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Malignant hyperthermia

Malignant hyperthermia (MH or MHS for "malignant hyperthermia syndrome", or "malignant hyperpyrexia due to anesthesia") is a life-threatening condition resulting from a genetic sensitivity of skeletal muscles to volatile anaesthetics and depolarizing neuromuscular blocking drugs that occurs during or after anaesthesia. It is related to, but distinct from, the neuroleptic malignant syndrome. more...

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Signs, symptoms and diagnosis

The phenomenon presents with muscular rigidity, followed by a hypermetabolic state showing increased oxygen consumption, increased carbon dioxide production and hypercarbia, and increased temperature (hyperthermia), proceeding to rhabdomyolysis with rapid rising of blood levels of myoglobin, creatine kinase (CK/CPK) and potassium.

Halothane, a once popular but now rarely used volatile anaesthetic, has been linked to a large proportion of cases, however, all volatile anesthetics are potential triggers of malignant hyperthermia. Succinylcholine, a neuromuscular blocking agent, may also trigger MH. MH does not occur with every exposure to triggering agents, and susceptible patients may undergo multiple uneventful episodes of anesthesia before developing an episode of MH. The symptoms usually develop within one hour after anesthesia.

Susceptibility testing

Testing for susceptibility to MH is by muscle biopsy done at an approved center under local anesthesia. The fresh biopsy is bathed in a solution containing caffeine and halothane (the "caffeine-halothane contracture test", CHCT) and observed for contraction; under good conditions, the sensitivity is 97% and the specificity 78% (Allen et al., 1998). Negative biopsies are not definitive, so any patient who is suspected to have MH by history is generally treated with non-triggering anesthetics even if the biopsy was negative. Some researchers advocate the use of the "calcium-induced calcium release" test in addition to the CHCT to make the test more specific.

Litman & Rosenberg (2005) give a protocol for investigating people with a family history of MH, where first-line genetic screening of RYR1 mutations is one of the options.

Pathophysiology

Disease mechanism

Malignant hyperthermia is caused in a large proportion (25-50%) of cases by a mutation of the ryanodine receptor (type 1) on sarcoplasmic reticulum (SR), the organelle within skeletal muscle cells that stores calcium (Gillard et al., 1991). In normal muscle, the receptor releases small amounts of calcium when triggered, which is then reabsorbed into the SR for the next cycle of contraction. In MH, the receptor does not close properly after having opened in response to a stimulus. The result is excessive release of calcium, which is reabsorbed into the SR in a futile cycle; this process consumes large amounts of ATP (adenosine triphosphate), the main cellular energy carrier, and generates the excessive heat (hyperthermia) that is the hallmark of the disease. The muscle cell is damaged by the depletion of ATP and possibly the high temperatures, and cellular constituents "leak" into the circulation, including potassium, myoglobin, creatine and creatine kinase.

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Astute assessment by a perioperative nurse in an expanded role saves patient from malignant hyperthermia
From AORN Journal, 7/1/97 by Jane M. Murphy

Editor's note: This column M the Journal focuses on outstanding examples of skilled perioperative nursing practice. Clinical exemplars capture the interpersonal, ethical, and clinical judgments that perioperative nurses make in actual practice.

After working for years as a perioperative nurse in the OR, I recently assumed a new role as a preoperative pediatric nurse practitioner (PNP). In this role, I am able to integrate and expand on my perioperative nursing experience.

Two weeks after I began my new position, I interviewed John, a 15-year-old boy with arthrogryposis multiplex congenita and a history of multiple orthopedic surgery procedures. Arthrogryposis multiplex congenita is a group of congenital disorders characterized by extreme joint stiffness and contractures and associated hypoplasia or absence of muscle, bone, and soft tissues.(1)

As I asked about John's anesthesia history, his mother commented that John's urine had been red and then dark brown after each surgical procedure. I immediately thought about muscle breakdown as a possible cause of the discolored urine. Mrs W stated that physicians had tested John's urine after each surgical procedure but that the tests had been normal. She also reported that John had very high fevers (ie, up to 105.8 [degrees] F [41 [degrees] C]) after each surgical procedure and "had to be packed in ice."

The reported combination of discolored urine and hyperthermia triggered an alarm in my mind and made me wonder if John had experienced malignant hyperthermia (MH) with his previous surgical procedures. Malignant hyperthermia is a hypermetabolic disorder of skeletal muscle that can result in death if not recognized and treated promptly. Inhalation agents (eg, halothane, isoflurane) and neuromuscular blocking agents (eg, succinylcholine chloride, decamethonium) can trigger MH crises in susceptible patients. During MH crises, hypermetabolism eventually depletes adenosine triphosphate stores, which results in the disruption of skeletal muscle cellular membranes and leakage of myoglobin into the bloodstream.(2)

I discussed my concern about John's possible MH susceptibility with Dr F, an anesthesia fellow. She concurred with my assessment that John probably had experienced unrecognized MH episodes after previous surgical procedures. We scanned John's past medical records but could find no mention of MH crises, although the records clearly documented the changes in John's urine color and the postoperative hyperthermia that his mother had reported.

When Dr F interviewed John and his parents, she discussed a plan to use nontriggering anesthetic agents (eg, nitrous oxide, vecuronium bromide, propofol) during the planned surgical procedure. John tolerated the anesthesia and surgery very well and did not develop any postoperative complications. John's parents were satisfied with his outcome and relieved that the mystery of his postoperative hyperthermia and discolored urine was solved.

We referred John and his parents to the Malignant Hyperthermia Association of the United States for further information about MH and encouraged his parents to obtain a medical identification bracelet for John. We also indicated clearly in John's medical record that he was MH susceptible.

I was pleased that Dr F credited the discovery of John's MH susceptibility to my careful preoperative assessment and that she valued the preoperative clinic PNP role. Most of all, I was gratified that I was able to use my perioperative nursing skills to make a difference in the life of this patient.

NOTES

(1.) R E Behrman, "Arthrogryposis," in Nelson's Textbook of Pediatrics, 14th ed, R E Behrman et al, eds (Philadelphia: W B Saunders CO, 1992) 1748.

(2.) D Dunn, "Malignant hyperthermia," AORN Journal 65 (April 1997) 728-754; A J Donnelly, "Malignant hyperthermia: Epidemiology, pathophysiology, treatment," AORN Journal 59 (February 1994) 393-405; C Beck, "Malignant hyperthermia: Are you prepared?" AORN Journal 59 (February 1994) 367-390; Malignant Hyperthermia Association of the United States, Understanding Malignant Hyperthermia (Sherburne, NY: Malignant Hyperthermia Association of the United States, 1996).

JANE M. MURPHY, RN, MS, CPNP, is a pediatric nurse practitioner in the preoperative clinic at Children's Hospital, Boston.

COPYRIGHT 1997 Association of Operating Room Nurses, Inc.
COPYRIGHT 2004 Gale Group

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