BIS-monitoring as a tool for evaluation regional anesthesia in ophthalmology: pilot study

BACKGROUND: General anesthesia in vitreoretinal surgeries may be combined with ophthalmic blocks. Prolonged sub-tenon block (PSB) in extensive surgery ensures the continuous administration of a local anesthetic into the episcleral space; however, its effectiveness has not been evaluated.

OBJECTIVE: To evaluate the effectiveness of sub-tenon block for vitreoretinal surgery in general anesthesia.

MATERIALS AND METHODS: The pilot study included 24 patients. All patients underwent retinal detachment surgery under general anesthesia with sevoflurane for >90 min. Patients were randomized into two groups. In group 1, analgesia was induced with intravenous tramadol. In group 2, general anesthesia was combined with sub-tenon block, and 1% lidocaine was used continuously. Bispectral index (BIS) monitoring was employed for anesthesia depth assessment. The mean blood pressure and heart rates were estimated for the evaluation of the oculovisceral reflex block. The Student and Wilcoxon–Bonferroni criterion was used for statistical analysis, and the statistical significance level was set at α=0.05.

RESULTS: The hemodynamic and consequently the degree of oculovisceral reflexes block had no statistically significant differences between the groups. The median BIS in groups 1 and 2 were 48.1±11.1 U and 42.6±8.2 U, respectively, and the difference between these values was statistically insignificant (p >0.05). However, in group 1, the BIS increased sharply during the laser phase. At this stage, the average BIS in groups 1 and 2 were 76.7±3.2 U and 40.4±6.9 U, respectively (p=0.001).

CONCLUSION: BIS-monitoring can be used as an indicator of the effectiveness of ophthalmic regional blocks in further studies.