Outline the potential side-effects of neuraxial opioids and their treatment

Outline the potential side-effects of neuraxial opioids and their treatment.

Side-effects of neuraxial opioids include respiratory depression, nausea, vomiting, pruritus, and urinary reten-tion. Respiratory depression is the most serious of these. When severe, it requires aggressive treatment with an intra-venous opioid antagonist (i.e., naloxone) and ventilatory support. However, with the use of proper dosing, respira-tory depression should not be seen clinically. A recent study (Liu et al., 1999) looking at 1,030 patients being treated with epidural fentanyl and bupivacaine for post-operative analgesia, placed the incidence of respiratory depression at 0.3%.

After the initial administration of neuraxial opioids, minimally appropriate monitoring calls for respiratory/ sedation checks every 2–4 hours. Respiratory depression can occur within the first 2 hours (early) or up to 24 hours (late) after opioid administration. Early respiratory depres-sion is primarily associated with the lipid-soluble opioids and is secondary to vascular uptake. Late respiratory depression occurs mostly with hydrophilic opioids and results from migration of the opioid within the cere-brospinal fluid (CSF), up to the respiratory centers in the brain.

Other side-effects respond to symptomatic treatments. Antiemetics, such as metoclopramide and ondansetron, are generally useful for treating nausea. However, patients after abdominal surgery must be evaluated prior to admin-istration of antiemetics to rule out any intra-abdominal pathology. Pruritus usually responds to diphenhydramine. Failing these measures, low-dose naloxone infusions (1–2 μg/kg/hr) will reduce the side-effects, while retaining analgesia.

Side-effects seem to occur more commonly with sub-arachnoid administration than with epidural administration. Lipid-soluble opioids may be associated with a decreased incidence of side-effects compared with hydrophilic opioids.

Low doses of epidural local anesthetics are often used to potentiate the analgesia obtained with neuraxial opioids. Although rare, motor blockade, hypotension, and urinary retention may occur. Motor strength in the lower extremi-ties needs to be checked prior to a patient getting out of bed for the first time while utilizing this therapy.