Remimazolam Concentration and Sedation Depth During Lower Extremity Surgery Under Spinal Anesthesia

This study will examine how the amount of remimazolam predicted to reach its site of action relates to the depth of sedation during lower extremity surgery under spinal anesthesia. Remimazolam is a sedative used to help patients relax and feel sleepy during surgery. People may respond differently to the same amount of this medicine, and age may explain some of these differences. Sixty adults will be enrolled at Seoul National University Hospital, with 20 participants in each age group: 19-49 years, 50-69 years, and 70 years or older. All participants will receive remimazolam using the same stepwise dose-adjustment rules. The dose will be adjusted according to repeated assessments of responsiveness. Researchers will record sedation scores, medication delivery, brain-wave signals, vital signs, recovery, and side effects. After surgery, a computer model will estimate the remimazolam concentration at its site of action. These estimates will not be available to the clinical team during surgery. The main goal is to measure how much the concentration associated with the target level of sedation varies between patients. The study will also examine the effect of age and whether early responses can help predict an individual patient's later response.