Requests from patients and obstetricians, coupled with an increased number of providers who have expertise and interest in regional anesthesia for obstetrics, have resulted in a substantial increase in the use of epidural analgesia during childbirth over the past two decades. A recent survey of obstetric anesthesia in the United States indicated that the percentage of women given intrapartum epidural analgesia increased from 22 percent in 1981 to 51 percent in 1992 at hospitals performing at least 1,500 deliveries annually.² Similar increases occurred in hospitals with 500 to 1,500 births per year (from 13 to 33 percent) and in those with less than 500 births per year (from 9 to 17 percent). Greater involvement by anesthesiologists appears to be responsible for much of the increase in larger hospitals. On the other hand, greater participation on the part of both anesthesiologists and certified registered nurse anesthetists has contributed to an increased use of epidural analgesia in smaller facilities.

The increased availability of epidural analgesia and the favorable experiences of women who have had painless labor with epidural block have reshaped the expectations of pregnant women entering labor. As more parturients demand pain-free labor, it is important that physicians managing labor have a clear understanding of the benefits of (Table 1), contraindications to and risks of epidural analgesia.

Pain of Parturition

Visceral distention originating from rhythmic uterine contractions and progressive cervical dilatation causes much of the pain experienced during the first stage of labor. Afferent impulses from the cervix and uterus are transmitted to the spinal cord via segments T10-L1. This usually produces pain over the lower abdomen and quite often causes pain over the lower back and the sacrum as well. More than two thirds of unanesthetized women described their pain intensity with terms such as “distressing,” “horrible” or “excruciating” at some point during the first stage of labor.³ Although the second stage of labor is briefer than the first, the pain is usually more intense. Perineal pain due to stretching of the vagina, vulva and perineum is superimposed on the pain of uterine contractions. Second-stage pain is principally somatic in nature and is transmitted through the spinal S2-4 segments.

Some women have excruciating pain during childbirth, whereas others experience only mild discomfort. Several variables may help physicians predict which parturients are more likely to have severe pain during labor and delivery, allowing them to know which patients would potentially receive the greatest benefit from continuous epidural block. Some factors shown to correlate with greater pain during labor and delivery include the following: nulliparity, intravenous induction or augmentation of labor with oxytocin (Pitocin), younger maternal age, low back pain during menstruation and increased maternal or fetal weight.^4–7 Of these, nulliparity and administration of intravenous oxytocin are the most useful predictors of women who may have more intense labor pain.

Decreased labor pain may be anticipated in women who have attended childbirth classes and in those who have performed aerobic conditioning exercises during pregnancy.^7,8

Preliminary Considerations

The American Society of Anesthesiologists has published guidelines for regional anesthesia in obstetrics.⁹ The guidelines state that anesthesia should be provided only by practitioners with appropriate privileges in facilities where resuscitation equipment and drugs are immediately available. This equipment should include sources of oxygen and suction, equipment to maintain an airway and perform endotracheal intubation, a means of providing positive pressure ventilation, and drugs and equipment for cardiopulmonary resuscitation. The guidelines also advise that regional anesthesia not be given before the patient has been examined and the maternal and fetal status and progress of labor have been evaluated by a physician with obstetric privileges. Furthermore, a physician should be readily available to manage obstetric complications that may arise during induction or maintenance of epidural analgesia.

Pain relief alone is an adequate medical indication for administration of epidural analgesia during labor. The American College of Obstetricians and Gynecologists and the American Society of Anesthesiologists have collectively published the opinion that “maternal request is sufficient justification for pain relief during labor.”¹⁰ Also, these groups point out that “there is no other circumstance where it is considered acceptable for a person to experience severe pain, amenable to safe intervention, while under a physician's care.”

There are few absolute contraindications to the use of epidural analgesia during labor. Contraindications to the use of a neuraxial (i.e., epidural or subarachnoid) technique include patient refusal, active maternal hemorrhage, septicemia, infection at or near the site of needle insertion and clinical signs of coagulopathy (Table 2).

The presence of a nonreassuring fetal heart rate pattern is not a contraindication to epidural analgesia. However, some physicians may be reluctant to recommend epidural anesthesia in this situation. The prior placement of a functioning epidural catheter may allow rapid extension of the block should cesarean delivery be required for fetal distress.

Timing Considerations

It is uncommon for spontaneously laboring parturients to request epidural analgesia before 3 cm of cervical dilation. However, women receiving augmentation of labor with oxytocin may request analgesia at minimal cervical dilation. It is appropriate to induce epidural analgesia after the diagnosis of active labor has been established and the patient has begun to request pain relief. Recent data do not support the conclusions of earlier studies that administration of epidural block before 5 cm of cervical dilation will adversely affect the subsequent course of labor.^11,12 While epidural block is not contraindicated in advanced labor, it is less common to initiate epidural block when cervical dilation exceeds 8 cm—especially in parous women.

Complications

Complications of epidural analgesia are listed in Table 3. Elimination of painful stimuli and the onset of peripheral vasodilation typically reduce maternal blood pressure during the onset of epidural blockade. Modest decreases (20 percent or less) in maternal blood pressure are of limited concern in a woman with a healthy fetus. More severe hypotension may result in a clinically significant decrease in uteroplacental blood flow, which could jeopardize a fetus with marginal reserve. The preanesthesia intravenous administration of an isotonic electrolyte solution (e.g., lactated Ringer's solution, 500 to 1,000 mL) will attenuate the decrease in maternal blood pressure that occurs with induction of epidural analgesia. Hypotension during epidural analgesia is treated with additional intravenous boluses of crystalloid solution and/or administration of small intravenous doses of a vasopressor (e.g., ephedrine, in a dosage of 5 to 10 mg).

Neurologic complications of epidural or spinal analgesia/anesthesia are rare. Perhaps the most common postpartum complication of epidural or spinal analgesia is postdural puncture headache. Once common with spinal anesthesia, postdural puncture headache occurs infrequently in patients who undergo dural puncture with a fine pencil-point spinal needle (e.g., Whitacre, Sprotte). However, most patients who experience unintentional dural puncture with a 16- or 18-gauge epidural needle are at risk for postdural puncture headache. The headache is typically postural in nature and results from leakage of cerebrospinal fluid, with the attendant decrease in intracranial pressure and compensatory cerebral vasodilation. In some cases (especially in patients whose dural puncture occurred with a small-gauge, pencil-point spinal needle) the postdural puncture headache resolves spontaneously. Consumption of a caffeinated beverage may provide partial relief in some patients. However, the definitive treatment for persistent postdural puncture headache is an autologous epidural blood patch (i.e., sterile injection of 15 to 20 mL of the patient's fresh blood into the epidural space, preferably at the site of the dural puncture).¹³

Rare but life-threatening complications from epidural analgesia include the following: (1) maternal convulsions or cardiovascular collapse after unintentional direct intravenous injection of a local anesthetic and (2) total spinal anesthesia following unintentional subarachnoid injection of local anesthetic. Slow, incremental administration of the local anesthetic with appropriate maternal and fetal monitoring will produce signs and symptoms of subarachnoid or intravenous injection before serious consequences occur. Many physicians administer an epidural “test dose” (e.g., 3 mL of 1.5 percent lidocaine [Xylocaine] with epinephrine 1:200,000) to detect subarachnoid or intravenous placement of the catheter.

Induction and Maintenance of Analgesia

A method of administering epidural analgesia is outlined in Table 4.¹⁴ The anesthesiologist's goal during the first stage of labor should be to provide segmental sensory anesthesia of the T10-L1 dermatomes. The dose of local anesthetic necessary to achieve effective labor analgesia will depend on the intensity and location of the patient's pain. These in turn depend on the variables discussed earlier, including the amount and rate of cervical dilation; the strength, frequency and duration of uterine contractions; and the position of the fetal head at the time epidural analgesia is requested. Approximately 10 mL of 0.125 to 0.25 percent bupivacaine (Marcaine) or 0.125 to 0.25 percent ropivacaine (Naropin), with or without a small dose of a lipid-soluble opioid (e.g., fentanyl [Sublimaze] or sufentanil [Sufenta]), establishes effective analgesia with minimal motor block. Thereafter, maintenance of epidural analgesia may be achieved with either intermittent bolus injections, continuous epidural infusion or patient-controlled epidural analgesia. In most cases, analgesia may be maintained with a solution of local anesthetic more dilute than that used for induction.

The supine position is contraindicated in women receiving epidural analgesia during labor. Compression of the abdominal aorta and the inferior vena cava (aortocaval compression) by the term gravid uterus may concurrently decrease uterine arterial pressure and increase uterine venous pressure. Consequently, uterine perfusion pressure (uterine arterial pressure minus uterine venous pressure) may be substantially reduced even in the presence of normal brachial arterial blood pressure measurements (concealed aortocaval compression). When maternal hypotension occurs during epidural analgesia, it is essential to verify that the patient is not supine.

The onset of fetal descent causes substantial distention of the vagina and perineum, typically resulting in severe pain. It is important to ensure that the segmental extent of epidural analgesia has spread to include the S2-4 nerve roots to maintain analgesia during this stage of labor. Achieving adequate perineal analgesia is especially important in women in whom episiotomy or the application of forceps is probable. Complaints of rectal pressure with progressive descent of the fetal head should alert the anesthesiologist that sacral analgesia may be inadequate for delivery. Women who progress into the second stage of labor soon after induction of epidural analgesia seldom have adequate sacral blockade and often require additional epidural boluses of local anesthetic before delivery. On the other hand, women who have been receiving continuous epidural analgesia for many hours often have excellent perineal analgesia at delivery.

Controversial Issues

In spite of the widespread acceptance that epidural analgesia has achieved among many physicians and patients, disagreement remains regarding the effect of intrapartum epidural analgesia on the subsequent progress of labor and the mode of delivery. Several retrospective studies consistently demonstrated an association between epidural analgesia and increased durations of both the first and second stages of labor, oxytocin augmentation, instrumental vaginal delivery and cesarean section for dystocia. In these studies, the probability of cesarean section for dystocia was reported to be increased three- to six-fold by the intrapartum administration of epidural analgesia.^15–17 Unfortunately, retrospective studies add little to the understanding of the impact of epidural analgesia on labor and delivery. Such studies are biased by the fact that women who progress rapidly through labor often have less pain and are less likely to request and receive regional analgesia.

Randomized, prospective studies have produced contrasting findings regarding the effects of epidural analgesia on labor and mode of delivery. It is unclear whether or not epidural block prolongs the first stage of labor.^18,19 However, maintenance of profound epidural analgesia beyond complete cervical dilation will increase the duration of the second stage of labor or increase the probability of an instrumental vaginal delivery—especially in nulliparous patients.^20,21

Controversy remains as to whether epidural analgesia predisposes parturients to a greater risk of cesarean delivery for dystocia.^22,23 This situation is illustrated by the opposing conclusions of two studies originating from the same institution. In the first of these studies, Ramin and colleagues²² reported that the risk of operative delivery for dystocia was increased nearly two-fold among women of mixed parity who were given epidural analgesia rather than intravenous meperidine (Demerol) analgesia. Two years later, Sharma and associates²³ observed identical cesarean section rates among women randomized to receive either epidural analgesia or patient-controlled intravenous meperidine analgesia. One important methodologic difference between these two investigations was that parturients in the latter study were analyzed on an intent-to-treat basis, regardless of the type of pain relief ultimately administered.

Perhaps most illuminating are data from institutions where the use of epidural analgesia has increased abruptly over a short period of time. Results from these studies refute the hypothesis that increased utilization of epidural analgesia is responsible for the cesarean section “epidemic.”¹⁵ For example, the introduction of an “on-demand” epidural analgesia service at one clinic produced a sudden increase (from zero to 41 percent) in the use of intrapartum epidural analgesia but no increase in the primary cesarean-section rate.²⁴ In a similar study, Lyon and colleagues²⁵ evaluated the impact of a Department of Defense mandate allowing the vast majority of military beneficiaries to receive intrapartum epidural analgesia on obstetric outcomes at one U.S. Air Force hospital. In the 12-month period preceding enforcement of the new policy, 13 percent of parturients received epidural analgesia; the incidence of cesarean delivery for dystocia was 8 percent. During the first year that epidural block became widely available, 59 percent of parturients were given epidural analgesia during labor. The incidence of cesarean section delivery for dystocia decreased (although the decrease was not statistically significant) to 5 percent—despite a 350 percent increase in the use of intrapartum epidural analgesia.

Other Techniques

Discovery of opioid-mediated spinal analgesia led to speculation that spinal morphine administration would result in acceptable labor analgesia without local anesthetic-induced sympathetic and motor block. Unfortunately, pain relief following subarachnoid administration of morphine is often slow in onset, inconsistent in quality (especially during the second stage) and accompanied by a high incidence of pruritus, nausea, urinary retention and sedation.

On the other hand, intrathecal administration of short-acting lipid-soluble opioids (e.g., fentanyl and sufentanil) has greater efficacy and results in fewer side effects than administration of a water-soluble opioid such as morphine. Specifically, subarachnoid sufentanil or fentanyl each produce excellent first-stage analgesia within five minutes that lasts about 90 minutes. Limitations to the intrathecal administration of a lipid-soluble opioid for labor analgesia include a propensity for intense (although brief) pruritus, a relatively short duration of action and an inability to produce adequate pain relief during the second stage of labor.

Some physicians have administered a lipid-soluble opioid with a very small dose of morphine (0.25 mg) intrathecally in an attempt to provide rapid-onset, long-acting labor analgesia with a single injection.²⁶ Unfortunately, this method (although offering analgesia superior to conventional intravenous opioid techniques) lacks the flexibility of continuous epidural analgesia and does not compare favorably with epidural analgesia in the quality of pain relief provided during advanced labor.

The unique ability of intrathecal lipid-soluble opioids to produce rapid onset of pain relief during the first stage of labor clearly cannot be equaled using epidural techniques. Thus, some anesthesiologists facilitate the onset of labor analgesia by injecting a single dose of fentanyl or sufentanil (with or without a local anesthetic) intrathecally before placing the epidural catheter (combined spinal-epidural analgesia). This technique allows prompt onset of pain relief through spinal anesthesia without sacrificing the flexibility of continuous epidural analgesia.

Final Comment

The increased availability and effectiveness of epidural analgesia have altered the expectations of many women regarding intrapartum pain control. A significant number of parturients are requesting this form of analgesia for relief of labor pain. Family physicians who perform obstetrics should discuss this method of pain control with their prenatal patients. The risks and benefits of epidural analgesia, as well as other options for pain control, should be objectively presented to each woman well before the onset of labor. In addition, women can be encouraged to attend childbirth classes to help them prepare for stresses that may arise during labor and delivery. Careful patient evaluation, meticulous technique during epidural catheter placement and appropriate dosing of medication minimize the risk of serious complications from epidural analgesia.