Hwang 2015.

Methods	Study design: randomized controlled trial (2 arms) Study duration: not reported Study setting: hospital, single centre, Korea
Participants	Adults undergoing elective supratentorial craniotomy for clipping of an unruptured cerebral aneurysm (n = 52) Inclusion criteria ASA I to II participants Exclusion criteria Ruptured cerebral aneurysm Allergy to local anaesthetics Chronic opioid usage Previous craniotomy incision Undergoing emergency surgery Unable to understand the numerical pain rating scale Glasgow Coma Score (GCS) < 14 Active psychiatric disease Mean age, range (years) 47 (19 to 75) Numbers allocated to each arm Group intervention: not reported but 23 were included in the analysis Group control: not reported but 23 were included in the analysis Male gender Group intervention: 6/23 Group control: 7/23
Interventions	Technique and timing Scalp block of the following nerves Supraorbital and supratrochlear Zygomaticotemporal Auriculotemporal Postauricular branches of the greater auricular Greater, lesser, and third occipital nerves with 0.75% bupivacaine with adrenaline 1:200,000 versus scalp block with saline, at the end of surgery Dosage 7 mL
Outcomes	Primary Pain as measured by the numerical rating score during the first 72 hours postoperatively (measured at 1, 2, 4, 6, 8, 12, 16, 24, 48 and 72 hours) Secondary PCA (patient‐controlled analgesia) consumption Adverse events – haemodynamic instability, seizures, nausea and vomiting, fever (axillary temperature > 37.8 degrees celsius), dizziness, respiratory depression (respirator rate < 8 or SaO2 < 90%), sleepiness, delirium
Notes	Funding None
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	A computer‐generated random number chart was used for randomization.
Allocation concealment (selection bias)	Low risk	An independent anaesthesiologist was responsible for patient allocation.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: ''syringes containing the same volume (7 mL) of normal saline (group C) or 0.75% levo bupivacaine with epinephrine (group L) were prepared by an anaesthetic nurse not involved in the study. The anaesthesiologist performing the scalp block, patients, and investigators were blinded to group assignments''.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: ''the anaesthesiologist performing the scalp block, patients, and investigators were blinded to group assignments."
Incomplete outcome data (attrition bias) All outcomes	Low risk	46 of the original 52 participants were included in the final analysis. 3 participants from the intervention group were too sedated to assess outcomes. 3 participants from the control group were not included due to delayed extubation. As the losses were equal in both groups and the reasons for the losses were clinically similar, their omission was unlikely to have had a significant impact on the results.
Selective reporting (reporting bias)	Low risk	All outcomes were reported in the priority in which they were specified.
Other bias	Unclear risk	Small study