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The anesthetic effect of lidocaine was evaluated in rats by determining the change in anesthetic requirement of cyclopropane MAC that was produced by blood concentrations of lidocaine in the clinically useful range. A linear reduction in anesthetic requirement was produced with concentrations up to 1 mug/ml. Further increases in lidocaine up to 5.5 mug/ml resulted in no further decrease in cyclopropane requirement. Lidocaine was found to contribute a maximum MAC fraction of 0.4.

Intracranial pressure (ICP) was recorded in 12 patients undergoing craniotomy and 2 patients for carotid arteriogram. ICP did not change in response to the injection of contrast medium but rose significantly and dramatically in response to laryngoscopy and intubation. The increase appeared related to initial ICP and thus may represent exhaustion of compensatory mechanisms in these patients. Special attention must be given to this factor during manipulation of the larynx in neurosurgical patients with raised initial ICP or space-occupying intracranial lesions.

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