Adequacy of Anaesthesia for Nociception Detection during Vitreoretinal Surgery

Vitreoretinal surgery (VRS) is one of the most widely performed precise procedures in ophthalmic surgery; the majority of cases are carried out under regional anaesthesia (RA) only. However, in specific situations (such as when the patient fails to cooperate with the operator for various reasons), general anaesthesia (GA), alone or in combination with GA (combined general–regional anaesthesia, CGR), is the only safe way to perform VRS. While monitoring the efficacy of an intraoperative rescue opioid analgesia (IROA) during surgery (assessing the adequacy of anaesthesia (AoA)) may be challenging, the surgical pleth index (SPI) is a useful tool for detecting the reaction to noxious stimuli and allows for the rational titration of opioid analgesics (AO) during surgery. The current study investigated the influence of the SPI-based titration of fentanyl (FNT) in combination with various pre-emptive analgesia (PA) techniques on intraoperative pain perception during various stages of VRS performed under AoA. A total of 176 patients undergoing VRS under GA were enrolled in the study. They were randomly assigned to one of the five following study arms: Group GA (control group)—patients who received general anaesthesia alone; Group PBB—GA with preprocedural peribulbar block (with 0.5% bupivacaine and 2% lidocaine); Group T—GA with preventive, topical 2% proparacaine; Group M—GA with a preprocedural intravenous infusion of 1.0 g of metamizole; and Group P—GA with a preprocedural intravenous infusion of 1.0 g of paracetamol. The whole procedure was divided in four stages: Stage 1 and 2—preoperative assessment, PA administration, and the induction of GA; Stage 3—intraoperative observation; Stage 4—postoperative observation. the SPI values were monitored during all stages. The occurrence of nociception (expressed as ∆SPI >15) during various manipulations in the surgical field was observed, as were cumulative doses of rescue analgesia, depending on the PA administered. During the course of VRS, rescue FNT doses varied depending on the stage of surgery and the group investigated. The majority of patients, regardless of their group allocation, needed complementary analgesia during trocar insertion, with Group GA patients requiring the highest doses. Likewise, the highest cumulative doses of IROA were noted during endophotocoagulation in Group GA. Preventive PBB and topical anaesthesia were proven to be most efficient in blunting the response to speculum installation, while topical anaesthesia and paracetamol infusion were shown to be more efficient analgesics during endophotocoagulation than other types used PA. In the performed study, none of the PA techniques used were superior to GA with FNT dosing under the SPI with respect to providing efficient analgesia throughout the whole surgery; there was a necessity to administer a rescue OA dose in both the control and investigated groups.