Background A dose of 5mg/kg lidocaine is considered appropriate for paediatric airway topicalisation. Existing literature suggests younger children are susceptible to toxic lidocaine plasma levels and achieve this at a faster rate. Aims The primary outcome of this 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. Methods Data was collected prospectively over 18 months at Royal Manchester Children’s Hospital. Children aged 0-8 years undergoing elective diagnostic or therapeutic airway endoscopy were included within the study. Standardised 2% lidocaine was used for airway topicalisation. Dose varied depending upon practitioner usual practice. Venous blood sampling occurred at 5, 10, 15 and 20 minutes post administration and plasma lidocaine levels (ng/ml) analysed. Results A significant relationship exists between higher peak plasma levels and ages <18 months (p=0.00973). Strong linear correlation exists between weight and age for our cohort (r=0.88). Higher peak plasma lidocaine levels occur with total dose volumes between 2 and 3mls of 2% lidocaine local anaesthetic (p=0.03) compared with <2ml total dose volumes. Data suggests a potential relationship of lower weights achieving higher peak plasma levels (p=0.0516). Reduced IQR variation of peak plasma lidocaine levels exists when lidocaine dosing is <5mg/kg. Conclusions Age and total dose volume of topicalised lidocaine have a significant relationship with plasma lidocaine levels. A dose of 5mg/kg topicalised lidocaine for paediatric airway endoscopy is safe and provides good operating conditions. Lower patient weights trend toward higher peak lidocaine plasma concentrations and require further investigation.