[The effects of propofol and midazolam on canine left ventricular contractility]

Pronounced decrease in arterial blood pressure during propofol or midazolam infusion for sedation of critically ill patients, has raised the possibility that they have a direct negative inotropic action. Accordingly, in the current study, changes in the left ventricular (LV) contractility were examined during i.v. infusion of these two sedatives in anesthetized dogs. Myocardial contractility was assessed with the slope (Ees) of the LV end-systolic pressure-volume relationship and the slope (Msw) of the LV end-diastolic volume-stroke work relationship. Propofol was administered at 5, 10 and 20 mg.kg-1.h-1, and midazolam at 0.3, 0.6 and 1.2 mg.kg-1.h-1 over 60 min. Propofol caused dose-dependent decrease in Ees (55 +/- 7 during the low dose to 27 +/- 3 mmHg.ml-1 during the high dose, P < 0.05) and in Msw (91 +/- 8 during the low dose to 67 +/- 6 erg.cm-3 x 10(-3) during the high dose, P < 0.05). Midazolam, also, decreased in Ees and Msw significantly. No significant differences were observed between three different doses of midazolam. It is concluded that propofol shows the dose-dependent inhibition of myocardial contractility, but midazolam induces dose-independent inhibition.