Effect of isoflurane plus nitrous oxide versus propofol on intraoperative motor evoked potentials after high frequency repetitive electrical stimulation during neurosurgical procedures

The goal of this study was to test the influence of two widespread techniques of general anaesthesia on motor evoked potentials [MEP] in response to transcranial and cortical high frequency repetitive electrical stimulation. Total intravenous anaesthesia [TIVA] based on propofol and alfentanil was studied in 17 patients [Group A] and balanced anaesthesia [BA] based on nitrous oxide, isoflurane and alfentanil was studied in 13 patients [Group B]. Distinct motor responses were available in 15 of 17 patients [88%]] of [Group A] and in one of 13 patients [8%] of [Group B]. Amplitudes increased significantly with increasing stimulus intensity and number of pulses under conditions of TIVA. At the same time, latencies decreased significantly with increasing stimulus intensity and decreasing inter-stimulus intensity interval, but not with increasing number of pulses. It is hypothesized that propofol suppresses corticospinal I-waves at the cortical level resulting in a conduction block at the level of the alpha-motor neuron; this effect may be overcome by high frequency repetitive stimulation. In contrast, nitrous oxide and isoflurane seem to have an additional suppressive effect on corticospinal D-waves which may be overcome by higher stimulation intensity. It was concluded that transcranial high frequency repetitive stimulation and TIVA provide a feasible setting for intraoperative MEP monitoring, while higher doses of nitrous oxide and isoflurane are not compatible with recording of muscular activity elicited by the stimulation technique as described

Intraoperative visual evoked potential monitoring in suprasellar tumors in children

In this study, visual evoked potentials [VEPs] were studied in 15 children undergoing surgery for parasellar tumors [12 craniopharyngiomas and 3 chiasmal gliomas]. The preoperative visual function was assessed by a standard ophthalmological work up. VEP was performed at different time intervals during surgery and postoperatively. Anesthesia was induced with fentanyl 2 mu kg-1, followed by diprivan 2 mg kg-1 i.v. and tracium 0.5 mg kg-1 i.v. to facilitate intubation. Anesthesia was maintained using diprivan 0.1 mg kg-1 min-1 using a syringe pump and was adjusted to give the patient 0.1 g kg-1 hr-1 together with 1% sevoflurane and O2. The patients were chemically ventilated to maintain normocapnia PaCO2 [30-35 mmHg]. The hemodynamics [B1 Pr and HR], O2 saturation and body temperature were maintained constant throughout the operation. The equipment used in measuring VEP was LED goggles LS-101J [Nihon Koden]. Averages were obtained after stimulation of both eyes separately and the side of stimulation was changed after two averages. Visual acuity was improved postoperatively in eight cases. A significant VEP change occurred if latency prolongation of more than 50% was seen. The changes of VEPs were so profound [complete potential loss occurred in ten cases]

EEG bispectral index monitor and end-tidal sevoflurane concentrations: comparison between children and adults

This prospective study was designed to evaluate the correlation between the electroencephalographic bispectral index [BIS] and the hypnotic component of anesthesia [CA] induced by sevoflurane in 27 children and 27 adult patients. BIS and CA were compared at loss of consciousness [LOC] and on recovery of consciousness [ROC]. Mean +/- SD, BIS decreased significantly at LOC in children and adults from 94.2 +/- 2.6 to 87.3 +/- 4.1 and from 95.8 +/- 2.3 to 86.5 +/- 4.3, respectively, without any difference between groups. Correlation coefficients [p] between BIS and CA at LOC were -0.761 in children and -0.911 in adults. BIS increased significantly at ROC in children and adults from 73.9 +/- 4.3 to 87.2 +/- 1.9 and from 80.1 +/- 5.2 to 91.3 +/- 3, respectively, without any difference between groups. Correlation coefficients between BIS and CA in ROC were -0.876 in children and -0.837 in adults. BIS values at ROC were not different from those at LOC in either group. These data demonstrated that BIS correlates with the hypnotic component of anesthesia induced by sevoflurane in children as well as in adults

Surgical Management of foramen magnum meningiomas

In this study, 12 patients with foramen magnum meningiomas were operated upon in the Neurosurgical Department, Cairo University, from January 1999 to January 2002. Two surgical approaches were used in the study [the inferior suboccipital approach and the far lateral approach]. Total excision of the meningioma was achieved in 90% of the cases. The operative morbidity was 25% [one case of CSF leakage, one case of motor weakness and one case of lower cranial nerve deficit]. No mortalities were encountered in this study. No tumor recurrence existed during an average follow up period of about 20 months