Epidural analgesia is indicated to treat the pain experienced by a woman in labor. In 2008 and 2010, respectively, the American College of Obstetricians and Gynecologists (ACOG)¹⁷ and the ASA¹⁸ reaffirmed an earlier, jointly published opinion that stated that “in the absence of a medical contraindication, maternal request is a sufficient medical indication for pain relief during labor.” Furthermore, the ACOG¹⁹ has stated that “decisions regarding analgesia should be closely coordinated among the obstetrician, the anesthesiologist, the patient, and skilled support personnel.” Neuraxial analgesia is an appropriate treatment for the pain of labor, including early labor (defined as regular uterine contractions that cause progressive effacement and dilation of the uterine cervix). Randomized controlled trials^20–24 and a meta-analysis²⁵ have confirmed that initiation of neuraxial analgesia in early labor does not increase the risk for cesarean delivery (see later discussion).

Epidural analgesia may facilitate an atraumatic vaginal breech delivery, the vaginal delivery of twin infants, and vaginal delivery of a preterm infant (see Chapters 34 and 35). By providing effective pain relief, epidural analgesia facilitates blood pressure control in preeclamptic women (see Chapter 36). Epidural analgesia also blunts the hemodynamic effects of uterine contractions (e.g., sudden increase in cardiac preload) and the associated pain response (tachycardia, increased systemic vascular resistance, hypertension, hyperventilation) in patients with other medical complications (e.g., mitral stenosis, spinal cord injury, intracranial neurovascular disease, asthma; see Chapters 42, 49, and 53).

Box 23-1 lists the contraindications to administration of epidural or spinal analgesia. Some anesthesiologists have suggested that systemic maternal infection, preexisting neurologic disease, or severe stenotic heart lesions are relative contraindications to neuraxial analgesia. However, most cases of systemic infection (especially if properly treated), or neurologic or cardiac disease, do not contraindicate the administration of neuraxial analgesia (see Chapters 37, 42, and 49). It is also controversial whether mild or isolated abnormalities in tests of blood coagulation preclude the use of neuraxial analgesia. The dose and timing of administration of drugs administered for thromboprophylaxis must also be considered (see Chapter 44).²⁶ The anesthesia provider should consider the risks and benefits of neuraxial analgesia for each patient individually.

Thorough preparation for neuraxial labor analgesia involves several steps (Box 23-2). These include (1) a review of the parturient’s obstetric history; (2) a focused preanesthetic evaluation that includes maternal obstetric, anesthetic, and health history; and (3) a brief physical examination (i.e., vital signs, airway, heart, lungs, and back).¹⁶ Routine measurement of the platelet count is not necessary; however, assessment of the platelet count and other laboratory measurements may be indicated in selected patients.¹⁶ Similarly, routine intrapartum blood typing and screening or crossmatching is not necessary in healthy parturients, although consideration should be given to sending a blood sample to the blood bank (to facilitate the rapid availability of blood products in case of emergency need).¹⁶ For parturients at increased risk for hemorrhage, intrapartum typing, and screening or crossmatching should be performed. Fetal well-being should be assessed by a skilled provider, and equipment (including resuscitation equipment) should be checked by the anesthesia provider (see Box 12-1). Informed consent should be obtained (see Chapters 12 and 33). Early and ongoing communication among the obstetric and anesthesia providers, nursing staff, and other members of the multidisciplinary team is encouraged.

The technical aspects of neuraxial analgesic/anesthetic techniques are discussed in detail in Chapter 12. These techniques include continuous epidural, combined spinal-epidural, and caudal analgesia and continuous and single-shot spinal analgesia. Continuous epidural and combined spinal-epidural analgesia are the most common techniques used for neuraxial labor analgesia. There are advantages and disadvantages to each technique (Table 23-1).

Informed Consent

Informed consent is an important aspect of preparation for neuraxial labor analgesia (see Chapters 12 and 33). The preanesthetic evaluation and informed consent process allow the physician to allay the patient’s concerns and to demonstrate a commitment to her care. Most laboring women understand the need for informed consent and appreciate the opportunity to participate in decisions about their care.

Equipment and Monitors

Resuscitation equipment, drugs, and supplies must be immediately available for the management of serious complications of neuraxial analgesia (e.g., hypotension, total spinal anesthesia, systemic local anesthetic toxicity) (see Box 12-1).¹⁶ Emergency airway equipment should be checked before the administration of neuraxial analgesia.

During the initiation of neuraxial analgesia, the parturient’s oxygen saturation is measured continuously and the blood pressure is assessed every 2 to 3 minutes for 15 to 20 minutes after the neuraxial anesthetic administration, or until the mother is hemodynamically stable (see Chapter 12). The FHR should be monitored before and after the initiation of neuraxial analgesia; it may be difficult to monitor the FHR during the actual procedure.¹⁶ During maintenance of neuraxial analgesia, maternal blood pressure is measured every 15 to 30 minutes, or more frequently if hypotension ensues. The sensory level of analgesia and the intensity of motor block (Box 23-3) are assessed after the administration of the test and therapeutic doses of local anesthetics. Subsequently, sensory level, motor block, and pain control are assessed at regular intervals.

Prior to the initiation of neuraxial analgesia, ultrasonographic imaging of the back may be helpful, especially in parturients whose landmarks are difficult to palpate.

Placement of an intravenous catheter (preferably 18-gauge or larger) and correction of hypovolemia with intravenous hydration are necessary before the initiation of neuraxial analgesia to mitigate hypotension that can result from sympathetic blockade. Data from small studies are conflicting as to whether a fluid bolus administered immediately before the initiation of analgesia decreases the risk for nonreassuring FHR patterns.^34–36 Most anesthesia providers administer approximately 500 mL of lactated Ringer’s solution (without dextrose), although the ASA Task Force on Obstetric Anesthesia has stated that a fixed volume of intravenous fluid is not required before neuraxial analgesia is initiated.¹⁶ Severe hypotension is less likely with the contemporary practice of administering a dilute solution of local anesthetic for epidural analgesia or an intrathecal opioid for spinal analgesia.

Studies of intravenous hydration and spinal anesthesia for cesarean delivery suggest that there is no advantage to administering the fluid before the initiation of anesthesia (preload) compared with administering the fluid at the time of initiation of anesthesia (co-load).³⁷ Rarely, hydration should be guided by serial assessment of intravascular fluid volume (e.g., central venous pressure, transthoracic echocardiography). Fluid administration should be judicious in parturients at risk for pulmonary edema (e.g., women with severe preeclampsia).

A balanced electrolyte solution (e.g., lactated Ringer’s solution) without dextrose is the most commonly used intravenous fluid for bolus administration. Data are conflicting as to whether the maintenance intravenous infusion of dextrose-containing fluid during labor is associated with a lower incidence of umbilical cord blood acidemia.^38,39 One randomized controlled trial demonstrated shorter labor in women who received an intravenous solution of normal saline with dextrose compared with saline without dextrose.⁴⁰ However, anesthesia and obstetric providers should avoid the bolus administration of dextrose-containing solutions in laboring women.

Maternal Positioning

Either the lateral decubitus or the sitting position can be used during initiation of neuraxial analgesia (see Chapter 12). Factors to consider when positioning the parturient for the procedure include patient comfort, avoidance of aortocaval compression, ability to monitor the FHR, provider comfort and experience, and optimal positioning of the spine and palpation of landmarks. Patient position relative to the baricity of the anesthetic solution should be considered during initiation of spinal analgesia/anesthesia. There is little evidence that patient position influences the extent of neuroblockade during initiation of epidural analgesia/anesthesia. After completion of the procedure, parturients should be assisted to the lateral position for the first 15 to 30 minutes after the neuraxial injection to alleviate aortocaval compression.

The purpose of the test dose is to help identify unintentional cannulation of a vein or the subarachnoid space. The test dose should contain a dose of local anesthetic and/or another marker sufficient to allow the recognition of intravenous or subarachnoid injection but not so large as to cause systemic toxicity or total spinal anesthesia. The most common intravascular test dose contains epinephrine (see Chapter 12).

The use of the epinephrine test dose in obstetrics is not without detractors. Some anesthesia providers fear that intravenous injection of epinephrine may decrease uteroplacental perfusion and precipitate fetal compromise. However, there has been no report of adverse neonatal outcome after intravenous injection of an epinephrine-containing test dose. Another argument against routine use of a test dose is that aspiration of multi-orifice catheters is 98% sensitive in identifying their intravascular location.⁴¹ (The sensitivity of aspiration is significantly lower for single-orifice catheters.) The epidural test dose contributes to undesirable motor blockade.^42,43 Finally, because modern epidural labor analgesia involves the infusion of a low concentration of local anesthetic solution, unintentional intravascular or intrathecal administration is not likely to result in cardiovascular collapse or total spinal anesthesia.

Others argue that the test dose still has a role in obstetric anesthesia practice.⁴⁴ Large volumes of a concentrated local anesthetic solution are still routinely administered for emergency cesarean delivery. Although not a safety issue, it is easier for the parturient and anesthesia provider to identify a misplaced catheter at the time of initial placement and to replace the catheter at that time rather than identify the misplaced catheter after the sterile field has been breached and the parturient repositioned.

The epinephrine test dose is less specific in laboring women because cyclic changes in maternal heart rate complicate interpretation of its effects.⁴⁵ For this reason, if used, the test dose should be given immediately after a uterine contraction so there is less confusion as to whether tachycardia is caused by pain or intravenous epinephrine. Other methods of detecting intravascular injection are discussed in Chapter 12.

No matter whether a formal test dose is used or not, it is imperative that the anesthesia provider take the time to look for evidence of unintentional intrathecal injection of local anesthetic. Finally, every anesthesia provider should remember that no single test dose regimen can exclude every case of unintentional intravenous or subarachnoid injection. Box 12-3 summarizes steps that may be taken to decrease the risk for unintentional intravenous or subarachnoid injection of local anesthetic.

Choice of Drugs

The ideal analgesic drug for labor would provide rapid onset of effective analgesia with minimal motor blockade, minimal risk for maternal toxicity, and negligible effect on uterine activity and uteroplacental perfusion. It would undergo limited transplacental transfer and thus have minimal direct effect on the fetus. Finally, this ideal agent would have a long duration of action. Although this perfect analgesic drug does not exist, the combination of a local anesthetic with an opioid allows us to approach this goal.

Traditionally, local anesthetics were administered to block both the visceral pain of labor (lower uterine segment distention and cervical dilation) and the somatic pain (descent of the fetus in the birth canal). Almost 40 years ago, investigators identified dense concentrations of opioid receptors in the dorsal horn of the spinal cord.⁴⁶ The application of small doses of an opioid to these receptor sites generates a specific and profound opioid response.⁴⁶ The introduction of neuraxial opioids to the armamentarium of the obstetric anesthesia provider moved us closer to the prediction made by Benjamin Rush in 1805: “A medicine would be discovered which should suspend sensibility altogether and leave irritability or powers of motion unimpaired.”⁴⁷ Intrathecal opioids effectively relieve the visceral pain of the early first stage of labor, although they must be combined with a local anesthetic to effectively relieve the somatic pain of the late first stage and the second stage of labor. The combination of a local anesthetic with a lipid-soluble opioid allows for the use of lower doses of each agent, thus minimizing undesirable side effects. For example, when used alone without an opioid, the local anesthetic dose required for effective epidural analgesia is associated with an unacceptably high incidence of motor blockade. Similarly, used alone, high doses of epidural opioid are required for satisfactory analgesia during early labor, and such doses are associated with significant systemic absorption and systemic side effects. The addition of an opioid to the local anesthetic also shortens latency,⁴⁸ an important aspect of labor analgesia, especially with the use of long-acting (and therefore, long-latency) local anesthetics. Thus, contemporary epidural labor analgesia practice most often incorporates low doses of a long-acting local anesthetic combined with a lipid-soluble opioid.

Local Anesthetics

Bupivacaine.

Traditionally, the amide local anesthetic bupivacaine has been the most commonly used agent for epidural labor analgesia. Bupivacaine is highly protein-bound, a feature that limits transplacental transfer. The umbilical vein–to–maternal vein concentration ratio is approximately 0.3.⁴⁹ After epidural administration of bupivacaine (without opioid) during labor, the patient first perceives pain relief within 8 to 10 minutes,⁵⁰ but approximately 20 minutes is required to achieve the peak effect. Duration of analgesia is approximately 90 minutes. Bupivacaine 6.25 to 12.5 mg (e.g., 10 to 20 mL of a 0.0625% solution, or 5 to 10 mL of a 0.125% solution) combined with fentanyl or sufentanil is adequate to initiate labor analgesia in most parturients (Table 23-2).

TABLE 23-2

Drugs Used for Initiation of Epidural and Spinal Labor Analgesia

^* The volume required to initiate epidural labor analgesia is 10 to 15 mL of local anesthetic solution.

^† The local anesthetic dose/concentration and the fentanyl or sufentanil dose are reduced if the drugs are combined or if a local anesthetic-containing epidural test dose is administered before the initial therapeutic dose. The dose of opioid should be reduced or the opioid omitted if the parturient has recently received systemic opioid analgesia.

^‡ Lidocaine, morphine, and meperidine are not commonly used for labor analgesia because of their short duration of action (lidocaine), long latency (morphine), and high incidence of nausea and vomiting (morphine and meperidine).

^§ Opioids may be administered without local anesthetics when spinal analgesia is induced in early labor. Women in active labor require a higher dose than women in latent labor.

Note: The suggested doses are based on clinical studies, potency ratios, and clinical experience.

NA, not applicable.

The potency of local anesthetics for neuraxial labor analgesia is often assessed by determining the median effective concentration of local anesthetic solution when administered as a 20-mL epidural bolus (this concentration is often referred to as the minimum local anesthetic concentration [MLAC]). It is lower for women in early labor than in late labor,⁵¹ and it is also lower when the local anesthetic is combined with a lipid-soluble opioid.⁵²

It is important to consider both the local anesthetic dose and concentration for initiation and maintenance of epidural analgesia. Christiaens et al.⁵³ randomly assigned parturients to receive epidural bupivacaine 20 mg diluted in 4 mL, 10 mL, or 20 mL (0.5%, 0.2%, and 0.1% solutions, respectively). Analgesia in the 10-mL and 20-mL groups was superior to that in the 4-mL group, and duration of analgesia was longest in the 20-mL group. Lyons et al.⁵⁴ compared the minimum local anesthetic volume (MLAV) and minimum local anesthetic dose (MLAD) for 0.125% and 0.25% bupivacaine for epidural labor analgesia. Bupivacaine 0.125% produced analgesia equivalent to that provided by bupivacaine 0.25%, with a 50% increase in required volume and a 25% reduction in dose (Table 23-3). Stated differently, a dose-sparing effect is achieved by administering a 0.125% solution of bupivacaine rather than a 0.25% solution. Ginosar et al.⁵⁵ randomized parturients to receive maintenance of analgesia with an epidural infusion of either bupivacaine 0.25% at 5 mL/h or bupivacaine 0.0625% at 20 mL/h (10 mg/h in both groups). The median bupivacaine dose was lower and patient satisfaction was greater with bupivacaine 0.0625% than with bupivacaine 0.25%. Together, these data suggest that epidural analgesia and safety are improved with the use of low concentration–high volume local anesthetic solutions.

TABLE 23-3

Comparison of Epidural Bupivacaine 0.25% and 0.125%: Median Effective Volume and Dose

^* Median effective volume at a fixed local anesthetic concentration.

^† Median effective dose at a fixed local anesthetic concentration.

^‡ 95% confidence intervals shown in parentheses, which were calculated using up-down sequential and probit analysis.

Modified from Lyons GR, Kocarev MG, Wilson RC, Columb MO. A comparison of minimum local anesthetic volumes and doses of epidural bupivacaine (0.125% w/v and 0.25% w/v) for analgesia in labor. Anesth Analg 2007; 104:412-5.)

Ropivacaine.

Ropivacaine, a relatively newer amide local anesthetic, is similar to bupivacaine in structure and pharmacodynamics.⁵⁶ It is a homologue of bupivacaine and mepivacaine, but unlike these other local anesthetics it is formulated as a single-levorotary enantiomer rather than a racemic mixture (see Chapter 13). Studies of pregnant sheep have demonstrated that clinically relevant plasma concentrations of ropivacaine do not adversely affect uterine blood flow.⁵⁷

Studies in vitro and in vivo have shown that ropivacaine is less cardiodepressant and arrhythmogenic than bupivacaine when doses of equal mass are compared.^58,59 Ropivacaine is cleared more rapidly than bupivacaine after intravenous administration in both pregnant and nonpregnant sheep. Consequently, a larger dose of drug—but not a higher plasma concentration—is required to produce systemic toxicity.⁶⁰ These findings suggest that ropivacaine may have a greater margin of safety than bupivacaine if unintentional intravenous injection occurs in pregnant women. However, many early investigations assumed that ropivacaine and bupivacaine are equipotent; subsequent studies have demonstrated that ropivacaine is 25% to 40% less potent than bupivacaine.^61–63 In one study that characterized the full dose-response curves, the slope of the bupivacaine and ropivacaine curves were similar, suggesting that the nature of the drug-receptor interaction is not different between the two drugs.⁶³ When ropivacaine concentrations are adjusted for this difference in potency, there is a less clear advantage for ropivacaine in terms of the risk for systemic toxicity.⁶¹ In reality, systemic toxicity is not a major concern with the contemporary administration of a dilute solution of local anesthetic for epidural labor analgesia.

Several studies that compared equal concentrations of ropivacaine and bupivacaine given by patient-controlled epidural analgesia (PCEA) have not found any significant difference in clinical efficacy between the two local anesthetics.^64–68 Other studies that adjusted for the potency difference and compared equipotent concentrations (e.g., 0.0625% bupivacaine versus 0.1% ropivacaine) also found no difference in clinical efficacy.^69,70 It is important to recognize that potency is an unchanging property of a drug, whereas clinical efficacy is influenced by multiple variables. For example, ropivacaine has a longer duration of analgesia than bupivacaine,⁶¹ which may offset its lesser potency when it is administered by continuous epidural infusion.

Early clinical studies suggested that ropivacaine is associated with less motor block than bupivacaine^71,72; avoidance of motor blockade is a desirable characteristic of a local anesthetic used for epidural analgesia during labor. However, these studies also compared equal concentrations of ropivacaine and bupivacaine, and the observed lower degree of motor blockade may reflect the lesser potency of ropivacaine. A study of the relative motor-blocking potencies of epidural ropivacaine and bupivacaine showed that ropivacaine was less potent than bupivacaine in terms of motor blockade,⁷³ a finding that corresponded to the relative analgesic potencies of the two drugs.^61,62 The differences in potency of motor blockade may not be relevant with the use of low concentrations of local anesthetic. Several clinical studies^64,66,74 and a well-conducted meta-analysis of studies that compared epidural ropivacaine and bupivacaine⁷⁵ did not demonstrate an advantage for ropivacaine in terms of outcome of labor (see later discussion), although the incidence of motor blockade was less in the ropivacaine groups.^66,74,75

There is no clear evidence of greater patient safety, lower risk for instrumental vaginal delivery, or other improved outcomes when ropivacaine is used to provide epidural labor analgesia.^74,76 A 2010 review concluded that there is no advantage to the routine use of ropivacaine compared with bupivacaine for labor analgesia.⁷⁶ In contrast, ropivacaine offers greater patient safety in settings in which high concentrations and greater volumes of drugs are administered (e.g., brachial plexus blockade or epidural anesthesia for cesarean delivery).⁷⁷

Like bupivacaine, ropivacaine is often combined with fentanyl or sufentanil for labor analgesia. Ropivacaine concentrations used to initiate epidural analgesia range from 0.08% to 0.2% (see Table 23-2). Higher concentrations are used if the drug is administered without an opioid.

Levobupivacaine.

Levobupivacaine is the levorotary enantiomer of bupivacaine (which is a racemic mixture). It is not available in the United States. Both preclinical and clinical studies have suggested that, like ropivacaine, levobupivacaine has less potential for cardiotoxicity than bupivacaine when equal doses of the two drugs are compared.^78,79 One study found that levobupivacaine was essentially equipotent to bupivacaine with a potency ratio of 0.98; however, the 95% CI was wide (0.67 to 1.41).⁸⁰ Other studies have suggested that levobupivacaine and ropivacaine have similar potency.^81,82 In an MLAC study that compared the motor blocking potency of bupivacaine and levobupivacaine,⁸³ levobupivacaine was less potent than bupivacaine (potency ratio, 0.87; 95% CI, 0.77 to 0.98).⁸³ Beilin et al.⁶⁶ compared epidural bupivacaine, ropivacaine, and levobupivacaine (0.0625% with fentanyl 2 µg/mL) for labor analgesia. There were no differences among groups in obstetric outcomes, although the incidence of motor blockade was lower in the ropivacaine and levobupivacaine groups. Therefore, although epidural bupivacaine is more potent than ropivacaine for both sensory and motor blockade during labor, and may be more potent than levobupivacaine, there do not appear to be any clinical advantages of one drug over the other two drugs for epidural labor analgesia.

Lidocaine.

Lidocaine is an amide local anesthetic with a duration of action intermediate between those of bupivacaine and 2-chloroprocaine. During labor, the administration of a 0.75% to 1.0% solution of lidocaine typically provides satisfactory analgesia. Lidocaine is not commonly used for initiation or maintenance of epidural labor analgesia, in part because of its shorter duration of action in comparison with bupivacaine, ropivacaine, and levobupivacaine. Lidocaine is less protein-bound than these other amide local anesthetics, and at delivery, the umbilical vein–to–maternal vein lidocaine concentration ratio is approximately twice that of bupivacaine.⁸⁴ Early studies discouraged the epidural administration of lidocaine in pregnant women because epidural lidocaine was associated with abnormal neonatal neurobehavioral findings.⁸⁵

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