The Effect of Hypothermia on Isoflurane MAC in Children

Liu, Mingzheng; Hu, Xiaoqin; Liu, Jin

doi:10.1097/00000542-200103000-00011

Cited by 64 publications

(34 citation statements)

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“…Cooling of the brain to 20°C in animals and humans, as commonly performed during surgical procedures, is known to produce effective anesthesia independently of chemical anesthetics (Antognini, 1993;Liu et al, 2001). Together with these previous observations, our present data support suggestions that actin-based mechanisms in dendritic spines may have widespread effects on brain function (Crick, 1982;Matus, 2000).…”

Section: Discussionsupporting

confidence: 87%

Hypothermia-Associated Loss of Dendritic Spines

Roelandse¹,

Matus²

2004

J. Neurosci.

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Mechanisms of synaptic plasticity in CNS circuits are commonly investigated using in vitro preparations such as brain slices or slice culture. During their preparation, slices are exposed to low temperatures, and electrophysiological measurements are sometimes made below physiological temperature. Because dendritic spines, which occur at the majority of excitatory synapses, are morphologically plastic, we investigated the influence of reduced temperature on their morphology and plasticity using live cell imaging of hippocampal slices from transgenic mice expressing a green fluorescent protein-based neuronal surface marker and electron microscopy of adult brain slices. Our data show that dendritic spines are highly sensitive to reduced temperature with rapid loss of actin-based motility followed at longer times by reversible loss of the entire spine structure. Thus, reduced temperature significantly affects synaptic morphology, which is in turn known to influence several key aspects of synaptic transmission. Evidence that hypothermia potentiates anesthesia and is associated with spine loss in hibernating animals further suggests that spine morphology may have a widespread influence on brain function.

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Section: Discussionsupporting

confidence: 87%

Hypothermia-Associated Loss of Dendritic Spines

Roelandse¹,

Matus²

2004

J. Neurosci.

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“…Our finding of a 6.3% decrease (in gas-phase partial pressure) in MAC per 1°C decrease in body temperature approximates the change previously found with potent volatile anesthetics [1][2][3][4][5][6][7] and exceeds the change seen with cyclopropane [2] and nitrous oxide [4]. It assumes a proportionate decrease per degree temperature decrease.…”

supporting

confidence: 85%

“…Key words Anesthetics · Alcohols · Anesthetic potency-MAC · ED 50 · Ethanol · Ethyl alcohol · Hypothermia · MeyerOverton hypothesis Although hypothermia decreases the partial pressures required to produce anesthesia (e.g., minimum alveolar concentration [MAC]) for potent, volatile inhaled anesthetics [1][2][3][4][5][6][7], room temperatures usually are used in studies of the effects of ethanol and other anesthetics in oocytes or isolated neurons. This change in potency mandates the use of different partial pressures at different temperatures to apply a constant anesthetic potency.…”

mentioning

confidence: 99%

Hypothermia decreases ethanol MAC in rats

Won

Brosnan

et al. 2006

J Anesth

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Despite the known capacity of hypothermia to increase anesthetic potency (decrease the partial pressure required to produce anesthesia), many in vitro studies examine the effects of ethanol and other anesthetics in oocytes or isolated neurons at room temperature. We tested whether, as predicted for potent inhaled anesthetics, a proportionate increase in solubility with hypothermia matched a decrease in ethanol minimum alveolar concentration (MAC), and thereby made the use of a single anesthetic concentration appropriate regardless of temperature. We determined ethanol MAC in normothermic (37.3 degrees C) and hypothermic (28.5 degrees C) rats, and, at the two temperatures, also determined ethanol solubilities in olive oil and saline. Ethanol MAC decreased, while olive oil/gas and saline/gas partition coefficients increased. However, the increase in the saline/gas partition coefficient did not match the decrease in MAC, and thus the aqueous-phase partial pressure producing absence of movement in 50% of rats (EC50) values for ethanol decreased by 17%. Although this decrease is not large, it may be important for comparative estimates of the in vitro effects of ethanol at different temperatures.

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“…As patient Clark-Price temperature decreases, inhalant anesthetic tissue solubility increases, resulting in increased anesthetic content in body tissues, including the brain, causing increased depth of anesthesia due to a relative anesthetic overdose. 21,22 Hypothermia can have profound effects on the cardiovascular system through several mechanisms. Alpha receptors show decreased affinity to norepinephrine with subsequent reduced vascular contractility and hypotension.…”

Section: Deleterious Effects Of Hypothermiamentioning

confidence: 99%