Yamauchi 2008.

Study characteristics
Methods	Randomised, double‐blind, placebo control
Participants	N = 202, about 30% women
Interventions	Ketamine 1 mg/kg bolus IV at skin incision + 42 µg/kg/h infusion IV for 24 h Ketamine 1 mg/kg bolus IV at skin incision + 83 µg/kg/h infusion IV for 24 h
Outcomes	Pain intensity (VAS) at rest and during movement at 1, 6, 12, 24, 36, 48 h and 3, 6 and 10 days after surgery. Analgesic consumption. AEs
Surgery type	Posterior cervical spine and lumbar spine surgery
Group numbers after end of study (treatment/control)	133/67
Age of patient population (treatment/control)	60.2 ± 16.9 57 ± 17.3
Notes	The study consists of cervical and lumbar surgery participants with 2 different interventions and corresponding control groups. These treatment arms (4 treatment arms and corresponding control groups) were analysed separately. No mention of sponsorship or funding
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation by shuffling envelopes
Allocation concealment (selection bias)	Low risk	Allocation concealment in envelopes
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Mentioned "double‐blind" but not described
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Blinding not described
Incomplete outcome data (attrition bias) All outcomes	Low risk	1% was withdrawn
Selective reporting (reporting bias)	Low risk	Predefined outcomes reported
Size	High risk	22, 23 and 23 participants in the cervical surgery groups. 42, 46 and 44 participants in the lumbar surgery groups