Pain Management
Acute Pain: Treating Opioid-Related Adverse Effects
Opioid side effects:
- Acute use: nausea, vomiting, itching (pruritus), sedation/respiratory depression, death.
- Chronic use: constipation, delirium, and myoclonus, and drug dependence.
Post-operative Nausea and Vomiting (PONV)
- PONV occurs in approximately 30% of all post-op patients
- PONV risk factors include: female gender, non-smoker, prior PONV, post-op opioid use
- Having no risk factors yield a risk of 10%, one risk factor raises it to 20% and each additional risk factor adds 20% risk (up to 80%)
- Risk reduction:
- Avoid general anesthesia if possible
- Use propofol for general anesthetic maintenance rather than volatile anesthetics and N2O.
- Minimize use of neostigmine and postoperative opioids (multimodal analgesia facilitates latter.
- Use prophylactic anti-emetics (no more than 2 of the drugs are combined at once)
Prophylaxis and treatment of PONV:
Prophylactic use of antiemetics for patients at high risk for PONV
Treating Established PONV
(Note: Must wait 6 hours before re- administering a medication already used prophylactically)
Potential side-effects
Dexamethasone 4 mg
Not usually used for established PONV
None noted with single dose of 4 mg. Potential risk of tumor lysis syndrome in at risk patients.
Ondansetron 4 mg
1 mg every 6 hours as needed.
Headache, elevated liver enzymes, constipation QTc prolongation.
Haldol 0.5-1mg
Droperidol is not usually used for established PONV
QTc prolongation with high doses
Dimenhydrinate 12.5-25 mg
Dimenhydrinate 12.5-25 mg every 4 hours as needed
Sedation
Pruritus
- Rare. Diphenhydramine administration is sufficient.
Sedation/Respiratory Depression
- Suspect the potentially fatal respiratory depression if RR <10 breaths/min and heavy sedation
- Patients at risk for respiratory depression are patients without previous exposure to opioids, and those with respiratory disorder (e.g. OSA and asthma)
- Tx: Hold opioids, administer naloxone (opioid antagonist) in small doses (0.04mg q3min) until the respiratory rate increases and/or sedation is reduced.
- Naloxone is short-acting, therefore observe patients for rebound depression, especially if long-acting opioid was given