Epidural analgesia for labor and delivery consists of injection of local anesthetic and an opioid analgesic agent into the lumbar epidural space.
The local anesthetic is lidocaine or bupivacaine and the analgesic is usually morphine or fentanyl.
The injected agents diffuse across the dura into the subarachnoid space where they act primarily on the spinal nerve roots and to a lesser degree on the spinal cord and paravertebral nerves.
Spinal analgesia is often combined with epidural analgesia and consists of injecting the analgesic agents directly into the subarachnoid space, increasing the rapidity of analgesic effect.
Produces segmental sympathetic and sensory block and decreases endogenous catecholamines with pain relief.
May cause hypotension or normalization of blood pressure secondary to vasodilation.
Associated reduction in vascular resistance improves uteroplacental blood flow in healthy individuals and those with preeclampsia.
Because neuraxial local anesthetics affect skeletal muscle, and not smooth muscle, these agents do not decrease amplitude or frequency of uterine contractions.
In a controlled trial of 992 nulliparous women randomized to epidural analgesia vs midwifery support: median pain score was 27 for epidural anagesia vs 75 with midwife support (Dickinson JE).
In a meta-analysis involving 2703 nulliparous women randomly assigned to epidural analgesia vs intravenous meperidine: pain significantly better in the epidural analgesic group with 95% of women in the first postpartum day reporting excellent or good relief compared to 69% in the meperidine group (Sharma SK).
Suppresses surgical stress, has a positive effect on postoperative nitrogen balance, provides a more stable cardiovascular hemodynamics, reduces blood loss, improves peripheral vascular circulation and provides improved postoperative pain control.
Thoracic epidural analgesia associated with a reduction in incidence of urinary retention, decrease incidence of hypotension, reduces myocardial oxygen consumption, pulmonary wedge pressure and pulmonary artery pressure, enhances coronary artery perfusion, improves postoperative pulmonary function and results in less inhibition of the gastrointestinal motility and therefore less ileus.
Arterial pressure decreases after institution of epidural block.