OBSTETRIC ANALGESIA AND ANESTHESIA

Introduction. Although the use of anesthesia or analgesia during labor and delivery must be individualized to each patient, the common goal is to maximize outcomes for both the mother and the neonate. Some laboring patients may not want or need anesthesia; however, others may desire a higher level of pain control or the mode of delivery may necessitate anesthetic intervention.Definitions. Analgesia is defined as relief of pain without the loss of consciousness or motor function. Anesthesia is defined as the loss of feeling or sensation and can include the loss of consciousness, motor power, and autonomic reflex activity.

Types of analgesia or anesthesia. The spectrum of anesthetic techniques useful in obstetrics includes the following: systemic, local infiltration, peripheral nerve block, major regional analgesia and anesthesia (spinal and epidural blocks), and general anesthesia. Each technique entails varying levels of pain control, alterations to the progression of labor, and effects on the parturient and fetus.

Analgesia for labor. The goal is to achieve adequate pain control without depressing the parturient or fetus or affecting the progress of labor. Nonpharmacologic approaches to pain control (e.g., Lamaze method and attendance of a doula) may be desired by the patient. However, systemic analgesia, epidural anesthesia, and combined spinal-epidural techniques are more often used.

Analgesia and anesthesia for vaginal delivery. For an anticipated vaginal birth, the caregiver must consider various factors when selecting an analgesic or anesthetic, including effectiveness of analgesia, maternal safety, fetal safety, alterations to maternal pushing efforts, and alterations to the musculature of the birthing canal. Major regional anesthesia (epidural or spinal block) is the technique of choice; local infiltration of the perineum and paracervical and pudendal blocks are used less frequently. Rarely, general anesthesia can be used for emergency forceps delivery, shoulder dystocia, or difficult vaginal breech delivery.

Analgesia and anesthesia for cesarean section. The anticipated length of surgery, medical conditions of the mother, maternal and fetal safety, and urgency of the delivery should dictate the type of anesthetic administered. Major regional anesthesia and, less often, general anesthesia are used. Rarely, local infiltration can be used in cases of emergency cesarean section in which rapid general anesthesia is not possible.

Analgesia for postoperative pain. Systemic and regional pain control methods have been found to be quite effective. In particular, patient-controlled intravenous (IV) and epidural anesthesia are often used until the patient can tolerate oral analgesics.Nonpharmacologic techniques. Some patients may prefer to use nonpharmacologic methods to help prepare for and manage the pains of labor and vaginal delivery. Lamaze or Bradley childbirth education are favored by some. Others may desire a doula, a trained layperson, to provide continuous support throughout the labor. The goal is to minimize the amount of pharmacologic intervention, as tolerated.

Systemic analgesia
Indications.
Systemic medications can be given in the latent or active phase of labor for effective pain relief. They can also be used for postoperative pain control.Sedatives and tranquilizers. A wide variety of these medications, such as phenothiazine, promethazine hydrochloride, and hydroxyzine hydrochloride, are used to supplement narcotic analgesia. Although these medications have the added benefit of an antiemetic effect and reduced narcotic demand, they do cause increased sedation.
Advantages. The advantage of this mode of analgesia is the ease of administration (orally, intramuscularly, subcutaneously, intravenously) and relatively low risk to mother and fetus.Limitations. Narcotics may provide inadequate pain relief for many patients.Risks.
The parturient can experience respiratory depression, orthostatic hypotension, nausea, vomiting, and delayed gastric emptying with increased risk of aspiration. The neonate can experience respiratory depression, lower Apgar scores, and neurobehavioral abnormalities. Narcotic administration should be minimized just before delivery to prevent delivery of a depressed neonate. Naloxone hydrochloride can be administered to antagonize the respiratory depression caused by narcotics. The usual dosage of naloxone is 0.1–0.4 mg IV for adults and 0.1 mg/kg IV for neonates.

Local infiltration (field block)
IndicationsVaginal delivery. Local infiltration of an anesthetic agent may be required to perform an episiotomy or repair any lacerations or episiotomies after vaginal delivery. Perineal infiltration with 5–15 mL of 1% lidocaine (or 0.25–0.5% bupivacaine hydrochloride, 2% chloroprocaine hydrochloride, or 1% mepivacaine hydrochloride) can provide sufficient analgesia for an episiotomy or repair and occasionally for an outlet operative delivery. The medication, which should not be mixed with epinephrine, must not be directly injected into a blood vessel. Extravascular placement can be verified by withdrawing on the syringe before injecting any anesthetic agent.Cesarean section. Occasionally, cesarean sections must be performed under local anesthesia in an emergency situation when alternate anesthesia is not immediately available or possible. Dilute concentrations of an agent such as lidocaine (0.5–1.0% to a maximum of 7 mg/kg) or chloroprocaine (1–2%) is used to infiltrate the skin and abdominal wall and bathe the parietal and visceral peritoneum. Local anesthesia alone is usually inadequate pain relief and is used only in rare emergency cases.
Advantages. The advantages of local infiltration are its ease of administration and minimal negative effects on the parturient and fetus.
Limitations. Field block offers no relief from the pains of uterine contractions. In addition, if the caregiver is concerned about a difficult vaginal delivery or a possible cesarean section, the patient should be advised that major regional anesthesia is highly recommended if timing permits.Peripheral nerve block. This form of analgesia involves injection of a local anesthetic agent in the vicinity of discrete peripheral nerves in the pelvis (paracervical or pudendal areas) to achieve pain control.

Paracervical blockIndications.
The paracervical block is a rarely used method of analgesia that can provide relief from uterine contractions. This block involves the transvaginal injection of a total of 10–20 mL of 1% lidocaine (or 2% chloroprocaine) just lateral to the cervix bilaterally at the 4 and 8 o'clock positions). This technique blocks the sensory nerves from uterus, cervix, and upper vagina.Limitations. The sensory fibers from the perineum are not affected. Therefore, the paracervical block has no benefit outside of the first stage of labor. In addition, it is difficult to administer late in the first stage.Risks. Although it is easy to perform and does not cause maternal hypotension, paracervical anesthesia can cause local vasoconstriction, increased uterine tone, and decreased perfusion to the uterus. There is an increased risk for fetal depression and transient fetal bradycardia.

Pudendal block
Indications. This method is used to achieve perineal analgesia and help the patient tolerate the pain of the second stage of labor and any postdelivery repairs. It is administered by transvaginally injecting a total of 10–20 mL of 1% lidocaine (or 2% chloroprocaine) just posterior to the ischial spines bilaterally. This method blocks the pudendal nerve, which provides afferent fibers to the genitalia and perineum.
Limitations. Complete analgesia may require infiltration of the perineum with a local anesthetic. In addition, if a complicated vaginal delivery or possible cesarean section is predicted, major regional anesthesia should be recommended.Risks.
The pudendal block carries little risk to the fetus. Its rare complications to the mother include accidental sciatic nerve block, formation of a hematoma, or puncture of the rectum.Major regional anesthesia and analgesia. This is the most commonly used form of anesthesia today. It involves the injection of anesthetic/analgesic agents into the epidural or subarachnoid (spinal) space to achieve adequate analgesia for vaginal delivery or anesthesia for cesarean section while allowing the parturient to maintain full consciousness.

Epidural anesthesia
Indications. An epidural block can be used for establishing analgesia during labor, analgesia and anesthesia for nonoperative and operative vaginal delivery, and anesthesia for cesarean section. After a cesarean section, postoperative pain can be managed with epidural patient-controlled anesthesia quite successfully.
Application. A 19- or 20-gauge plastic indwelling catheter is placed into the epidural space at the level of L2–L5. Verification of placement into the epidural space includes the inability to aspirate blood or cerebrospinal fluid and the administration of a test dose that does not indicate IV or subarachnoid placement. Repeated epidural injections, patient-controlled pumps, and continuous infusion of a mixture of local anesthetic plus narcotic analgesic (e.g., bupivacaine and fentanyl) has allowed lower concentration of medications to be used for effective pain control with minimal risk to patient and fetus.
Advantages. There is often less fetal depression and respiratory compromise to the mother than with general anesthesia or systemic narcotics. The epidural anesthetic can be titrated to fulfill the pain control needs of the parturient, maintain her full consciousness, and allow her to push in a vaginal delivery. In addition, it is the only mode of anesthesia that can be used throughout all stages of labor and vaginal delivery as well as be dosed for proper anesthesia for a cesarean section.
Limitations. An epidermal block takes longer to initiate than spinal or general anesthesia. Therefore, it is not indicated for expected imminent vaginal delivery or an emergent cesarean section.Contraindications. Possible contraindications include neurologic problems (e.g., sciatica), spine abnormalities, infection at the site, acute maternal hemorrhage, or bleeding disorders.Risks
1. Maternal hypotension. The most common complication of an epidural block is maternal hypotension, which can cause uteroplacental insufficiency and can lead to fetal distress. Prophylactic intravascular volume expansion with 500–1000 mL of lactated Ringer's solution is usually administered before placing an epidural catheter. If hypotension still occurs, additional IV fluids, ephedrine (10.0 mg IV), or both may be needed. Left uterine displacement (placement of the patient in left lateral tilt position) can be helpful.
2. Accidental dural puncture (“wet tap”). Complications after a wet tap include spinal headache. Treatment includes administration of abdominal binders, administration of caffeine, and increased fluid intake. Severe cases may require injection of autologous blood in the epidural space near the dural puncture (i.e., “blood patch”).
3. Accidental intravascular injection. CNS toxicity from intravascular injection of an anesthetic includes dizziness, slurred speech, metallic taste, tinnitus, convulsions, and in rare cases cardiac arrest. Treatment is supportive and may involve establishing an airway to provide assisted ventilation and administering short-acting benzodiazepines or barbiturates for seizure control.
4. Accidental subarachnoid injection. If accidental subarachnoid placement of the catheter is not detected by a test dose, a usual epidural dose may result in high or total spinal anesthesia, leading to apnea and hypotension that must be rapidly treated with supportive care.
5. Effect on progress of labor. If an epidural block is too dense or administered too early in labor, the musculature of the pelvic floor can become too relaxed, which potentially results in malrotation of the fetal head during descent. In addition, the parturient may lose the urge or ability to push effectively because of lack of sensation. As a result, the duration of the second stage of labor may be prolonged.Spinal anesthesia and analgesiaIndications. Spinal analgesia may be administered for labor and vaginal delivery. Spinal anesthesia can be used for cesarean sections.Application. For cesarean section, a local anesthetic (tetracaine hydrochloride, bupivacaine, or lidocaine) is injected into the subarachnoid space through a needle placed at the level of L2–L5. A sensory level of T5 is preferable for adequate anesthesia for a cesarean section. For labor and vaginal delivery, small amounts of narcotic (fentanyl, sufentanil citrate, or morphine sulfate) or local anesthetic or both can be used for analgesia. T10–L1 block is needed to minimize the pain of uterine contractions and S2–S4 block is needed for perineal analgesia.
Advantages. The advantages of the spinal block are its rapid onset of effect and ease of administration (relative to an epidural).Limitations. The analgesia of a spinal block lasts only for a limited time period. Therefore, this type of anesthesia is not indicated to relieve the pain of a lengthy labor. Likewise, if concern exists about a very complicated, prolonged cesarean section, epidural or general anesthesia is preferred. Spinal anesthesia is not appropriate for an extremely emergent cesarean section.
Contraindications. These are the same as those listed for epidural anesthesia (see sec. VI.A.5).Risks. As with the epidural block, the spinal block can have complications associated with induced maternal hypotension, spinal headache, and high block (see risks of epidural anesthesia, sec. VI.A.6). Spinal headache can be less likely if a smaller-caliber needle (e.g., 26 or 27 gauge) is used. Respiratory depression and pruritus may occur after spinal analgesia with narcotics [treatment is with naloxone hydrochloride (Narcan)].

Combined spinal-epidural anesthesia (CSE)Indications.
This type of anesthesia is useful for providing analgesia or anesthesia or both for labor, vaginal deliveries, or cesarean sections.
Application. The most frequently used technique is the needle-through-needle method. The epidural space is identified, a spinal needle is then passed through the epidural needle and advanced beyond its tip to puncture the dura, and spinal anesthesia is administered. The spinal needle is then removed, and an epidural catheter is placed through the remaining needle.
Advantages. The CSE combines the rapidity, density, and reliability of the spinal block with the facility to modify or prolong the anesthesia with use of the epidural catheter.Contraindications. These are the same as those listed for epidural anesthesia (see sec. VI.A.5).Risks. In addition to the risks of spinal and epidural anesthesia, there may be difficulty interpreting the epidural test dose after a spinal block has been administered.

General anesthesia.
This form of anesthesia is used far less than regional anesthesia. It requires endotracheal intubation to protect the parturient's airway and minimize the risk of aspiration.Indications. Because of its rapid induction, general anesthesia is usually used for extremely emergent cesarean sections and less often for emergent vaginal deliveries (forceps delivery, severe shoulder dystocia, difficult breech delivery). It may also be used when a patient is hypovolemic or has a contraindication to use of regional anesthesia.

Application. The most popular regimen is to use sodium thiopental (3–4 mg/kg) or ketamine hydrochloride (1–2 mg/kg) as the induction agent, followed by succinylcholine chloride (1 mg/kg) for muscle relaxation to facilitate intubation. Preoxygenation with 100% oxygen increases the oxygen stores in the maternal lungs. Additional inhalation agents (halothane, isoflurane, nitrous oxide) are commonly used.

Advantages. General anesthesia has the advantages of providing rapid induction and producing less hypotension.Limitations. Because of its increased risks to the mother and fetus, general anesthesia is usually reserved for situations when all other forms of anesthesia are contraindicated or inadequate.Risks. Data suggest that the rate of maternal death contributable to general anesthesia may be at least double the rate due to regional anesthesia. The primary cause of death associated with general anesthesia is difficulty with airway management.Failed intubation or aspiration. A careful preoperative evaluation should be performed to identify any potential challenges to intubation. Awake intubation may be necessary. Preoxygenating with 100% oxygen decreases the risk of hypoxia. To reduce the risk of aspiration, cricoid pressure is applied until the endotracheal tube is inserted and the cuff is inflated. Ideally, the patient should have an empty stomach. An antacid is also administered before general anesthesia to increase the pH of the stomach contents.Increased uterine bleeding. Because halogenated anesthetic agents (halothane, isoflurane) cause uterine relaxation, their prolonged use may increase blood loss, although several studies have shown no increased blood loss when these agents are used appropriately.Fetal depression. General anesthetics have the potential for causing neonatal depression. In addition, induction of general anesthesia is associated with a significant decrease in uterine blood flow.

Source:
The Johns Hopkins Manual of Gynecology and Obstetrics 2nd edition (May 2002): By Brandon J., Md. Bankowski (Editor), Amy E., MD Hearne (Editor), Nicholas C., MD Lambrou (Editor), Harold E., MD Fox (Editor), Edward E., MD Wallach (Editor), The Johns Hopkins University Department (Producer) By Lippincott Williams & Wilkins Publishers.