[Correlation between the Narcotrend index, the cerebral state index and the predicted effect site concentration during different state of consciousness in elderly patients with target controlled infusion of propofol].

OBJECTIVE: To study the correlation between the Narcotrend index, cerebral state index and predicted effect site concentration during different state of consciousness in the absence of surgery in elderly patients with target controlled infusion of propofol.

METHODS: Twenty patients aged from 65-75 years categorized as ASA class I - II who were scheduled to undergo general surgery under general anesthesia with target controlled infusion of propofol were recruited. During the target controlled infusion of propofol, the propofol infusion was set at an initial effect site concentration of 0.5 mg/L and increased by 0.5 mg /L every 5 min until the modified observer's assessment of alertness / sedation scale (OAA/S) values of zero. The predicted effect site concentration of propofol, the values of CSI and NCT were recorded and the sedation level was examined by the modified OAA/S every 20 s. The predicted effect site concentrations of propofol in target controlled infusion (TCI) system were recorded when they increased by more than 0.1 mg/L. The predicted effect site concentrations of propofol and the values of NCT and CSI at LVC and LOC of the patients were recorded.

RESULTS: There was a good linear correlation between NCT and the predicted effect site concentration of propofol (R2 = 0. 867, P < 0.01), as well as that between CSI and the predicted effect site concentration of propofol (R2 = 0.893, P < 0.01). The predicted effect site concentrations of propofol at LVC was (1.56 +/- 0.13) mg/L while the values of NCT was 74.00 +/- 4.69 and CSI 69.82 +/- 5.47. The predicted effect site concentrations of propofol at LOC was (2.15 +/- 0.27) mg/L while the values of NCT and CSI were 63.30 +/- 7.50 and 58.78 +/- 6.90 respectively. All of the values of NCT, CSI and the predicted effect site concentrations had a good linear correlation with OAA/S. There was a negative correlation between OAA/S and the predicted effect site concentration. At the same time, there was a positive correlation between OAA/S and NCT as well as that between OAA/S and CSI. And the correlation coefficients were - 0.968, 0.938, 0.940 respectively (P < 0.01). The values of NCT were higher significantly than that of CSI in different degree of LOC (P < 0.01).

CONCLUSION: During elder people's target controlled infusion of propofol, LVC and LOC occur within a definite range of predicted effect site concentrations. There is a good linear correlation between NCT, CSI and the predicted effect site concentrations of propofol. For the elders, both NCT and CSI reflect the sedation level of propofol. Although there is a significant correlation between NCT and CSI, a deviation does exist in a certain range. Therefore a simple 1:1 transfer from NCT to CSI is inadequate.