CHAPTER 170 Intrathecal Analgesia in Labor

Intrathecal analgesia uses the subarachnoid (dural) space for the injection of analgesic narcotics and anesthetics. This space is filled with cerebrospinal fluid (CSF) and is the same space used for a spinal or saddle block (see Chapter 175, Saddle Block Anesthesia). Analgesics injected into this space diffuse through the CSF to coat the visceral pain receptors in the dorsal horn of the spinal cord (T10–L1). Although it does not provide complete pain relief, this technique provides considerably more pain relief than the parenteral or intravenous (IV) route. In addition, pain relief is more rapid than with epidural analgesia. In comparison to spinal or saddle block anesthesia, which often uses hyperbaric anesthetic solutions (i.e., solutions more dense than CSF so they drift caudally), the dose with intrathecal analgesia is significantly less. Overall, intrathecal analgesia allows for profound analgesia without clinically significant motor or autonomic blockade (i.e., minimal anesthesia).

This procedure is not technically difficult to perform and does not adversely affect the infant or the progress of labor. Clinicians comfortable with performing lumbar puncture can easily learn this procedure and perform it without an anesthesiologist. It is useful in many clinical settings, especially where epidural analgesia is not readily available or when complete anesthesia is not necessary (Box 170-1). It is also used in combination with epidural analgesia (combined spinal-epidural [CSE]).

Often performed with a needle-through-needle technique, CSE provides faster onset of analgesia with a smaller dose of anesthetic than epidural alone. Although it was thought, at one time, that a smaller dose of anesthetic would result in less motor block and maternal leg numbness and therefore improved mobility, it turns out this may not be the case. A recent Cochrane Review comparing CSE with epidural alone concluded that although there was no difference in postdural puncture headache (PDPH), progress of labor, incidence of instrumented deliveries or cesareans, or adverse effects on the infant, there was also no difference in maternal mobility during labor. Although analgesia was faster in onset with CSE, more women had pruritus than with epidural alone. Consequently, there was no difference in patient satisfaction in the CSE group compared with epidural alone.

Intrathecal analgesia is ideally suited for patients in the first stage of labor who are anticipated to deliver vaginally (if cesarean is anticipated, epidural or CSE may be preferred). The pain in this stage is primarily due to uterine contractions and cervical dilation. Pain in the second stage of labor is due to both uterine contractions and fetal descent through the birth canal. Because fetal descent stimulates the pudendal nerve (S2–S4), intrathecal analgesia is less effective; however, it does continue to provide analgesia for the uterine contractions. The real overall benefit for intrathecal analgesia is improved tolerance of the contractions, thereby resulting in a more rested mother for the second stage of labor. This in turn should enhance the overall birthing experience.

Because the duration of intrathecal analgesia is limited, it should be used as the sole method for pain control only when the remaining duration of the first stage of labor is expected to be less than 6 hours. Although the procedure can be repeated later in labor, each additional dural puncture increases the risk of PDPH. If a cesarean section becomes necessary, general, spinal, or epidural analgesia may be used after intrathecal analgesia.

Equipment and Supplies

• Spinal anesthesia kit, which includes sterile preparation materials, local anesthetic, a 25-gauge or smaller atraumatic spinal anesthesia needle, and an 18- or 19-gauge introducer

NOTE: Thin, atraumatic spinal needles (Sprotte or Whitacre needles, with rounded or pencil-point, conical ends) have been proven to decrease the risk of PDPH.

• Syringe with filter-tip needle for drawing up narcotic for injection

• Narcotic for injection (Table 170-1)

• Bupivacaine 0.5% to 0.75% suitable for spinal injection, 2.5 mg total

• Ephedrine for injection

• Naltrexone, 25-mg tablet

• Naloxone ampules, 0.4 mg

• Continuous fetal monitoring (internal or external)

• Sterile gloves

• Personnel to monitor for side effects, including monitoring blood pressure

• Pulse oximeter

TABLE 170-1 Duration and Onset of Action for Intrathecal Narcotics

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