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Case 1
A 75-year-old man underwent total knee replacement under spinal anesthesia with local anesthetic and 300 μg of diamorphine or 100 μg of morphine. Late that evening he appears extremely sleepy and has oxygen saturation of 94% on nasal oxygen.
Case 2
A 60-year-old woman underwent a total vaginal hysterectomy under spinal anesthesia with local anesthetic and 300 μg of diamorphine. In the recovery room the patient complains of severe itching and nausea with vomiting. Her oxygen saturation is 98% on room air.
Epidural and intrathecal administration of opioids has been in practice for decades. Neuraxial opioids produce profound segmental antinociception in doses much smaller than would be required if administered systematically. The addition of fentanyl to spinal anesthesia prolongs the duration of sensory blockade without increasing the time to discharge, making it a popular choice in the ambulatory setting. Intrathecal opioids for labor analgesia have made it possible to lower the amount of local anesthetic used so that the mother can ambulate while the epidural is running (walking epidural).
Side effects of intrathecal and epidural opioids are listed in Box 104.1 . The most common are as follows:
Respiratory depression
Sedation
Pruritus
Nausea and vomiting
Respiratory depression
Sedation
Pruritus
Nausea and vomiting
Urinary retention
Gastrointestinal dysfunction
Anaphylaxis
Hyperalgesia
Behavioral problems
Dizziness or hypotension
Thermoregulatory dysfunction
In general the side effects associated with neuraxial opioids are similar to those seen with intravenous, intramuscular, or oral opioid use. However, the severity, incidence, and timing differ owing to the interaction of opioids with their receptors in the spinal cord and the brain. The most serious complication is respiratory depression, which can be early or delayed.
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