Prior Hypothermia Attenuates Malignant Hyperthermia in Susceptible Swine

Abstract

This study was designed to determine the extent by which mild or moderate hyperthermia attenuates the triggering of malignant hypothermia (MH) induced by the combined administration of halothane and succinylcholine. Sixteen susceptible swine were initially anesthetized with nontriggering drugs and then either kept normothermic (approximately equal to 38 degrees C, n = 6) or cooled to induce mild (approximately equal to 35 degrees C, n = 6), or moderate (approximately equal to 33 degrees C, n = 4) hypothermia. Next, after a 30-min control period, the normothermic and mildly hypothermic animals were administered 1 minimum alveolar anesthetic concentration (MAC) halothane followed by a bolus dose of succinylcholine (2 mg/kg). Within 10 min all normothermic animals developed fulminant MH, whereas the onset of MH was slowed or was absent in the mildly hypothermic group. To test whether moderate hypothermia could more effectively minimize the signs of a MH episode, this group of animals was exposed to 1.5 MAC halothane followed 10 min later by a 3-mg/kg bolus of succinylcholine. MH was not induced and anesthesia was then changed to nontriggering drugs (ketamine and pancuronium). The animals were then aggressively rewarmed to 38 degrees C: a slight increase in the ETCO2 was detected, but MH episodes did not spontaneously occur. Subsequently, the readministration of halothane and succinylcholine rapidly provoked fulminant MH. We concluded that the induction of mild hypothermia impairs triggering and reduces the progression of MH induced by the combined administration of halothane and succinylcholine, whereas moderate hypothermia was completely protective and thus could be considered for prophylaxis.

Hipotermia no período peri-operatório

“…La hipotermia posee efecto directo sobre la inmunidad celular y humoral 50,52 y efecto indirecto a través de la disminución de la oferta de O2 a los tejidos periféricos 76,77 . La disminución de 1,9 o C en la temperatura central triplica la incidencia de infección en el local de la operación después de resección del colon y aumenta en 20% la duración de la hospitalización, lo que también genera aumento del costo hospitalar.…”

“…Un estudio experimental demostró menor incidencia de HM en pacientes susceptibles sometidos a hipotermia, bien como menor gravedad de las crisis una vez desencadenadas 77 .…”

Malignant hyperthermia

“…However, the clinical presentations and first signs of MH episode are highly variable, especially when some individuals exhibit only one or a few symptoms of varying intensity; it is not easy to diagnose MH with confidence [31,32]. Although the underlying causes for the variability of the clinical presentation are poorly understood, different potency, concentration and duration of exposure to the triggering inhalation anesthetics, as well as additional factors, such as temperature, age and genetic variability, may be related with the heterogeneous clinical presentations [31,33,34]. The variability in the order and time of onset of signs often makes the clinical diagnosis rather difficult [7,35,36].…”

Malignant hyperthermia

“…The underlying causes for the variability of the clinical picture have not yet been identified. Varying potency, concentration and duration of exposure to the trigger, as well as additional factors such as temperature [68,69], age and genetic variability [70], might explain the heterogeneous picture.…”

“…On the contrary, MHN swine did not show any reaction at all. Iaizzo and his colleagues demonstrated that mild hypothermia had a harmful influence on the onset and extent of the syndrome whereas moderate hypothermia even prevented MH induction with halothane and succinylcholine [69]. After rewarming, MH could be triggered by the same drugs.…”