The aim of this work was to establish the correlation between the bispectral index (BIS) and different rates of continuous infusion of propofol.

Twenty-four adult dogs were randomly divided into 3 groups (P2, P4, P8). All animals were induced with propofol (10 mg/kg/IV), followed immediately by the continuous infusion of the agent: 0.2 mg/kg/min (P2), 0.4 mg/kg/min (P4) and 0.8 mg/kg/min (P8). The BIS values were measured before any drug administration (M0) and 10, 20, 30, 40 and 50 minutes after the start of the continuous infusion of propofol. The Analysis of Variance was used to calculate the correlation between the infusion rates of propofol and the BIS values.

BIS demonstrated significant difference between groups at the moment M40, where P8 (72 ± 9,7) was smaller than P2 (84 ± 7,4) and P4 (33 ± 8,5), while in M50 this difference was observed in P8 (69 ± 13,5) that was smaller than P2 (84 ± 6,4).

The effects of induction dose of propofol were not more presented in M40, therefore, the BID values were correlated with the infusion rate of each group. When the infusion rate was increased, the BIS values decreased. Leslie et al. (1995) observed that when propofol is used alone, there is a correlation between BIS values and plasmatic concentration of this drug.

The results allowed us to conclude that the BIS values are a reliable reference to help monitoring the anesthetized patient, and that the increase in the rates of propofol are related with the decrease of the BIS values.

References

1.  Leslie, K et al. Propofol blood concentration and Bispectral index predict suppression of learning during propofol/epidural anesthesia in volunteers. Anesth. Analg., Baltimore, v. 81, n. 6, p. 1269-1274, 1995.