The Effect of Midazolam Premedication on Intraocular Pressure Following Induction of Different Intravenous Anaesthesia: A Randomised Clinical Trial

Introduction: Thiopentone sodium, ketamine and propofol are commonly used intravenous induction agents for endotracheal intubation with suxamethonium and long-acting muscle relaxants for the maintenance of anaesthesia with air, oxygen and nitrous oxide. Premedication, induction agents, muscle relaxants, inhalational anaesthetics and anaesthetic technique can influence Intraocular Pressure (IOP). These factors are often not considered in anaesthetic practice. Aim: To compare changes in IOP after various intravenous induction agents with premedication using midazolam or without premedication. Materials and Methods: This triple-arm randomised, singleblinded clinical trial was conducted at Government Medical College, Latur, Rajasthan, India, from January 2023 to August 2024 included 210 patients of either sex, aged 20-45 years, scheduled for various operative procedures. They were randomly divided into two main groups of 105 each, with subgroups according to the induction agent and whether midazolam premedication was given. Group I-A: thiopentone 5 mg/kg; Group I-B: ketamine 2 mg/kg; Group I-C: propofol 2 mg/ kg. Group II-A: thiopentone 5 mg/kg + midazolam 2 mg; Group II-B: ketamine 2 mg/kg + midazolam 2 mg; Group II-C: propofol 2 mg/kg + midazolam 2 mg. Before induction of anaesthesia, all patients were informed and consented for intraocular pressure measurement. The IOP was measured with a Schiotz tonometer at predefined time intervals. Differences in demographic data and baseline values between groups were analysed using one-way Analysis of Variance (ANOVA). For comparisons of observations within and between groups, repeated-measures ANOVA was used. Results: There were no statistically significant differences among the groups in terms of demographic variables, American Society of Anaesthesiologists (ASA) classification, type of surgery, or preoperative IOP. Intragroup analysis showed a significant increase in IOP in the ketamine group (Group I-B) immediately after induction (p=0.0231), whereas propofol (Group I-C) and all Group II subgroups (with midazolam) showed significant decreases in IOP at multiple time points (p<0.05). Intergroup comparisons revealed that the addition of midazolam significantly attenuated the rise in IOP across all induction agents, particularly in the early post-induction period (p<0.05). No adverse ophthalmic or systemic events were reported during the study. Conclusion: Midazolam, when combined with intravenous induction agents, significantly lowers IOP, counteracting the rise caused by ketamine and muscle relaxants. Routine intraoperative IOP monitoring is recommended, especially in ophthalmic patients and ketamine should be used cautiously or with sedatives to prevent IOP elevation.