Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery

Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery.

Rational use of regional anesthesia necessitates an understanding of the pain pathways involved during labor. Labor is traditionally divided into three distinct stages:

·  First stage: begins with the onset of regular contractions and ends with complete cervical dilation.

·  Second stage: begins when the cervix is completely dilated and ends with delivery of the fetus.

·  Third stage: begins after delivery of the fetus and con-cludes with delivery of the placenta.

The first stage of labor is associated with uterine and cer-vical pain mediated by spinal segments T₁₀–L₁ (Fig. 59.1). Local anesthetics administered to the epidural, spinal, or caudal spaces readily anesthetize these pain pathways. In addition, subarachnoid opioids and paracervical blocks can be used for pain relief during the first stage of labor.

Caudal anesthesia is rarely used because of the risk of inadvertent fetal scalp penetration and the associated high fetal levels of local anesthetic.

The second stage of labor is associated with perineal and vaginal distention mediated by spinal segments S₂–S₄. Epidural, spinal, and caudal anesthetics are also effective during the second stage of labor. In addition, pudendal nerve blocks can be used for second-stage analgesia.

Epidural analgesia is the most popular technique for the relief of labor pain. Its popularity is first and foremost related to its efficacy. Women can obtain almost complete relief from the pain of labor. From the anesthesiologist’s perspective, because a catheter is threaded into the epidural space, it is also a versatile technique. During the earlier stages of labor, dilute solutions of local anesthetic can be used to achieve analgesia. As labor progresses, a more con-centrated solution of local anesthetic may be necessary or an adjunct, such as an opioid, may be needed. Additionally, the epidural catheter can be utilized to maintain a low dermatomal level of anesthesia for labor (T₁₀–L₁) and, when needed, the dermatomal level can be raised to T₄ for cesarean section.

Patient-controlled epidural analgesia (PCEA) is a tech-nique that allows the patient to self-medicate, thereby controlling her own analgesia. Compared with continuous infusion or intermittent bolus techniques, PCEA is associ-ated with a lower total dose of local anesthetic, less motor blockade, and fewer interventions by anesthesiologists. Although maternal satisfaction may be greater with PCEA, the above-stated advantages have not been documented in all studies. Therefore, this technique is not routinely offered.

A commonly used PCEA regimen is bupivacaine 0.0625% with fentanyl 2 μg/mL with the following PCEA settings: basal rate of 10 mL/hr, bolus dose of 5 mL, 10 minute lockout, and a 30 mL/hr maximum limit. A basal rate is not always used because it may be associated with a greater total milligram dose of local anesthetic when compared with the total milligram dose when a basal rate is used. Theoretical risks of PCEA, such as high der-matomal levels or overdose, have been described in the general surgical patient. Overdose occurs because of catheter migration into the subarachnoid space or from excessive administration by the patient or a helpful family member. To date, these complications have not been reported in the parturient during labor.

There are a number of disadvantages with labor epidural analgesia that have prompted the search for alter-native techniques. One disadvantage is the time it takes to provide analgesia to the patient. The time from epidural catheter placement until the patient is comfortable is vari-able, but depending on the local anesthetic used can take up to 30 minutes. Other disadvantages of labor epidural analgesia include: maternal hypotension, inadequate anal-gesia (15–20% of cases), and motor blockade, even with the very dilute local anesthetic solutions.

Subarachnoid opioids offer rapid, intense analgesia with minimal changes in blood pressure or motor function. Most patients can, if desired, ambulate with this technique. The opioid is usually administered as part of a combined spinal-epidural (CSE) technique where a spinal and an epidural are performed at the same time. After locating the epidural space in the usual manner, a long small-gauge spinal needle is inserted through the epidural needle into the subarachnoid space. An opioid (usually fentanyl 25 μg or sufentanil 5 μg), either alone or in combination with a local anesthetic, is administered through the spinal needle. The spinal needle is removed and an epidural catheter is inserted for future use. Analgesia begins within 3–5 min-utes and lasts 1–1.5 hours.

There are several advantages to the CSE technique. The primary advantage is the rapid (3–5 min) onset of analge-sia. There is also less motor blockade. Because of these advantages there is greater satisfaction by women who receive a CSE than those who receive the “standard” epidural technique of bupivacaine 0.25%.

There are some concerns about CSE, most of which are only theoretical but have not been documented. There is no increased risk of subarachnoid catheter migration of the epidural catheter. Metallic particles are not produced as a result of passing one needle through another. The incidence of postdural puncture headache is not increased by the intentional dural puncture. Fetal bradycardia in association with a hypertonic uterus may occur immedi-ately or shortly after induction of either epidural or subarachnoid labor analgesia. There does not appear to be any difference in the incidence of fetal heart rate decel-erations or emergent cesarean section following labor epidural or spinal anesthesia. One proposed theory for increased uterine tone after CSE is related to the rapid decrease in maternal catecholamines associated with the rapid onset of pain relief. The decrease in circulating β-adrenergic agonists results in a predominance of α activ-ity, which causes uterine contractions. If this should occur, treatment is with subcutaneous terbutaline or intravenous nitroglycerin.