PRIS: The Propofol Infusion Syndrome

If you’re like me, propofol infusion syndrome is one of those rare but catastrophic events where the treatment itself is the cause. Propofol is one of the most useful drugs in our armamentarium — and in ICU settings, high-dose prolonged infusions create a specific, lethal, and initially insidious syndrome. On the anesthesiology oral boards, PRIS tests whether you know the risk threshold, can recognize the early warning signs, and understand that the only treatment is stopping the drug.

The classic context is an ICU patient — TBI, status epilepticus, or post-cardiac surgery — who has been on high-dose propofol for more than 48 hours. Or a pediatric patient, who is disproportionately susceptible. The syndrome develops insidiously and is frequently fatal if not recognized early.

The Core Logic

Propofol impairs mitochondrial function at high doses and prolonged exposure. The specific mechanism involves inhibition of the mitochondrial electron transport chain and disruption of free fatty acid metabolism. The result is impaired cellular energy production — ATP depletion across multiple organ systems simultaneously. Cardiac, skeletal muscle, and hepatic function are most affected.

The clinical syndrome: metabolic acidosis (high anion gap, lactic acidosis), cardiac arrhythmias (Brugada-pattern ECG changes, new right bundle branch block), rhabdomyolysis (elevated CK, dark urine, myoglobinuria), hepatomegaly, and lipemia (propofol is in a lipid emulsion). Bradyarrhythmias and ventricular fibrillation can be the terminal event.

The dose-time relationship: risk increases dramatically above 4-5 mg/kg/hr or with use beyond 48 hours. Pediatric patients and those with high catecholamine states (sepsis, TBI, exogenous catecholamine infusions) are at higher risk. Carbohydrate-deficient states (prolonged NPO, inadequate caloric supplementation) exacerbate lipid metabolism impairment and increase risk.

How the Examiner Tests This

Classic scenario: a 45-year-old TBI patient has been in the NICU on propofol 60 mcg/kg/min (3.6 mg/kg/hr) for 72 hours for sedation and ICP management. The nurse calls because the patient has developed new bradycardia and the ECG shows a Brugada-pattern. "What do you do?" Stop the propofol immediately. This is PRIS until proven otherwise. Switch to an alternative sedative (midazolam, ketamine, or dexmedetomidine). Send CK, lactate, LFTs, urinalysis.

Follow-up probe: "What if the neurosurgeon insists propofol is needed for ICP control?" The risk of continuing propofol in established or suspected PRIS outweighs any ICP benefit. Ketamine — despite historical concerns about ICP elevation — has not been shown to increase ICP at sedating doses in ventilated patients and is an acceptable alternative. Dexmedetomidine, fentanyl infusion, and midazolam are additional options.

The Board Trap

The "keep the propofol, add treatments" trap: attempting to manage the metabolic derangements while continuing propofol. This is incorrect. There is no treatment for PRIS except removing the cause. Bicarbonate for the acidosis, CRRT for the lactate — these are supportive while the cause is eliminated, not while it continues. Stop the propofol first.

The pediatric dose trap: using ICU propofol infusion dosing in children. Propofol is approved for procedural sedation in pediatrics but is NOT approved for ICU sedation in children under 16. PRIS was first described in pediatric patients receiving high-dose infusions for status epilepticus. In the pediatric ICU, propofol infusions for prolonged sedation should not be used — alternatives exist and are safer.

Lead-In Phrases

• "My threshold for concern about PRIS is any patient on propofol above 4-5 mg/kg/hr or beyond 48 hours — I will follow daily CK, lactate, LFTs, and ECG monitoring in these patients."
• "The Brugada-pattern ECG change — right bundle branch block with ST elevation in V1-V3 — is an early cardiac warning sign of PRIS. If I see this in a patient on a propofol infusion, I stop the propofol immediately."
• "There is no treatment for PRIS except removing the cause. I will switch to an alternative sedative immediately — dexmedetomidine, midazolam, or ketamine — and support the patient through the metabolic derangements."
• "Propofol is absolutely contraindicated for prolonged ICU sedation in pediatric patients — I will use age-appropriate alternatives and reserve propofol for procedural sedation only in this population."
• "I will ensure adequate carbohydrate supplementation for any patient on prolonged propofol — carbohydrate deficiency worsens the impaired lipid metabolism that underlies PRIS."

FAQs

How do I distinguish PRIS from other causes of metabolic acidosis in the ICU?

The combination is specific: metabolic acidosis + elevated CK + ECG changes (Brugada pattern, new RBBB) + lipemia in a patient on high-dose prolonged propofol. No other common ICU condition produces this particular constellation. Sepsis produces lactic acidosis but not the characteristic ECG changes. Rhabdomyolysis from other causes lacks the ECG component. The context — high-dose, prolonged propofol — is the key clue.

Can PRIS occur with short-term propofol use in the OR?

Rare but reported. PRIS has been described with high-dose propofol for prolonged OR procedures (typically 6+ hours at high infusion rates). The risk is substantially lower than in ICU settings because the exposure duration is shorter. Nonetheless, for very prolonged cases requiring high propofol doses, CK monitoring post-operatively is reasonable. Standard TIVA cases with normal dosing do not carry meaningful PRIS risk.

What are the survival predictors in PRIS?

Early recognition and immediate cessation of propofol are the most important factors. Patients who develop cardiac arrest before PRIS is recognized have very high mortality. ECMO has been used as a bridge in refractory PRIS-associated cardiac collapse. Hemodialysis or CRRT can help with metabolic clearance but does not eliminate propofol or its metabolites quickly. Prognosis depends heavily on how much end-organ injury has occurred before the drug is stopped.

PRIS is prevention first, recognition second. Know the dose threshold (4 mg/kg/hr, 48 hours), monitor for the early ECG and CK changes, and stop the propofol the moment you suspect it. Practice the recognition-to-drug-discontinuation sequence in Boards Bot until the Brugada-pattern ECG triggers an immediate propofol stop.