IMMEDIATE ACTION Malignant hyperthermia rescue supplies should be readily available and administered as soon as possible.

Malignant hyperthermia is a rare but potentially fatal complication. If a patient is determined to be at risk, it's almost 100% preventable, and if it presents unexpectedly, immediate action can drastically reduce its mortality. These precautions can help you stay a step ahead of MH.

Pre-op screening
Preventing MH begins by identifying patients at risk. As MH is an inherited disorder and often triggered by exposure to certain anesthetics, those compiling medical histories should cover personal and family anesthetic experiences in detail. Keep in mind that previous successful administrations of general anesthetics don't rule out MH susceptibility.

Suggested screening questions:

• Is there a family history of MH?
• Have family members experienced adverse reactions, complications or unexpected deaths as a result of anesthesia?
• Have you experienced a high fever, muscle disorder or dark-colored urine following anesthesia?

Pay particular attention to very young and very old patients, male patients, patients with trismus (also known as masseter muscle rigidity) and patients suffering musculoskeletal disorders, as they may be considered high-risk populations for MH.

Research has shown that 70% of MH cases are caused by mutations in the gene RYR1 (tinyurl.com/9prdjp3). Because genetic testing is available to identify this mutation, it stands to reason that it can truly prevent MH among high-risk patients. Certain muscle biopsy tests, such as the caffeine-halothane contracture test and the in-vitro contracture test, can also indicate susceptibility to MH. The Malignant Hyperthermia Association of the United States (www.mhaus.org) can provide a list of qualified testing centers.

Preventive measures
If a patient with a history of or at high-risk for MH is scheduled for surgery, your anesthesia provider should play a lead role in taking preventive action.

The use of certain anesthesia agents must be avoided. Known triggering agents include muscle relaxants, such as the paralytic succinylcholine, and volatile inhalational drugs such as desflurane, sevoflurane and isoflurane. In some situations, anesthesia providers may consider administering a pre-operative, prophylactic dose of dantrolene (2mg/kg 30 minutes before surgery).

Schedule an MH-susceptible patient's case as the first of the day in order to avoid inadvertent exposure to traces of agents used in other surgeries.

Install a new soda lime canister in the anesthesia machine. Another safeguard is a device consisting of an activated-charcoal filter that you place between the machine and the inspiratory and expiratory sections of the breathing circuit. Designed to absorb potential anesthetic vapors that may induce an MH reaction, it also prevents the vapors from contaminating the machine's internal components.

Prevention is a key defense, but so are prompt recognition and preparedness. Your OR team's response plan should be based on guidelines set forth by MHAUS — which provides evidence-based information regarding protocols, algorithms, the latest scientific news and recommendations for optimal care in a crisis — tailored to your facility and drilled routinely.

A well-stocked MH cart and resuscitative devices must be regularly maintained and readily available (see "Contents of an MH Cart"). At least 18 vials of dantrolene must be immediately available. Most states and accreditation agencies require surgical facilities to have at least 36 vials on site. Keep a code cart nearby as well, as its medications may be needed as an MH emergency progresses.

Know your roles
The early signs of MH include tachycardia, a rapid rise in end-tidal CO2 and arrhythmia. They're followed by symptoms of acidosis, hyperkalemia, muscle rigidity, high fever, myoglobinurea and elevated creatine kinase. If you see these signs, get help, get dantrolene and notify the surgeon immediately.

The anesthetist should immediately discontinue the succinylcholine and anesthetic agents. Hyperventilating the patient with 100% oxygen (at least 10L/minute) will offset the high CO2 that can lead to respiratory acidosis. MHAUS doesn't recommend changing the breathing circuit or CO2 absorbent due to time constraints, but switching to a non-rebreather bag or open breathing circuit can reduce inspired agents.

The first dose of dantrolene must be administered as soon as possible, via a large-bore intravenous or central venous line. Improved formulations are much more soluble than earlier versions, making reconstitution much quicker. Only use preservative-free sterile water to reconstitute dantrolene. But don't hang the bag while drawing it up. In the rush of activity, it might be inadvertently spiked and used as a line on the patient, in whom its hypotonic properties might cause hemolysis or other harmful effects.

Lower the patient's body temperature with cold packs in the axilla and groin, a gastric or rectal ice saline lavage, IV fluid cooling or other means. Start an arterial line to administer drugs that counteract acidosis, arrhythmias or other complications. Monitor urine output, observing the color: brownish urine indicates myoglobinurea. Draw blood frequently for arterial blood gases, calcium levels, electrolytes, CK levels, coagulation studies and myoglobin levels. Freestanding surgical facilities should decide whether transfer to a hospital is warranted.

Once stabilized, the post-operative patient should be observed closely and maintained on dantrolene 1mg/kg for 24 to 48 hours. It may be administered orally or by continuous infusion for several days (along with continued bloodwork) to forestall recurrence until symptoms are resolved.