Intrathecal Morphine

1. Indication
   1. Analgesia and Anesthesia for First Stage of Labor
   2. Gives four hours of Labor Anesthesia
2. Mechanism of Action
   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
3. Labs
   1. Complete Blood Count with platelets
      1. Confirm no coagulopathy
4. Technique
   1. Patient lying in lateral decubitus position or seated
   2. Spinal needle Insertion
      1. Site: L3-4 interspace
      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. Fentanyl 25 ug
      2. Morphine (preservative-free) 0.25 mg
5. 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
6. Adverse reactions
   1. Maternal Hypotension
   2. Nausea or Vomiting
   3. Pruritus
   4. Skin hypersensitivity
   5. Postdural Puncture Headache
7. Reference
   1. Stephens (1997), Am Fam Physician 56(2):463-70