The Biased Coin Design Up-and-down Sequential Method To Explore The 90% Effective Concentration Of Ropivacaine For Pecto-intercostal Fascial Block

Objective:The biased coin design up-and-down sequential method was used to determine the 90%effective concentration of ropivacaine for Pecto-intercostal Fascial Block.Methods:Patients proposed for median open heart surgery from August 2022 to January 2023,of either sex,aged 18-65 years,with a BMI of 18.5-24 kg/m²were selected.The patient underwent ultrasound-guided Pecto-intercostal Fascial Block before operation,and 10m L ropivacaine solution was injected into the 2-3 and 4-5costal spaces on both sides of parasternal respectively,totaling 40m L.The concentration of ropivacaine was adjusted by the biased coin design up-and-down sequential method,the initial concentration was 1.0 mg/m L,the interval concentration gradient was 0.3 mg/m L,and the maximum concentration was set at5.0 mg/m L.The concentration of subsequent patients is determined by the blocking effect of the previous patient.If the blocking effect of the previous patient is judged to be ineffective,the concentration of the next patient is increased by one level（0.3mg/m L）;If the blocking effect of the previous patient was judged to be effective,the biased coin random was performed,and the concentration of ropivacaine used by the next patient was reduced by one level（0.3mg/m L）with 11%probability and remained unchanged with 89%probability.Collect the general information and surgical incision length of the subjects;measure and record the block range of the subject every 5min;At the same time,observe whether the subject has signs of local anesthetic poisoning,such as dizziness,tinnitus,numbness around the mouth,etc.;Mean arterial pressure（MAP）was recorded before and after skin incision and before and after sternal sawing.Numeric Rating Scale（NRS）scores were recorded at 12 and24 hours postoperatively.Probit regression was used to calculate the EC₉₀of ropivacaine and its 95%effective interval.Results:1 patient was excluded due to reoperation.The EC₉₀of ropivacaine was3.057 mg/m L with 95%confidence interval（CI）of（2.891-3.410）mg/m L in 59patients.Pecto-intercostal Fascial Block can reduce the circulation fluctuation of skin incision and sternum sawing during operation,and reduce postoperative pain;No local anesthetic intoxication events were observed during the trial.Conclusion:When PIFB was performed by four-point injection in the left and right2-3 and 4-5 rib spaces of the sternum,the block was able to cover the T₂-T₆plane,providing good analgesia for patients undergoing median open heart surgery.we recommend the use of ropivacaine concentration of 3.057 mg/m L when 40 m L of ropivacaine solution was used for PIFB operation;it is relatively safe to use this concentration for PIFB,and no local anesthetic poisoning events have been observed.