NEUROMUSCULAR CASE OF THE MONTH - NOVEMBER 2003

SPECIAL FEATURE- Safe Anesthesia For Patients With Inherited Myopathies- Increased Anesthetic Risk?
Contributed by David B Brunson DVM, MS, DACVA
University of Wisconsin
Madison, WI

             “Malignant hyperthermia” (MH) is a clinical syndrome classically characterized by skeletal muscle rigidity, tachypnea, rapid elevation of core body temperature, severe metabolic acidosis, hypercarbia and cardiac arrhythmias that, left untreated, invariably leads to death. In reality, this description is often the exception rather than the rule. In most cases MH is a much more subtle disorder. In human medicine, MH is no longer considered to be a single disease but rather a clinical syndrome (MHS) with a shared pathophysiologic cascade and multiple genetic and environmental points of entry. In particular, all clinical and laboratory manifestations of MHS derive from a breakdown of calcium sequestration in the sarcoplasmic reticulum of skeletal muscle in the presence of halogenated volatile anesthetics and non-depolarizing muscle relaxants. Human MH can be viewed as a complex syndrome embracing many genetic disorders of muscle calcium regulation.
             Malignant hyperthermia syndrome falls under the rubric of diseases broadly known as channelopathies. These disorders are well recognized in human medicine but poorly characterized in companion animal species. Many of these human disorders are characterized by episodic stiffness or weakness, a clinical presentation not uncommonly observed in dogs. Diseases that may be associated with MHS in humans include but are not limited to mitochondrial myopathies, myoadenylate deaminase deficiency, hypokalemic periodic paralysis, central core disease, proximal myotonic myopathy, exercise induced rhabdomyolysis (stress), and heat stroke. A similar spectrum of disorders likely occurs in dogs.
             Multiple clinical studies have shown that the mortality associated with general anesthesia for dogs is high. The rate of complications associated with anesthesia is as high as 2.1% and a death rate of 0.11% in Canada (Dyson 1998), 0.43% and 0.11% in the USA (Dodman 1992, Gaynor 1999), and 0.23% in England (Clarke 1990). Animals with a suspected genetic muscle disease should be assumed as having an increased risk for anesthetic complications. A muscle biopsy procedure requiring anesthesia is necessary for an accurate diagnosis and prognosis. An accurate diagnosis is also important to the development of DNA based genetic testing and selective breeding programs. In animals with a suspected inherited muscle disease it would be wise to follow “safe anesthesia” rules. Fortunately for the animal owner and the veterinarian, Malignant Hyperthermia Syndrome (MHS) is a preventable clinical problem.

AVOID: ALL VOLATILE ANESTHETHICS INCLUDING HALOTHANE, ISOFLURANE, SEVOFLURANE, AND DEPOLARIZING NEUROMUSULAR BLOCKING AGENTS (SUCCINYLCHOLINE)

SAFE AGENTS FOR INDUCTION AND MAINTENANCE OF ANESTHESIA

More information on MHS will be Forthcoming in Neuromuscular Diseases II, Veterinary Clinics of North America to be published November 2004.

References

Clarke C, Hall LW. A survey of anaesthesia in small animal practice. AVA/BSAVA Report. J assoc Vet Anaesth 17: 4-10, 1990.

Dodman NH, Lamb LA. Survey of small animal anesthetic practice in Vermont. J Am Anim Hosp Assoc 28: 439-445, 1992

Dyson DH, Maxie MG, Schnurr D. Morbidity and mortality associated with anesthetic management in small animal veterinary practice in Ontario. J Am Anim Hosp Assoc 34: 325-335, 1998.

Gaynor JS, Dunlop CI, Wagner AE, Wertz EM, Golden AE, Demme WC. Complications and mortality associated with anesthesia in dog and cats. J Am Anim Hosp Assoc 35:13-17, 1999

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