ANALGESIA AND SEDATION DURING LABOR
SPINAL (SUBARACHNOID) BLOCK
LOCAL INFILTRATION FOR CESAREAN DELIVERY
Obstetrical anesthesia presents unique challenges. Labor begins without warning, and anesthesia may be required within minutes of a full meal. Vomiting with aspiration of gastric contents is a constant threat. The usual physiological adaptations of pregnancy require special consideration, especially with disorders such as preeclampsia, placental abruption, or sepsis syndrome.
Of all anesthesia-related deaths in the United States from 1995 to 2005, 3.6 percent were in pregnant women (Li, 2009). Berg and colleagues (2010) analyzed deaths of women during or within 1 year of pregnancy in the United States from 1998 through 2005. They found that 54 of 4693—1.2 percent—such deaths were attributable to anesthesia complications. Hawkins and associates (2011) analyzed anesthesia-related maternal mortality in this country between 1979 and 2002. As shown in Table 25-1, anesthetic-related maternal mortality rates decreased nearly 60 percent during this time, and there currently is approximately one anesthetic death per million live births. About two thirds of deaths associated with general anesthesia were caused by intubation failure or induction problems during cesarean delivery. Deaths associated with regional analgesia were 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 was especially notable considering that such anesthesia is now used for the highest-risk patients and the most hurried emergencies, that is, decision-incision intervals < 15 minutes (Bloom, 2005).
TABLE 25-1. Case-Fatality Rates and Rate Ratios of Anesthesia-Related Deaths During Cesarean Delivery by Type of Anesthesia in the United States, 1979–2002
Several factors have contributed to improved obstetrical anesthesia safety (Hawkins, 2011). The most significant is the increased use of regional analgesia. Increased availability of in-house anesthesia coverage almost certainly is another important reason. Despite these encouraging results suggesting the safety of general anesthesia, there are now reports of increasing complications with regional analgesia techniques.
Obstetrical Anesthesia Services
The American College of Obstetricians and Gynecologists (2008) reaffirmed its joint position with the American Society of Anesthesiologists 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 in women for whom such anesthesia would be especially hazardous.
TABLE 25-2. Maternal Factors That May Prompt Anesthetic Consultation
Severe edema or anatomical abnormalities of the face, neck, or spine, including trauma or surgery
Abnormal dentition, small mandible, or difficulty opening the mouth
Extremely short stature, short neck, or neck arthritis
Serious maternal medical problems, such as cardiac, pulmonary, or neurological disease
Prior anesthetic complications
Obstetrical complications likely to lead to operative delivery—examples include placenta previa, preterm breech presentation, or higher-order multifetal gestation
Adapted from the American Academy of Pediatrics and American College of Obstetricians and Gynecologists: Guidelines for Perinatal Care, 7th ed. Washington, 2012.
Goals for optimizing obstetrical anesthesia services have been jointly established by the American College of Obstetricians and Gynecologists and the American Society of Anesthesiologists (2009) 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, p. 615)
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 the surgical suite
7. Immediate availability of personnel, other than the surgical team, to assume responsibility for resuscitation of a depressed newborn (Chap. 32, p. 625).
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 have fewer than 500 deliveries per year (American College of Obstetricians and Gynecologists, 2009).
Bell and coworkers (2000) calculated the financial burden that may be incurred to provide 24/7 obstetrical anesthesia coverage. Given the average indemnity and Medicaid reimbursement for labor epidural analgesia, they concluded that such coverage could not operate profitably at their tertiary referral institution. 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 and the American Society of Anesthesiologists (2008).
Role of an Obstetrician
Every obstetrician should be proficient in local and pudendal analgesia that may be administered in appropriately selected circumstances. In general, however, it is preferable for an anesthesiologist or anesthetist to provide pain relief so that the obstetrician can focus attention on the laboring woman and her fetus.
Principles of Pain Relief
In a scholarly review, 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 and preparation through education, the presence of 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 and other choices during labor and delivery.
FIGURE 25-1 Sources of pain during labor and maternal physiological responses. (From Hawkins, 2010, with permission.)
Maternal physiological responses to labor pain may influence maternal and fetal well-being and labor progress. For example, hyperventilation may induce hypocarbia. An increased metabolic rate increases oxygen consumption. Increases in cardiac output and vascular resistance may increase maternal blood pressure. Pain, stress, and anxiety cause release of stress hormones such as cortisol and β-endorphins. The sympathetic nervous system response to pain leads to a marked increase in circulating catecholamines that can adversely affect uterine activity and uteroplacental blood flow. Effective analgesia attenuates or eliminates these responses.
ANALGESIA AND SEDATION DURING LABOR
If uterine contractions and cervical dilatation cause discomfort, pain relief with a narcotic such as meperidine (Demerol), plus one of the tranquilizer drugs such as promethazine (Phenergan), is usually appropriate. With a successful program of analgesia and sedation, the mother should rest quietly between contractions. In this circumstance, discomfort usually is felt at the acme of an effective uterine contraction. Appropriate drug selection and administration of the medications shown in Table 25-3 should safely accomplish these objectives.
TABLE 25-3. Some Parenteral Analgesic Agents for Labor Pain
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 its half-life in the newborn is approximately 13 hours or longer (American College of Obstetricians and Gynecologists, 2013b). 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 from labor. Tsui and associates (2004) found meperidine to be superior to placebo for pain relief in the first stage of labor. In a randomized investigation of epidural analgesia conducted 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 50-mg meperidine with 25-mg promethazine 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 need for naloxone treatment in the delivery room, was identified in 3 percent of newborns.
This synthetic narcotic, given in 1- to 2-mg doses, compares favorably with 40 to 60 mg of meperidine (Quilligan, 1980). 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. Hatjis and Meis (1986) described a transient sinusoidal fetal heart rate pattern following butorphanol administration but with no short-term maternal or neonatal adverse sequelae (Chap. 24, p. 482).
This short-acting and potent synthetic opioid may be given in doses of 50 to 100 μg intravenously every hour. Its main disadvantage is a short duration of action, which requires frequent dosing or use of a patient-controlled intravenous pump. Moreover, Atkinson and coworkers (1994) reported that butorphanol provided better initial analgesia than fentanyl and was associated with fewer requests for additional medication or for epidural analgesia.
Efficacy and Safety of Parenteral Agents
Parenteral sedation is not without risks. Hawkins and colleagues (1997) reported that 4 of 129 maternal anesthetic-related deaths were from such sedation—one from aspiration, two from inadequate ventilation, and one from overdosage.
Narcotics used during labor may cause newborn respiratory depression. Naloxone is a narcotic antagonist capable of reversing respiratory depression induced by opioid narcotics. 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 (American Academy of Pediatrics and American College of Obstetricians and Gynecologists, 2012). After adequate ventilation has been established, naloxone may be given to reverse respiratory depression in a newborn infant whose mother received narcotics (Chap. 32, p. 626).
A self-administered mixture of 50-percent nitrous oxide (N2O) and oxygen may provide satisfactory analgesia during labor (Rosen, 2002a). Some preparations are premixed in a single cylinder (Entonox), and in others, a blender mixes the two gases from separate tanks (Nitronox). The gases are connected to a breathing circuit through a valve that opens only when the patient inspires. The use of intermittent nitrous oxide for labor pain has been reviewed by Rosen (2002a).
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.
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 increasing the dose. 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.
TABLE 25-4. Local Anesthetic Agents Commonly Used in Obstetrics
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. Local analgesic agents are manufactured in more than one concentration and ampule size, which increases the potential for dosing errors.
Central Nervous System Toxicity
Early symptoms are those of stimulation but, as serum levels increase, 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.
For management, the convulsions should be controlled, an airway established, and oxygen delivered. Succinylcholine abolishes the peripheral manifestations of the convulsions and allows tracheal intubation. Diazepam (Valium) can be used to inhibit convulsions. Magnesium sulfate, administered according to the regimen for eclampsia, also controls convulsions (Chap. 40, p. 758). Abnormal fetal heart rate patterns such as late decelerations or persistent bradycardia may develop from maternal hypoxia and lactic acidosis induced by convulsions. With arrest of convulsions, administration of oxygen, and application of other supportive measures, the fetus usually recovers more quickly in utero than following immediate cesarean delivery. Moreover, the mother is better served if delivery is forestalled until the intensity of hypoxia and metabolic acidosis has diminished.
These manifestations generally develop later than those from cerebral toxicity, and they may not develop at all because they are induced by higher serum drug levels. The notable exception is bupivacaine, which is associated with the development of neurotoxicity and cardiotoxicity at virtually identical levels (Mulroy, 2002). Because of this risk of systemic toxicity, use of 0.75-percent solution of bupivacaine for epidural injection has been proscribed by the Food and Drug Administration. Similar to neurotoxicity, cardiovascular toxicity is characterized first by stimulation and then by depression. Accordingly, there is hypertension and tachycardia, which soon is followed by hypotension, cardiac arrhythmias, and impaired uteroplacental perfusion.
Hypotension is managed initially by turning the woman onto either side to avoid aortocaval compression. A crystalloid solution is infused rapidly along with intravenously administered ephedrine. Emergency cesarean delivery is considered if maternal vital signs have not been restored within 5 minutes of cardiac arrest (Chap. 47, p. 956). As with convulsions, however, the fetus is likely to recover more quickly in utero once maternal cardiac output is reestablished.
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 posterior surface of 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 S2through 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 sheath and guide a 15-cm 22-gauge needle into position over 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 25-3). 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 it pierces the loose areolar tissue behind the ligament, the resistance of the plunger decreases. Another 3 mL of solution is injected into this region. Next, the needle is withdrawn into the introducer, which is moved to just above the ischial spine. The needle is inserted through the mucosa and 3 more mL is deposited. The procedure is then repeated on the other side.
FIGURE 25-2 Local infiltration of the pudendal nerve. Transvaginal technique showing the needle extended beyond the needle guard and passing through the sacrospinous ligament to reach the pudendal nerve.
Within 3 to 4 minutes of injection, the 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).
This block usually provides satisfactory pain relief during first-stage labor. However, because the pudendal nerves are not blocked, additional analgesia is required for delivery. For paracervical blockade, usually lidocaine or chloroprocaine, 5 to 10 mL of a 1-percent solution, is injected into the cervix laterally at 3 and 9 o’clock. Because these anesthetics are relatively short acting, paracervical block may have to be repeated during labor. We do not use it at Parkland Hospital.
Fetal bradycardia is a worrisome complication that occurs in approximately 15 percent of paracervical blocks (Rosen, 2002b). Bradycardia usually develops within 10 minutes and may last up to 30 minutes. Doppler studies have shown an increase in the pulsatility index of the uterine arteries following paracervical blockade (Chap. 10, p. 219). These observations support the hypothesis of drug-induced arterial vasospasm as a cause of fetal bradycardia (Manninen, 2000). For these reasons, paracervical block should not be used in situations of potential fetal compromise.
Neuraxial Regional Blocks
Epidural, spinal, or combined spinal-epidural techniques were the more common methods used for relief of pain during labor and/or delivery in the United States in 2008 (Osterman, 2011b). Nearly two out of three mothers receive neuraxial anesthesia for relief of pain either during labor or during vaginal or cesarean delivery. Neuraxial techniques were more common in vaginal deliveries assisted by forceps—84 percent or vacuum extraction—77 percent than spontaneous vaginal deliveries—60 percent (Osterman, 2011a). Among first births, 68 percent of women delivered vaginally received neuraxial pain relief compared with 57 percent of women delivering their second or higher number child.
Epidural analgesia via a catheter as shown in Figure 25-3 is typically used for relief of labor pain, although it can also be used for anesthesia during operative vaginal and cesarean delivery. Spinal analgesia is typically given as a single intrathecal injection of a local anesthetic at the time of operative vaginal delivery or cesarean. Continuous spinal analgesia during labor via an indwelling spinal catheter is also under investigation. Combined spinal-epidural analgesia/anesthesia also illustrated in Figure 25-3 consists of a single intrathecal injection followed by a catheter placed into the epidural space for either patient- or provider-controlled infusion of a local anesthetic and/or an opioid such as fentanyl. The combined spinal-epidural technique has the advantages of immediate pain relief from the spinal injection coupled with a portal for continuous analgesia via the epidural catheter. Unlike the spinal injection, the relief provided by the epidural catheter takes approximately 30 minutes to become effective. Perhaps as many as a third of epidural catheter tips will migrate during labor, resulting in ineffective pain control should cesarean be necessary.
FIGURE 25-3 Neuraxial analgesia. A. Combined spinal-epidural analgesia. B. Epidural analgesia.
Spinal (Subarachnoid) Block
Introduction of a local anesthetic into the subarachnoid space to effect analgesia has long been used for delivery. Advantages include a short procedure time, rapid blockade onset, and high success rate. Because of the smaller subarachnoid space during pregnancy, likely the consequence of internal vertebral venous plexus engorgement, the same amount of anesthetic agent in the same volume of solution produces a much higher blockade in parturients than in nonpregnant women.
Low spinal block can be used for operative vaginal delivery. The level of analgesia should extend to the T10 dermatome, which corresponds to the level of the umbilicus. Blockade to this level provides excellent relief from the pain of uterine contractions (Fig. 25-4).
FIGURE 25-4 Dermatome distribution.
Several local anesthetic agents have been used for spinal analgesia (see Table 25-4). Addition of glucose to any of these agents creates a hyperbaric solution, which is heavier and denser than cerebrospinal fluid. A sitting position causes a hyperbaric solution to settle caudally, whereas a lateral position will have a greater effect on the dependent side. Lidocaine given in a hyperbaric solution produces excellent analgesia and has the advantage of a rapid onset and relatively short duration. Bupivacaine in an 8.25-percent dextrose solution provides satisfactory anesthesia to the lower vagina and the perineum for more than 1 hour. Neither is administered until the cervix is fully dilated, and all other criteria for safe forceps delivery have been fulfilled (Chap. 29, p. 575). Preanalgesic intravenous hydration with 1 L of crystalloid solution will prevent or minimize hypotension in many cases.
A level of sensory blockade extending to the T4 dermatome is desired for cesarean delivery (see Fig. 25-4). Depending on maternal size, 10 to 12 mg of bupivacaine in a hyperbaric solution or 50 to 75 mg of lidocaine hyperbaric solution are administered. The addition of 20 to 25 μg of fentanyl increases the rapidity of blockade onset and reduces shivering. The addition of 0.2 mg of morphine improves pain control during delivery and postoperatively.
Shown in Table 25-5 are some of the more common complications associated with neuraxial analgesia. Importantly, obese women have significantly impaired ventilation and thus close clinical monitoring is imperative (Vricella, 2011).
TABLE 25-5. Complications of Regional Analgesia
Hypotension. This common complication 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 alpha- and beta-receptors but also indirectly enhances norepinephrine release. It raises blood pressure by increasing heart rate and cardiac output and by variably elevating peripheral vascular resistance. In animal studies, ephedrine preserves uteroplacental blood flow during pregnancy compared with alpha1-receptor agonists. Accordingly, it is a preferred vasopressor for obstetrical use. Phenylephrine is a pure alpha agonist and raises 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. But although fetal acidemia has been reported with prophylactic ephedrine use, this was not observed with prophylactic phenylephrine use (Ngan Kee, 2004).
Hypotension is the more common blood pressure perturbation. However, paradoxically, hypertension from ergonovine or methylergonovine injections following delivery is more common in women who have received a spinal or epidural block.
High Spinal Blockade. Most often, complete spinal blockade follows administration of an excessive dose of local anesthetic. This is certainly not always the case, because accidental total spinal block has even occurred following an epidural test dose. With complete spinal blockade, hypotension and apnea promptly develop and 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 ephedrine are given to correct hypotension.
Postdural Puncture Headache. Leakage of cerebrospinal fluid (CSF) from the meningeal 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.
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 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 headache. Vigorous hydration may be of value, but compelling evidence to support its use is also lacking.
If a headache develops, the administration of caffeine, a cerebral vasoconstrictor, has been shown in randomized studies to afford temporary relief (Camann, 1990). With severe headache, an epidural blood patch is most effective. Ten to 20 mL of autologous blood are obtained aseptically by venipuncture into a tube without anticoagulant. This blood is then injected into the epidural space at the site of dural puncture. Further CSF leakage is halted by either mass effect or coagulation. Relief is immediate, and complications are uncommon. In a randomized trial of 64 women, Scavone and coworkers (2004) found that prophylactic blood patch did not decrease either the incidence of postdural puncture headache or the need for a subsequent therapeutic blood patch.
If a headache does not have the pathognomonic postural characteristics or persists despite treatment with a blood patch, other diagnoses should be considered. For example, Chisholm and Campbell (2001) described a case of superior sagittal sinus thrombosis that manifested as a postural headache. Chan and Paech (2004) have described persistent CSF leak in three women. 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 blood patch was usually effective in these cases.
Bladder Dysfunction. With spinal 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 (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.
Arachnoiditis and Meningitis. Local anesthetics are no longer preserved in alcohol, formalin, or other toxic solutes, and disposable equipment is used by most. These practices, coupled with aseptic technique, have made meningitis and arachnoiditis rare but have not eliminated them (Centers for Disease Control and Prevention, 2010).
Contraindications to Spinal Analgesia
Shown in Table 25-6 are the absolute contraindications to regional analgesia according to the American College of Obstetricians and Gynecologists (2013b). Obstetrical complications that are associated with maternal hypovolemia and hypotension—for example, severe hemorrhage—are contraindications to spinal blockade. The additive cardiovascular effects of spinal blockade in the presence of acute blood loss in nonpregnant patients were documented by Kennedy and coworkers (1968).
TABLE 25-6. Absolute Contraindications to Neuraxial Analgesia
Refractory maternal hypotension
Thrombocytopenia (variously defined)
Low-molecular-weight heparin within 12 hours
Untreated maternal bacteremia
Skin infection over site of needle placement
Increased intracranial pressure caused by a mass lesion
Disorders of coagulation and defective hemostasis also preclude spinal analgesia use. Although there are no randomized studies to 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 there is cellulitis at the needle entry site. Neurological disorders are considered by many to be a contraindication, if for no other reason than that exacerbation of the neurological disease might be attributed without cause to the anesthetic agent. Other maternal conditions, such as significant aortic stenosis or pulmonary hypertension, are also relative contraindications to spinal analgesia (Chap. 49, p. 983).
As with significant hemorrhage, severe preeclampsia is another complication 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. There were no differences in maternal or neonatal outcomes. 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 was between 15 and 25 percent.
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 (see 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 given, usually an indwelling catheter is placed for subsequent agent administration or continuous infusion. Infusions use a volumetric pump controlled either by the patient or by a caregiver. The American College of Obstetricians and Gynecologists and the American Society of Anesthesiologists (2008) believe 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 (Figs. 25-1 and 25-4). For cesarean delivery, a block extending from the T4 to the S1dermatomes is desired. The effective spread of anesthetic depends upon 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 spinal blockade from subarachnoid injection. If these are absent, only then is a full dose given. Analgesia is maintained by intermittent boluses of similar volume, or small volumes of the drug are delivered continuously by infusion pump (Halpern, 2009). 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, it is imperative that close monitoring, including the level of analgesia, be performed by trained personnel. Appropriate resuscitation equipment and drugs must be available during administration of epidural analgesia.
TABLE 25-7. Technique for Labor Epidural Analgesia
Informed consent is obtained, and the obstetrician consulted
Monitoring includes the following:
Blood pressure every 1 to 2 minutes for 15 minutes after giving a bolus of local anesthetic
Continuous maternal heart rate monitoring during analgesia induction
Continuous fetal heart rate monitoring
Continual verbal communication
Hydration with 500 to 1000 mL of lactated Ringer solution
The woman assumes a lateral decubitus or sitting position
The epidural space is identified with a loss-of-resistance technique
The epidural catheter is threaded 3 to 5 cm into the epidural space
A test dose of 3 mL of 1.5% lidocaine with 1:200,000 epinephrine or 3 mL of 0.25% bupivacaine with 1:200,000 epinephrine is injected after careful aspiration to avert intravascular injection and after a uterine contraction. This minimizes the chance of confusing tachycardia that results from labor pain with that of tachycardia from intravenous injection of the test dose
If the test dose is negative, one or two 5-mL doses of 0.25% bupivacaine are injected to achieve a sensory T10 level
After 15 to 20 minutes, the block is assessed using loss of sensation to cold or pinprick. If no block is evident, the catheter is replaced. If the block is asymmetrical, the epidural catheter is withdrawn 0.5 to 1.0 cm and an additional 3 to 5 mL of 0.25% bupivacaine is injected. If the block remains inadequate, the catheter is replaced
The woman is positioned in the lateral or semilateral position to avoid aortocaval compression
Subsequently, maternal blood pressure is recorded every 5 to 15 minutes. The fetal heart rate is monitored continuously
The level of analgesia and intensity of motor blockade are assessed at least hourly
From Glosten, 1999, with permission.
Total Spinal Blockade. As shown in Table 25-5, there are certain problems inherent in epidural analgesia use. 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 on page 504.
Ineffective Analgesia. Using currently popular continuous epidural infusion regimens such as 0.125-percent bupivacaine with 2-mg/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, heavier fetal weights, and epidural catheter placement at an earlier cervical dilatation. Dresner and colleagues (2006) 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 not sufficient 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 may cause hypotension and decreased cardiac output. 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 pregnant women, 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. Danilenko-Dixon and associates (1996) showed that maintaining a lateral position compared with the supine position minimized hypotension. Despite these precautions, hypotension is the most frequent side effect and is severe enough to require treatment in a third of women (Sharma, 1997).
Central Nervous Stimulation. Convulsions are an uncommon but serious complication, the immediate management of which was described previously (p. 507). Also cited was the case described by Smarkusky and coworkers (2006) of acute onset of intrapartum headache due to a postdural pneumocephalus.
Maternal Fever. Fusi and colleagues (1989) observed that the mean temperature increased 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 result suggested that infection was unlikely to be the cause of fever associated with epidural analgesia during labor. Whatever the mechanism, women with persistent fever are usually treated with antimicrobials for presumed chorioamnionitis.
Back Pain. An association between epidural analgesia and 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 rare (Darouiche, 2006). Uncommonly, the plastic epidural catheter is sheared off (Noblett, 2007).
Effect on Labor
Most studies, including the combined five randomized trials from Parkland Hospital shown in Table 25-8, report that epidural analgesia prolongs labor and increases the use of oxytocin stimulation. Alexander and associates (2002) examined the effects of epidural analgesia on the Friedman (1955) labor curve described in Chapter 22 (p. 445). There were 459 nulliparas randomly assigned to patient-controlled epidural analgesia or patient-controlled intravenous meperidine. 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, without adverse neonatal effects (Chestnut, 1999). This association between epidural analgesia and prolonged second-stage labor as well as operative vaginal delivery has been attributed to local-anesthetic induced motor blockade and resultant impaired maternal expulsive efforts. Craig and colleagues (2014) 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. Neither obstetrical nor neonatal outcomes were different between the two study groups. Patient satisfaction was high, irrespective of the method.
TABLE 25-8. Selected Labor Events in 2703 Nulliparous Women Randomized to Epidural Analgesia or Intravenous Meperidine Analgesia
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 common in fetuses whose mothers received meperidine (Chap. 24, p. 479). 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. Evidence that it did was from the era when dense blocks of local anesthetic agents were used that impaired motor function and therefore likely did contribute to increased rates of cesarean delivery. As techniques were refined, however, many investigators believed that epidural administration of dilute anesthetic solutions did not increase cesarean delivery rates. Some observational studies have suggested a decreased risk for cesarean delivery with oxytocin induction (Hants, 2013).
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 25-5 and show that epidural analgesia does not significantly increase cesarean delivery rates.
FIGURE 25-5 Results of five studies comparing the incidence of cesarean delivery in women given either epidural analgesia or intravenous meperidine. The individual odds ratios (ORs) with 95-percent confidence intervals (CIs) for each randomized study, as well as overall crude and adjusted ORs with 95-percent CIs, are shown. An OR of less than 1.0 favored epidural over meperidine analgesia. From Sharma, 2004, with permission.
Yancey and colleagues (1999) described the effects of an on-demand labor epidural analgesia service at Tripler Army Hospital in Hawaii. This followed a policy change in military medical centers. As a result, the incidence of labor epidural analgesia increased from 1 percent before the policy to 60 percent within 2 years. The primary cesarean delivery rate was 13.4 percent before and 13.2 percent after this dramatic change. In a follow-up study, Yancey and coworkers (2001) reported that fetal malpresentations at vaginal delivery were not more common after epidural usage increased. The only significant difference that they found was an increased duration of second-stage labor of approximately 25 minutes (Zhang, 2001).
Based on these randomized studies and a metaanalysis of 14 such trials, Sharma and Leveno (2003) and Leighton and Halpern (2002) concluded that epidural analgesia is not associated with an increased cesarean delivery rate.
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; Luxman, 1998; 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. The American College of Obstetricians and Gynecologists (2013b) recommends that the decision for epidural analgesia should be made individually with each patient and that women should not be required to reach 4 to 5 cm cervical dilation before receiving epidural analgesia.
The relative safety of epidural analgesia is reflected by the extraordinary experiences reported by Crawford (1985) from the Birmingham Maternity Hospital in England. From 1968 through 1985, more than 26,000 women were given epidural analgesia for labor, and there were no maternal deaths. The nine potentially life-threatening complications followed either inadvertent intravenous or intrathecal injection of lidocaine, bupivacaine, or both. Similarly, according to the Confidential Enquiries into Maternal Deaths in the United Kingdom between 2003 and 2005, there were few anesthesia-related deaths associated with epidural use (Lewis, 2007).
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 finally, 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.
As with spinal analgesia, contraindications to epidural analgesia include actual or anticipated serious maternal hemorrhage, infection at or near the puncture site, and suspicion of neurological disease (see Table 25-6).
Thrombocytopenia. 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 (2007). 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 (2013b) has concluded that women with a platelet count of 50,000 to 100,000/μL may be candidates for regional analgesia.
Anticoagulation. Women receiving anticoagulation therapy who are given regional analgesia are at increased risk for spinal cord hematoma and compression (Chap. 52, p. 1039). The American College of Obstetricians and Gynecologists (2013b) has concluded 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 those with severe preeclampsia include hypotension as well as hypertension from pressor agents given to correct hypotension. Additionally, there is the potential for pulmonary edema following infusion of large volumes of crystalloid. 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 trained anesthesiologists and obstetricians are responsible for the woman and her fetus. In a study from Parkland Hospital, Lucas and colleagues (2001) randomly assigned 738 women with hypertension to epidural analgesia or patient-controlled intravenous analgesia during labor. A standardized protocol for prehydration, incremental epidural administration, and ephedrine use was employed. They concluded that labor epidural analgesia was safe in women with hypertensive disorders.
Women with severe preeclampsia have remarkably diminished intravascular volume compared with normal pregnancy (Zeeman, 2009). Conversely, total body water is increased because of the capillary leak caused by endothelial cell activation (Chap. 40, p. 734). 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) cited earlier, 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.
With vigorous intravenous crystalloid therapy, there is also concern about development of cerebral edema (Chap. 40, p. 745). Finally, Heller and coworkers (1983) demonstrated that most cases of pharyngolaryngeal edema were related to aggressive volume therapy.
Epidural Opiate Analgesia
Injection of opiates into the epidural space to relieve pain from labor has become popular. Their mechanism of action derives from interaction with specific receptors in the dorsal horn and dorsal roots. Opiates alone usually will not provide adequate analgesia, and they most often are given with a local anesthetic agent such as bupivacaine. 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. Naloxone, given intravenously, will abolish these symptoms without affecting the analgesic action.
Combined Spinal–Epidural Techniques
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 Figure 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 (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 than was epidural analgesia alone. 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. This neuraxial technique was first used more than 60 years ago (Hinebaugh, 1944). Frequent severe postdural puncture headaches led to its abandonment. With redesigned needles and catheters, Arkoosh (2008) subsequently randomized 429 women to either continuous spinal or conventional epidural analgesia during labor. There were no differences in complications between these two neuraxial techniques. However, the technique remains investigational.
Local Infiltration for Cesarean Delivery
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 emergency cesarean delivery to save the life of a fetus in the absence of anesthesia support. Young (2012) reviewed regional analgesia techniques used for cesarean delivery that provide analgesia to the parietal peritoneum as well as skin and muscles of the anterior abdominal wall.
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. A dilute solution of lidocaine—30 mL of 2-percent with 1:200,000 epinephrine diluted with 60 mL of normal saline—is prepared, and a total of 100 to 120 mL is infiltrated. 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. As shown in Figure 25-6, 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 transversalis 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.
FIGURE 25-6 Local anesthetic block for cesarean delivery. The first injection site is halfway between the costal margin and iliac crest in the midaxillary line to block the 10th, 11th, and 12th intercostal nerves. A second injection at the external inguinal ring blocks branches of the genitofemoral and ilioinguinal nerves. These sites are infiltrated bilaterally. A final site is along the line of proposed skin incision.
Trained personnel and specialized equipment—including fiberoptic intubation—are mandatory for the safe use of general anesthesia. This is because a common cause of death cited for general anesthesia is failed intubation. This occurs in approximately 1 of every 250 general anesthetics administered to pregnant women—a tenfold higher rate than in nonpregnant patients (Hawkins, 2011; Quinn, 2013). The American College of Obstetricians and Gynecologists (2013b) has concluded that this relative increase in morbidity and mortality rates suggests that 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). Butwick and coworkers (2014) cited a higher incidence of general anesthesia use among non-white women.
Before anesthesia induction, several steps should be taken to help minimize the complication risks. These include antacid use, lateral uterine displacement, and preoxygenation.
Antacid administration shortly before anesthesia induction has probably decreased mortality rates from general anesthesia more than any other single practice. The American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2007) recommends timely administration of a nonparticulate antacid, an H2-receptor antagonist, or metoclopramide. For many years, we have recommended administration of 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.
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 (Crawford, 1972).
Last, because functional reserve lung capacity is reduced, the pregnant woman becomes hypoxemic more rapidly during periods of apnea than do nonpregnant patients. Obesity exacerbates this tendency (McClelland, 2009). To minimize hypoxia between the time of muscle relaxant injection and intubation, it is important first to replace nitrogen in the lungs with oxygen. 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 of Anesthesia
Thiopental given intravenously was widely used and offered easy and rapid induction, prompt recovery, and minimal risk of vomiting. Unfortunately, this thiobarbiturate is no longer available in the United States because the sole European manufacturer stopped production on the basis that the drug was also being used for capital punishment (American Society of Anesthesiologists, 2011). It was deemed “an unfortunate irony that many more lives will be lost or put in jeopardy as a result of not having thiopental available for its legitimate medical use.” Drugs now being used in lieu of thiopental include propofol or etomidate. Propofol has the undesirable side effect of hypotension.
Ketamine also may be used to render a patient unconscious. Doses of 1 mg/kg induce general anesthesia. Alternatively, given intravenously in low doses of 0.2 to 0.3 mg/kg, ketamine may be used to produce analgesia and sedation just before vaginal delivery. Ketamine may also prove useful in women with acute hemorrhage because it is not associated with hypotension. Conversely, it usually causes a rise in blood pressure, and thus it generally should be avoided in women who are already hypertensive. Unpleasant delirium and hallucinations are commonly induced by this agent.
Immediately after a patient is rendered unconscious, a muscle relaxant is given to aid intubation. Succinylcholine, a rapid-onset and short-acting agent, frequently is used. Cricoid pressure—the Sellick maneuver—is applied by a trained assistant to occlude the esophagus from the onset of induction until intubation is completed. Before the operation begins, proper placement of the endotracheal tube must be confirmed.
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 the 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 also a major risk factor for failed or difficult intubation. The American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2007) stresses the importance of appropriate preoperative preparation. This includes the immediate availability of specialized equipment such as different-shaped laryngoscopes, laryngeal mask airways, fiberoptic bronchoscope, and transtracheal ventilation set, as well as liberal use of awake oral intubation techniques.
Management. An important principle is to start the operative procedure 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 in which 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 response to such an emergency.
Once the endotracheal tube is secured, a 50:50 mixture of nitrous oxide and oxygen is administered to provide analgesia. Usually, a volatile halogenated agent is added to provide amnesia and additional analgesia. The mechanisms of action of inhaled anesthetics have been reviewed by Campagna and associates (2003).
The most commonly used volatile anesthetics in the United States include isoflurane and two of its derivatives, desflurane and sevoflurane. They are usually added in low concentrations to the nitrous oxide-oxygen mixture to provide amnesia. They are potent, nonexplosive agents that produce remarkable uterine relaxation when given in high concentrations. These are used when relaxation is a requisite, such as for internal podalic version of the second twin, breech decomposition, and replacement of the acutely inverted uterus.
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 should be given to emptying the stomach via a nasogastric tube before extubation. As induction has become safer, extubation may now be more perilous. Of 15 anesthesia-related deaths of pregnant women from 1985 to 2003 in Michigan, none occurred during induction, whereas five resulted from hypoventilation or airway obstruction during emergence, extubation, or recovery (Mhyre, 2007).
Massive gastric acidic inhalation may cause pulmonary insufficiency from aspiration pneumonitis. Such pneumonitis has in the past been the most common cause of anesthetic deaths in obstetrics and therefore deserves special attention. To minimize this risk, antacids should be given routinely, intubation should be accompanied by cricoid pressure, and regional analgesia should be employed when possible.
According to the American Society of Anesthesiologists Task Force on Obstetrical Anesthesia (2007) and the American College of Obstetricians and Gynecologists (2013a), there are insufficient data 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. Obvious solid foods should be avoided. A fasting period of 6 to 8 hours, depending on the type of food ingested, is recommended for uncomplicated parturients 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 for cesarean deliveries, and this greatly minimized the pulmonary aspiration risk associated with general anesthesia. Given the low prevalence of aspiration, this trial, albeit large, was not powered to measure whether feeding during labor was safe. Our policy at Parkland Hospital is to prohibit oral intake during labor and delivery.
In 1952, Teabeaut demonstrated experimentally that if the pH of aspirated fluid was below 2.5, severe chemical pneumonitis developed. It was later demonstrated that the gastric juice pH of 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 signs. 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. Therefore, chest radiographs alone should not be used to exclude aspiration.
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. There is no convincing clinical or experimental evidence that corticosteroid therapy or prophylactic antimicrobial administration is beneficial (Marik, 2001). If clinical evidence of infection develops, however, then vigorous treatment is given. If acute respiratory distress syndrome develops, mechanical ventilation with positive end-expiratory pressure may prove lifesaving (Chap. 47, p. 944).
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