Anesthesiology APPLIED Exam › Regional anesthesia and acute pain

PCA and multimodal analgesia

T1Regional anesthesia and acute pain·795 words · ~4 min read·v0.1DRAFT

Why examiners ask this

Postoperative pain is in nearly every post-op section, and the examiner wants a plan, not a list of drugs. The topic tests application of knowledge about PCA settings and multimodal agents, judgment about who should not have a basal infusion, and adaptability when the patient on a PCA is found somnolent with a respiratory rate of 6. It is also a vehicle for questions on opioid tolerance, sleep apnea and safety monitoring.

The 60-second answer

I build the plan from the bottom up. Regularly scheduled acetaminophen and an NSAID if there is no renal, bleeding or cardiac contraindication, plus a regional technique when one fits the surgery. I add dexamethasone, ketamine, lidocaine infusion or gabapentinoids selectively, based on the patient and procedure. For opioids, I use a PCA when the patient cannot yet take oral medication or needs rapid titration: hydromorphone 0.2 mg or morphine 1 mg demand dose, a 6–10 minute lockout, no basal infusion in an opioid-naive patient, and a 4-hour limit. I order sedation scoring, continuous pulse oximetry or capnography for high-risk patients, and naloxone. I transition to oral opioids as soon as the patient tolerates intake.

Decision points and the "why"

No basal infusion in the opioid-naive — the safety of PCA rests on the patient falling asleep before they press again; a basal rate breaks that loop and increases respiratory depression without improving analgesia.
Basal infusion in the opioid-tolerant — I replace the home opioid as a basal rate or continue it orally, because withdrawal and under-treatment are the bigger risks.
Nobody else presses the button — PCA by proxy defeats the safety mechanism; I educate families and nurses.
Ketamine for opioid sparing — 0.5 mg/kg at induction and 0.1–0.25 mg/kg/h reduces opioid consumption, particularly in tolerant patients and spine surgery.
Lidocaine infusion — 1.5 mg/kg bolus and 1–2 mg/kg/h helps after open abdominal surgery and return of bowel function; I do not combine it with a peripheral nerve or fascial plane block 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.
Monitoring — sedation precedes respiratory depression; I use the Pasero Opioid-induced Sedation Scale and continuous monitoring in sleep apnea and the elderly.

The complication they will inject

The nurse finds a 70-year-old with obstructive sleep apnea, on hydromorphone PCA after a hip replacement, difficult to rouse with a respiratory rate of 6 and SpO2 84%. I tell her to stimulate the patient, give oxygen, support the airway, stop the PCA and call a rapid response. I give naloxone 40 mcg IV every 2 minutes, titrated to breathing rather than full reversal, to avoid acute pain and pulmonary edema. Because naloxone is shorter-acting than hydromorphone, I start an infusion if needed and move the patient to a monitored bed. I check for contributing factors: the basal rate, renal impairment, benzodiazepines or gabapentin, and CPAP not applied. I then restart analgesia with multimodal agents and a lower opioid dose.

Pitfalls that cost points

Listing drugs without a plan or dosing order.
Starting a basal infusion for an opioid-naive patient.
Giving naloxone 0.4 mg as a bolus to an opioid-tolerant patient.
Forgetting sleep apnea and renal function when choosing the opioid and monitoring.
Using NSAIDs without considering renal function, bleeding and anastomotic risk.

Rapid-why

Q: Why avoid morphine in renal failure? A: Morphine-6-glucuronide accumulates and causes prolonged sedation and respiratory depression; hydromorphone or fentanyl is preferable.

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 6–10 minutes make sense? A: It allows the peak effect of each dose before the next can be given.

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, 6–10 min lockout
Morphine PCA	1 mg demand, 6–10 min lockout
Naloxone titration	40 mcg IV every 2 min
Ketamine	0.5 mg/kg bolus; 0.1–0.25 mg/kg/h
Lidocaine infusion	1.5 mg/kg bolus; 1–2 mg/kg/h
Acetaminophen	1 g every 6 h; max 4 g/day

Sources

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