PCA and multimodal analgesia
Stem
A 71-year-old man, 96 kg, with obstructive sleep apnea on home CPAP and an eGFR of 38 mL/min, has just had an elective total hip arthroplasty under spinal anesthesia without intrathecal morphine. He takes no opioids at home. The spinal is regressing in recovery and his pain is 7/10.
Question
What is your postoperative analgesic plan for him?
Ideal answer
HeadlineMultimodal first, then a hydromorphone PCA with no basal rate, monitored for sedation, because sleep apnea and his kidneys make respiratory depression the risk.
- Scheduled acetaminophen; no NSAID, because of his kidneys. Regional if it still fits; dexamethasone or a ketamine infusion selectively, by patient and procedure.
- Hydromorphone PCA, not morphine, because morphine's active metabolites accumulate in renal impairment:1 0.2 mg demand, 6–15 minute lockout, no basal infusion because he is opioid-naive,1 and an hourly or 4-hour limit.
- Sedation scoring plus continuous oximetry or capnography, because sedation usually precedes respiratory depression and is a more reliable warning than respiratory rate.1
- His own CPAP whenever he sleeps; naloxone at the bedside, and no benzodiazepines or gabapentinoids alongside the opioid, since each deepens opioid respiratory depression.
- Oral opioids as soon as he tolerates intake, as the PCA is for rapid titration.
Breaking down the answer
- No basal infusion in the opioid-naive — PCA safety rests on the patient falling asleep before pressing again; a basal rate breaks that loop and increases side effects and respiratory depression without improving analgesia.1
- Basal infusion in the opioid-tolerant — I replace the home opioid as a basal rate or continue it orally, from an equianalgesic conversion reduced by 25–50%, because withdrawal and under-treatment are the bigger risks.1
- Nobody else presses the button — PCA by proxy defeats the safety mechanism; I educate families and nurses.
- Ketamine — 0.5 mg/kg at induction and 0.1–0.25 mg/kg/h spare opioid, most in tolerant patients and spine surgery. Outside the OR, boluses above 0.35 mg/kg or infusions above 1 mg/kg/h belong in a monitored setting.2
- Lidocaine infusion — 1.5 mg/kg bolus and 1–2 mg/kg/h helps after open abdominal surgery and return of bowel function. Changes if: a peripheral nerve or fascial plane block is running; I do not combine them, because of LAST risk.
- Gabapentinoids selectively — they add sedation and respiratory depression with opioids, especially in the elderly, so I do not use them routinely.
- The scale I name — the Pasero Opioid-induced Sedation Scale, with continuous monitoring in sleep apnea and the elderly and conservative dosing when there is sleep apnea, renal failure or a benzodiazepine on board.1
Follow-up question
At 3 a.m. the nurse finds him difficult to rouse, with a respiratory rate of 6 and SpO2 84%. His CPAP is still in the bag. What do you do?
Follow-up answer
HeadlineOpioid-induced respiratory depression; I tell the nurse to stimulate him, stop the PCA and call a rapid response.
Oxygen and airway support. Naloxone 40 mcg IV every 2 minutes, titrated to breathing rather than full reversal, to avoid acute pain and pulmonary edema; naloxone is shorter-acting than hydromorphone, so I start an infusion if needed and move him to a monitored bed. Then the contributors: a basal rate programmed in error, PCA by proxy, his renal impairment, benzodiazepines or gabapentin, CPAP not applied. I restart analgesia with multimodal agents, a lower opioid dose and CPAP on, and review the event with the team.
Pitfalls that cost points
- Listing drugs without a plan or dosing order.
- Giving naloxone 0.4 mg as a bolus to an opioid-tolerant patient.
- Using NSAIDs without considering renal function, bleeding and anastomotic risk.
Rapid-fire
Q: Why avoid morphine in renal failure? A: Morphine-6-glucuronide accumulates and causes prolonged sedation and respiratory depression; hydromorphone or fentanyl is preferable.1
Q: Why is sedation a better early warning than respiratory rate? A: Sedation increases before respiratory depression and is detected at the bedside, giving time to intervene.
Q: Why does a lockout of 6–15 minutes make sense? A: It allows the peak effect of each dose before the next can be given; fentanyl suits the shorter end and morphine the longer.1
Q: Why is multimodal analgesia better than more opioid? A: Drugs acting on different pathways are additive, while opioid side effects such as nausea, ileus, sedation and respiratory depression are dose-related.
Numbers to know
| Item | Value |
|---|---|
| Hydromorphone PCA | 0.2 mg demand, 6–15 min lockout1 |
| Morphine PCA | 1 mg demand, 6–15 min lockout1 |
| Naloxone titration | 40 mcg IV every 2 min |
| Ketamine | 0.5 mg/kg at induction; 0.1–0.25 mg/kg/h; monitored bed above 0.35 mg/kg bolus or 1 mg/kg/h2 |
| Lidocaine infusion | 1.5 mg/kg bolus; 1–2 mg/kg/h |
| Acetaminophen | 1 g every 6 h; max 4 g/day |
Links
- Acute pain in the opioid-tolerant patient, Opioids and postoperative respiratory depression, Obstructive sleep apnea, TAP, ESP, PECS, QL and fascia iliaca blocks, Dexmedetomidine and ketamine
- ASA Practice Guidelines for Acute Pain Management in the Perioperative Setting; ASRA/AAPM/ASA consensus guidelines on intravenous ketamine for acute pain (2018)
Sources
- 1.Pearls and Pitfalls of Patient-Controlled Analgesia · U.S. Pharmacist, 2017 · uspharmacist.com
- 2.Intravenous Ketamine Guidelines for Pain Management · ASRA Pain Medicine, 2018 · asra.comSummary of the 2018 ASRA/AAPM/ASA ketamine consensus guidelines (Schwenk, Reg Anesth Pain Med 2018;43:456-66); the full article could not be opened.
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.