Armstrong 1990.

Methods	Randomized controlled 3‐arm parallel trial at a metropolitan hospital in Scotland
Participants	120 pre‐medicated female patients undergoing minor gynaecological day‐case surgery. "There were no statistical differences among the three groups in respect of age and weight"
Interventions	Group 1 received no treatment before cannulation Group 2 received 0.2 mL lidocaine injected intradermally through a 25G needle at the puncture site Group 3 received ethyl chloride spray around the skin puncture site from a height of 8 inches for 10 seconds
Outcomes	Pain of anaesthetic application, pain of catheter insertion, skin pain 1 minute after insertion Vein visibility before and after skin anaesthesia and ease of cannulation
Funding	"Dr P Armstrong was in receipt of a grant from the Association of Anaesthetists of Great Britain and Ireland"
Notes	For analysis, no treatment was used
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were "allocated to one of three equal sized treatment groups using a table of random numbers"
Allocation concealment (selection bias)	Unclear risk	Not described
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not described
Selective reporting (reporting bias)	Unclear risk	Protocol not available, but all expected outcomes reported
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants not blinded. Investigator present during procedure
Blinding of outcome assessment (detection bias) All outcomes	High risk	Investigator present during procedure