Study outcomes
The primary outcome of the study was to ascertain peak plasma lidocaine levels after topicalisation for airway endoscopy. Secondary endpoints included: time to peak lidocaine plasma levels, signs of lidocaine toxicity (restricted to ECG changes or seizures when under anaesthesia) and clinical adverse events of laryngospasm, coughing or desaturation during the procedure.
Statistical analysis 
Normally distributed variables were summarised by mean (standard deviation, SD) and non-normally distributed variables by median (interquartile, IQR) [range]. Categorical variables were summarised by count (percentage). In comparison tests, ANOVA or equivalent non-parametric tests were used for continuous variables. In assessing the relationship between peak plasma and age, weight or volume univariable regression models were used. As a result, multivariable models were not followed due to the small sample size. Due to the exploratory nature of the study, a nominal p-value of <0.05 indicates areas for further investigation.
Sample size
The sample size was derived from recruitment frequency at a specialist institution and a quantity that allowed a clear relationship between the primary outcome and defined variables to be explored. Fifty patients undergoing airway endoscopy were recruited within the study and a total of 198 samples were sent for analysis. A total of 198 human serum samples were received frozen on dry ice and in good condition from the [removed for blind peer review] on 26 Oct 2018 for preparation and analysis at [removed for blind peer review]. Sample analysis was performed between 17 Feb 2019 and 22 Feb 2019.