The Median Effective Concentration of Lidocaine for ultrasound-guided cervical vagus nerve block to prevent oculocardiac reflex in ocular Surgery: a double-blind randomised trial

Background: The oculocardiac reflex (OCR) is a common complication associated with ocular surgery. While cervical vagus nerve block (CVB) has demonstrated efficacy in reducing oculocardiac reflexe, the minimum effective preventing concentration of lidocaine in these procedures remains unvalidated. We investigated the median effective concentration (EC50) of lidocaine required to inhibit the left and right vagus nerves in ocular surgery. Methods: A prospective, randomized study was conducted on 60 patients undergoing hydroxyapatite orbital implantation at Daping Hospital, Army Medical University between October 2022 and November 2023. Patients were randomly allocated to receive either right or left cervical vagus nerve block. According to the up-down sequential allocation method, the initial concentration of lidocaine was 0.40% in all cases, while the concentration in the same group of two neighboring patients differed by 0.10%. The groups were classified as effective or ineffective based on whether the OCR occurred or not. We examined voice changes, nausea, and vomiting within 24 hours of the operation. Results: EC50 of lidocaine was 0.48% ± 0.39 (95% CI: 0.42%-0.62%) for right-sided blocks and 0.62% ± 0.40 (95% CI: 0.59%-0.76%) for left-sided blocks. The EC95 values were 0.72% (95% CI: 0.61%-1.49%) and 0.85% for right and left blocks, respectively. Patients with effective nerve blocks exhibited a higher incidence of postoperative hoarseness compared to those with ineffective blocks ( P =0.02). Conclusion: Ultrasound-guided cervical vagus nerve block using 0.48% lidocaine on the right side and 0.62% on the left side effectively suppresses OCR in 50% of patients undergoing hydroxyapatite orbital implantation surgery. These findings provide valuable guidance for anesthesiologists in managing OCR during ophthalmic procedures. Trial registration : ClinicalTrials.gov, NCT04950881 (registered on 20 June 2021). Written informed consent was obtained from all the patients.