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A variety of regional techniques are used in obstetric anesthesia to provide optimal analgesia with minimal depressant effects on the mother and fetus. These techniques are the most effective means of providing analgesia for labor and delivery. Regional techniques present the most flexible, effective, and least depressant options when compared with parenteral and inhalation techniques. Regional analgesia does not produce drug-induced depression in the mother or fetus. The most commonly performed regional techniques for labor are epidural, spinal, and combined spinal-epidural. Less frequently, lumbar sympathetic blocks are performed.[104] Paracervical, pudendal, and local perineal infiltration techniques are occasionally performed by the obstetrician. Each technique has advantages and disadvantages and can be used to block pain transmission during parturition.
It is important to assess all patients before placement of a regional block by obtaining a focused medical and obstetric history, performing a clinical examination, and evaluating the airway. The use of herbal medications by the general population is gaining in popularity,[105] and obstetric patients are no different. A 7.1% incidence of herbal remedy use by parturients after 20 weeks' gestation has recently been reported.[106] Preparations containing garlic, ginkgo, ginseng, ginger, and feverfew may have anesthetic implications.
The obstetric plan and fetal well-being should be noted during this preoperative assessment. Informed consent must be obtained, and the anesthesiologist should explain the procedure and the potential complications of the technique. A retrospective study of patients' satisfaction with labor analgesia and their attitude toward the consent process revealed that distress during labor did not interfere with the women's ability to understand the information associated with the consent process before epidural placement. Furthermore, patients thought that the most valuable information received was either from the anesthesiologist who placed the epidural or from an antenatal course. Patients also wanted to know about the potential complications with the greatest morbidity and mortality before consenting.[107] A full check of emergency equipment should be performed to ensure the immediate availability of resuscitative drugs and equipment. An intravenous infusion should be started, and appropriate maternal and fetal monitoring should be in place before starting the procedure.
Lumbar epidural analgesia offers a safe and effective method of pain relief during labor. It is versatile and may be extended to provide anesthesia for instrumental or operative delivery. Low doses of local anesthetic or opioid combinations are administered (usually by infusion) to provide a continuous T10-L1 sensory block during the first stage of labor. Further supplementation may be required during the late first stage and second stage to achieve a sacral block. The benefits of epidural analgesia include effective pain relief without appreciable motor block, reduction in maternal catecholamines, and a means to rapidly achieve surgical anesthesia. Despite numerous relative contraindications, there are very few absolute contraindications to neuraxial analgesia. Such contraindications
The issue of whether a test dose is needed when administering labor epidural analgesia is controversial. Because ultradilute solutions are commonly used and aspiration is often diagnostic, some authors believe that a test dose is unnecessary.[108] However, because catheter aspiration is not always predictive (especially when using a single-orifice epidural catheter), others maintain the importance of a test dose to improve detection of intrathecal or intravascular placement of an epidural catheter.[109] Part of the controversy surrounding the testing of epidural catheters involves the use of epinephrine. Epinephrine has been shown to produce a reliable increase in heart rate in volunteers and surgical patients when the epidural has been sited in a blood vessel.[110] However, in a laboring patient, maternal heart rate variability from the pain of uterine contractions may confuse interpretation of the heart rate response, and intravenous epinephrine may have deleterious effects on uterine blood flow.[111] Means to improve the reliability of epinephrine include injecting the dose between uterine contractions and repeating the test dose when the response is equivocal. However, the lack of sensitivity and specificity of the test dose calls into question its usefulness as a diagnostic tool. Leighton and colleagues have described an alternative means of testing an epidural catheter for intravascular placement. They advocate the injection of 1 to 2 mL of air into the epidural catheter while listening over the precordium with the maternal external Doppler monitor for evidence of air.[112] If continuous infusion of dilute local anesthetic is administered and the patient remains comfortable without a motor block, proper epidural catheter placement is likely. That is, if the epidural catheter were intravascular, the patient should have inadequate pain relief, and if the catheter were subarachnoid, a solid motor block would develop. Although infusions of ultradilute local anesthetics do not pose a serious threat, such is not true of concentrated local anesthetics used for operative delivery. Some authors have suggested that a test dose is essential for any parturient receiving epidural anesthesia.[109] Regardless of the technique used, the safe practice of administering labor epidural analgesia dictates initial catheter aspiration, incremental injections, and continuous monitoring for evidence of local anesthetic toxicity.
A single-shot subarachnoid injection of local anesthetic or opioid provides effective and rapid onset of labor analgesia. It is particularly suitable in very early labor or in a very distressed parturient to enable epidural placement under more controlled conditions. Single-shot spinals may also be used for instrumental deliveries in women who do not have an indwelling epidural catheter. Though used for routine labor analgesia in some hospitals, this technique does not provide the flexibility of an indwelling catheter. Continuous spinal analgesia with a "macrocatheter" may be considered in cases of accidental dural puncture or very high-risk parturients; it provides excellent analgesia. This practice may also reduce the incidence of post-dural puncture headache (PDPH) after an accidental dural puncture with an epidural needle.[113] It is imperative to inform all personnel involved in the care of a parturient with a spinal catheter in place to avoid accidental overdose of local anesthetic. Small-bore spinal ("micro") catheters were introduced into clinical practice in the late 1980s and quickly gained popularity because of convenience, fast onset, and the potential for decreased risk of PDPH. However, reports of cauda equina syndrome associated with their use for cesarean section led the Food and Drug Administration (FDA) to withdraw these microcatheters from clinical practice. Possible explanations proposed for the occurrence of cauda equina syndrome included inadequate mixing of local anesthetic within the intrathecal space and the use of high concentrations of potentially neurotoxic local anesthetic (5% lidocaine) that can result in neural damage.[114] [115] Recent work revisiting microcatheters in labor is still ongoing and may provide the necessary safety evidence to allow their reintroduction into clinical practice. [116]
The combined spinal-epidural (CSE) technique is widely used in obstetric practice to provide optimal analgesia for parturients. It offers effective, rapid-onset analgesia with minimal risk of toxicity or impaired motor block. In addition, this technique provides the ability to prolong the duration of analgesia, as required, through the use of an epidural catheter. Furthermore, should an operative delivery become necessary, that same catheter can be used to provide operative anesthesia. The onset of spinal analgesia is almost immediate, and the duration is between 2 and 3 hours, depending on which agent or agents are chosen. The duration of spinal analgesia, however, has been found to be decreased when administered to a woman in advanced labor versus one in early labor.[117] Patients may have greater satisfaction with CSE than with standard epidurals, perhaps because of a greater feeling of self-control.[118] The original description of spinal labor analgesia involved sufentanil or fentanyl, [119] but the addition of isobaric bupivacaine to the opioid produces a greater density of sensory blockade while still minimizing motor blockade.[120] Originally, 25 µg of fentanyl or 10 µg of sufentanil was advocated, but more recent studies have suggested using smaller doses of opioid combined with a local anesthetic.[121] For example, many clinicians are now routinely using 5 µg of sufentanil or 15 µg of intrathecal fentanyl. Recent studies have suggested that ropivacaine and levobupivacaine can be substituted for intrathecal bupivacaine to provide labor analgesia.[122] [123]
The CSE technique has also made ambulation possible for many women receiving neuraxial analgesia. Because of the minimal motor block with this technique, it has been termed "the walking epidural." This term, however, is imprecise because many neuraxial techniques allow ambulation in labor and many women who receive CSE never actually ambulate. In addition to the advantage of rapid onset of pain relief, the CSE technique may reduce
Many methods may be used to perform a CSE block, including (1) epidural catheter insertion followed by spinal needle placement at a lower interspace; (2) an epidural needle beside the spinal needle at the same interspace with the use of specially designed needles; and the most commonly used, (3) the "needle-through-needle" technique, which involves identification of the epidural space and insertion of a long fine-bore atraumatic (pencil point) spinal needle through the epidural needle until the tip of the spinal needle pierces the dura as shown in Figure 58-9 . Free flow of cerebrospinal fluid (CSF) confirms correct placement, and the opioid, alone or in combination with a local anesthetic, is then injected. After spinal injection, the spinal needle is withdrawn, and the epidural catheter is placed approximately 4 to 5 cm into the epidural space via the epidural needle. Side effects of intrathecal opioid include pruritus, nausea and vomiting, and urinary retention. Respiratory depression as a result of cephalad spread of opioid is rare but has occurred when using lipid-soluble opioids. Use of a continuous epidural infusion of dilute local anesthetic plus opioid (0.0625% to 0.1% bupivacaine) provides sensory analgesia without motor block; consequently, it permits many parturients to ambulate during labor. Before ambulation, however, women should be observed for the preceding 30 minutes to ensure maternal and fetal well-being, and they should be assessed for adequate motor function.
Figure 58-9
Illustration depicting the epidural and spinal spaces
during combined spinal-epidural insertion.
Reports in the literature suggest an increased frequency of non-reassuring FHR tracings and fetal bradycardia associated with CSE.[125] [126] The etiology of fetal bradycardia after CSE remains elusive, but it may be related to an acute reduction in circulating maternal catecholamine levels after the quick onset of analgesia. In addition, it has been postulated that an imbalance between epinephrine/norepinephrine levels causes unopposed α-adrenoceptor effects on uterine tone and decreases uterine blood flow. However, preliminary reports suggest that there may be no alteration in uteroplacental blood flow.[127]
The resulting fetal bradycardia is usually short lived and typically resolves within 5 to 8 minutes.[125] A retrospective study of 1240 patients who received regional labor analgesia (mostly CSE) and 1140 patient who received systemic medication or no analgesia demonstrated no significant difference in the rate of cesarean delivery, with rates of 1.3% and 1.4%, respectively. That study also reported that no emergency cesarean deliveries for acute fetal "distress" were necessary in the absence of obstetric indications up to 90 minutes after intrathecal sufentanil administration.[56]
Most obstetric anesthesiologists now advocate the use of continuous infusions of dilute local anesthetic solutions. Local anesthetics such as bupivacaine, ropivacaine, and levobupivacaine in concentrations ranging from 0.0625% to 0.125% are used either alone or in combination with opioid. The addition of epinephrine may enhance the quality of the analgesia by reducing vascular uptake and systemic absorption of local anesthetics and by a direct agonist effect on α2 spinal receptors.[128] [129] From a parturient's perspective, a continuous infusion offers numerous benefits because it allows for a continuous level of comfort rather than waiting for intermittent epidural top-ups. Typical doses for continuous infusions used for labor analgesia are reviewed in Table 58-6 .
| Drug | Initial Injection | Continuous Infusion |
|---|---|---|
| Bupivacaine | 10–15 mL of a 0.25%–0.125% solution | 0.0625%–0.125% solution at 8–15 mL/hr |
| Ropivacaine | 10–15 mL of a 0.1%–0.2% solution | 0.5%–0.2% solution at 8–15 mL/hr |
| Fentanyl | 50–100 µg given in a 10-mL volume | 1–4 µg/mL |
| Sufentanil | 10–25 µg given in a 10-mL volume | 0.03–0.05 µg/mL |
| Epinephrine |
|
1:200,000–1:800,000 concentration |
| From Birnbach DJ (ed): Ostheimer's Manual of Obstetric Anesthesia, 3rd ed. New York, Churchill Livingstone, 2000, p 92. | ||
Patient-controlled epidural analgesia (PCEA) is a safe and effective technique.[130] This method of delivery offers equally effective labor analgesia and excellent patient satisfaction. It reduces the total amount of local anesthetic used; consequently, it lessens unwanted effects such as motor block and hypotension. It also reduces the demands on staff on the labor floor, and it gives many patients a feeling of empowerment. Typically, after analgesia is established by means of either a spinal or epidural, the catheter is connected to the PCEA device, and the patient can then self-administer further boluses as required. Some authors advocate a continuous infusion with patient-controlled top-ups, whereas others suggest a bolus-only technique.[131] Suggested regimens for PCEA settings are outlined in Table 58-7 .
The paracervical block is an alternative technique for a pregnant woman who does not want or cannot receive a neuraxial block. It is a relatively simple block to perform, provides pain relief for the first stage of labor, and does not adversely affect the progress of labor. Local anesthetic is injected submucosally into the fornix of the vagina lateral to the cervix to block nerve transmission through the paracervical ganglion, which lies lateral and posterior to the junction of the cervix and uterus. Because this block does not affect somatic sensory fibers from the perineum, it offers no pain relief for the second stage of labor. Although this technique is still used by obstetricians for nonobstetric surgery, its use in obstetrics has been limited by profound fetal bradycardia, systemic local anesthetic toxicity, postpartum neuropathy, and infection.[132] The etiology of this fetal bradycardia appears to be related to decreased uterine blood flow and high fetal blood levels of local anesthetic.[133] [134]
The pudendal nerves are derived from the lower sacral nerve roots
(S2–S4) and provide sensory innervation for the lower part of the vagina, the
vulva, and the perineum, as well as motor innervation to the perineal muscles. The
nerves are easily anesthetized through a transvaginal approach, which is accomplished
by depositing local anesthetic behind each sacrospinous ligament.[135]
This nerve block provides satisfactory analgesia for vaginal delivery as well as
outlet forceps delivery. However, it is generally inadequate for midforceps delivery,
repair of vaginal lacerations, or exploration of the uterine cavity.[136]
Maternal complications from this technique are rare, but include systemic local
anesthetic toxicity, infection, and
| Mode | Epidural Solution | Basal Infusion Rate (mL/hr) | Bolus Dose (mL) | Lockout Interval (min) | Hourly Maximum (mL) |
|---|---|---|---|---|---|
| Demand only | Bupivacaine (0.125%–0.25%) | 0 | 4 | 10–20 | 15–20 |
| Continuous infusion plus demand | Bupivacaine (0.0625%–0.125%) | 4–8 | 2–4 | 10–20 | 15–20 |
| From Birnbach DJ (ed): Ostheimer's Manual of Obstetric Anesthesia, 3rd ed. New York, Churchill Livingstone, 2000, p 93. | |||||
Another nerve block that can be considered an alternative to central neuraxial blocks is the paravertebral lumbar sympathetic technique. This block can be used to impede transmission of pain from the uterus during the first stage of labor.[138] Although it is a technically difficult block to perform, it appears to be associated with far fewer complications than paracervical blockade is.
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