Table 3: Summary of Findings From Studies on Awareness and Recall.
| Study (year) and location |
Ekman et al. (2004) Sweden (24) |
Kreuer et al. (2003) Germany (25) |
Kerssens et al. (2003) The Netherlands (26) |
|---|---|---|---|
| Type of study | Prospective cohort – BIS-monitored patients were compared with an historical cohort (no BIS). |
RCT Group1: Narcotrend Group 2: BIS Group 3: SP |
Prospective cohort, part of an RCT on memory function during deep sedation |
| Quality of evidence | 3-b | 2 | 4-c |
| Primary purpose | To evaluate if BIS monitoring significantly reduces the incidence of awareness | To investigate the impact of Narcotrend monitoring on recovery times and propofol consumption compared with BIS monitors or standard anesthetic practice | To investigate response to command during deep sedation (BIS score of 60–70) and the ability of BIS monitors to indicate awareness and predict recall |
| Number of patients and type of surgery | Cases: 4,945 consecutive surgical patients with BIS monitoring Controls: 7,862 similar cases from an historical group with no cerebral monitoring |
120 patients (40 patients per group) Minor orthopedic surgery expected to last at least 1 hour |
56 healthy outpatients scheduled for elective surgery |
| Mean age, years (SD) | BIS: 50 (19) SP: 49 (19) |
BIS: 43.8 (4.2) SP: 46.1 (4.5) |
37 (10) (range, 19–58) |
| Female/male | BIS: 64/36 SP: 61/39 |
Equal number of males and females in each group (40) | 25/31 |
| Premedication | Premedication: Benzodiazepine: BIS: 967 (20%) No BIS: 1818 (23%) No premedication: BIS: 2306 (47%) SP: 2113 (27%) Opioid before induction: BIS: 4383 (89%) SP: 7550 (96%) |
Yes | No |
| Anesthetic agent | Propofol/thiopental for induction: BIS: 28/71 SP: 33/66 Concomitant regional anesthesia: BIS: 664 (13%) SP: 752 (10%) |
Propofol & remifentanil | Induction: Propofol Maintenance: Target controlled of propofol and alfentanil |
| Tracheal intubation | BIS: 4926 (100%) SP: 7796 (100%) |
Yes | Yes |
| Muscle relaxant | BIS: 4729 (96%) SP: 7752 (99%) |
Yes | Yes |
| Methods | Assessment by the anesthesiologists using a visual analogue scale as follows: - To what extent BIS monitors had been used to guide anesthesia - To what extent they felt confident that the BIS monitor worked properly Patients were interviewed on 3 occasions: - Before leaving the PACU - 1–3 days after operation. - 7–14 days after operation. |
A second independent investigator recorded BIS and Narcotrend data in intervals of 5 minutes. In the SP group, both monitors were covered behind a curtain and hidden from the attending anesthesiologist. |
Anesthesia was induced 30 minutes before surgery to avoid noxious stimulation and confounding effects. During this presurgical period, and while a hypnotic state was maintained at a BIS score of 60–70, responses to commands were investigated. BIS readings were taken on the following occasions:- No response to command - Equivocal response - Unequivocal response Anesthesia was induced 30 minutes before surgery. Once every 50 seconds, the observer called the patient’s name to determine his/her awareness. Patients were then asked to squeeze observer’s hand during the target-controlled fusion of the anesthetic agent. Patients who squeezed once were then asked to squeeze twice. Failure to squeeze twice was considered an equivocal response, whereas squeezing twice showed an adequate (unequivocal) response indicating awareness. Investigated the incidence of recall by Interviewing the patients |
| Intraoperative measurements | BIS scores | HR, systemic arterial pressure, respiratory rate, oxygen saturation, pulse oximetry, and end-tidal concentration of anesthetic carbon dioxide. | HR, MAP, spectral edge frequency, median frequency alpha, beta, theta, and delta power |
| BIS values | All staff members were instructed to maintain BIS values between 40 and 60 and to avoid values greater than 60 during induction and maintenance. Mean BIS values:During the induction phase: 46 (SD, 11) During the maintenance phase:38 (SD, 8) |
Not reported | BIS scores were maintained between 60 and 70 after induction/intubation and before surgery. During surgery, BIS values were maintained at about 45. |
| Incidence of recall | BIS: 2 patients (0.04%) Control: 14 patients (0.18%) P <.038 (77% reduction) |
No patient had intraoperative recall. | Response to commands: No response: 887 (82%) commands(15 patients) Equivocal responses: 56 (5%) commands Unequivocal responses: 139 (13%) commands Conscious recall: Of the 37 patients (66%) with an unequivocal response to commands, 9 (25%) reported conscious recall after recovery. For those who had conscious recall: BIS: 67.6 (SD, 5.5) HR: 72.9 (SD, 16.1) MAP: 87 (SD, 15.5) For those who did not have conscious recall: BIS: 67.1 (SD, 3.7) HR: 67.4 (SD, 11.7) MAP: 89.8 (SD, 17.9) |
| Accuracy data/prediction probability | N/A | N/A | N/A |