Harmon 2003.

Methods	Observer‐blind randomized controlled trial
Participants	Age (years, mean (range)): Group C = 40 (16 to 77), Group n = 39 (19 to 65), Group L = 45 (17 to 79) Gender (M:F): Group C = 18:27, Group n = 13:32, Group L = 16:29 Inclusion criteria: age 16 years to 79 years old, ASA I–II, elective surgery Exclusion criteria: patients in ASA III–V and those who suffered from cardiac conduction defects, epilepsy, those taking antidysrrhythmic drugs or receiving analgesic drugs in the previous 24 hours Recruitment: 140 were recruited, but 135 adult patients were randomly assigned (45 patients in each group) Setting: Ireland
Interventions	Admixture C = preoxygenated with 100% oxygen (120 sec) N = preoxygenated with 50% nitrous oxide in oxygen (120 sec) Both C and N groups, anaesthesia was induced with propofol with no added lidocaine L = preoxygenated with 100% oxygen and anaesthesia was induced with 1% propofol 18 ml premixed with 1% lidocaine 2 ml (20 mg) (lidocaine concentration of 1 mg/ml) The speed of injection was carefully controlled by hand Propofol was injected at 1 ml/sec, the injection was stopped at 5 sec and then continued after pain scores were assessed at 10 sec On initial injection (after 5 sec), the degree of pain experienced by the patient was scored by observation of any verbal response and behavioural signs such as facial grimacing or arm withdrawal. At 10 sec, if there was no observed pain response, the patient was asked a standard question about comfort at the injection site
Outcomes	Pain intensity assessed on 4‐point scale 0 = no pain 1 = mild pain (pain reported in response to questioning only) 2 = moderate pain (pain reported in response to questioning and accompanied by behavioural signs, or pain reported spontaneously) 3 = severe pain (strong verbal response or a response accompanied by behavioural signs) Outcomes reported and used Incidence of high‐intensity pain Incidence of pain Outcomes sought but not reported Adverse effects Patient satisfaction
Notes	Period of the study: dates not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Randomization was conducted by a computer with the code sealed until arrival of the patient in operating room."
Allocation concealment (selection bias)	Unclear risk	N/A
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"A member of the anaesthesia team took responsibility for anaesthesia was unblinded."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"The investigator recording the pain scores was blinded to the drugs given and the gas mixture administered to the patients (flowmeters were covered by cardboard)."
Incomplete outcome data (attrition bias) All outcomes	Low risk	"Five were excluded before randomization due to difficulty with venous cannulation."
Selective reporting (reporting bias)	Unclear risk	N/A
Other bias	Low risk	The study appears to be free of other sources of bias.