Anaes Cases · Physiology
Slow wake-up after a prolonged propofol-fentanyl infusion
A short hot case on the context-sensitive half-time and the failure of the elimination half-life to predict recovery after an infusion. The candidate must recognise that the slow wake-up is pharmacokinetic (a rising CSHT for fentanyl and, to a lesser degree, propofol, after a long infusion as the peripheral compartment fills), exclude residual neuromuscular blockade and other causes, and explain how the choice of an opioid with a flat CSHT (remifentanil) would have avoided the problem. Tests compartment modelling, the context-sensitive half-time, and recovery-room pharmacology.
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A 78-year-old woman (78 kg) has just finished a 6-hour laparotomy for bowel resection under total intravenous anaesthesia: propofol TCI (Marsh model, target 3.5 micrograms per mL) and a fentanyl infusion at 2 micrograms per kg per hour, with rocuronium for relaxation. Neuromuscular blockade has been fully reversed (train-of-four ratio 0.9, no fade on tetanus). The propofol and fentanyl infusions are turned off, but 25 minutes later she is still not breathing spontaneously and does not open her eyes to command. The end-tidal CO2 is 48 mmHg with no spontaneous breaths. The processed EEG (bispectral index) reads 62.
References6ShowHide
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