Background and Goal 
The Continual Reassessment Method (CRM) is an adaptive Bayesian design used for dose-finding studies. It can directly estimate the ED95 dose of a drug providing precise results, generating high-quality evidence.1,2 We aim to find out the ED95 of prilocaine 1% and lidocaine 1% with adrenaline for USG supraclavicular block using this method filling a knowledge gap in the literature.   
Materials and Methods 
After gaining all essential approvals, a double-blind randomized prospective trial was commenced including ASA I-III patients presenting for awake upper limb surgery. Patients were randomized between ‘prilocaine’ or ‘lidocaine with adrenaline’ groups using sealed envelope method. All blocks were performed using ultrasound by two operators who are experts (> 1000 blocks) in the field. The starting dose for both groups was 27 ml. Figure 1 shows the dose allocation and schematic representation of the study design. The success of a block was assessed using the cold and the pin-prick sensation in the distribution of radial, median, ulnar and musculocutaneous nerves of brachial plexus by an independent assessor at 10 min intervals up to 30 min. If the ED95 dose was not in the doses studied or if 40 patients were recruited the study was stopped as per statistical advice.
Results and Discussion 
A total of 30 patients were recruited in the prilocaine group and 40 patients in the lidocaine with adrenaline group. For an USG supraclavicular block using our method, the ED95 of prilocaine 1% lies beyond 400 mg, while for lidocaine 1% with adrenaline, the dose estimated to be closest to the ED95 is 400 mg with the attached success probability of 0.922 (0.824-0.976). A detailed data analysis is waited for both groups at the time of submission of this abstract.
Conclusion
The ED95 of prilocaine 1% and lidocaine 1% with adrenaline lie beyond 400 mg which was our testing dose range for these agents. However, 40 ml of lidocaine 1% with adrenaline could be successful in more than 92% of cases.
Reference
1.	Saranteas T, Finlayson RJ, Tran DQH. Dose-Finding Methodology for Peripheral Nerve Blocks. Regional Anesthesia and Pain Medicine 2014; 39(6): 550-5.
2.	Houle TT, Turner DP. Bayesian statistical inference in anesthesiology. Anesthesiology 2013; 119(1): 4-6.



04 / The use of Continual Reassessment Method (CRM) for finding ED95 of prilocaine 1% and lidocaine 1% with adrenaline (1:200,000) for ultrasound guided (USG) supraclavicular block.