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Acute postoperative pain and opioids
Good postoperative analgesia is multimodal — paracetamol, an NSAID and a nerve block reduce the need for opioids — and the opioid is chosen according to the patient's kidney, liver and genetics.
Why it matters in the exam
The exam asks which opioid is dangerous in renal failure (morphine), why codeine is forbidden in children after tonsillectomy, what the danger of pethidine and tramadol is (seizures, serotonin syndrome), and how respiratory depression is treated — including the danger that naloxone wears off before the opioid. It also asks about PCA settings, remifentanil and the patient who takes buprenorphine or methadone regularly.
The early sign of opioid respiratory depression is sedation — it comes before the fall in respiratory rate and saturation, so the level of alertness is monitored. NSAIDs are forbidden or used with caution in renal failure, gastrointestinal bleeding and heart failure. Remifentanil is broken down by blood esterases, so its effect wears off within minutes even after a long infusion — another analgesic must be given before the end of surgery.
Poorly treated pain after surgery is not only suffering: it limits deep breathing and coughing, delays mobilisation and increases lung complications and thrombosis. On the other hand, excess opioids cause nausea, constipation, urinary retention and delirium, and sometimes long-term use after discharge. So a discharge plan with a limited opioid supply and a review of the need is set in advance. In exam questions the good answer usually combines several routes and does not rely on an opioid alone.
Key points
- Multimodal analgesia: paracetamol, NSAID, nerve block, and an opioid for rescue.
- Morphine accumulates in renal failure.
- Codeine and tramadol depend on CYP2D6; codeine is forbidden in children under 12.
- Sedation is the early sign of respiratory depression; naloxone in small doses and prolonged monitoring.
- Remifentanil wears off within minutes — give other analgesia before the end of surgery.
Summary table
| Drug | Special feature | Main caution |
|---|---|---|
| Morphine | Active metabolite (M6G) excreted by the kidney | Accumulation and respiratory depression in renal failure |
| Codeine, tramadol | Depend on CYP2D6 | Ultra-rapid metabolisers — toxicity; codeine forbidden under 12 years and after tonsillectomy under 18 |
| Pethidine | Metabolite (norpethidine) causes seizures | Serotonin syndrome with MAOIs; not for prolonged use |
| Fentanyl, remifentanil | Lipid-soluble and fast; remifentanil broken down by esterases | Chest wall rigidity at high dose; hyperalgesia after remifentanil |
| Naloxone | 0.04–0.1 mg IV in repeated doses | Short duration (30–90 minutes) — recurrent depression; pain, hypertension and pulmonary oedema with abrupt reversal |
A free exam question
מהם השיקולים בבחירת משככי כאבים לפני ?ניתוח ברך אמבולטורי (the question as examined, in Hebrew)
- א. NSAIDs מראים אפקט חזק של preemptive analgesia
- ב. חוסמי COX-2 עדיפים על פני NSAIDs מסורתיים בניתוחים אמבולטוריים בשל יעילות גבוהה
- ג. ו לר ב Acetaminophen שניתן דרך הפה לפני ניתוח אינו מביא לרמות תרפויטיות בסוף ניתוח
- ד. NSAIDs ( בשחרור מושהה Slow release )אינם עדיפים על פני NSAIDs מסורתיים
In the full version for subscribers
- A simple algorithm
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- Exam traps
- 5 review cards
- Enough for IMLE
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Sources
- Miller's Anesthesia, 9th edition (2020) — Opioid Analgesics; Acute Postoperative Pain
- Morgan & Mikhail's Clinical Anesthesiology, 7th edition (2022) — Analgesic Agents; Perioperative Pain Management
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.