Table 3: Summary of Findings From Studies on Awareness and Recall (cont).
| Study (year) and location |
McCann et al. (2002) United States (34) |
Yeo and Lo (2002) Singapore (35) |
Tsai et al. (2002) Taiwan (36) |
Sleigh et al. 2001 New Zealand (37) |
|---|---|---|---|---|
| Type of study | Prospective cohort | Observational | RCT | Prospective cohort |
| Quality of evidence | 4-c | 4-c | 4-c | 4-c |
| Primary purpose | To measure the incidence of recall during the intraoperative wake-up examination in patients undergoing 2 different anesthesia techniques (isoflurane [group 1] or no isoflurane [group 2]) | To examine the adequacy of the general anesthetic technique for avoiding explicit recall without the knowledge of BIS scores | To compare the effects of isoflurane or propofol supplementation on the BIS index | To compare the ability of BIS monitors to differentiate the awake and anesthetized states during the induction of general anesthesia with: • components of BIS (Beta ratio, SyncFastSlow) • SE50d • SE50d30Hz |
| Number of patients and type of surgery | 34 children and adolescents undergoing scoliosis surgery | 20 patients undergoing Cesarean section | 24 healthy patients undergoing elective Cesarean section (12 per group) | 84 patients undergoing routine surgery and 9 healthy volunteers |
| Mean age, years (SD) | 14.3 (2.8) | 31 (5.7) | Isoflurane: 33.46 (1.33) Propofol: 33.42 (1.79) |
Patient group: 57 (9) |
| Female/male | Not reported | All female | All female | Patient group: 52/32 |
| Premedication | Midazolam IV The mean dose of midazolam during the maintenance of anesthesia and before the wake-up test was significantly lower in group 1 compared with the dose in group 2. |
Ranitidine | Glycopyrrolate | Patient group: Oral: Midazolam (n=3) Intravenous: Midazolam (n=42) Fentanyl (n=67) Droperidol (n=5) |
| Anesthetic agent | Induction: fentanyl and thiopentone or propofol Maintenance: nitrous oxide, fentanyl, and isoflurane (Isoflurane was not administered in group 2.) |
Thiopentone, isoflurane, nitrous oxide, and morphine | Group 1: isoflurane, fentanyl, and droperidol Group 2: propofol, nitrous oxide, fentanyl, and droperidol |
Patient group: Induction agents: propofol (n=63), thiopentone (n=13), and etomidate (n=8) |
| Tracheal intubation | Yes (for both groups) | Yes | Yes | Patient group: Yes |
| Muscle relaxant | Yes (for both groups) | Yes | Yes | Patient group: Suxamethonium (n=7) Rocuronium (n=31) |
| Methods | Applied 2 anesthetic techniques: • Group 1 had isoflurane • Group 2 had no isoflurane BIS reading: • Before starting the wake-up test (T1) • At patient movement to command (T2) • After anesthetizing patients again after the wake-up test (T3) To minimize blood loss, controlled hypotension was used for all patients (55–65 mm Hg). During anesthesia and when patients moved to a command, the patients were told to remember a specific colour (teal). Anesthesiologists were blinded to the changes in BIS scores during the surgery. On the second postoperative day, patients were interviewed for recall, pain during surgery, and recall of the color specified at the time of the wake-up test. |
All anesthesiologists were blinded to the BIS values during the operation. Patients were interviewed in the recovery room and on the first postoperative day for recall or awareness. |
After delivery, patients were randomly assigned to 1 of the 2 anesthetic groups (isoflurane or propofol). | The clinical stages were defined as follows: Awake: start time LOC: time of loss of consciousness determined by a failure to respond to verbal commands (repeated twice) LOC 60: LOC+60 seconds Surgery: start of surgery The clinical anesthetist was blinded to the EEG monitoring. |
| Intraoperative measurements | BIS, HR, MAP, CO2, and end-tidal gas concentration | HR, MAP, ECG, pulse oximetry, end-tidal CO2, and end-tidal isoflurane concentration | HR, BP, and MAP | BIS, EMG, SEF, SE50d, SE50d30Hz, Beta ratio, SyncFastSlow, total bispectral score, and high bispectral score |
| BIS values | 37 wake-up tests were performed in 34 patients. Overall means (SD): T1: 72 (8) T2: 90 (8) (T2 vs. T1and T2, P <.001) T3: 54 (19) (T3 vs. T1, P <.001) T1: Group 1: 69.7 (7.7) Group 2: 75.6 (8) (P = .05) T2: Group 1: 88.4 (8.9) Group 2: 92.9 (5.9)(NS) T3: Group 1: 51.8 (19.9) Group 2: 58.2 (16)(NS) A significant increase in BIS score from T1 to T2 was observed in both groups (P <.001), and a significant decrease in BIS score from T2 to T3 was observed (P <.01). There were no significant differences in T2 or T3 BIS scores between the 2 groups. |
At skin incision: median, 70 At intubation, uterine incision and delivery: median, 60 (range, 52–70) |
Patients in the isoflurane group had higher cumulated mean BIS index values than the patients in the propofol group during the maintenance of anesthesia. | Awake: 97 (95–98) LOC: 94 (87–97) LOC 60: 56 (39–75) Surgery: 48 (39–67) Note: Values are medians (range, 25thto 75th percentile) |
| Incidence of recall | No patients recalled intraoperative pain. Patients did not recall intraoperative events before or after the wake-up test. All patients had a satisfactory postoperative recovery without significant morbidity. 6 patients had explicit auditory recall (17.6%). 1 patient in group 1 recalled the wake-up test but not the colour. 5 patients (2 in group 1 and 3 in group 2) recalled the specified colour. |
No patient experienced intraoperative dreams, recall, or awareness. | No patient from either group reported recall of the operative procedure. | N/A |
| Accuracy data/prediction probability | N/A | N/A | N/A | For detection of unconsciousness: Sensitivity: 61% Specificity: 98% PPV: 97% NPV: 75% ROC curve (areaunder the curve): 0.95 (SE, 0.12) |
*
Abbreviations: AEP indicates auditory evoked potential (awareness monitor); awareness, intraoperative awareness; BIS, bispectral index; BP, blood pressure; CABG, coronary artery bypass graft; CPB, cardiopulmonary bypass; CO2, carbon dioxide; ECG, electrocardiogram; EEG, electroencephalogram; EMG, electromyogram; HR, heart rate; IV, intravenous; LOC, loss of consciousness; MAP, mean arterial blood pressure; MF, median frequency (awareness monitor); NA, not applicable; NPV, negative predictive value; NS, not significant; O2, oxygen; PACU, post anesthesia care unit; Pk, prediction probability; PPV, positive predictive value; PSI, patient state index (awareness monitor; RCT, randomized controlled trial; ROC, return of consciousness; SEF, spectral edge frequency (awareness monitor); SP, standard practice.