Renna 2000.
| Methods | Study design: randomized parallel groups Study dates: not given |
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| Participants | Country: UK Sex: female Age: mean 41.7 ASA: NA Procedure: minor gynaecological surgery Study size: 48 |
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| Interventions |
Randomized portion of anaesthetic: volatile agent different doses/word test: implicit memory/positive and neutral suggestion Intervention 1: sevoflurane 1.2% ET + either word list A or B + either positive or neutral suggestion, N = 16 Intervention 2: sevoflurane 1.5% ET + either word list A or B + either positive or neutral suggestion, N = 16 Intervention 3: sevoflurane 2% ET + either word list A or B + either positive or neutral suggestion, N = 16 |
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| Outcomes | Primary outcomes: primary outcome implicit memory; secondary outcome: awareness BIS, word lists, neutral suggestion Secondary outcome: awareness/wakefulness as defined using an awareness classification system (see Table 1): class 2 Quote: "...there was evidence of implicit memory...There was no evidence of a therapeutic effect of positive suggestion...The bispectral index ...not... statistical significance ...indicator... susceptibility to priming....no patient had recall of priming or intra‐operative events" |
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| Notes |
Non‐randomized portion of anaesthetic: volatile agent/N2O no/100% O2/facemask/no muscle relaxants/ADM BIS recorded Breathing induction and maintenance: sevoflurane and O2 only with facemask; at each of the 3 target ET points in induction word tests and suggestion transmitted by headphones Quote: "Anaesthesia was induced by inhalation ofsevoflurane in oxygen via a facemask. At loss of eyelid reflex...After the target end‐tidal concentration...stable...bi spectral index ...noted, headphones ...common two‐syllable words ...prime implicit memory... then ...neutral ('You will be having your operation today') or the positive ('You will feel great after the operation!') suggestion...Surgical anaesthesia ...established ...operation performed. At no point during surgery did patients receive drugs other than sevoflurane and oxygen" Comment: one of the few volatile agent only anaesthetics No email address available for ROB survey |
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| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | Quote: "Allocation was randomised by drawing a code from a hat, which ensured 16 patients in each concentration group and equal numbers of A and B, and of positive and neutral suggestion, within each concentration group" |
| Allocation concealment (selection bias) | Unclear risk | Quote: "Each patient was allocated to one of three groups characterised by their target end‐tidal sevoflurane concentration (1.2, 1.5 or 2%), then to a subgroup, A or B, to balance the test of perceptual facilitation, and finally, to a second subgroup for positive or neutral suggestion (a stimulus requiring semantic processing)..." |
| Blinding of participants and personnel (performance bias) All outcomes | High risk | Comment: not blinded to sevoflurane doses |
| Blinding of outcome assessment (detection bias) All outcomes | Unclear risk | Quote: "...Two to three hours after the operation, each patient was interviewed and asked if they remembered hearing anything while they were asleep" |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | Quote: "One patient was not included in the analysis because she required propofol to control her movements during the excitement phase of inhalational induction" Comment: dropout rate 1/48 (2%): high‐risk awareness dropout; imbalanced across groups but no significant difference between groups:sevoflurane 1.2% (1/16) vs sevoflurane 2.5% and 2% (0/32), Peto OR 0.05 (0.00 to 3.18) |
| Selective reporting (reporting bias) | Low risk | Comment: awareness outcome part of inclusion criteria |
| Other bias | Unclear risk | Comment: insufficient information provided |