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Background and Aims The Continual Reassessment Method can provide a direct and reliable estimate of the dose at the desired percentile level. We used it to estimate the optimal doses of lidocaine 1% and 2% (both with adrenaline 1:200,000) for ultrasound-guided axillary plexus blocks as there is a lack of high-quality evidence in the literature regarding them.
Methods Following local ethics committee approval, we invited patients of ASA grade I-III, BMI ≤40, presenting for an awake upper limb surgery to participate in this triple-blind, prospective trial. We randomised consenting patients between the two study drugs using the sealed envelope method. Two expert operators (experience of >1000 USG blocks) administered all the blocks under ultrasound guidance. We used 30mLs and 15mLs as the starting doses for lidocaine 1% and lidocaine 2% with adrenaline 1:200,000 respectively. Figure-1 shows the summary of the study design. We considered a block successful if there were no cold or pin prick sensations in the distribution of the four main peripheral nerves of the brachial plexus 30 minutes after the block was sited.
Flow chart illustrating the trial design based on the continual reassessment method: a bayesian adaptive method
Dose allocation sequence and patient outcomes in the study using lidocaine 1% with adrenaline. Blue dot=Successful block; Red dot=Ineffective block
Dose allocation sequence and patient outcomes in the study using lidocaine 2% with adrenaline. Blue dot=Successful block; Red=Ineffective block
Results We recruited forty analysable patients in each group (figures 2 and 3) and estimated the ED95 for lidocaine 1% and 2% with adrenaline 1:200,000 as 400 mgs (95% Credibility Interval: 89.5% to 99.2%) and 300mgs (95% Credibility Interval: 87.4% to 97.5%) respectively.
Conclusions We estimate 40mLs of lidocaine 1% (adrenaline 1:200,000) and 15mLs of lidocaine 2% (adrenaline 1:200,000) have a 95% probability of success for an ultrasound-guided axillary block sited using ‘in-plane’ multiple injections technique. Reference:Garrett-Mayer E. Clin Trials. 2006;3(1):57-71