Key Abbreviations
Advanced cardiovascular life support ACLS
American College of Obstetricians and Gynecologists ACOG
American Society of Anesthesiologists ASA
Basic life support BLS
Confidence interval CI
Central nervous system CNS
Combined spinal-epidural CSE
Induction-to-delivery interval I-D
Laryngeal mask airway LMA
N-methyl-D-aspartate receptor NMDA receptor
Odds ratio OR
Para-aminobenzoic acid PABA
Patient-controlled analgesia PCA
Patient-controlled epidural analgesia PCEA
Postanesthesia care unit PACU
Postdural puncture headache PDPH
Randomized controlled trial RCT
Relative risk RR
Society of Obstetric Anesthesia and Perinatology SOAP
Uterine incision–to-delivery interval U-D
Obstetric anesthesia encompasses all techniques used by anesthesiologists and obstetricians to alleviate the pain associated with labor and delivery: this includes general anesthesia, neuraxial anesthesia (spinal or epidural), local anesthesia (local infiltration, paracervical block, pudendal block), and parenteral analgesia. Pain relief during labor and delivery is an essential part of good obstetric care. Unique clinical considerations guide anesthesia provided for obstetric patients; physiologic changes of pregnancy and increases in certain complications must be considered. This chapter reviews the various methods that can be used for obstetric analgesia and anesthesia as well as their indications and complications.
Personnel
In larger hospitals in the United States, anesthesiologists—working either independently or supervising a team of residents—along with anesthesiologist assistants and certified nurse anesthetists provide anesthesia for 98% of obstetric procedures. Nurse anesthetists working independent of anesthesiologists rarely provide anesthesia for obstetric cases in larger hospitals but provide anesthesia for 34% of obstetric procedures in hospitals with fewer than 500 births per year. The American Society of Anesthesiologists (ASA) partnered with the American College of Obstetricians and Gynecologists (ACOG) to issue a Joint Statement on the Optimal Goals for Anesthesia Care in Obstetrics, which recommends that a qualified anesthesiologist assume responsibility for anesthetics in every hospital that provides obstetric care. The statement notes: “There are many obstetric units where obstetricians or obstetrician-supervised nurse anesthetists administer labor anesthetics. The administration of general or neuraxial anesthesia requires both medical judgment and technical skills. Thus a physician with privileges in anesthesiology should be readily available.” To provide optimal care for the parturient, the ASA also states in their Practice Guidelines for Obstetric Anesthesia that “ A communication system should be in place to encourage early and ongoing contact between obstetric providers, anesthesiologists, and other members of the multidisciplinary team. ”
Pain Pathways
Pain during the first stage of labor results from a combination of uterine contractions and cervical dilation. Painful sensations travel from the uterus through visceral afferent (sympathetic) nerves that enter the spinal cord through the posterior segments of thoracic spinal nerves 10, 11, and 12 ( Fig. 16-1 ). During the second stage of labor, additional painful stimuli are added as the fetal head distends the pelvic floor, vagina, and perineum. The sensory fibers of sacral nerves 2, 3, and 4 (i.e., the pudendal nerves) transmit painful impulses from the perineum to the spinal cord during the second stage and during any perineal repair (see Fig. 16-1 ). During cesarean delivery, although the incision is usually around the thoracic spinal nerve 12 (T-12) dermatome, anesthesia is required to the level of thoracic spinal nerve 4 (T-4) to completely block peritoneal discomfort, especially during uterine exteriorization. Pain after cesarean delivery is due to both incisional pain and uterine involution.
Effects of Pain and Stress
The process of labor involves significant pain and stress for most women. Using the McGill Pain Questionnaire, which measures intensity and quality of pain, Melzack found that 59% of nulliparous and 43% of parous women described their labor pain in terms more severe than did those suffering from cancer pain. The most substantial predictors of pain intensity were ultimately low socioeconomic status and prior menstrual difficulties.
The maternal and fetal stress response to the pain of labor has been difficult to assess. Most investigators have described and quantified stress in terms of the release of the adrenocorticotropic hormone (ACTH) cortisol, catecholamines, and β-endorphins ( Fig. 16-2 ). Furthermore, animal studies indicate that both epinephrine and norepinephrine can decrease uterine blood flow in the absence of maternal heart rate and blood pressure changes, which contributes to occult fetal asphyxia. As demonstrated in baboons and monkeys, maternal psychological stress (induced by bright lights or toe clamping) can detrimentally affect uterine blood flow and fetal acid-base status. In pregnant sheep, catecholamines increase and uterine blood flow decreases after painful stimuli and after nonpainful stimuli such as loud noises induce fear and anxiety, as evidenced by struggling ( Fig. 16-3 ).
Although some of the physiologic stress of labor is unavoidable, analgesia and anesthesia may reduce stress responses secondary to pain. Postpartum women suffer objective deficits in cognitive and memory function when compared with nonpregnant women, and intrapartum analgesia does not exacerbate but rather lessens the cognitive defect compared with unmedicated parturients. Epidural analgesia is associated with a decreased risk of postpartum depression. In one study, depression occurred in 14% of parturients who received epidural labor analgesia and in 34.6% of those who did not. Analgesia also reduces paternal anxiety and stress, increases fathers’ feelings of helpfulness, and enhances their involvement and satisfaction with the childbirth experience. Epidural analgesia prevents increases in both cortisol and 11-hydroxycorticosteroid levels during labor, but systemically administered opioids do not. Epidural analgesia also attenuates elevations of epinephrine and norepinephrine and endorphin levels ( Fig. 16-4 ). Assuming any hypotension is rapidly treated and that perfusion is preserved by preventing aortocaval compression with uterine displacement, fetal acid-base status (as measured by base deficit) of human infants whose mothers receive epidural anesthesia during the first stage of labor is altered less than that of infants of mothers who receive systemic opioid analgesia.
Analgesia for Labor
Table 16-1 presents the frequency with which the various forms of analgesia are used during labor. The data are from a large survey of hospitals in the United States, stratified by the size of their delivery service.
| HOSPITAL SIZE (BIRTHS/YEAR) | NO ANESTHESIA (%) | NARCOTICS, BARBITURATES, TRANQUILIZERS (%) | PARACERVICAL BLOCK (%) | SPINAL OR EPIDURAL BLOCK (%) |
|---|---|---|---|---|
| <500 | 12 | 37 | 3 | 57 |
| 500-1499 | 10 | 42 | 3 | 59 |
| >1500 | 6 | 34 | 2 | 77 |
Psychoprophylaxis and Nonpharmacologic Analgesia Techniques
Psychoprophylaxis is any nonpharmacologic method that minimizes the perception of painful uterine contractions. Relaxation, concentration on breathing, gentle massage, and partner or doula participation contribute to effectiveness. One of the method’s most valuable contributions is that it is often taught in prepared childbirth classes, where parents tour the labor and delivery suite and learn about the normal processes of labor and delivery, which in many instances mitigates their fear of the unknown.
Although psychoprophylactic techniques can be empowering, the majority of women will still ultimately blend them with pharmacologic methods. Because the majority of first-time mothers choose epidural analgesia, teaching that use of drug-induced pain relief represents failure or will harm the child are counterproductive and can heighten fear and anxiety during labor.
Nonpharmacologic techniques for labor analgesia may be used alone or in conjunction with parenteral or neuraxial techniques. Table 16-2 shows frequently used techniques and the evidence that supports their use. A systematic review of acupuncture concluded that the evidence for efficacy is promising but few data are available. From the three randomized controlled trials (RCTs) they reviewed, the authors suggest that acupuncture alleviates labor pain and reduces use of both epidural analgesia and parenteral opioids. Acupuncture may be helpful for patients who feel strongly about avoiding epidural analgesia in labor, although arranging to have a qualified and credentialed acupuncturist available at the time of delivery may be challenging. An RCT of laboring in water found no advantage in labor outcome or in reducing the need for analgesia, but the request for epidural analgesia was delayed by about 30 minutes. The ACOG has expressed concerns about delivering in water because of the lack of trials to demonstrate safety and the rare but reported unusual complications, such as infection or asphyxia. They state that “the safety and efficacy of immersion in water during the second stage of labor have not been established, and immersion in water during the second stage of labor has not been associated with maternal or fetal benefit. Given these facts and case reports of rare but serious adverse effects in the newborn, the practice of immersion in the second stage of labor (underwater delivery) should be considered an experimental procedure that should only be performed within the context of an appropriately designed clinical trial with informed consent.”
| NONPHARMACOLOGIC ANALGESIC TECHNIQUES FOR LABOR | COCHRANE DATABASE SYSTEMATIC REVIEWS |
|---|---|
| Continuous support (e.g., doula) | CD003766 |
| Alternative therapies | CD003521 |
| Massage, reflexology | CD009290 |
| Acupuncture, acupressure | CD009232 |
| Immersion in water | CD000111 |
| Transcutaneous electrical nerve stimulation | CD007214 |
| Sterile water injection | CD009107 |
Intradermal sterile water injections at four sites in the lower back were once thought to have a similar gating mechanism as acupuncture and are simple to perform, but little evidence exists for their efficacy (see Table 16-2 ). A number of studies have examined transcutaneous electrical nerve stimulation (TENS) during labor. Patients tend to rate the device as helpful despite the fact that it does not decrease pain scores or the use of additional analgesics. As one study noted, TENS units do not appear to change the degree of pain but may have somehow made the pain less disturbing (see Table 16-2 ). Although the efficacy of these techniques is largely unproven because of a lack of RCTs, no serious safety concerns exist with any of these techniques, which is attractive to patients and their caregivers. Women expect to have choices and a degree of control during childbirth, and their caregivers should provide analgesic options for them to choose from, including nonpharmacologic methods.
Systemic Opioid Analgesia
Opioids can be given in intermittent doses by intramuscular (IM) or intravenous (IV) routes at the patient’s request, or the patient can self-administer with patient-controlled analgesia (PCA). All opioids provide sedation and a sense of euphoria, but their analgesic effect in labor is limited, and their primary mechanism of action is sedation. Opioids can also produce nausea and respiratory depression in the mother, the degree of which is usually comparable for equipotent analgesic doses. Also, all opioids freely cross the placenta to the newborn and decrease beat-to-beat variability in the fetal heart rate (FHR). They can increase the likelihood of significant respiratory depression in the newborn at birth and can increase the subsequent need for treatment. A meta-analysis aggregated the results of several randomized trials and revealed that opioid treatment is associated with an increased risk of Apgar scores below 7 at 5 minutes (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.2 to 5.6), and increased need for neonatal naloxone (OR, 4.17; 95% CI, 1.3 to 14.3), although the overall incidence of both was low. An important and significant disadvantage of opioid analgesia is the prolonged effect of these agents on maternal gastric emptying. When parenteral or epidural opioids are used, gastric emptying is prolonged, and if general anesthesia becomes necessary, the risk of aspiration is increased.
The opioids in common use today are meperidine, nalbuphine, fentanyl, and remifentanil. Morphine fell out of favor in the 1960s to 1970s because of a single study that reported increased respiratory depression in the newborn compared with meperidine, but no recent study has compared the relative safety of opioids for the newborn in the setting of modern practice.
Patient-Controlled Analgesia
IV patient-controlled analgesia (PCA) is often used for women who have a contraindication to neuraxial analgesia (e.g., severe thrombocytopenia). The infusion pump is programmed to give a predetermined dose of drug upon patient demand. The physician will program the pump to include a lockout interval to limit the total dose administered per hour. Advantages of this method include the sense of autonomy, which patients appreciate, and elimination of delays in treatment while the patient’s nurse obtains and administers the dose. In general, PCA results in a decreased total dose of opioid during labor. Fentanyl, remifentanil, and meperidine are the opioids most commonly used with this technique.
Meperidine (Demerol)
Meperidine is a synthetic opioid, and 100 mg is roughly equianalgesic to morphine 10 mg but has been reported to have a somewhat less depressive effect on respiration. Usually, 25 to 50 mg are administered intravenously; it may also be used intramuscularly or in a PCA pump to deliver 15 mg of meperidine every 10 minutes as needed until delivery. Intravenously, the onset of analgesia begins almost immediately and lasts approximately 1.5 to 2 hours. Side effects may include tachycardia, nausea and vomiting, and delayed gastric emptying.
Normeperidine is an active metabolite of meperidine and potentiates meperidine’s depressant effects in the newborn. Normeperidine concentrations increase slowly; therefore it exerts its effect on the newborn during the second hour after administration. Multiple doses of meperidine result in greater accumulation of both meperidine and normeperidine in fetal tissues ; thus administration of large doses of meperidine in the first stage of labor, rather than during the second stage, leads to high doses accumulated in the fetus. A randomized controlled study using intravenous PCA with meperidine for labor analgesia found that 3.4% of infants required naloxone at delivery (vs. 0.8% with epidural analgesia). Normeperidine accumulation in the fetus can result in prolonged neonatal sedation and neurobehavioral changes. These neurobehavioral changes are evident into day 2 and day 3 of life.
Nalbuphine (Nubain)
Nalbuphine is a synthetic agonist-antagonist opioid, meaning it has opioid-blocking properties as well as analgesic properties. Its analgesic potency is similar to that of morphine when compared on a milligram-per-milligram basis, and usual doses are 5 to 10 mg intravenously every 3 hours. A reported advantage of nalbuphine is its ceiling effect for respiratory depression, that is, respiratory depression from multiple doses appears to plateau. One limitation of nalbuphine is that its antagonist activity may also limit the analgesia it can produce, and it may interfere with spinal and epidural opioids given as part of a neuraxial technique. Nalbuphine causes less maternal nausea and vomiting than meperidine, but it tends to produce more maternal sedation, dizziness, and dysphoria and increases the risk of opioid withdrawal in susceptible patients.
Fentanyl
Fentanyl is a fast-onset, short-acting synthetic opioid with no active metabolites. In a randomized comparison with meperidine, fentanyl 50 to 100 µg every hour provided equivalent analgesia with fewer neonatal effects and less maternal sedation and nausea. The main drawback of fentanyl is its short duration of action, which requires frequent redosing or the use of a patient-controlled IV infusion pump. A sample PCA setting for fentanyl is a 50 µg incremental dose with a 10-minute lockout and no basal rate.
Remifentanil
Remifentanil is an even faster-onset, shorter-acting synthetic opioid with no active metabolites; it is metabolized by plasma esterases and is not affected by impaired renal or hepatic function. It should be administered as PCA because of its half-life of only 3 minutes. The ideal dosing regimen has not been determined, but a sample PCA setting might be 0.5 µg/kg boluses every 2 to 3 minutes with no basal rate. Sedation and hypoventilation with oxygen desaturations are more common than with other opioids; therefore respiratory monitoring is required. Placental transfer occurs, but in the neonate it appears to be rapidly metabolized or redistributed.
Sedatives
Sedatives such as barbiturates, phenothiazines, and benzodiazepines do not possess analgesic qualities. All sedatives and hypnotics cross the placenta freely, and except for the benzodiazepines, they have no known antagonists. Sedation is rarely desirable during the childbirth experience.
Promethazine may actually impair the analgesic efficacy of opioids. In a randomized double-blind trial, women received placebo, metoclopramide, or promethazine as an antiemetic with meperidine analgesia. Analgesia after placebo or metoclopramide was significantly better than that after promethazine as measured by pain scores and need for supplemental analgesics. Metoclopramide 10 mg has also been shown to improve PCA analgesia during second-trimester termination of pregnancy. In two randomized double-blind studies, the group that received metoclopramide (vs. saline) used 54% and 66% less IV morphine.
Two major disadvantages of benzodiazepines are that they cause undesirable maternal amnesia and may disrupt thermoregulation in newborns, which renders them less able to maintain an appropriate body temperature. Presumably this can occur with any of the benzodiazepines. As with many drugs, beat-to-beat variability of the FHR can be reduced even with a single IV dose, although these changes do not reflect alterations in the acid-base status of the newborn. Flumazenil, a specific benzodiazepine antagonist, can reliably reverse benzodiazepine-induced sedation and ventilatory depression.
Inhaled Nitrous Oxide (N 2 O)
Nitrous oxide, an inhaled anesthetic gas commonly used during general anesthesia and dental care, has been used in many parts of the world for labor analgesia. It is administered in a 50 : 50 mix with oxygen using a blender device and a mask held by the mother. A one-way valve allows her to inhale nitrous oxide before and during contractions. Patients report that nitrous oxide does not completely relieve pain, but in many women, it diminishes the perception of pain. Nitrous oxide is safe for the mother and the fetus and does not diminish uterine contractility; the main side effects are nausea and dizziness. It can also be used for short painful procedures such as perineal repair or manual removal of the placenta.
Placental Transfer
Essentially, all analgesic and anesthetic agents except highly ionized muscle relaxants cross the placenta freely ( Box 16-1 ). The limited transfer of muscle relaxants such as succinylcholine enables anesthesiologists to use general anesthesia for cesarean delivery without causing fetal paralysis.
Drug
- •
Molecular weight
- •
Lipid solubility
- •
Ionization, pH of blood
- •
Spatial configuration
Maternal
- •
Uptake into bloodstream
- •
Distribution via circulation
- •
Uterine blood flow: amount, distribution (myometrium vs. placenta)
Placental
- •
Circulation: intermittent spurting arterioles
- •
Lipid membrane: Fick’s law of simple diffusion
Fetal
- •
Circulation: ductus venosus, foramen ovale, ductus arteriosus
Because the placenta has the properties of a lipid membrane, most drugs and all anesthetic agents cross by simple diffusion. Thus the amount of drug that crosses the placenta increases as concentrations in the maternal circulation and total area of the placenta increase. Diffusion is also affected by the properties of the drug itself, including molecular weight, spatial configuration, degree of ionization, lipid solubility, and protein binding. For example, bupivacaine is highly protein bound, a characteristic that some believe explains why fetal blood concentrations are so much lower than with other local anesthetics. On the other hand, bupivacaine is also highly lipid soluble. The more lipid soluble a drug is, the more freely it passes through a lipid membrane. Furthermore, once in the fetal system, lipid solubility enables the drug to be taken up by fetal tissues rapidly (i.e., redistribution), which again contributes to the lower blood concentration of the agent.
The degree of ionization of a drug is also important. Most drugs exist in both an ionized and nonionized state, and the nonionized form more freely crosses lipid membranes. The degree of ionization is influenced by the pH; this may become relevant when there is a significant pH gradient between the mother (normal pH of 7.40) and an acidotic infant (pH <7.2). For example, local anesthetics are more ionized at a lower pH, so the nonionized portion of the drug in the maternal circulation (normal pH) crosses to the acidotic fetus, becomes ionized, and thus remains in the fetus, potentially leading to higher local anesthetic concentrations in the fetus/newborn. Whether this has relevant adverse clinical effects on the fetus is unknown.
Neuraxial Analgesic and Anesthetic Techniques
Neuraxial analgesic and anesthetic techniques—spinal, epidural, or a combination—use local anesthetics to provide sensory blockade, as well as various degrees of motor blockade, over a specific region of the body. In obstetrics, neuraxial and other regional analgesic techniques include major blocks, such as lumbar epidural and spinal, and minor blocks, such as paracervical, pudendal, and local infiltration (see Fig. 16-1 ).
Lumbar Epidural Analgesia/Anesthesia
Epidural blockade is a neuraxial anesthetic used to provide analgesia during labor or surgical anesthesia for vaginal or cesarean delivery. Epidural analgesia offers the most effective form of pain relief and is used by the majority of women in the United States. In most obstetric patients, the primary indication for epidural analgesia is the patient’s desire for pain relief. Medical indications for epidural analgesia during labor may include anticipated difficult intubation due to morbid obesity or other causes, a history of malignant hyperthermia, selected forms of cardiovascular and respiratory disease, and prevention or treatment of autonomic hyperreflexia in parturients with a high spinal cord lesion. The technique uses a large-bore needle (16, 17, or 18 gauge) to locate the epidural space. Next, a catheter is inserted through the needle, and the needle is removed over the catheter. After aspirating the catheter, a test dose of local anesthetic with a “marker” such as epinephrine may be given first to be certain the catheter has not been unintentionally placed in the subarachnoid (spinal) space or in a blood vessel. Intravascular placement will lead to maternal tachycardia because of the epinephrine, and rapid onset of sensory and motor block will occur if the local anesthetic is injected into the spinal fluid. Once intravascular and intrathecal placement have been ruled out, local anesthetic is injected through the catheter, which remains taped in place to the mother’s back to enable subsequent injections throughout labor ( Fig. 16-5 ; see also Fig. 16-1 ). Thus it is often called continuous epidural analgesia . Anesthesiologists also use a technique described as segmental epidural analgesia ( Fig. 16-6 ), in which low concentrations of local anesthetic (<0.25% bupivacaine) are injected at L2 to L5 and affect the small, easily blocked sympathetic nerves that mediate early labor pain but spare the sensation of pressure and motor function of the perineum and lower extremities. The patient should be able to move about in bed and perceive the impact of the presenting part on the perineum.
A dilute local anesthetic combined with an opioid such as fentanyl is administered for maintenance of epidural analgesia. Although the administration may be by continuous infusion at a rate of 5 to 15 mL/hr, patient-controlled epidural analgesia (PCEA) allows for patient-controlled epidural boluses combined with a continuous infusion. More recently, programmed epidural boluses have been combined with patient-controlled boluses as supplements. Patients vary in their responses to local anesthetics, and infusions may need to be adjusted to a lower rate or concentration if the patient develops excessive motor block. If perineal anesthesia is needed for delivery, a larger volume of local anesthetic can be administered at that time through the catheter (see Fig. 16-6 ). Alternatively, for perineal anesthesia, the obstetrician can perform a pudendal block or provide local infiltration of the perineum.
A variant of the epidural technique involves passing a small-gauge pencil-point spinal needle through the epidural needle before catheter placement. This combined spinal-epidural (CSE) technique provides more rapid onset of analgesia using a very small dose of opioid or a local anesthetic and opioid combination. An RCT in a private practice setting compared CSE and traditional epidural analgesia in 800 term parturients. They found that patients who received CSE had better pain scores during the first stage of labor and required fewer top-ups by the anesthesiologist, an important consideration when anesthesia manpower is limited. Some practitioners have used this technique to allow parturients to ambulate during labor (the “walking epidural”) because there is little or no interference with motor function. Because the dose of drug used in the subarachnoid space is much smaller than that used for epidural analgesia, the risks of local anesthetic toxicity or high spinal block are avoided. Side effects of spinal opioids are usually mild and easily treated and include pruritus and nausea.
Nonreassuring fetal heart rate changes may occur more often in patients who receive combined spinal-epidural analgesia than in those who receive epidural analgesia alone. Although the incidence of hypotension is similar between the two techniques, the etiology of fetal bradycardia after spinal analgesia may relate more to uterine hypertonus than to hypotension. Maternal endogenous catecholamines, specifically the β-agonist epinephrine, decrease rapidly with the onset of spinal analgesia. Loss of β-agonist activity may result in uterine hypertonus, especially in the presence of exogenous oxytocin infusions. Fortunately, these nonreassuring FHR changes do not seem to affect labor outcome. In a review of 2380 deliveries in a community hospital, no increase was found in emergency cesarean delivery in the 1240 patients who received neuraxial analgesia for labor (98% of which were CSE) compared with the 1140 patients who received systemic or no medication. A systematic review of randomized comparisons of intrathecal opioid analgesia versus epidural or parenteral opioids in labor found that the use of intrathecal opioids significantly increased the risk of fetal bradycardia (OR, 1.8; 95% CI, 1.0 to 3.1). However, the risk of cesarean delivery for FHR abnormalities was similar in the two groups (6.0% vs. 7.8%). FHR should be monitored during and after the administration of either epidural or intrathecal medications to allow for timely intrauterine resuscitation.
Complications of Neuraxial Blocks
The Serious Complication Repository Project of the Society of Obstetric Anesthesia and Perinatology (SOAP) reported that high neuraxial block, respiratory arrest in labor and delivery, and unrecognized spinal catheters were the most frequently reported serious complications in more than 257,000 anesthesia procedures over a 5-year study period ( Table 16-3 ). Other side effects of epidural or CSE analgesia include hypotension, local anesthetic toxicity, allergic reaction, neurologic injury, and postdural puncture headache. In addition, epidural analgesia use may increase the rate of intrapartum fever and can lengthen the second stage of labor. The effect of epidural analgesia on labor progression is discussed in detail below.
| COMPLICATION | COMPLICATIONS (N) | INCIDENCE | 95% CI |
|---|---|---|---|
| Postdural puncture headache | 1647 | 1 : 144 | 1 : 137, 1 : 151 |
| High neuraxial block | 58 | 1 : 4336 | 1 : 3356, 1 : 5587 |
| Respiratory arrest in labor suite | 25 | 1 : 10,042 | 1 : 6172, 1 : 16,131 |
| Unrecognized spinal catheter | 14 | 1 : 15,435 | 1 : 9176, 1 : 25,634 |
| Serious neurologic injury | 27 | 1 : 35,923 | 1 : 17,805, 1 : 91,244 |
| Epidural abscess/meningitis | 4 | 1 : 62,866 | 1 : 25,074, 1 : 235,620 |
| Epidural hematoma | 1 | 1 : 251,463 | 1 : 46,090, 1 : 10,142,861 |
Because epidural anesthesia is associated with side effects and complications, some of which are dangerous, those who administer it must be thoroughly familiar not only with the technical aspects of its administration but also with the signs and symptoms of complications and their treatment. Specifically, the ASA and ACOG have stated: “Persons administering or supervising obstetric anesthesia should be qualified to manage the infrequent but occasionally life-threatening complications of major regional anesthesia such as respiratory and cardiovascular failure, toxic local anesthetic convulsions, or vomiting and aspiration. Mastering and retaining the skills and knowledge necessary to manage these complications requires adequate training and frequent application.” The ASA practice guidelines also state that “When a neuraxial technique is chosen, appropriate resources for the treatment of complications (e.g., hypotension, systemic toxicity, high spinal anesthesia) should be available.”
Hypotension
Hypotension is defined variably but most often as a systolic blood pressure less than 100 mm Hg or a 20% decrease from baseline. It occurs after approximately 10% of spinal or epidural blocks given during labor. Hypotension occurs primarily as a result of the effects of local anesthetic agents on sympathetic fibers, which normally maintain blood vessel tone. Vasodilation results in decreased venous return of blood to the right side of the heart, with subsequent decreased cardiac output and hypotension. A secondary mechanism may be decreased maternal endogenous catecholamines following pain relief. Hypotension threatens the fetus by decreasing uterine blood flow. However, when recognized promptly and treated effectively, few if any untoward effects result in either mother or fetus. Special care should be taken to avoid or promptly treat hypotension, especially when acute or chronic fetal compromise is suspected.
Treatment of hypotension begins with prophylaxis, which includes IV access for volume expansion and administration of pressors and left uterine displacement to prevent aortocaval compression by the gravid uterus and to maintain cardiac preload and cardiac output. Isotonic crystalloid boluses should not contain dextrose because of the association with subsequent neonatal hypoglycemia. Proper treatment of hypotension depends on immediate diagnosis; therefore the individual administering the anesthesia must be present and attentive. Once diagnosed, hypotension is corrected by increasing the rate of IV fluid infusion and exaggerating left uterine displacement. If these simple measures do not suffice, a vasopressor is indicated.
The vasopressor of choice has evolved from ephedrine given in 5- to 10-mg doses to phenylephrine in 50- to 100-µg increments. Ephedrine is a mixed α- and β-agonist and was thought to be less likely to compromise uteroplacental perfusion than the pure α-agonists, but ephedrine has been associated with fetal tachycardia. Recent clinical studies have suggested that phenylephrine may be given to safely treat hypotension during neuraxial anesthesia for cesarean delivery and that it leads to higher umbilical artery pH values in the fetus and results in less maternal nausea and vomiting. When compared with phenylephrine for treatment of hypotension following neuraxial analgesia in multiple randomized trials, ephedrine was associated with higher degrees of fetal acidosis. The β-agonist action of ephedrine may increase fetal oxygen requirements and can lead to hypoxia in cases of uteroplacental insufficiency. Phenylephrine corrects maternal hypotension, apparently without causing clinically significant uterine artery vasoconstriction or decreased placental perfusion even in extremely high doses. Rather than causing abnormal increases in systemic vascular resistance, these doses may simply return vascular tone to normal after spinal anesthesia. It is also possible that constricting peripheral arteries may preferentially shunt blood to the uterine arteries. The parturient has decreased sensitivity to all vasopressors, and that may also protect the fetus from excessive vasoconstriction. The α-adrenergic agents, such as methoxamine and phenylephrine, cause reflex bradycardia that may be useful when a parturient is excessively tachycardic in association with hypotension, or if tachycardia associated with ephedrine would be detrimental. Ephedrine may be preferable if the patient’s heart rate is below 70 at baseline.
Local Anesthetic Toxicity
The incidence of systemic local anesthetic toxicity (high blood concentrations of local anesthetic) after obstetric lumbar epidural analgesia is less than 1 in 250,000. Cases of local anesthetic toxicity were absent from the most recent review of the ASA Closed Claims Project database. Toxicity occurs when the local anesthetic is injected into a blood vessel, rather than into the epidural space, or when too much is administered even though injected properly. These reactions can also occur during placement of pudendal or paracervical blocks. All local anesthetics have maximal recommended doses, and these should not be exceeded. For example, the maximum recommended dose of lidocaine is 4 mg/kg when used without epinephrine and 7 mg/kg when used with epinephrine. Epinephrine delays and decreases the uptake of local anesthetic into the bloodstream. Package inserts for all local anesthetics contain appropriate dosing information ( Table 16-4 ).
| WITH EPINEPHRINE * | WITHOUT EPINEPHRINE | |||
|---|---|---|---|---|
| LOCAL ANESTHETIC | mg/kg | DOSE (mg/70 kg) | mg/kg | DOSE (mg/70 kg) |
| Bupivacaine | 3.0 | 210 | 2.5 | 175 |
| Chloroprocaine | 14.0 | 980 | 11.0 | 770 |
| Etidocaine | 5.5 | 385 | 4.0 | 300 |
| Lidocaine | 7.0 | 490 | 4.0 | 300 |
| Mepivacaine | – | – | 5.0 | 350 |
| Tetracaine | – | – | 1.5 | 105 |
Local anesthetic reactions have two components, central nervous system (CNS) and cardiovascular. Usually, the CNS component precedes the cardiovascular component. Prodromal symptoms of the CNS reaction include excitation, bizarre behavior, ringing in the ears, and disorientation. These symptoms may culminate in convulsions, which are usually brief. After the convulsions, cognitive depression follows, manifested by the postictal state. The cardiovascular component of the local anesthetic reaction usually begins with hypertension and tachycardia but is soon followed by hypotension, arrhythmias, and in some instances, cardiac arrest. Thus the cardiovascular component also has excitant and depressant characteristics. Often the CNS component occurs without the more serious cardiovascular component, although bupivacaine may represent an exception to this principle. Resuscitation of patients who receive an intravascular injection of bupivacaine is extremely challenging, likely owing to the prolonged blocking effect on sodium channels. Laboratory evidence supports bupivacaine’s increased cardiotoxicity over equianalgesic doses of other amide local anesthetics such as ropivacaine and lidocaine. The manufacturers of bupivacaine have recommended that the 0.75% concentration not be used in obstetric patients or for paracervical block. However, use of a more dilute concentration does not guarantee safety; bupivacaine and all local anesthetics should be administered by slow, incremental injection.
Adverse events due to local anesthetic toxicity have decreased because of greater emphasis on incremental dosing and use of a test dose, typically one containing 15 µg of epinephrine, to exclude unintentional IV or subarachnoid catheter placement. Others have questioned the lack of specificity of test doses during labor and the potential harm to the fetus or hypertensive mother. Intravascular injection of 15 µg epinephrine produces maternal tachycardia, which may be difficult to differentiate from that seen during a contraction. Nonreassuring fetal heart tones due to decreased uterine blood flow may also occur after administration of intravascular epinephrine, especially when the fetus is already compromised.
Treatment of a local anesthetic reaction depends on recognizing the signs and symptoms. Prodromal symptoms should trigger the immediate cessation of the injection of local anesthetic. If convulsions have already occurred, treatment is aimed at maintaining proper oxygenation and preventing the patient from harming herself. Convulsions use considerable amounts of oxygen, which results in hypoxia and acidosis. Should the convulsions continue for more than a brief period, small IV doses of propofol (30 to 50 mg) or a benzodiazepine (2 to 5 mg midazolam) are useful. The cardiac and respiratory depressant effects of these agents add to the depressant phase of the local anesthetic reaction; therefore appropriate equipment and personnel must be available to maintain oxygenation and a patent airway and to provide cardiovascular support. Rarely, succinylcholine is needed for paralysis to prevent the muscular activity and to facilitate ventilation and perhaps intubation. In cases of complete cardiac collapse, delivery of the infant may facilitate maternal resuscitation. IV lipid emulsion may be an effective therapy for cardiotoxic effects of lipid-soluble local anesthetics such as bupivacaine or ropivacaine. Intralipid should be available wherever regional anesthesia is provided.
The SOAP developed a consensus statement on the management of cardiac arrest in pregnancy that aims to improve maternal resuscitation by providing health care providers critical information relevant to maternal cardiac arrest. The document includes key cognitive and technical interventions to be undertaken that include immediate basic life support (BLS) and calls for help, chest compressions monitored by capnography if possible, manual left uterine displacement while supine on a backboard, defibrillation, airway management and ventilation, IV access to administer drugs per current advanced cardiovascular life support (ACLS) guidelines, and perimortem cesarean or operative vaginal delivery. Delivery should be performed as soon as possible, striving to make the skin incision for cesarean delivery at 4 minutes after the start of cardiac arrest.
Allergy to Local Anesthetics
The two classes of local anesthetics are amides and esters . A true allergic reaction to an amide-type local anesthetic (e.g., lidocaine, bupivacaine, ropivacaine) is extremely rare. Allergic reactions to the esters (2-chloroprocaine, procaine, tetracaine) are also uncommon but can occur and are often associated with a reaction to para-aminobenzoic acid (PABA) in skin creams or suntan lotions. When a patient reports that she is “allergic” to local anesthetics, she is frequently referring to a normal reaction to the epinephrine that is occasionally added to local anesthetics, particularly by dentists. Epinephrine can cause increased heart rate, pounding in the ears, and nausea—symptoms that may be interpreted as an allergic reaction. Therefore it is important to document the situation in which the reaction occurred.
High Spinal OR “Total Spinal” Anesthesia
This complication occurs when the level of anesthesia rises dangerously high and results in paralysis of the respiratory muscles, including the diaphragm (C3-C5). The incidence of total spinal anesthesia after neuraxial blocks is 1 in 4336 (see Table 16-3 ). This is the most frequent complication encountered secondary to spinal or epidural anesthesia. Total spinal anesthesia can result from a miscalculated dose of drug or unintentional subarachnoid injection during an epidural block. The ASA Closed Claims Project analysis of obstetric anesthesia liability claims found that the most common cause of maternal death or brain damage in neuraxial anesthesia claims was high block; 80% were associated with dosing epidural anesthesia and 20% involved spinal anesthesia. The accessory muscles of respiration are paralyzed earlier, and their paralysis may result in apprehension and anxiety and a feeling of dyspnea. The patient usually can breathe adequately as long as the diaphragm is not paralyzed, but treatment must be individualized. Dyspnea, real or imagined, should always be considered an effect of paralysis until proved otherwise. Cardiovascular effects, including hypotension and even cardiovascular collapse, may accompany total spinal anesthesia.
Treatment of total spinal anesthesia includes rapidly assessing the true level of anesthesia; therefore individuals who administer major regional anesthesia should be thoroughly familiar with dermatome charts ( Fig. 16-7 ) and should also be able to recognize what a certain sensory level of anesthesia means with regard to innervation of other organs or systems. For example, a T4 sensory level may represent total sympathetic nervous system blockade. Numbness and weakness of the fingers and hands indicates that the anesthesia has reached the cervical level (C6-C8), which is dangerously close to the innervation of the diaphragm. If the diaphragm is not paralyzed, the patient is breathing adequately, and cardiovascular stability is maintained, administration of oxygen and reassurance may suffice. If the patient remains anxious or if the level of anesthesia seems to involve the diaphragm, assisted ventilation is indicated, and endotracheal intubation will be necessary to protect the airway. In addition, cardiovascular support is provided as necessary. Delay in treatment due to inadequate monitoring, absence of the anesthesia provider, lack of airway equipment or emergency drugs in the labor room, or delay in resuscitation during transfer of the patient to the operating room for delivery will worsen outcome. With prompt and adequate treatment, serious sequelae should be extremely rare.
