2.4 Pain Management, Analgesia & Anesthesia Care

Pain Management, Analgesia & Anesthesia Care

Intrapartum pain management requires an understanding of labor pain pathways, non-pharmacologic comfort measures, systemic analgesics, neuraxial anesthesia, and peripheral nerve blocks. RNC-OB certified nurses play a key role in advocating for maternal pain relief preferences while continuously monitoring maternal-fetal safety and hemodynamics.

Neurophysiology of Labor Pain

Labor pain originates from distinct anatomical structures as labor progresses:

[ Neurophysiology of Labor Pain Pathways ]

First Stage (Visceral Pain)  --> Uterine contraction & Cervical dilation
                                  Transmitted via T10, T11, T12, L1 Sympathetic Nerves

Second Stage (Somatic Pain) --> Perineal distension, Vaginal stretching & Pelvic floor pressure
                                  Transmitted via S2, S3, S4 Pudendal Nerves

• First-Stage Pain (Visceral): Caused by uterine muscle ischemia, lower uterine segment stretching, and cervical effacement/dilation. Pain signals travel through visceral afferent fibers entering the spinal cord at T10, T11, T12, and L1 segments. Pain is poorly localized and referred to the lower abdominal wall, sacrum, and lower back.
• Second-Stage Pain (Somatic): Caused by stretching of the fascia, vagina, levator ani muscles, and perineum by the descending fetus. Pain signals travel along somatic afferent fibers via the pudendal nerve (sacral segments S2, S3, and S4). Pain is sharp, localized, and intense.

Non-Pharmacologic Pain Modalities

Non-pharmacologic comfort techniques reduce anxiety, enhance maternal coping, and decrease endogenous catecholamine release (which can otherwise reduce uterine blood flow):

• Continuous Labor Support: One-on-one support by a trained labor nurse or doula reduces analgesia requirements and instrumental delivery rates.
• Hydrotherapy: Immersion in warm water during active labor ($36.0^\circ\text{C} - 37.5^\circ\text{C}$) reduces pain perception and neuraxial analgesia uptake without increasing infection risk when membranes are intact or ruptured.
• Sacral Counterpressure: Firm manual pressure applied to the sacrum relieves severe back pain caused by fetal occiput posterior (OP) presentation.
• Intradermal Sterile Water Papules: Injection of $0.05 - 0.1\text{ mL}$ sterile water intradermally over four sacral points creates localized gate-control counter-irritation, relieving severe lower back labor pain for 60–120 minutes.

Systemic Pharmacologic Analgesia

Systemic opioids cross the placenta readily via passive diffusion. They must be administered thoughtfully relative to anticipated delivery timing to prevent neonatal respiratory depression.

Neonatal Opioid Exposure

Naloxone is not part of initial neonatal resuscitation. If a newborn is apneic, gasping, or bradycardic, establish effective ventilation according to NRP first. Coordinate postresuscitation assessment for medication exposure and withdrawal; naloxone must not substitute for positive-pressure ventilation and can precipitate acute withdrawal after chronic opioid exposure.

Neuraxial Analgesia & Anesthesia: Epidural, Spinal & CSE

Epidural Analgesia

Epidural analgesia involves inserting a needle into the epidural space (between the ligamentum flavum and dura mater at L3–L4 or L4–L5) and threading a catheter for continuous infusion of dilute local anesthetic (bupivacaine $0.0625% - 0.125%$ or ropivacaine) combined with an opioid (fentanyl $2\text{ mcg/mL}$).

Pre-Epidural Nursing Checklist:

1. Obtain baseline maternal vital signs and continuous FHR trace for $\ge 20\text{ minutes}$.
2. Verify pre-procedure laboratory results: Review platelet count and trend, etiology, bleeding history, and coagulopathy risk; consensus guidance often considers neuraxial procedures reasonable at $\ge 70,000/\mu\text{L}$ in defined obstetric thrombocytopenia without added risk.
3. Use an individualized crystalloid coload or bolus when indicated, avoiding routine large volumes in patients at risk of fluid overload.

Post-Epidural Management & Hypotension Protocol:

Sympathetic nervous system blockade causes peripheral vasodilation, venous pooling, and maternal hypotension (defined as a drop in systolic BP $>20%$ from baseline or absolute systolic BP $<100\text{ mmHg}$):

• Monitoring: Assess maternal BP every 2 to 5 minutes for the first 15 to 30 minutes after initiation or bolus, then every 15 minutes.
• Immediate Interventions for Hypotension:
  1. Position the patient laterally.
  2. Give indicated crystalloid and an ordered vasopressor based on hemodynamics.
  3. Give supplemental oxygen for maternal hypoxemia, not solely for an FHR deceleration when saturation is normal.
  4. Administer IV vasopressors: Ephedrine $5\text{--}10\text{ mg}$ IV or Phenylephrine $50\text{--}100\text{ mcg}$ IV as ordered.

Spinal Anesthesia (Subarachnoid Block)

Local anesthetic is injected directly through the dura into the subarachnoid space containing cerebrospinal fluid (CSF). Produces rapid onset (1–2 minutes) with dense sensory and motor block. Primarily used for scheduled or urgent cesarean deliveries.

• Post-Dural Puncture Headache (PDPH): Occurs when CSF leaks through a dural puncture site. Characterized by severe postural headache (worsens when upright, relieved when lying flat). Evaluate with anesthesia; conservative analgesia or caffeine may be used, and a therapeutic epidural blood patch is offered when indicated ($15 - 20\text{ mL}$ autologous blood injected into epidural space to form a seal).

Combined Spinal-Epidural (CSE)

Combines the rapid, low-dose sensory onset of intrathecal spinal analgesia ("walking epidural") with the continuous flexibility of an epidural catheter.

Peripheral & Regional Blocks

• Pudendal Nerve Block: Transvaginal injection of local anesthetic (e.g., 1% lidocaine) around the pudendal nerves near the ischial spines bilaterally. Blocks S2–S4 sensory distribution, providing rapid anesthesia to the lower vagina, vulva, and perineum for forceps/vacuum delivery, episiotomy, or complex laceration repair. Does not alter contraction pain or produce motor block.
• Local Perineal Infiltration: Direct subcutaneous injection of local anesthetic into the perineum prior to episiotomy incision or suture repair.