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Critical Care·CA-3 / Fellow

Malignant Hyperthermia Crisis

High-stakes metabolic emergency management. Test your rapid response, Dantrolene pharmacology, and situational leadership.

The stem

A 12 y.o. boy is 45 minutes into a knee repair under General Anesthesia (GA) with sevoflurane and succinylcholine. You notice a sudden rise in ETCO2 from 38 to 72 mmHg, despite increasing minute ventilation. His heart rate is 155 and his temperature is 39.5C. Masseter spasm was noted on induction.

Focus

Management of the MH crisis, dantrolene dosing, and the logistics of mobilizing a team during a metabolic catastrophe.

Examination relevance

A 'Must-Know' clinical scenario. Examiners look for immediate cessation of triggers and rapid deployment of dantrolene.

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Expert sample response

I will manage this as a suspected Malignant Hyperthermia (MH) crisis. My immediate priority is calling for help and declaring an MH emergency to mobilize the Dantrolene cart and extra staff. Simultaneously, I will stop all halogenated agents (triggering agents), change the circuit or add charcoal filters, and hyperventilate with 100% oxygen at high flows (at least 10L/min).

I will administer Dantrolene (2.5 mg/kg IV) immediately and repeat until the physiologic state stabilizes. For his hyperkalemia and acidosis, I will provide bicarbonate, glucose/insulin, and calcium. I'll initiate active cooling with ice packs and cold saline and notify the surgical team to conclude the procedure as fast as possible. I will manage his arrhythmias with standard Advanced Cardiovascular Life Support (ACLS) protocols but avoid calcium-channel blockers if Dantrolene has been given, as this combination can cause fatal hyperkalemia and cardiovascular collapse. My goal is stabilization and transfer to an ICU for 24-48 hours of monitoring.

Full walkthrough

What the Examiner Is Testing

This case tests your ability to declare an emergency, eliminate the trigger, and deploy dantrolene — in that order, with no hesitation. The examiner is watching for whether you lead the team response or freeze trying to confirm the diagnosis with more tests. In MH, you treat first and confirm later.

The Board Trap

The trap is the calcium channel blocker — specifically verapamil or diltiazem given for the tachycardia. When dantrolene is on board, calcium channel blockers cause a fatal interaction: hyperkalemia and cardiovascular collapse. Any arrhythmia management must use standard ACLS agents — lidocaine, amiodarone, procainamide — but not calcium channel blockers.

Walk-Through: How This Case Plays Out

Examiner: ETCO2 has risen to 72 despite increasing minute ventilation. What do you do first?

Me: I'm calling a malignant hyperthermia emergency right now. I need more people — calling for help is step one. While I'm calling, I'm stopping sevoflurane immediately and switching to total IV anesthesia. I'm also asking the circulator to get the dantrolene cart. I'll change the breathing circuit or use activated charcoal filters to purge the volatile agent. Hyperventilate with 100% oxygen at 10 L/min or more.

Examiner: The cart arrives. How much dantrolene do you give?

Me: I would give 2.5 mg/kg IV as the initial bolus and repeat every 5 minutes until the ETCO2 starts dropping, the rigidity improves, and the temperature stabilizes. There's no maximum dose — I keep going until the crisis breaks. This is a 12-year-old, so I need his weight to calculate precisely — I'd ask the circulator immediately. Dantrolene should be mixed with sterile water, not saline.

Examiner: His potassium comes back at 7.2 and the EKG shows widened QRS. What do you do?

Me: I would push calcium chloride 1 gram IV to stabilize the cardiac membrane immediately. Then sodium bicarbonate, dextrose with insulin, hyperventilation — all the standard hyperkalemia treatments. I will not use a calcium channel blocker for the wide complex tachycardia — with dantrolene on board, that combination causes fatal cardiovascular collapse. If I need an antiarrhythmic, I'd use lidocaine or amiodarone.

Examiner: The surgical team asks if they can finish the case. What do you say?

Me: I would ask them to close as fast as possible and get out. The goal is to minimize ongoing muscle metabolism and heat production. The longer the procedure continues with active MH, the harder the crisis is to break. Once the case is done, this patient goes directly to the ICU for monitoring — he'll need 24 to 48 hours of observation for recurrence, continued dantrolene every 6 hours, and monitoring for compartment syndrome and DIC.

Key Phrases That Score Points

  • "Call for help and declare the MH emergency — mobilize the team before troubleshooting."
  • "Stop the triggering agent first — sevoflurane off, TIVA on, circuit flushed."
  • "Dantrolene 2.5 mg/kg IV, repeat every 5 minutes until the crisis breaks — no maximum dose."
  • "No calcium channel blockers with dantrolene — fatal hyperkalemia and cardiovascular collapse."
  • "ICU for 24-48 hours post-crisis — MH can recrudesce, especially if dantrolene is discontinued too early."

Why This Case Appears on the Boards

MH is a must-know clinical emergency. The examiner uses it to test whether you can manage a metabolic catastrophe while leading a team response, making real-time drug decisions under pressure, and avoiding the one dangerous drug interaction that kills patients.