II. Indication

  1. Analgesia and Anesthesia for First Stage of Labor
  2. Gives four hours of Labor Anesthesia

III. Mechanism

  1. Acts at Opioid receptors
    1. Substantia gelatinosa of dorsal horn
    2. Affects afferent visceral pain impulses only
  2. Contrast with Epidural Anesthesia
    1. ITM does not affect second stage somatic pain
    2. ITM does not interfere with maternal pushing
      1. Does not inhibit efferent muscular paths

IV. Labs

V. Advantages

  1. Single injection into the intrathecal space offers nearly immediate relief without retained catheter

VI. Technique

  1. Patient lying in lateral decubitus position or seated
  2. Spinal needle Insertion
    1. Site: L3-4 interspace
      1. Insertion must be below L1-2 to prevent Spinal Cord Injury
    2. Needle Gauge: 25 gauge ("Pencil point")
      1. Decreases Incidence of Postdural Puncture Headache
    3. Enter the dural sac as in Lumbar Puncture
      1. Clear Cerebrospinal Fluid should return promptly
  3. Instill Intrathecal medications
    1. Hyperbaric Lidocaine 25-50 mg
    2. Additional agents
      1. Fentanyl (Duragesic) 10-25 mcg
      2. Morphine (preservative-free) 0.25 mg

VII. Monitoring

  1. Initial
    1. Blood Pressure, Pulse every 5 minutes for 30 minutes
    2. Respiratory Rate every 15 minutes for 1 hour
  2. Later
    1. Monitor hourly for 24 hours
  3. Naloxone by bedside for respiratory depression

VIII. Adverse Effects

  1. Maternal Hypotension
  2. Nausea or Vomiting
  3. Pruritus
  4. Skin Hypersensitivity
  5. Postdural Puncture Headache
  6. Associated with increased instrument-assisted Vaginal Delivery (vacuum or forceps)

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