Impact of Bispectral Index Monitoring on Fast Tracking of Gynecologic Patients Undergoing Laparoscopic Surgery

After Institutional Review Board (Northwestern University, Chicago, Illinois) approval and written, informed consent were obtained, 99 patients undergoing gynecologic laparoscopy were enrolled and randomized, using a closed envelope technique with random numbers, to one of two groups: group one, in which BIS monitoring electrodes were applied to the forehead prior to induction of anesthesia, and group two, in which no BIS monitoring electrodes were used. All patients received a standardized anesthetic. No premedication was administered.

General anesthesia was induced with sevoflurane and oxygen using the vital capacity inhalation induction technique. In the BIS-monitored group, sevoflurane was titrated to maintain the BIS value in the 50–60 range, while in the non–BIS-monitored group, sevoflurane was titrated to maintain blood pressure and heart rate within 20% of awake values noted on admission on the day of surgery. Neuromuscular blocking agents were used to facilitate tracheal intubation and intraoperative paralysis in all patients. The neuromuscular blocking agent and dose were left to the discretion of the anesthesiologist, as were the neuromuscular blockade reversal agent and dose.

Mechanical ventilation was adjusted to maintain the partial pressure of expired carbon dioxide between 32 and 36 mmHg. Upon removal of the laparoscope from the abdomen, sevoflurane was discontinued. At this stage, in the BIS-monitored group, nitrous oxide was added to help to maintain the BIS value below 60, while in the non–BIS-monitored group, nitrous oxide was added if blood pressure and/or heart rate increased to more than 20% of awake values until completion of surgery.

Ten micrograms of sufentanil was administered before induction of anesthesia, and a total sufentanil dose of 1 μg per kilogram of lean body mass was administered within the first 15 min after induction. Supplemental sufentanil doses of 5 μg were administered for blood pressure elevation or heart rate increases amounting to more than 20% of baseline, despite a BIS value of 50–60 or an end-tidal sevoflurane concentration of 2%. Dexamethasone, 0.15 mg/kg, was administered intravenously after induction as a preemptive antiemetic. An orogastric tube and a Foley catheter were inserted following induction and were removed at the end of surgery. Normothermia was maintained by use of a Bair Hugger® blanket (Augustine Medical, Eden Prairie, MN) and Hot Line® fluid warmer (Level 1 Technologies, Rockland, MA). Thirty minutes before the end of surgery, intravenous metochlorpropamide, 0.15 mg/kg, and intramuscular ephedrine, 0.5 mg/kg, were administered to provide additional antiemetic prophylaxis, 4and 30 mg ketorolac was administered intravenously for opiate-sparing analgesic effects.

At the completion of all surgical manipulation, the research nurse evaluated all patients in the operating room for suitability to bypass the phase I recovery area. The research nurse started a stopwatch and scored the subjects at 5, 7, and 10 min using the modified Aldrete scoring system (table 1). Patients with scores of 9 or higher were considered suitable to bypass the phase I recovery area, and those who met the criteria within 10 min were transferred to the phase II recovery area; all other patients recovered in the phase I recovery area until they met discharge criteria (modified Aldrete score) and were then transferred to the phase II recovery area. Postoperative analgesics and antiemetics were prescribed by the anesthesiologist in accordance with the standardized postoperative regimen for all patients undergoing gynecologic laparoscopy at the institution.

All subjects were given a patient satisfaction questionnaire to complete in the phase II recovery area when they met home discharge criteria (table 2).

An a priori  power analysis based on previous studies 5,6indicated that treatment groups of 40 subjects each can determine a 20% difference in the incidence of fast tracking between the two groups (power = 0.83, α= 0.05). Demographic and study data were analyzed using chi-square and Fisher exact tests for nonparametric data and t  test with Bonferroni correction for multiple comparisons for parametric data. The sevoflurane concentrations were analyzed using the Mann–Whitney U and two-sample Kolomogorov–Smirnov tests. P < 0.05 was considered statistically significant, and data were expressed as mean ± SD or numbers and percentages.

Data from 99 patients were analyzed; 2 patients required inpatient hospitalization postoperatively for surgical complications and were withdrawn from the final analysis. There were 49 subjects in the BIS-monitored group and 48 in the non–BIS-monitored group. The two groups were comparable with respect to age, weight, height, ASA physical status, duration of anesthesia, and duration and type of surgical procedure (table 3) Dosages of anesthetic drugs were also similar in both groups. The mean dose of sufentanil was 57.81 ± 7.78 μg in the BIS-monitored group and 60 ± 14.1 μg in the non–BIS-monitored group (P = 0.94); the mean concentration of sevoflurane was 2.14 ± 0.25% in the BIS-monitored group and 2.17 ± 0.87% in the non–BIS-monitored group (P = 0.375). Similarly, there was no statistically significant difference in the dosages of rocuronium used in the two groups of subjects: in the BIS-monitored group, the mean dose was 48.36 ± 13.89 mg, and in the non-BIS-monitored group, the mean dose was 46.02 ± 15.77 mg (P = 0.09).

There also was no statistically significant difference between the two groups with respect to the number of patients who successfully bypassed the phase I recovery area: 42 subjects (86%) in the BIS-monitored group and 43 subjects (90%) in the non–BIS-monitored group successfully bypassed the phase I recovery area (fig. 1). No subjects had to return to the phase I recovery area for any reason after having successfully met bypass criteria.

Subjects were evaluated postoperatively at 15-min intervals by the nursing staff and were discharged home when discharge criteria were met (table 2). The mean duration of stay in the phase II recovery area prior to discharge was 203 ± 78 min in the BIS-monitored group and 200 ± 74 min in the non–BIS-monitored group; this difference was not statistically significant. Pain and nausea and/or vomiting were the most common symptoms experienced postoperatively. The incidence of pain in the phase II recovery area was higher in the non–BIS-monitored group, but there was no significant difference in the dosage of hydromorphone required by either group of subjects. Ten of the 49 BIS-monitored subjects required 1.0 ± 0.49 mg hydromorphone, and 20 of the 48 non–BIS-monitored subjects required 0.72 ± 0.48 mg hydromorphone (P = 0.14). There was no difference in the incidence of postoperative nausea and/or vomiting in the two groups: 28 of the 49 BIS-monitored subjects received 4.5 ± 1.8 mg ondansetron, while 26 of the 49 non–BIS-monitored subjects received 3.9 ± 1.2 mg ondansetron.

Patient satisfaction scores were analyzed only for those subjects who completed the entire survey. In the BIS-monitored group 34 of 35 subjects (97%) reported being “very satisfied” with the experience, and 1 of the 35 (3%) was “moderately satisfied.” In the non–BIS-monitored group, 37 of 38 were very satisfied, while 1 of 38 was moderately satisfied. None of the subjects reported being “dissatisfied.”

The term fast tracking  has been applied in anesthesia to describe the process of moving patients rapidly through the hospitalization process associated with their surgery. 2The main purpose of fast tracking is to decrease the cost of patient care. It has been found that significant cost savings result from decreasing staffing needs in the phase I recovery area when suitable patients are able to bypass the area and recover in the less labor-intensive phase II recovery area. Candidates for direct transfer must rapidly achieve phase I recovery area discharge criteria 3following completion of surgery.

The BIS® monitor provides the anesthesiologist with information regarding the depth of hypnosis during general anesthesia. 7Several studies have suggested that shorter recovery duration and faster emergence are associated with the use of BIS monitoring and the use of newer anesthetic agents that permit rapid awakening after surgery. 5,6However, in some of these studies, the BIS-monitored patients received lower concentrations of anesthetic agents and actually exhibited signs of inadequate anesthetic depth. 5Some studies also referred to subjects as meeting fast-track criteria or being fast-track eligible, but it has never been demonstrated that these categories do, in fact, represent patients who would successfully bypass the phase I recovery area.

This study demonstrates the significance of a strictly controlled anesthetic regimen in successfully fast tracking outpatients following general anesthesia. Over 80% of patients successfully bypassed the phase I recovery area, regardless of whether the BIS® monitor was used. Because the anesthesiologist was required to adhere to a prescribed anesthetic regimen, there was essentially no difference in the outcomes analyzed in the two groups of patients, and the role of the BIS® monitor was minimized.

Another recent study in a similar population reported a fast-track rate of 8–11%8; in our study, over 85% of the subjects successfully bypassed the phase I recovery area, which exceeds any previous fast-track rates reported. The scoring system we used to evaluate home readiness has been validated previously, and the postoperative length of stay was comparable to the durations reported by other investigators using similar discharge criteria. 9As in previous reports, in our study there were no differences in other outcome measures, such as length of stay, 10,11because both groups received standardized analgesic and antemetic treatment and did not differ with respect to variables that impact discharge times, such as postoperative pain and nausea and vomiting. 12 

A major criticism of most studies that attempt to demonstrate the usefulness of the BIS® monitor in facilitating fast tracking of outpatients has been the lack of discrimination between the role of the monitor and that of the anesthetic regimen. 13This study has attempted to clarify the issue and to demonstrate the significance of standardized anesthetic regimens when consistent results are important. By incorporating a tightly controlled anesthetic regimen, the study design eliminated the possibility of contamination of the study results by anesthesiologists who learned from their experience using the BIS® monitor and transferred the knowledge to their treatment of the unmonitored subjects. This is known as learning contamination bias  and is an important factor that must be addressed in all technology assessment studies. 14This study also eliminated user bias by requiring strict adherence to the anesthetic regimen prescribed in the study.

In conclusion, this study clearly demonstrates that the application of the BIS® monitor does not have a significant impact on the ability to successfully fast track outpatients following general anesthesia for gynecologic laparoscopy using a tightly controlled, standardized anesthetic regimen and strict scoring criteria.