Earlier this year, I managed the anesthesia of a 19-year-old male patient who suffered a malignant hyperthermic crisis more than 10 hours into a lengthy orthopedic procedure. My experience with MH was stressful but ended well, thanks to pre-emptive planning and proven treatment protocols that worked when it mattered most. The event impressed upon me the importance of having a fully stocked MH cart, a clearly written response protocol, and a surgical team trained in the recognition and management of MH. Be sure you can answer the following questions in order to avoid an MH emergency or avert disaster when the disorder strikes unexpectedly.

1. What are MH's risk factors? MH is inherited, so having close relatives with the disorder is probably the biggest risk factor. Patients with muscular dystrophy and myotonia may have adverse reactions to triggering medications — sevoflurane, desflurane, isoflurane, halothane, enflurane, methoxyflurane and succinylcholine — but these reactions are not considered to be true forms of MH. Susceptible patients can rather easily receive general anesthesia with non-triggering medications as long as the anesthesia provider knows to plan for the use of alternative agents, which include narcotics, nitrous oxide, propofol, ketamine, barbiturates, benzodiazepines and etomidate. Any local or regional anesthetics would also be safe for use on MH-susceptible patients.

2. How can you recognize early warning signs and symptoms? Patients experiencing an MH reaction will usually demonstrate a steadily increasing expired carbon dioxide level, tachycardia, muscle rigidity, and severe metabolic and respiratory acidosis. The rapid rise in body temperature often occurs later, manifesting as the syndrome's last symptom. As muscle breaks down, myoglobinuria may be evident on gross inspection of the urine.

The earliest sign of a metabolic disturbance in the case I worked was sinus tachycardia that increased steadily over about 10 minutes into the range of 160 beats per minute. The patient's end tidal carbon dioxide rose rapidly, reaching its peak around 80mmHg, despite a doubling of the minute ventilation. Peak airway pressures increased rapidly from 20cm to 45cm water, which may have resulted from chest wall rigidity or a reduced endotracheal tube diameter due to masseter spasm. The patient was in lateral position, facing away from the anesthesia team, making examination and evaluation more challenging. The only triggering agent to which he had been exposed was isoflurane. Fortuitously, a venous blood gas had been drawn 45 minutes earlier and was completely normal. In that short interval, a repeat venous blood gas showed that the patient's pH level had decreased to 7.0, his pCO2 was 98mmHg, his pO2 was 27mmHg and the lactic acid level had increased from 1 to 11. That is an impressive metabolic deterioration.

We decided to terminate the volatile anesthetic and begin the treatment protocol for MH, which began with a call to the Malignant Hyperthermia Association of the United States' hotline (800-MH-HYPER). Within moments, we spoke to an expert who provided invaluable suggestions and advice.

3. What should an MH cart contain? MHAUS recommends that a response cart should contain a minimum of 36 vials of dantrolene, sterile water (non-bacteriostatic) in sufficient quantity to reconstitute those vials, sodium bicarbonate, furosemide, dextrose 50%, calcium chloride, regular insulin and lidocaine for injection. Supplies like 60ml syringes (for dantrolene), IV catheters, NG tubes and Toomey irrigation syringes should also be available. A full description of recommended MH cart contents can be found at www.mhaus.org.

4. What's the quickest way to prepare dantrolene sodium? This agent must be reconstituted from its dehydrated form with preservative-free sterile water. If a well-developed protocol and supplies have not been (continued on page 16) assembled in advance, you'll waste valuable time trying to locate the appropriate diluents.

During a crisis, recruit as many helpers as possible to reconstitute the dantrolene. Almost anyone can assist with this low-tech but time-consuming task; adult doses may require 8 to 9 vials, and may need to be repeated several times until symptoms abate. It may take 2 minutes or more for dantrolene to solubilize, so some experts advocate using warmed diluent to speed the preparation process. This may require storing the sterile water in a different location from the rest of the rescue supplies.