Malignant Hyperthermia at 02:10 With a Short Dantrolene Supply

First dose: 2.5 mg/kg x 70 kg = 175 mg.

Traditional dantrolene (20 mg/vial):

• 175 / 20 = 8.75, so 9 vials.
• Each vial is reconstituted with 60 mL of preservative-free sterile water.
• That is 540 mL of diluent to draw up - a two-person job, and it takes minutes.

Ryanodex (250 mg/vial):

• Reconstituted with 5 mL to 50 mg/mL.
• 175 mg / 50 mg/mL = 3.5 mL from one vial. Far faster, and it is already in the room.

24-hour requirement: up to 10 mg/kg = 700 mg = 35 vials of 20 mg, or about three Ryanodex vials. Repeat doses are 2.5 mg/kg (175 mg) as needed until symptoms abate, then 1 mg/kg every 6 hours.

What the math tells you: 12 vials of 20 mg is only 240 mg. That covers the first 175 mg dose and one 1 mg/kg (70 mg) follow-up - barely. There is no margin for a second full 2.5 mg/kg dose.

Action: give the first dose now (the Ryanodex is fastest and is in hand), and simultaneously send a runner with a named person and a phone number to break into the pharmacy supply, call the MH hotline, and alert the receiving ICU. Do not wait for the full 24-hour supply before treating.

1. Call for help and declare malignant hyperthermia - name it aloud, assign one person to the MH cart and one to the phone.
2. Stop surgery and tell the surgeon to close or pack as fast as safely possible.
3. Discontinue sevoflurane and succinylcholine. Turn the vaporizer off and remove it if possible; do not give any more triggering agent.
4. 100% O2 at high flow (10 L/min or more) with a new circuit and charcoal filters if available; hyperventilate, aiming for two to three times the minute ventilation.
5. Give dantrolene 2.5 mg/kg = 175 mg IV now, repeat until the CO2, rigidity, and tachycardia resolve.
6. Stop all warming; begin active cooling if the temperature is above 38.5 or rising - chilled IV fluids, surface cooling, lavage as needed. Do not overshoot into hypothermia.
7. Establish or confirm large-bore access and an arterial line, and send labs: ABG, potassium, ionized calcium, CK, myoglobin, coagulation studies, and a urine sample.
8. Treat hyperkalemia and any dysrhythmia per protocol; watch the potassium as the temperature falls.
9. Protect the kidneys - urine output target, fluid, and treat myoglobinuria.
10. Prepare the machine for the next patient: new circuit, new CO2 absorbent, charcoal filters, and flush at 10 L/min for at least 10 minutes per MHAUS guidance, or take the machine out of service entirely.

Avoid: calcium channel blockers (verapamil, diltiazem) - they interact with dantrolene to cause hyperkalemia and cardiovascular collapse.

Post-event plan:

• Admit to intensive care for at least 24 hours with continuous temperature, ECG, and urine output monitoring. Recrudescence is the reason for the admission; it can occur hours later.
• Dantrolene 1 mg/kg every 6 hours for 24-48 hours per protocol, or as directed by the MH hotline.
• Track CK, potassium, renal function, and urine output until they normalize; rhabdomyolysis is the main delayed threat.
• Tell the patient and the family what happened, that this is an inherited susceptibility, and that all blood relatives are at risk.
• Refer for confirmation - caffeine-halothane contracture testing or genetic testing - and offer registration with the MH registry.
• Report the event to the pharmacy and to the MH hotline, and document the full sequence in the record.

Before the room is used again:

• The anesthesia machine must be prepared per MHAUS guidance or replaced; the vaporizer must be removed, the soda lime changed, a new circuit and charcoal filters fitted, and the machine flushed.
• The MH cart must be fully restocked and the dantrolene par level raised - 12 vials of 20 mg was not enough for one 70 kg patient.
• The pharmacy night-access process needs a fix: a locked supply four floors away with an unanswered phone line is a system failure that nearly cost this patient.
• Hold a team debrief within 24 hours and feed the findings into the next drill.