Anesthesiology
-
Comparative Study
A comparison of the effects of hypothermia, pentobarbital, and isoflurane on cerebral energy stores at the time of ischemic depolarization.
In an accompanying article, we report that hypothermia (27-28 degrees C) delayed postischemic cortical depolarization longer than did large-dose pentobarbital or isoflurane anesthesia, even though preischemic cerebral metabolic rates for glucose were similar in the three groups. To examine the mechanism that may underlie these differences, we measured the cerebral concentrations of high-energy phosphates (including adenosine triphosphate [ATP] and adenosine diphosphate) in normal conditions and at the moment of depolarization. ⋯ The ATP/energy charge threshold for cortical depolarization was similar in all groups despite differing temperature or anesthetic conditions. Because hypothermia increased the time until depolarization, the rate of decrease in ATP concentration must have been slower in these animals than in the two groups receiving large-dose anesthetics, despite similar preischemic cerebral metabolic rates for glucose. This finding is similar to that of earlier studies and indicates that factors other than preischemic metabolic rate are responsible for controlling energy utilization after ischemia.
-
The effects of inhalation anesthetics on Ca2+ regulation in malignant hyperthermia-susceptible skeletal muscle are considered to be responsible for triggering malignant hyperthermia. The intravenous anesthetic propofol does not trigger malignant hyperthermia in susceptible patients or experimental animals, suggesting that there are important differences between the effects of propofol and the effects of inhalation anesthetics on Ca2+ regulation in malignant hyperthermia-susceptible muscle. Understanding these differences may help to clarify the mechanisms responsible for triggering malignant hyperthermia. ⋯ In contrast to malignant hyperthermia-triggering inhalation anesthetics, propofol does not stimulate malignant hyperthermia-susceptible or normal ryanodine receptor channel activity, even at > 100 times clinical concentrations. Effects on dihydropyridine receptor and Ca(2+)-ATPase function, however, are similar to the effects of inhalation anesthestics and require much lower concentrations of propofol. These findings, demonstrating that propofol does not activate ryanodine receptor Ca2+ channels, suggest a plausible explanation for why propofol does not trigger malignant hyperthermia in susceptible persons.
-
Randomized Controlled Trial Clinical Trial
Oral clonidine premedication blunts the heart rate response to intravenous atropine in awake children.
Clonidine, which is known to have analgesic and sedative properties, has recently been shown to be an effective preanesthetic medication in children. The drug may cause side effects, including bradycardia and hypotension. This study was conducted to evaluate the ability of intravenous atropine to increase the heart rate (HR) in awake children receiving clonidine preanesthetic medication. ⋯ Oral clonidine premedication (4 micrograms.kg-1) blunted the increase in HR after intravenous atropine in awake children, although clonidine 2 micrograms.kg-1 did not. A larger dose of atropine was required to increase the HR by 20 beats.min-1 in children receiving the premedicant in the larger dose.
-
Succinylcholine-induced masseter muscle rigidity (MMR) is a potentially life-threatening complication of anesthesia and is closely correlated with the heterogeneous disorder malignant hyperthermia (MH) susceptibility. MMR also is identified with a variety of neuromuscular disorders, including the myotonias, that are associated with abnormal in vitro contracture test (IVCT) results. Recently, mutations in the adult skeletal muscle sodium channel alpha-subunit gene (SCN4A) have been shown to cause generalized nondystrophic myotonias, some of which are associated with mild nonspecific symptoms. The purpose of the current investigation was to begin to evaluate the molecular genetic relationship between known mutations in the SCN4A gene, MMR, and the results of the IVCT used to diagnose MH-susceptibility. ⋯ The current report provides direct evidence that succinylcholine-induced MMR, whole-body rigidity, and an abnormal IVCT result are associated with a mutation in the SCN4A gene.