Effects of sufentanil on median nerve somatosensory evoked potentials.

We have studied the effects of a single i.v. dose of sufentanil 5 micrograms kg-1 in combination with pancuronium on the median nerve short latency somatosensory evoked potentials (SSEP) in 15 unpremedicated patients undergoing thoracic or lumbar spinal surgery. The latency and amplitude of the SSEP response over the second cervical vertebra (SC) and sensory cortex (P17, N20, P25), heart rate and arterial pressure were recorded for 30 min after the injection of sufentanil. A significant increase in mean latency occurred for N20 (P less than 0.003) and P25 (P less than 0.002) within 2 min, but the absolute increase in latency was small. The mean amplitudes of all peaks decreased to 60% (SC), 70% (P17), 60% (N20) (P less than 0.012) and 45% (P25) of the baseline value within 7 min. The results suggest that the major change in median nerve SSEP produced by this dose of sufentanil is a reduction in amplitude, and that major changes in latency after sufentanil and pancuronium are probably caused by other influences.

Surgical and electrophysiological observations during clipping of 134 aneurysms with evoked potential monitoring.

Somatosensory evoked potentials (SEPs) were monitored during 113 operations for the clipping of 134 cerebral aneurysms. Changes in peak latency and amplitude of early cortical SEP as well as central conduction time were evaluated. In 58 cases surgical occlusion of arterial vessels or other events occurred, and in 17 of these cases such events were associated with SEP changes or loss. Arterial occlusions resulted from temporary clipping of a feeding blood vessel (22), accidental clipping of a vessel (12), and intentional permanent vessel occlusion (8). A total SEP loss was seen in 2 cases of accidental vessel occlusion and in 6 cases of temporary vessel clipping. Significant SEP changes were found in 6 patients with temporary clipping, and once each with retraction of the cerebellum, retraction of the middle cerebral artery, and after intentional permanent vessel occlusion. Response to these changes included reapplication of aneurysm clips, repositioning of retractors, or removal of temporary clips. Stable SEP signals during 13 cases allowed the surgeon to proceed with the surgical course. Despite the limitations of SEP monitoring in certain anatomical locations, it has been found to be helpful in the operative management of some cases such as multilobed aneurysms of the middle cerebral artery, giant aneurysms, trapping procedures, and procedures requiring temporary vessel occlusion.

Effects of etomidate, midazolam, and thiopental on median nerve somatosensory evoked potentials and the additive effects of fentanyl and nitrous oxide.

In 30 patients undergoing spinal disc operations, the effects of bolus injections followed by intravenous infusions of thiopental, etomidate, and midazolam on median nerve somatosensory-evoked potentials (SSEPs) were studied. Possible additive effects of fentanyl and nitrous oxide were also evaluated. Serial SSEP measurements were made before and for 25 minutes after the start of anesthesia. After induction with one of the three intravenous agents, fentanyl (10 micrograms/kg) was administered and SSEPs were again measured 1 and 5 minutes after administration. Sixty-five% nitrous oxide in 35% oxygen was administered after tracheal intubation and was followed by final SSEP measurements. The three intravenous agents affected SSEP signals differently. Etomidate increased both amplitude and latency. Thiopental decreased amplitude and increased latency. Midazolam had no effect on amplitude but increased latency. The addition of fentanyl and nitrous oxide had different effects in response to the three intravenous induction agents. This study emphasizes the differences in SSEP responses not only to different intravenous induction agents but also to the addition of fentanyl and nitrous oxide.

Anesthesia and evoked potentials: overview.

Evoked potentials are increasingly used for intraoperative monitoring. Their use is based on their ability to detect early changes caused by surgical maneuvers which may result in post operative deficits. However, not all changes are surgically related and any decrease in the non surgical causes of evoked potential changes increases the yield of intraoperative monitoring. In this review I will discuss the anesthetic effects on evoked potentials; these include a general description of the anesthetic effects on evoked potentials followed by the effects of premedication, induction, and maintenance agents. Also, described are the effects of adjunct anesthetic agents and techniques. Changes related to anesthesia are not similar and the knowledge of such differences is essential for the planing of anesthesia during the use of evoked potentials. An out line of the anesthetic techniques are described at the end of this review.

Depression of cortical somatosensory evoked potentials by nitrous oxide.

The effects of the inhalation of 50% nitrous oxide on somatosensory evoked potentials during a fentanyl-oxygen anaesthetic technique for central nervous system surgery were evaluated. The latency and amplitude of the first cortical wave were obtained using conventional somatosensory techniques with median or posterior tibial nerve stimulation. Data were collected before and after the inhalation of 50% nitrous oxide in oxygen introduced at the conclusion of the surgical procedure. The addition of nitrous oxide was associated with consistent decreases in the amplitude of somatosensory evoked potentials, but with no significant changes in latency. Since no electrical, physiological, or surgical event was associated with these changes, the results suggest that they were attributable to nitrous oxide per se.

Serum potassium levels during prolonged hypothermia.

Hypokalemia (mean serum potassium 2.3 +/- 0.4 mEq/l) was observed in six hypothermic patients (30 degrees - 32 degrees C) with head injuries or brain hypoxia. In the first three patients, potassium was administered to maintain serum levels above 3.5 mEq/l and on rewarming after 48 h of hypothermia hyperkalemia (peak serum potassium = 7.1 +/- 0.5 mEq/l) associated with cardiac arrhythmias developed. The remaining three patients received sufficient potassium to approximately replace measured losses during the hypothermic period. These patients did not become hyperkalemic on rewarming. Clinically insignificant sinus bradycardia, premature atrial contractions and junctional rhythms were seen during hypothermia with hypokalemia. We conclude that hypothermia produces hypokalemia by a shift of potassium from the extracellular to intracellular or extra vascular spaces. Potassium therapy during controlled hypothermia in the range 30 degrees - 32 degrees C should only replace measured losses.

Anesthesiologic considerations in laser neurosurgery.

The laser has been welcomed to the neurosurgical armamentarium because of the inherent precision and gentleness of the no-touch technique. In order to maximize laser safety and efficacy, however, certain anesthesiologic considerations, specific to neurosurgery, must be realized. Motion of patient (target) during routine anesthesiologic checks or as the result of physiologic excursions during myocardial contraction and respiration must be minimized. Ventilatory parameters, anesthetic agents, and cardio active drugs are considered.