The 90% effective dose (ED 90) of 0.75% intrathecal ropivacaine for day-care surgery in patients undergoing lower abdominal, inguinal, and urological surgery: Estimation with the biased coin up-and-down sequential method

Abstract

The increasing demand for day-care surgeries highlights the necessity for efficient anesthesia techniques. While general anesthesia is often preferred to prevent prolonged motor blockades, spinal anesthesia offers notable advantages, such as enhanced pain management and fewer postoperative complications. Newer local anesthetics such as ropivacaine have renewed the interest in subarachnoid block due to shorter duration of motor blockade and improved safety profile. Our study aimed to determine the effective dosage of intrathecal ropivacaine for lower abdominal surgeries using the biased coin up-and-down method. Our goal was to find a dose that allowed patients to be discharged on the same day. Forty male patients aged 18–60 years (American Society of Anesthesiologists 1 and 2), with heights between 150 and 160 cm, weighing 50–80 kg, participated in the study. Exclusion criteria included spinal abnormalities, infections, and an expected duration of surgery of more than 2 h. After obtaining informed consent, comprehensive preoperative assessment was conducted. In the operating room, standard monitoring protocols were established, and the first patient received 1.5 mL of 0.75% isobaric ropivacaine. Sensory and motor block levels were assessed, and subsequent doses were adjusted using the biased coin method, with dosage information kept confidential from both patients and surgeons. The estimated 90% effective dose for 0.75% ropivacaine was 1.91 mL (95% confidence interval: 1.78–1.98 mL). Mean recovery times for sensory and motor functions were 186.4 min (52.07) and 39.2 min (16.68), respectively, with a mean time to meet post anesthesia care unit discharge criteria of 195.7 (41.87) min. Intrathecal ropivacaine enabled rapid recovery, facilitating same-day discharge.