Bispectral Index Monitoring During Anesthesia Promotes Early Postoperative Recovery of Cognitive Function and Reduces Acute Delirium in Elderly Patients with Colon Carcinoma: A Prospective Controlled Study using the Attention Network Test

Abstract

BACKGROUND Bispectral index (BIS) monitoring can reduce the duration of anesthesia. This study aimed to evaluate the effects of BIS monitoring during surgery for resection of colon carcinoma in elderly patients using the Attention Network Test (ANT) to study alerting, orienting, and executive functions, and the Confusion Assessment Method (CAM). MATERIAL AND METHODS Eighty-one patients (65-75 years) underwent radical surgery for colon carcinoma with general intravenous anesthesia, propofol (6-8 mg/kg/h), vecuronium (0.03-0.05 mg/kg/min), and remifentanil (0.1-0.2 μg/kg/min). The BIS group (n=41) underwent adjustment of anesthesia to maintain a BIS value between 40-60; the non-BIS group (N=40) underwent standard intraoperative hemodynamic monitoring. Primary endpoints were alerting, orienting, and executive functions assessed pre-operatively and on postoperative days 1 and 5 using the ANT; the secondary endpoint was delirium during the first five postoperative days, assessed using the CAM. RESULTS Propofol and remifentanil doses were significantly lower in the BIS group compared with the non-BIS group (P<0.001). Alerting, orienting, and executive functions showed no differences between the two groups pre-operatively but were impaired in both groups on postoperative day 1 compared with pre-operative levels (P<0.001). On postoperative day 5, alerting (P=0.607) and orienting (P=0.851) functions recovered in the BIS group but remained impaired in the non-BIS group (P<0.001). Delirium was significantly lower in the BIS group compared with the non-BIS group (17.5% vs. 27.5%) (P<0.001). CONCLUSIONS BIS-guided anesthesia was associated with reduced anesthetic exposure, early postoperative recovery of alerting and orienting functions, and reduced postoperative delirium.

Figure 1

Schematic representation of the Attention Network Test (ANT). Shown are the three target stimuli, the four cue conditions, and the sequence of events for the Attention Network Test (ANT) used in the present study. Adapted from Fan et al. [24,25].

Figure 2

Flowchart of the study design. BIS – bispectral index; MMSE – mini-mental state examination; ANT – Attention Network Test; CAM – Confusion Assessment Method.

Figure 3

Efficiency of the attention networks in the bispectral index (BIS) monitored group (BIS group). Attention network (alerting, orienting, and executive control) functions in the bispectral index (BIS) group were assessed pre-operatively and at day 1 and day 5 postoperatively. * P<0.05 vs. corresponding pre-operative value; ^# P<0.05 vs. corresponding pre-operative value.

Figure 4

Efficiency of the attention networks in the group not monitored using the bispectral index (BIS) (non-BIS group). Attention network (alerting, orienting, and executive control) functions in the non-bispectral index (BIS) group were assessed pre-operatively and at day 1 and day 5 postoperatively. * P<0.05 vs. corresponding pre-operative value; ^# P<0.05 vs. corresponding pre-operative value.