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Malignant Hyperthermia: Turn COM Malignant hyperthermia: Turn COM . THEISPOT / USTIN A ICHAEL M Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. down the heat By Fay Mitchell-Brown, MSN, BSN, RN AN INHERITED DISORDER, malignant hyperthermia (MH) is a life- threatening reaction to certain common inhalational anesthetic agents or 2.1 the depolarizing skeletal muscle relaxant succinylcholine in susceptible ANCC people. Characterized by a hypermetabolic state, it causes tachycardia, sus- CONTACT HOURS tained generalized muscle contractions, and high body temperature that may exceed 110º F (43.3º C).1,2 MH usually occurs during surgery or with- in an hour after exposure to the triggering agent, but it can develop up to 36 hours later.1-3 When MH was first identified, mortality from the disorder was 80%. With greater awareness of the risk and the discovery of dantrolene sodium, the only drug that effectively treats MH, mortality has dropped to about 5%.3 Death from MH is usually secondary to cardiovascular collapse.2 Nurses who care for patients during or after surgery must be knowledge- able about signs, symptoms, and treatments so they can identify MH imme- diately and respond appropriately. In addition, nurses assessing patients preoperatively must be able to identify patients at risk so the anesthesia provider can administer drugs that don’t trigger MH. Finally, because sus- ceptibility to MH is inherited, nurses must educate patients and their fami- lies about the risk. This article discusses how to identify patients at risk, respond to a crisis, and educate patients and their families. Genetic basis Over 80 genetic defects have been linked to MH. Because MH susceptibility is an autosomal dominant inherited disorder, a child or sibling of a suscep- tible patient has a 50% chance of inheriting a defective gene.2 Two dramatic experiences from my career illustrate the risks faced by families susceptible to MH. As a nursing instructor in a rural hospital, I met RB, a 15-year-old male scheduled for an orthopedic procedure. Admitted via the outpatient surgi- cal center, RB was taken to the OR where he underwent induction of gen- eral anesthesia with sevoflurane and succinylcholine. Thirty minutes into the procedure, RB developed tachycardia: HR 102/ minute from a baseline of 72/minute. His end-tidal carbon dioxide (ETCO2) level was slightly elevated and his temperature increased to 101.5º F (38.6º C) from a baseline of 99.3º F (37.4º C). Arterial blood gas (ABG) values showed respiratory acidosis with pH of 7.3 (normal, 7.35 to 7.45) and a PaCO2 of 48 mm Hg (normal, 35 to 45 mm Hg). The surgeon suspected that RB was experiencing MH and aborted the procedure. www.Nursing2012.com May l Nursing2012 l 39 Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. RB was hyperventilated with choline. Shortly after induction, TJ MH occurs most commonly in 100% oxygen and the surgical team developed a rapid rise in ETCO2, children and young adults. It’s more initiated the MH protocol developed sinus tachycardia with frequent pre- common in men than in women, by the Malignant Hyperthermia mature ventricular contractions, and and found equally among various Association of the United States generalized muscular rigidity. ABG ethnicities.3 (MHAUS), which includes I.V. ad- values indicated severe respiratory MH occurs worldwide but is ministration of dantrolene. RB was acidosis. TJ was cyanotic and his more common in areas that have transferred to the ICU for observation. core body temperature was 103.6º F MH-susceptible families. In the Fortunately, he responded quickly (39.8º C). The MH protocol was ini- United States, the incidence of MH to treatment and was transferred tiated immediately and TJ was trans- is especially high in Wisconsin, West out of the ICU in 24 hours. ferred to an acute care hospital for Virginia, Nebraska, and Michigan due Several months later, I assisted a higher level of care. But despite to concentrations of MH-susceptible with the care of RB’s uncle, who was prompt and appropriate treatment, families.1,2 Patients with certain pre- admitted to the ICU with an acute TJ died. existing muscle disorders associated MH crisis. TJ, 43, had been sched- with genetic abnormalities, such as uled for abdominal surgery in an Who’s at risk? central core myopathy, are also at outpatient surgical center. He too In susceptible patients, MH is trig- risk.3 However, most muscular and was given sevoflurane and succinyl- gered by certain specific drugs: the neuromuscular disorders aren’t as- depolarizing muscle relaxant succinyl- sociated with MH.2 choline and the inhalational anes- Safe or unsafe?1,2 thetic agents isoflurane, desflurane, What goes wrong? These drugs are MH triggers sevoflurane, enflurane, halothane, MH is a hypermetabolic crisis set in ether, and methoxyflurane.2 (See Safe motion by excess calcium release Inhalation anesthetic agents: • desflurane or unsafe?) Patients may develop an from muscle. After a susceptible per- • enflurane acute MH crisis at initial exposure to son is exposed to a triggering agent, • halothane a triggering drug, or after several ap- genetic muscle receptor abnormali- 3 • isoflurane parently uneventful exposures. Some ties lead the sarcoplasmic reticulum • methoxyflurane evidence indicates that strenuous ex- in skeletal muscle to release exces- • sevoflurane ercise or heat exposure can also trig- sive calcium. (See Making a muscle.) • ether ger MH in susceptible people.4 This leads to sustained muscle con- Depolarizing muscle relaxant: Patients at risk for MH can safely traction and rigidity, increasing me- • succinylcholine undergo surgery as long as they’re tabolism and generating heat.2,3 induced with nontriggering agents, Eventually the overworked cells are These drugs are safe to use as anesthetic agents in MH-susceptible such as propofol. Local anesthetics depleted of oxygen and adenosine 2 patients: are also safe. triphosphate (ATP), their energy • barbiturates/I.V. anesthetics such as Not all patients susceptible to MH source. These changes produce car- ketamine and propofol are diagnosed because they may never bon dioxide and cellular acidosis. • the inhaled nonvolatile general an- be exposed to triggering agents—or, An eventual switch to anaerobic esthetic nitrous oxide if their exposure time is brief, their metabolism accelerates acidosis.2,5 • local anesthetics such as lidocaine signs and symptoms may escape no- As stores of ATP in muscle cells and mepivacaine tice because they’re nonspecific and are depleted, cells die and release • opioids such as fentanyl and mor- mild. Uncomplicated cases can be potassium into the bloodstream. The phine difficult to diagnose.1 resulting hyperkalemia can trigger • muscle relaxants such as doxacu- For these reasons, the exact inci- fatal cardiac dysrhythmias. rium and vecuronium • antianxiety agents such as midazolam dence of MH is unknown. The inci- Dying cells also release the pigment and diazepam. dence of MH episodes may range myoglobin, causing myoglobinemia. Note: Visit the Malignant Hyperthermia Association from 1 in 5,000 to 1 in 65,000 ad- Myoglobin forms precipitate in the of the United States website for a more complete ministrations of general anesthesia renal tubules, resulting in acute kid- list of safe drugs: www.mhaus.org. with triggering agents.2 ney injury.1 40 l Nursing2012 l May www.Nursing2012.com Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. If the acute MH crisis continues, Making a muscle the patient will experience multiple potentially fatal complications, such Bone Skeletal muscle surrounded as acute kidney injury, left ventricu- by epimysium lar dysfunction secondary to hyper- tension, pulmonary edema, and dis- seminated intravascular coagulation Fascicle surrounded by perimysium (DIC).1 Tendon An MH crisis must be differenti- Muscle fiber (cell) A surrounded by ated from disorders causing similar Blood vessel endomysium signs and symptoms, such as trau- Sarcomere matic brain injury; hypoxic encepha- M line Myofibrils lopathy; neuroleptic malignant syn- contained drome; heat stroke; thyroid storm; in muscle fiber pheochromocytoma; sepsis; cocaine, T tubules H zone I band amphetamine, and salicylate toxicity; Z line or alcohol withdrawal.3,6 B A band Relaxation Recognizing the danger Actin Signs and symptoms of MH include Myosin the following. Note that hyperthermia is a later sign of MH and is usually C Contraction D Sarcoplasmic reticulum not present early in the crisis.3 • Hypercapnia. A progressive, unex- (A) Connective tissue components of a skeletal muscle. pected increase in ETCO2 is the ear- (B) Striations of the myofibril showing the overlap of contractile proteins and the liest and most sensitive sign that a A and I bands, the H zone, and the Z and M lines. (C) The relaxed and contracted patient might be experiencing MH.3,5 states of the myofibril showing the position of actin filaments (blue) between the 7 myosin filaments (pink) in the relaxed muscle (top) and pulling of the Z membranes Normal ETCO2 is 35 to 45 mm Hg. toward each other (bottom) as the muscle contracts. (D) The sarcoplasmic reticulum In MH, the ETCO2 value may dou- ble or even triple on capnography. with T tubules. Be suspicious if you find an unex- Source: Porth CM. Essentials of Pathophysiology. 3rd ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins; 2011:26. plained increase in ETCO2 that doesn’t respond to increased ventila- tion or additional administration of succinylcholine and doesn’t necessar- urine myoglobin, which peak about anesthetic.8 ily indicate MH unless it persists 14 hours after the acute MH episode, • Tachycardia. Although an early sign after potential triggering agents are vary depending on the patient’s of MH, tachycardia is nonspecific. discontinued.3 muscle mass and the severity of the • Generalized muscle rigidity, espe- • ECG changes. Hyperkalemia may patient’s condition.3 cially of the jaw, trunk, and extremi- cause premature ventricular contrac- • Hyperthermia.
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