Keld 2000.

Methods	Randomization: yes Participant blinding: yes Provider blinding: no Assessor blinding: yes Dropouts: 1 outcome reported
Participants	Country: Denmark ASA: I and II Gender: men and women Mean age: lido: 43; bupi: 46 years Procedures: orthopaedic, general surgery Ambulatory surgery: unclear Surgical positioning: supine Number of participants: 70
Interventions	Drug 1: 5% lido, hyperbaric, fixed dose (2 mL) Drug 2: 0.5% bupi, hyperbaric, fixed dose (2.5 mL) Needle: 25 G, pencil‐point
Outcomes	TNS at 1 day Back pain
Notes	Follow‐up duration: 1–3 days Follow‐up methods: telephone contact TNS therapy: unclear TNS resolution: 41 hours
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "the patients were randomised to receive…" did not specify the method of randomisation (referring to a random number table, computer‐generated random number sequence, tossing coin, etc.).
Allocation concealment (selection bias)	Unclear risk	No mention of allocation concealment.
Participant blinding (performance bias and detection bias)	Low risk	Quote: "the study was performed as a prospective double‐blinded study…"
Provider blinding (performance bias)	High risk	Quote: "this anaesthesiologist used the local anaesthetic according to the random patient number and was therefore not blinded to the anaesthetic used."
Assessor blinding (detection bias)	Low risk	Quote: "the patient was contacted… by a different anaesthesiologist, who was blinded to the anaesthetic used…"
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "one patient in the bupivacaine group received general anaesthesia due to insufficient spinal anaesthesia and was excluded from the study." Comment: outcome from dropout not reported.
Selective reporting (reporting bias)	Unclear risk	Study protocol not available.