In the first stage of labor (cervical dilation), the pain is visceral, produced by the distention of the lower uterus and cervix and ischemia of the uterine and cervical tissues. Visceral pain signals traverse T10 to L1 white rami communicantes and enter the spinal cord.

The second stage involves both visceral and somatic pain. The parturient experiences more somatic pain in the late first stage of labor (7 to 10 cm cervical dilation), entering into the second stage from distention of the vagina, perineum, and pelvic floor. Somatic pain signals traverse the pudendal nerve (S2 to S4) and enter into the anterior spinal cord. The parturient also experiences rectal pressure. See Chapter 30 for more on biologic basis of pain perception.

Local, regional, and systemic methods of analgesia and anesthesia are used in obstetrics. Local and regional methods include local injection, peripheral nerve
block, and regional block. Systemic methods can be administered intramuscularly, intravenously, or by inhalation. General anesthesia is often used in cases where total motor and sensory loss is necessary (Table 25-1) or when contraindications to neuraxial anesthesia are present.

During the first stage of labor, visceral pain is mollified by the preferred use of regional anesthesia, such as an epidural, spinal, or a combination of both.

In vaginal deliveries, the goal is to block nociceptive pathways while preserving motor function so that the parturient is comfortable but can participate actively with second stage expulsive effort. Local anesthesia or peripheral nerve block with pudendal injection or more systemic analgesia with intravenous (IV) pain medication or spinal/epidural block can be used during the second stage of labor.

In cesarean delivery, anesthetic selection is often determined by the condition of the mother and fetus, the urgency of the procedure, and physician preference. Operative anesthesia requires a denser motor and sensory block than that used for a vaginal delivery. Neuraxial anesthesia is often the preferred method used because it provides adequate pain control while minimizing the maternal risk of aspiration or unanticipated difficult airway. In addition, neuraxial anesthesia decreases systemic catecholamine release and systemic response to surgery, avoids the side effects of postoperative IV narcotics, and allows the mother to interact with the newborn soon after delivery. Effective neuraxial anesthesia can be achieved by epidural, spinal, or combined spinal epidural approaches. General anesthesia is appropriate when the patient presents with contraindications to neuraxial anesthesia, medical indications, or in emergency cases where neuraxial anesthesia cannot be administered in a timely manner. Supplemental local anesthesia can be used by the obstetrician on the operative field as well.