Differential diagnosis of thyroid crisis and malignant hyperthermia in an anesthetized porcine model

The intra-operative differential diagnosis between thyroid crisis and malig nant hyperthermia can be difficult. Also stress alone can trigger MH. The p urposes of this study were: 1) to investigate the metabolic and hemodynamic differences between thyroid crisis and MH, 2) determine how thyroid crisis affects the development of MH, and 3) determine if the stress of thyroid c risis can trigger MH in susceptible individuals. We studied MH susceptible and normal swine. Two groups of animals (MH susceptible and normal) were in duced into thyroid crisis (critical core hyperthermia, sustained tachycardi a and increase in oxygen consumption) by pretreatment with intraperitoneal triiodothyronine (T-3) followed by large hourly intravenous injections of T -3. Two similar groups were given intravenous T-3 but no pretreatment. Thes e animals did not develop thyroid crisis and served as controls. Thyroid cr isis did not result in metabolic changes or rigidity characteristic of an a cute episode of MH. When the animals were subsequently challenged with MH t riggering agents (halothane plus succinylcholine) dramatic manifestations o f fulminant MH episodes (acute serious elevation in exhaled carbon dioxide, arterial CO2, rigidity and acidemia) were noted only in the MH susceptible animals. Although thyroid crisis did not trigger MH in the susceptible ani mals it did decrease the time to trigger MH (14.1 rt 7.2 minutes versus 47. 2 +/- 17.7 minutes, p< 0.01) in susceptible animals. Hormone induced elevat ions in temperature and possibly other unidentified factors during thyroid crisis may facilitate the triggering of MH following halothane and succinyl choline challenge.