Neuraxial Anatomy and Anesthetic Technique in Labor and Delivery

Introduction

• Neuraxial anesthesia is the preferred and most effective method of pain relief during labor and delivery, providing superior analgesia and high maternal satisfaction compared with systemic techniques.
• Techniques include epidural, spinal, combined spinal-epidural, and dural puncture epidural approaches, tailored to the stage of labor and clinical urgency.
• Physiologic changes of pregnancy, such as epidural venous engorgement, increased sensitivity to local anesthetics, and reduced cerebrospinal fluid volume, alter neuraxial block characteristics and dosing.
• Benefits extend beyond analgesia, offering flexibility for conversion to surgical anesthesia if cesarean delivery or obstetric intervention becomes necessary.
• Successful neuraxial analgesia supports maternal participation in labor, minimizes catecholamine-mediated hemodynamic changes, and contributes to improved obstetric outcomes.
• Placement requires careful patient counseling, appropriate monitoring, and multidisciplinary coordination among anesthesia, obstetrics, and nursing teams to ensure safety for both mother and fetus.

Pain Pathways

First Stage

• From the onset of labor to full cervical dilation.
• Visceral pain from uterine contractions and cervical dilation is transmitted via T10–L1 visceral afferents.
• Described as dull, cramping, poorly localized pain felt in the lower abdomen, back, and thighs.

Second Stage

• From complete cervical dilation to delivery of the neonate.
• Adds somatic pain from distension of the vagina, perineum, and pelvic floor via the pudendal nerve (S2–S4).
• Pain becomes sharp, intense, and well localized; it may increase with episiotomy or instrumental delivery.

Third Stage and Immediate Postpartum

• From the delivery of the neonate to the expulsion of the placenta and early recovery.
• Persistent visceral pain from uterine involution and somatic pain from perineal trauma or repair.
• There may be continued visceral pain caused by induced uterine contraction to help prevent postpartum hemorrhage and somatic pain secondary to delivery-related perineal trauma.

Anatomy for Neuraxial Technique in Labor and Delivery

• Understanding the anatomy of the spinal canal is essential for safe and effective neuraxial anesthesia, as accurate identification of its borders and contents guides needle placement, minimizes the risk of dural puncture or neural injury, and optimizes delivery of local anesthetic within the intended space.
• In the parturient, neuraxial anesthetic techniques are performed by palpation, rather than fluoroscopy, as in the chronic pain clinic.
• The epidural space extends from the foramen magnum to the sacral hiatus.
• Pregnancy accentuates lumbar lordosis and epidural vein distension, increasing the risk for unintentional dural puncture.
• Ultrasound can aid in the identification of vertebral structures (Figure 2) but is not routinely used in obstetric settings.

Patient Counselling, Indications, and Contraindications

Patient Counseling

• Neuraxial anesthesia is an elective procedure that requires informed consent and includes indications, benefits, risks, and alternatives.
• Discuss potential need for conversion to cesarean anesthesia and risks of rare but serious complications (e.g., high spinal, infection, hematoma).
• Reassure the patient that their request alone is a valid indication for labor analgesia; obstetric permission is not required.
• Address common side effects: hypotension, pruritus, nausea, urinary retention, shivering, and fever.

Indications

• Pain relief during labor, vaginal delivery, or cesarean birth.
• Facilitation of perineal repair or manual placental extraction.
• Surgical anesthesia for cesarean or other obstetric procedures.

Contraindications

• Always interpret contraindications in the clinical context; many relative factors can be managed with risk stratification and multidisciplinary discussion.
• The Society for Obstetric Anesthesia and Perinatology⁴ and the American Society of Regional Anesthesia and Pain Medicine guidelines⁵ (2021, 2018 updates) remain the most authoritative references for platelet thresholds and anticoagulation timing.
• Document risk–benefit discussions and coordinate with obstetric and hematology teams for complex coagulopathies (e.g., HELLP (Hemolysis, Elevated Liver enzymes and Low Platelets) syndrome, immune thrombocytopenia).
• See Table 2 for further details.

Alternatives

Nonpharmacologic Methods

• Behavioral and relaxation techniques (breathing, visualization, hypnobirthing)
• Hydrotherapy, massage, continuous labor support (doula), upright positioning
• Transcutaneous electrical nerve stimulation for early labor

Pharmacologic, Nonneuraxial Options

• Nitrous oxide (50% N₂O/50% O₂): self-administered via demand valve; provides mild analgesia and anxiolysis with rapid onset and offset.
• Systemic opioids: IV or IM fentanyl, remifentanil patient-controlled analgesia (PCA), or meperidine; reduce pain perception but may cause maternal sedation and transient neonatal respiratory depression.
  • Of note, remifentanil PCA is not always feasible due to the usual requirement for a 1:1 nursing-to-patient ratio.

Regional Obstetric Blocks

• Paracervical block—visceral pain relief during the first stage (rarely used due to fetal bradycardia risk).
• Pudendal block—somatic analgesia for the second stage, perineal repair, or operative vaginal delivery.

Neuraxial Technique Overview

General Preparation and Monitoring

• Establish IV access with continuous fluid infusion; ensure quick access to resuscitation equipment and emergency medications. Baseline maternal vitals and fetal heart rate should be documented.
• Monitor blood pressure (BP) every 3–5 minutes for 15–30 minutes after placement, then at least hourly during labor. Continuous pulse oximetry is optional in healthy parturients per institutional policy.
• Maintain left uterine displacement in the supine position to reduce aortocaval compression.

Positioning and Preparation

• Performed with the patient sitting or lying on their side; a seated position often facilitates better landmark alignment.
• Lumbar flexion widens interspinous spaces; shoulders relaxed, hips and knees flexed in a “curled” posture.
• Prep with chlorhexidine (avoid pooling; let it dry) and use full sterile technique.
• Identify the L3–L4 or L4–L5 interspace using the iliac crest line as a landmark.

Typical Local Anesthetic and Adjuvant Regimens

• Epidural infusions: dilute local anesthetic (e.g., bupivacaine 0.0625–0.125% or ropivacaine 0.1–0.2%) + fentanyl 2 µg/mL via programmed intermittent epidural bolus ± patient-controlled epidural analgesia.
• Spinal for labor: bupivacaine 1.25–2.5 mg + fentanyl 10–25 µg.
• Spinal for cesarean: 0.75% bupivacaine with dextrose 10–12 mg + fentanyl 10–25 µg ± morphine 100–200 µg.
• Adjust dose downward in pregnancy due to increased sensitivity and reduced cerebral spinal fluid volume.

Ongoing Management

• Supplement or re-dose via epidural catheter as labor progresses.
• For cesarean delivery, an existing functioning epidural can be bolused to achieve a T4 level for surgical anesthesia.
• Monitor for complications: hypotension, high spinal, inadequate block, or intravascular injection.
• Be vigilant for an inadequate or failed block. A replacement is usually recommended if two “top-offs” have been ineffective.
  • Labor epidural “top-offs” should be high volume and dilute bupivacaine (e.g., 10-20 cc of 0.125% bupivacaine).

Monitoring, Side Effects, and Complications

Monitoring and Safety

• Ensure continuous availability of airway equipment, suction, and emergency medications.
• Record baseline maternal heart rate, blood pressure, and oxygen saturation before initiation.
• After dosing, monitor BP every 3–5 minutes for the first 15–30 minutes, then at least hourly.
• Continuous fetal heart rate monitoring during and immediately after block placement per institutional protocol.
• Maintain left uterine displacement to minimize aortocaval compression and maternal hypotension.
• Early recognition and prompt management of hypotension are critical for maternal and fetal safety.
• Maintain clear communication with obstetric and nursing teams to coordinate dosing, redosing, and conversion timing for cesarean delivery.
• Document complications, interventions, and outcomes thoroughly in the anesthesia record.