RESUMO
BACKGROUND: Delay in the propofol pharmacodynamics effect is commonly observed in total intravenous anesthesia (TIVA). To face the delay in the hypnosis control, we have proposed a proportional-integral (PI) controller with a Smith predictor (PI+Smith). We have evaluated the feasibility of this closed-loop control for propofol administration and compared the performance with manual administration guided by the Bispectral Index (BIS). METHODS: Fifty-seven adult patients under TIVA with propofol and remifentanil were randomly assigned to a PI+Smith or a manual control (MC) group. The BIS target was set to 50. The performance was compared through the global score (GS), median performance error (MDPE), median absolute performance error (MDAPE), offset and Wobble. RESULTS: A total of 29 patients in the MC and 25 in the PI+Smith groups completed this study. Performance was significantly better in the PI+Smith group: global score was 25 (19 to 37) for PI+Smith versus 44 (32 to 57) for MC (P<0.001); MDPE was -0.9 (-5.6 to 2) for PI+Smith versus -11 (-16 to -4.3) for MC (P<0.001); MDAPE was 10.8 (8.8 to 14.3) for PI+Smith versus 17 (12.8 to 19.2) for MC (P<0.001); offset was -0.6 (-3.2 to 0.06) for PI+Smith versus -3.7 (-7.0 to -0.8) for MC (P=0.01). The percentage time of BIS within the 40-60 range during the maintenance phase was higher in the PI+Smith group 80.8 (68.7 to 87.9) than in the MC group 59.1 (53.4 to 72.5) (P<0.001). CONCLUSIONS: The use of a specific mechanism in the PI controller to deal with the delay outperformed satisfactorily manual practice. The controller was able to regulate propofol administration, maintaining the BIS value within a desirable range and coping with oscillations.
