Effects of ketamine on dopamine metabolism during anesthesia in discrete brain regions in mice: comparison with the effects during the recovery and subanesthetic phases.

The effects of ketamine on the levels of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were examined in discrete brain regions in mice. A high dose of ketamine (150 mg/kg, i.p.) did not change DA metabolism in the frontal cortex, nucleus accumbens, striatum and hippocampus, but did decrease it in the brainstem during anesthesia. In contrast, during recovery from the ketamine anesthesia, the high dose increased the level of homovanillic acid (HVA) in all brain regions. A low subanesthetic dose of ketamine (30 mg/kg, i.p.) increased the concentrations of both 3,4-dihydroxyphenylacetic acid (DOPAC) and HVA only in the nucleus accumbens. The DA level was not affected by any ketamine treatment. During ketamine anesthesia, the content of 3-methoxy-4-hydroxy-phenylglycol (MHPG) was decreased in the brainstem, whereas during recovery from anesthesia, the MHPG level was increased in the frontal cortex, nucleus accumbens and brainstem. The NE content was not altered in any region by ketamine treatment. The concentration of 5-hydroxyindoleacetic acid (5-HIAA) was reduced in the frontal cortex, striatum, hippocampus and brainstem during ketamine anesthesia. The 5-HT level was unaltered in all regions except the brainstem where it was reduced. In contrast, after anesthesia, the concentrations of both 5-HT and 5-HIAA were increased in the striatum. During the subanesthetic phase, however, the levels of NE, 5-HT and their metabolites were unchanged. These neurochemical results are consistent with the electrophysiological findings that a high dose of ketamine does not change the basal firing rates of nigrostriatal DA neurons during anesthesia, while low subanesthetic doses significantly increase those of ventral tegmental DA neurons.

Displacement of the endotracheal tube caused by postural change: evaluation by fiberoptic observation.

Unexpected displacement of the endotracheal tube during anesthesia caused by postural change of the neck or passive compression by the mouth gag was investigated under transluminal fiberoptic observation. Twenty-two patients were divided into orotracheal and nasotracheal intubation groups according to the technical requirements of the planned oral and maxillofacial surgery. Under nasotracheal intubation, the mean length of displacement from the carina was 21 mm by extension of the neck, and 8 and 7 mm by lateral rotation of the neck to the right and left sides, respectively. Under orotracheal intubation, the mean length of displacement from the carina was 12 mm by extension of the neck and almost 28 mm with application of the mouth gag. To avoid accidental extubation or one-sided bronchial intubation during anesthesia, the tip (distal end) of the endotracheal tube should be located less than 32 mm from the carina before extension of the neck and more than 41 mm from the carina before application of the mouth gag.