The aim of this work was to evaluate fortuitous electrocardiographic alterations in dogs, promoted by increasing dose of propofol administrated by continuous infusion, associated or not to nitrous oxide.

Ten adult healthy mongrel dogs, males or females, were used. The animals were distributed into two equal groups (G1 and G2). General anesthesia was induced by intravenous administration of propofol (10 mg/kg), and immediately after, the dogs were intubated, and G1 received oxygen (30%) with nitrous oxide (70%), and G2 received oxygen (100%). Concomitantly, continuous infusion of propofol (0.4mg/kg/min) was initiated using an infusion pump. Measurements of heart rate (HR), duration and amplitude of P wave (Ps and PmV), P-R interval (PR), QRS complex duration (QRSs), R wave amplitude (RmV), Q-T interval (QT) and R-R interval (RR) were evaluated 30 minutes after the infusion beginning (M1), then 10 and 20 minutes after M1 (M2 and M3, respectively). After M3, infusion rate was increased to 0.6mg/kg/min, and elapsed 30, 40, and 50 minutes new measurements were realized (M4, M5 and M6, respectively). After M6 the infusion rate was increased again to 0.8mg/kg/min, and 30, 40 and 50 minutes after M6, further evaluations were repeated (M7, M8, and M9, respectively). Statistical analyses of the data were performed using analysis of variance (ANOVA), followed by the Tukey test (p<0.05).

The G2 demonstrated RR interval diminished when compared with G1 in M1 (G1=627.6±11.4; G2=437.4±74.72), and M2 (G1=587.4±105.26; G2=453.2±56.89), and in the equal moments, we could observe that G2 demonstrated HR values greater than G1 (M1: 99±17.63<139±24.44; M2: 105±22.4<135±19.19). These results probably were due to high induction rate and not due to infusion rates used.

We conclude that continuous infusion of propofol on these studied rates does not promote significant alterations in the electrocardiogram, and both anesthetic protocols analyzed could be safe methods to be used in patients with some cardiac damage.