent cesarean delivery to save the life of a fetus in the absence of anesthesia support (Young, 2012).

In one technique, the skin is infiltrated along the proposed incision, and the subcutaneous, muscle, and rectus sheath layers are injected as the abdomen is opened. Up to a total of 70 mL of 0.5-percent lidocaine with 1:200,000 epinephrine is prepared for infiltration. Injection of large volumes into the fatty layers, which are relatively devoid of nerve supply, is avoided to limit the total dose of local anesthetic needed.

A second technique involves a field block of the major branches supplying the abdominal wall, to include the 10th, 11th, and 12th intercostal nerves and the ilioinguinal and genitofemoral nerves (Nandagopal, 2001). As shown in Figure 25-5, the former group of nerves is located at a point midway between the costal margin and iliac crest in the midaxillary line. The latter group is found at the level of the external inguinal ring. Only one skin puncture is made at each of the four sites (right and left sides). At the intercostal block site, the needle is directed medially, and injection is carried down to the fascia, avoiding injection of the subcutaneous fat. Approximately 5 to 8 mL of 0.5-percent lidocaine is injected. The procedure is repeated at a 45-degree angle cephalad and caudad to this line. The other side is then injected. At the ilioinguinal and genitofemoral sites, the injection is started at a site 2 to 3 cm lateral from the pubic tubercle at a 45-degree angle. Finally, the skin overlying the planned incision is injected.

Trained personnel and specialized equipment including alternative airways, video laryngoscopes, and fiberoptic intubation scopes are mandatory for the safe use of general anesthesia. A common cause of death cited for general anesthesia is failed intubation. This occurs in approximately 1 of every 400 general anesthetics administered to pregnant women (Kinsella, 2015). There is a growing trend to continue surgery with a supraglottic airway device, such as a laryngeal mask airway, in the event of a failed intubation (Mushambi, 2015). Because of these relatively greater morbidity and mortality rates, neuraxial analgesia is the preferred method of pain control and should be used unless contraindicated (see Table 25-6). Indeed, in two reports from the MFMU Network, 93 percent of more than 54,000 cesarean deliveries were performed using neuraxial analgesia (Bloom, 2005; Brookfield, 2013). A higher incidence of general anesthesia use for nonwhite women has been reported (Butwick, 2014).

Patient Preparation

Before anesthesia induction, several steps are taken to help minimize complication risks:

1. Antacid administration shortly before anesthesia induction has probably lowered mortality rates from general anesthesia more than any other single practice. The American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2016) recommends timely administration of a nonparticulate antacid, an H₂-receptor antagonist, or metoclopramide. For many years, we have administered 30 mL of Bicitra—sodium citrate with citric acid—a few minutes before anesthesia induction by either general or major neuraxial block. If more than 1 hour has passed after the first dose was given and anesthesia has not yet been induced, then a second dose is given.

2. Lateral uterine displacement is also provided, as the uterus may compress the inferior vena cava and aorta when the mother is supine. With uterine displacement, the duration of general anesthesia has less effect on neonatal condition than if the woman remains supine.

3. Preoxygenation is done because functional reserve lung capacity is reduced and the pregnant woman becomes hypoxemic more rapidly during periods of apnea. Obesity exacerbates this tendency (McClelland, 2009). To minimize hypoxia between the time of muscle relaxant injection and intubation, oxygen is introduced into the lungs in place of nitrogen. This preoxygenation is accomplished by administering 100-percent oxygen via face mask for 2 to 3 minutes before anesthesia induction. In an emergency, four vital capacity breaths of 100-percent oxygen via a tight breathing circuit will provide similar benefit (Norris, 1985).

Induction and Intubation

Almost all parturients are considered to have a full stomach, which necessitates a rapid-sequence induction. Namely, an intravenous anesthetic and rapid-onset muscle relaxant are simultaneously administered while cricoid pressure is applied by an assistant.

Of anesthetics, intravenous propofol or etomidate is widely used and offers a smooth, rapid induction. Propofol is associated with a quick onset and recovery, and it may lower the incidence of nausea and vomiting. Since thiopental is no longer available, propofol is used as the primary agent for induction of general anesthesia with a reasonable safety record. Etomidate is the induction agent of choice for hemodynamically unstable parturients. Alternatively, ketamine can be used but is avoided in hypertensive women. For muscle relaxation, succinylcholine is an ultrafast-onset, short-acting agent commonly used in obstetrics. It offers intense muscle relaxation to aid endotracheal intubation but also allows for the rapid return of spontaneous respiration in the case of failed intubation. Rocuronium is an alternative muscle relaxant if succinylcholine is contraindicated or unavailable. Its duration is much longer than succinylcholine unless its effect is reversed by sugammadex (Bridion), a specific binding agent recently approved by the FDA. To decrease the incidence of fetal respiratory depression, an intermediate or long-acting opioid is usually avoided upon induction of general anesthesia. The intense stimulation from direct laryngoscopy may worsen hypertension and tachycardia in certain women. Remifentanil, an ultrashort-acting narcotic, has been used during induction for cesarean deliveries with favorable maternal hemodynamics and fetal outcome (Heesen, 2013).

During induction and intubation, cricoid pressure is applied by a trained assistant to occlude the esophagus and thereby minimize regurgitation of the gastric contents—the Sellick maneuver. Positive mask ventilation during rapid sequence induction is typically avoided to lower the risk of increased intragastric pressure, which raises the risk of vomiting. Surgery should begin only after an airway is secured or, depending on the status of the mother and fetus, effective ventilation has been established.

Failed Intubation

Although uncommon, failed intubation is a major cause of anesthesia-related maternal mortality. A history of prior difficult intubation and a careful anatomical assessment of the neck and maxillofacial, pharyngeal, and laryngeal structures may help predict intubation complications. Even in cases in which the initial airway assessment was unremarkable, edema may develop intrapartum and present considerable challenges. Morbid obesity is another major factor for failed or difficult intubation. The American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2016) stresses the importance of appropriate preoperative preparation. This includes the immediate availability of specialized equipment such as different-shaped laryngoscopes, laryngeal mask airways, a fiberoptic bronchoscope, and a transtracheal ventilation set, as well as liberal use of awake oral intubation techniques.

Management

Ideally, an operative procedure is initiated only after it has been ascertained that tracheal intubation has been successful and that adequate ventilation can be accomplished. Even with an abnormal fetal heart rate pattern, cesarean delivery initiation will only serve to complicate matters if there is difficult or failed intubation. Frequently, the woman must be allowed to awaken and a different technique used, such as an awake intubation or regional analgesia.

Following failed intubation, the woman is ventilated by mask and cricoid pressure is applied to reduce the aspiration risk. Surgery may proceed with mask ventilation, or the woman may be allowed to awaken. In those cases in which the woman has been paralyzed and ventilation cannot be reestablished by insertion of an oral airway, by laryngeal mask airway, or by use of a fiberoptic laryngoscope to intubate the trachea, then a life-threatening emergency exists. To restore ventilation, percutaneous or even open cricothyrotomy is performed and jet ventilation begun. Failed intubation drills have been recommended to optimize the response to such an emergency.

Inhalational Anesthetics

With the endotracheal tube secured, anesthesia is maintained with a halogenated agent, typically mixed with air or nitrous oxide. The most commonly used inhalational anesthetics in the United States include desflurane and sevoflurane. Both have low solubility in blood and fat. As a result, they offer faster onset and clearance than more traditional gases such as isoflurane. In addition to providing amnesia, they produce profound uterine relaxation when given in high concentrations. This is advantageous when relaxation is a requisite, such as for internal podalic version of the second twin, for breech decomposition, or for replacement of the acutely inverted uterus. That said, unless the woman is already under general anesthesia, intravenous nitroglycerine is preferred by many in such situations.

Extubation

The endotracheal tube may be safely removed only if the woman is conscious to a degree that enables her to follow commands and is capable of maintaining oxygen saturation with spontaneous respiration. Consideration is given to emptying the stomach via a nasogastric tube before extubation. As induction has become safer, extubation may now be relatively more perilous. Of 15 anesthesia-related deaths of pregnant women from 1985 to 2003 in Michigan, none occurred during induction. Five resulted from hypoventilation or airway obstruction during emergence, extubation, or recovery (Mhyre, 2007).

Aspiration

Massive gastric acidic inhalation may cause pulmonary insufficiency from aspiration pneumonitis. In the past, this was the most common cause of anesthetic deaths in obstetrics and therefore deserves special attention. To minimize this risk, antacids are given routinely, intubation is accompanied by cricoid pressure, and regional analgesia is employed when possible.

Fasting

According to the American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2016) and the American College of Obstetricians and Gynecologists (2017b), data are insufficient regarding fasting times for clear liquids and the risk of pulmonary aspiration during labor. Recommendations are that modest amounts of clear liquids such as water, clear tea, black coffee, carbonated beverages, and pulp-free fruit juices be allowed in uncomplicated laboring women (Chap 22, Oral Intake). Obvious solid foods are avoided. A fasting period of 6 to 8 hours for solid food is recommended for uncomplicated parturients prior to undergoing elective cesarean delivery or puerperal tubal ligation.

O’Sullivan (2009) randomized 2426 low-risk nulliparas to consume either water and ice chips alone or small amounts of bread, biscuits, vegetables, fruits, yogurt, soup, and fruit juice. Approximately 30 percent of women in each arm of the study underwent cesarean delivery. No cases of aspiration occurred during the study, although approximately a third of women in each study arm vomited during labor or delivery. Epidural analgesia during labor was used in this study, although the authors did not report the type of anesthesia used for cesarean deliveries. Presumably, neuraxial analgesia was used, and this greatly minimized the pulmonary aspiration risk. Given the low prevalence of aspiration, this trial was not powered to measure whether feeding during labor was safe (Sperling, 2016).

Pathophysiology

In 1952, Teabeaut demonstrated experimentally that if the pH of aspirated fluid was <2.5, severe chemical pneumonitis developed. It was later demonstrated that the pH of gastric juice in nearly half of women tested intrapartum was <2.5 (Taylor, 1966). The right mainstem bronchus usually offers the simplest pathway for aspirated material to reach the lung parenchyma, and therefore, the right lower lobe is most often involved. In severe cases, there is bilateral widespread involvement.

The woman who aspirates may develop evidence of respiratory distress immediately or several hours after aspiration, depending in part on the material aspirated and the severity of the response. Aspiration of a large amount of solid material causes obvious airway obstruction. Smaller particles without acidic liquid may lead to patchy atelectasis and later to bronchopneumonia.

When highly acidic liquid is inspired, decreased oxygen saturation along with tachypnea, bronchospasm, rhonchi, rales, atelectasis, cyanosis, tachycardia, and hypotension are likely to develop. At the injury sites, there is pulmonary capillary leakage and exudation of protein-rich fluid containing numerous erythrocytes into the lung interstitium and alveoli. This causes decreased pulmonary compliance, shunting of blood, and severe hypoxemia. Radiographic changes may not appear immediately, and these may be variable, although the right lung most often is affected. Thus, chest radiographs alone should not be used to exclude aspiration.

Treatment

The methods recommended for treatment of aspiration have changed appreciably in recent years, indicating that previous therapy was not very successful. Suspicion of aspiration of gastric contents demands close monitoring for evidence of pulmonary damage. Respiratory rate and oxygen saturation as measured by pulse oximetry are the most sensitive and earliest indicators of injury.

Inhaled fluid should be immediately and thoroughly wiped from the mouth and removed from the pharynx and trachea by suction. Saline lavage may further disseminate the acid throughout the lung and is not recommended. If large particulate matter is inspired, bronchoscopy may be indicated to relieve airway obstruction. No convincing evidence supports that corticosteroid therapy or prophylactic antimicrobial administration is beneficial (Marik, 2001). If infection develops, however, then vigorous treatment is given. If acute respiratory failure develops, mechanical ventilation with positive end-expiratory pressure may be lifesaving (Chap. 47, Clinical Course).

Goals for postoperative pain management include maximizing patient satisfaction, minimizing side effects, aiding functional capacity, and preventing prolonged hospital stays (Lavoie, 2013). In a prospective study, 96 percent of women reported pain immediately after delivery (Eisenach, 2008). The incidence of persistent pain 1 and 2 years following cesarean delivery was reported to approximate 20 percent (Hannah, 2004; Kainu, 2010).

The American Society of Anesthesiologists (2016) recommends neuraxial opioids for postoperative analgesia. Although most cesarean deliveries in the United States are performed under neuraxial anesthesia, in certain situations a peripheral nerve block such as a transversus abdominis plane (TAP) block may be considered (McDonnell, 2007). These include cases in which the parturient did not receive neuraxial opioids, underwent general anesthesia, or has persistent pain following neuraxial anesthesia. It is usually performed under ultrasound guidance and involves injection of a local anesthetic into the transversus abdominis plane between the internal oblique and transversus abdominis muscles. The nerves lying in this plane supply the anterior abdominal wall at the T₆ to L₁ dermatomes. A metaanalysis of 31 controlled trials showed that ultrasound-guided TAP block marginally reduced opioid consumption at 6 hours following abdominal surgery (Baeriswyl, 2015).