Is the Patient State Index a reliable parameter as guide to anaesthesiology in cranial neurosurgery? A first intraoperative study and a literature review.

BACKGROUND: Patient State Index (PSI) and Suppression Ratio (SR) are two indices calculated by quantitative analysis of EEG used to estimate the depth of anaesthesia but their validation in neurosurgery must be done. Our aim was to investigate the congruity PSI and SR with raw EEG monitoring in neurosurgery. METHODS: We included 34 patients undergoing elective cranial neurosurgery. Each patient was monitored by a SedLine device (PSI and SR) and by raw EEG. To appraise the agreement between PSI, SR and EEG Suppr%, Bland-Altman analysis was used. We also correlated the PSI and SR recorded at different times during surgery to the degree of suppression of the raw EEG data by Spearman's rank correlation coefficient. For a comparison with previous data we made an international literature review according to PRISMA protocol. RESULTS: At all recording times, we found that there is a strong agreement between PSI and raw EEG. We also found a significant correlation for both PSI and SR with the EEG suppression percentage (p < 0.05), but with a broad dispersion of the individual values within the confidence interval. CONCLUSION: The Masimo SedLine processed EEG monitoring system can be used as a guide in the anaesthetic management of patients during elective cranial neurosurgery, but the anaesthesiologist must be aware that previous correlations between PSI and SR with the suppression percentage may not always be valid in all individual patients. The use of an extended visual raw EEG evaluated by an expert electroencephalographer might help to provide better guidance.

Feasibility of Intraoperative Visual Evoked Potential Monitoring by Cortical Strip Electrodes in Patients During Brain Surgery: A Preliminary Study.

OBJECTIVE: The role of visual evoked potentials (VEPs) monitoring during neurosurgical procedure in patient remains unclear. The purpose of our study was to determine the feasibility of intraoperative VEP recording using a strip cortical electrode during surgical resection of intracranial lesions. METHODS: In this prospective, monocentric, observational study, we enrolled consecutive patients undergoing neurosurgical procedure for intracranial lesions. After dural opening, a cortical strip was positioned on the lateral occipital surface. Flash VEPs were continuously recorded using both subdermal corkscrew electrodes and strip electrodes. An electroretinogram was also recorded to guarantee delivery of adequate flash stimuli to the retina. RESULTS: We included 10 patients affected by different intracranial lesions. Flash VEPs were recorded using subdermal corkscrew electrodes in all patients except 1 in whom they were never identified during the recording. Flash VEPs were recorded using strip electrodes in all patients and showed a polyphasic morphology with a significantly larger amplitude compared with that of flash VEPs measured using subdermal corkscrew electrodes. No patient reported worsened postoperative vision and a >50% decrease in the VEPs amplitude was never registered. CONCLUSIONS: We have reported for the first time in the literature that VEP monitoring during a neurosurgical procedure is feasible via a cortical strip located on the occipital surface. The technique demonstrated greater stability and a larger amplitude compared with recordings with scalp electrodes, facilitating identification of any changes. Studies with more patients are needed to assess the clinical reliability of the technique.

Cooperative patient general anesthesia (Co.Pa.Ge.A.): the new anesthetic technique for neurological monitoring of the "cooperative" patient during endovascular treatment of elective brain arteriovenous malformations with Onyx18.

BACKGROUND: An anesthetic technique, which allows for neurological monitoring as well as continuous and safe monitoring of the airways with orotracheal intubation (cooperative patient general anesthesia [Co.Pa.Ge.A.]) has been described in patients undergoing elective thromboendoarterectomy surgery. The aim of this paper is to evaluate the effectiveness and the safety of Co.Pa.Ge.A. during scheduled endovascular treatments of brain arteriovenous malformations with a polymeric embolization agent, Onyx18. METHODS: Ten patients (3 F, 7 M; median age: 33.5±6.0 y, range: 20 to 39 y, American Society of Anesthesiologists class I to II) underwent endovascular embolization of brain arteriovenous malformations located in an eloquent area. Remifentanil was administered i.v. until an anesthetic target level was reached which allowed the anesthesiologists and the neuroradiologists to perform neurological monitoring during the entire procedure. The degree of patient satisfaction was evaluated based on a questionnaire administered the day after the procedure. RESULTS: Co.Pa.Ge.A. was successfully performed on all of the patients. No intraprocedural or postprocedural adverse events occurred. Hemodynamic stability was maintained in 5 cases with Remifentanil alone, in 2 cases with Remifentanil and Clonidine and in 1 case with Remifentanil and Nimodipine. CONCLUSIONS: At the moment and to the best of our knowledge, this is the first report in the medical literature on this new anesthetic technique in interventional neuroradiology. Co.Pa.Ge.A. can be considered a safe, effective, and satisfactory technique characterized by hemodynamic stability and good control of the respiratory pattern, offering the possibility to perform real-time neurological monitoring and easy conversion to general anesthesia in case of intraprocedural complications or anesthetic necessity.