Ibarra 2011.

Methods	Blinded (PACU nurses, outcome assessor), controlled, randomized clinical trial Computer‐generated randomization in blocks of 2 using sealed, opaque envelopes Follow‐up: 5 months
Participants	Participants: 40 adults in a university hospital setting in Albacete, Spain Operation: radical mastectomy and conservative breast surgery for breast cancer 2 groups, size: 20/20 Age: not reported Men/women: 0/40
Interventions	Group 1 (preoperative PVB): single shot PVB at T4 with ropivacaine (0.5% without epinephrine, 25 mL to 30 mL, doses maximum 150 mg; using nerve stimulations according to Naja but only one single injection), GA (LMA using sevoflurane and remifentanil 0.05 to 0.1 mcg/kg/min only in the first 20‐30 min), post‐op: intravenous morphine (0.1 mg/kg), dexketoprofen 50 mg IV plus 25 mg every 8 h as needed for pain and paracetamol (1 g every 6 h) Group 2 (no block): no block, GA (LMA using sevoflurane and remifentanil 0.05 mcg/kg/min to 0. 02 mcg/kg/min), post‐op: IV morphine (0.1 mg/kg), dexketoprofen 50 mg IV plus 25 mg every 8 h as needed for pain and paracetamol (1 g every 6 h) Adjuvants: none Immediate post‐op pain control: not significantly improved
Outcomes	Dichotomous: number of participants with pain (including detailed number per group on myofascial pain, breast phantom pain or neuropathic pain) at 3 and 5 months per group Continuous: not reported Effective regional anaesthesia: one participant had an unsuccessful block but was NOT excluded, yet PVBs did not reduced the severity of postoperative pain.
Notes	We acknowledge the study author's response regarding randomization, allocation concealment and blinding, dosing and attrition Funding sources: source of funding not stated Conflicts of interest: conflict of interest not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: “computer generated list”, “randomization in blocks of two”. Low risk of bias
Allocation concealment (selection bias)	Low risk	Quote: “patients were assigned as they arrived in the preoperative clinic”, “The anaesthesiologist [enrolling the participant] did not know in which group the patient was going to be enrolled”. “The anaesthesiologist [in the OR] did not know the group allocation, until the patient reached the operating room.” “The randomization number was included in the chart in a sealed opaque envelope.”  Low risk of bias
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: “the recovery room nurses did not know the anaesthetic technique used in each case.” “The surgeon knew” if a block was performed. Participants were not blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: “the outcome observer conducting the interview did not know the group allocation.”
Incomplete outcome data (attrition bias) All outcomes	High risk	The numbers excluded in each group for radiotherapy and lost to follow‐up, respectively are unclear. Significant attrition with unclear group allocation may have caused bias, but no ITT analysis considered.
Selective reporting (reporting bias)	Low risk	Expected primary outcomes fully reported on
Null bias	High risk	Quote: "no significant differences in acute pain were observed"