Aceto 2002.

Methods	Study design: Randomized controlled trial Study grouping: Parallel group
Participants	Baseline Characteristics Nitrous oxide‐free ‐ A Number randomized: 10 Number analysed: 10 Age (mean): 54 (50 ± 58) % male: 50 Type of surgery: Laparoscopic cholecystectomy Nitrous oxide‐based ‐ A Number randomized: 10 Number analysed: 10 Age (mean): 49 (39 ± 59) % male: 40 Type of surgery: Laparoscopic cholecystectomy Nitrous oxide‐free ‐ B Number randomized: 10 Number analysed: 10 Age (mean): 52 (47 ± 57) % male: 40 Type of surgery: Laparoscopic cholecystectomy Nitrous oxide‐based ‐ B Number randomized: 10 Number analysed: 10 Age (mean): 50 (43 ± 57) % male: 60 Type of surgery: Laparoscopic cholecystectomy Included criteria: ASA I ‐ II undergoing elective laparoscopic cholecystectomy, aged 18 ‐ 70 yrs, Christians Excluded criteria: History of neurological or mental disease and hearing impairment. Patients having major haemodynamic changes (mean arterial pressure and heart rate) greater than 15% compared with baseline values), and blood loss with acute anaemia as a result of intraoperative surgical complications were also excluded
Interventions	Intervention Characteristics Nitrous oxide‐free ‐ A Name: sevoflurane + air (FiO₂ 40%) Induction: Thiopental sodium (5 mg/kg), fentanyl (5 mcg/kg) and vecuronium bromide (0.08 mg/kg) Maintenance: sevoflurane + air (FiO₂ 40%) Recovery: NR Other drugs used: Boluses of fentanyl (2 mcg/kg) and additional vecuronium according to clinical necessity Premedication: None Duration of anaesthesia (min): 91 (70 ± 112) Nitrous oxide‐based ‐ A Name: Sevoflurane + N₂O (60%) in air (FiO₂ 40%) Induction: Thiopental sodium (5 mg/kg), fentanyl (5 mcg/kg) and vecuronium bromide (0.08 mg/kg) Maintenance: Sevoflurane + N₂O (60%) in air (FiO₂ 40%) Recovery: NR Other drugs used: Boluses of fentanyl (2 mcg/kg) and additional vecuronium according to clinical necessity Premedication: None Duration of anaesthesia (min): 107 (89 ± 125) Nitrous oxide‐free ‐ B Name: isoflurane + air (FiO₂ 40%) Induction: Thiopental sodium (5 mg/kg), fentanyl (5 mcg/kg) and vecuronium bromide (0.08 mg/kg) Maintenance: Isoflurane + air (FiO₂ 40%) Recovery: NR Other drugs used: Boluses of fentanyl (2 mcg/kg) and additional vecuronium according to clinical necessity Premedication: None Duration of anaesthesia (min): 90 (65 ± 115) Nitrous oxide‐based ‐ B Name: Isoflurane + N₂O (60%) in air (FiO₂ 40%) Induction: Thiopental sodium (5 mg/kg), fentanyl (5 mcg/kg) and vecuronium bromide (0.08 mg/kg) Maintenance: isoflurane + N₂O (60%) in air (FiO₂ 40%) Recovery: NR Other drugs used: Boluses of fentanyl (2 mcg/kg) and additional vecuronium according to clinical necessity Premedication: None Duration of anaesthesia (min): 97 (78 ± 116) Monitoring: (ML‐AERs) recorded before anaesthesia, at 1 MAC and 30 mins after awakening. The concentration of anaesthetic, monitored with an anaesthetic‐respiratory gas analyser, was maintained at 1 MAC for at least 20 mins before the intraoperative recording of MLAERs, 5 mins after surgical incision
Outcomes	Accidental awareness 24 hrs after awakening participants were assessed for explicit and implicit memory. Explicit memory was assessed with a recall test. Participants were asked about the last thing they remembered before going to sleep; the first thing they remembered when they woke up; and anything which happened in between, including sounds, dreams, and imagination. (i.e. modified Brice questionnaire) Other stimulation during surgery One of 4 audiotapes was played immediately after completion of MLAER recording. Each audiotape contained 1 of the following stories: (i) The fox and the grapes; (ii) Jesus's birth; (iii) The prodigal son; and (iv) The miracle of the loaves and fishes. At the end of each of the stories, 4 key words had been recorded. Recall of relevant words in these stories used to detect implicit recall
Identification	Country: Italy Setting: Department of Anaesthesiology and Intensive Care Authors name: P Aceto Institution: Catholic University of the Sacred Heart Email: gdecosmo@rm.unicatt.it Address: Department of Anaesthesiology and Intensive Care, Policlinico A. Gemelli, L.go A. Gemelli 8,I‐00168 Rome, Italy
Aim of study	The aim of this study was to investigate the presence of subconscious awareness during anaesthesia and to examine its relationship to the ML‐AERs
Notes	Sponsorship source: No details given
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "using randomization tables"
Allocation concealment (selection bias)	Unclear risk	Comment: No details reported
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "The patients were blinded to the method of anaesthesia used and to the contents of the tape (they were not told that there would be a story on the tape)." Comment: Participants were blinded, as was the anaesthetist playing the tapes. No mention of the anaesthetist giving the anaesthesia, presumably not
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The anaesthesia resident that conducted the post‐ operative interview did not know which anaesthetic had been used or which story had been played." Comment: Outcome assessor and participants were blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: No losses to follow‐up reported
Selective reporting (reporting bias)	Low risk	Comment: All relevant outcomes specified in Methods reported
Other bias	Low risk	Comment: None identified