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LETTER TO THE EDITOR

If It Quacks Like a Duck Then ...!

Department of Anesthesiology; Weill-Cornell Medical Center; New York; New York; divemd{at}att.net (Lichtman) Cardiothoracic Intensive Care Unit; New York Methodist Hospital; Brooklyn; New York (Oribabor)

In Response:

Drs. Girard and Urwyler (1) take issue with our recent diagnosis and treatment of a hypermetabolic state (2). We agree that not all hypermetabolic states are due malignant hyperthermia (MH). Our differential diagnosis included sepsis and hypoperfusion. Neuroleptic malignant syndrome was ruled out as no agents implicated in the neuroleptic syndrome were used. Hypoperfusion was a possibility. However, the patient had a stable hemodynamic profile (cardiac index of greater than 2.5 L/min) upon arrival to the intensive care unit and the hypotension and decrease in MVO2 was precipitous. We were unable to acutely rule out sepsis.

This patient’s clinical presentation was entirely consistent with MH, including a combined respiratory and metabolic acidosis, skin mottling, skeletal muscle rigidity, a rapid rise in core temperature, and a drop in mixed venous oxygen saturation. The diagnosis was supported by the family history of unexplained intraoperative hyperpyrexia and acidosis in two different blood relatives under anesthesia. The most conservative course of action was to assume the worst and treated accordingly. Following the administration of dantrolene there was complete resolution of his metabolic derangement. Impending septic or cardiogenic shock would not have resolved following dantrolene.

There are several problems with attributing this patient’s hypermetabolic state to propofol infusion syndrome. The patent developed a combined respiratory and lactic acidosis despite adequate minute ventilation. The propofol infusion lasted only 3 h at a rate of 100 mcg/kg/min, and was discontinued well before the event in question.

Drs. Girard and Urwyler’s assertion that MH is strictly a pharmacogenetic disease requiring a pharmacological trigger has been disproven in the literature as evidenced by MH occurring without a classic trigger (3).

We elected to administer oral dantrolene to this patient due to his size (100 kg) and muscular build. The use of oral dantrolene for several days following an acute event of MH is described on page 538 in the most recent edition of the textbook Clinical Anesthesia (4). We proposed off-pump CABG as a means to avoid systemic rewarming from cardiopulmonary bypass based on our theory that warming was the inciting cause of this case report. This theory is not without both clinical human and experimental animal support.

Obviously we cannot force a patient to undergo diagnostic testing, but this patient did ultimately consent for molecular diagnostic studies. His RYR1 gene sequencing was negative for known pathological variants associated with MH. However, the clinical sensitivity of this test is roughly 40%, leaving the other 60% of the MH susceptible individuals unaccounted for. As such, we look forward to new and better diagnostic studies in the future (5).

This patient’s daughter will require a tonsillectomy in the near future. Any takers?

REFERENCES

1. Girard T, Urwyler, A. Not every hypermetabolic state is due to malignant hyperthermia! Anesth Analg 2007;104:1611–2.[Free Full Text]
2. Lichtman AD, Oribabor C. Malignant hyperthermia following systemic rewarming after hypothermic cardiopulmonary bypass. Anesth Analg 2006;102:372–5.[Abstract/Free Full Text]
3. Gronert GA, Thompson RL, Onofrio BM. Human malignant hyperthermia: awake episodes and correction by dantrolene. Anesth Analg 1980;59:377–8.[Free Full Text]
4. Barash PG, Cullen B, Stoelting RK, eds. Clinical anesthesia. Philadelphia: Lippincott Williams & Wilkins, 2005.
5. Galli L, Orrico A, Lorenzini S, et al. Frequency and localization of mutations in the 106 exons of the RYR1 gene in 50 individuals with malignant hyperthermia Hum Mutat 2006;27:830.[Medline]

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