Patient-Controlled Analgesia – Opioid Toxicity in Renal Failure MCQ — NEET PG Practice Question | NEETPGAI
Patient-Controlled Analgesia – Opioid Toxicity in Renal Failure
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A 52-year-old male with chronic kidney disease (eGFR 28 mL/min/1.73m²) and poorly controlled diabetes mellitus is admitted for open cholecystectomy. On postoperative day 1, he is prescribed patient-controlled analgesia (PCA) with morphine (demand dose 2 mg, lockout interval 10 minutes, 4-hour limit 30 mg). By 18 hours post-op, he develops confusion, miosis, and shallow breathing (RR 10/min, SpO₂ 88% on room air). Which of the following is the MOST appropriate immediate intervention?
A. Administer naloxone 0.4 mg IV bolus, followed by infusion at 0.5 mg/hour
B. Switch to intravenous paracetamol 1 g every 6 hours with topical NSAIDs
C. Perform emergency intubation and mechanical ventilation
D. Reduce the PCA demand dose to 1 mg with a 15-minute lockout interval
Explanation
Opioid Overdose in PCA: Recognition and Management
Clinical Presentation
The patient exhibits the classic triad of opioid toxicity:
Respiratory depression (RR 10/min, SpO₂ 88%)
Altered mental status (confusion)
Miosis (pinpoint pupils)
Why This Patient Is at High Risk
1.
Renal impairment (eGFR 28): Morphine and its active metabolites (M3G, M6G) accumulate in renal failure, prolonging effect and increasing toxicity risk
2.
Diabetes mellitus: Associated with delayed gastric emptying, altered pharmacokinetics, and increased sensitivity to opioids
3.
PCA parameters: 30 mg in 4 hours is standard, but in renal failure this becomes excessive
Immediate Management
Naloxone (Option 0) is the GOLD STANDARD for acute opioid overdose:
Dose: 0.4 mg IV bolus (can repeat every 2–3 minutes up to 10 mg total)
Followed by: Continuous infusion at 0.5 mg/hour to prevent re-sedation (naloxone half-life ~30–60 min; morphine metabolites persist longer)
Mechanism: Competitive antagonism at μ-opioid receptors
Onset: 1–2 minutes IV
Monitoring: Watch for acute withdrawal, hypertension, tachycardia, pulmonary edema
Why Other Options Are Incorrect
Option 1 (Reduce PCA dose):
Merely reducing future doses does NOT address acute respiratory depression and hypoxemia NOW
The patient is actively hypoxic and confused; waiting for the next PCA cycle is dangerous
This is a preventive measure, not an acute intervention
Option 2 (Switch to paracetamol + NSAIDs):
Paracetamol is safe in renal impairment but provides inadequate analgesia post-operatively
NSAIDs are contraindicated in CKD (eGFR 28) due to risk of acute kidney injury and hyperkalemia
Does not reverse the ongoing opioid toxicity or respiratory depression
Option 3 (Emergency intubation):
Intubation is a last resort if naloxone fails or respiratory arrest is imminent
Naloxone should be tried first; most patients respond within 2–3 minutes
Premature intubation bypasses the definitive, reversible antidote
Increases ICU stay, ventilator complications, and mortality risk
Key Point
Naloxone is the antidote of choice for acute opioid overdose. In PCA overdose with respiratory depression, administer naloxone IV bolus immediately, followed by infusion to prevent re-sedation due to the longer half-life of morphine metabolites in renal failure.
Clinical Pearl
In patients with renal impairment on PCA, consider:
Reduced initial doses (morphine 1 mg demand, 15 min lockout)
Alternative opioids: Fentanyl (hepatic metabolism, no active metabolites) or remifentanil (ester hydrolysis) are safer
Morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) accumulate in renal failure and contribute to prolonged analgesia and toxicity—this is why renal patients are at higher overdose risk on standard PCA protocols.
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