Pang 1999.

Methods	Randomized controlled trial
Participants	Age (years, mean ± SD): Group T = 38.3 ± 15.2, Group L = 42.3 ± 18.7, Group NS = 39.6 ± 19.0 Gender (M:F): Group T = 19:16, Group L = 17:18, Group NS = 15:20 Inclusion criteria: ASA I‐II, elective surgery Exclusion criteria: patients with communication difficulties Recruitment: 105 adult patients randomly assigned (35 in each group) Setting: Taiwan
Interventions	Pretreatment with venous occlusion Group T received 50 mg tramadol (Tramal ®, Grunenthal, Germany) in NS 3mL Group L received 60 mg lidocaine (3 ml of 2% solution) Group NS received 3 ml normal saline, serving as the control Propofol 10 ml was injected at rate 0.5 ml/sec
Outcomes	Pain intensity assessed on 11‐point scale (VAS) with 0 being no pain and 10 being most excruciating pain Outcomes reported and used Incidence of high‐intensity pain Incidence of pain Adverse effects Outcomes sought but not reported Patient satisfaction
Notes	Period of the study: dates not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	N/A
Allocation concealment (selection bias)	Unclear risk	N/A
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"The pretreatment drug was prepared in an unlabeled syringe and randomly handed for pretreatment to the anaesthesiologist who was unaware of the identity of the drug."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	N/A
Incomplete outcome data (attrition bias) All outcomes	Low risk	No withdrawals
Selective reporting (reporting bias)	Unclear risk	N/A
Other bias	Low risk	The study appears to be free of other sources of bias