Effects of pentobarbital on inotropic state of isolated canine left ventricle

Although pentobarbital has been found to depress myocardial function, the magnitude of its direct effects on ventricular contraction at anesthetic concentrations has not been well quantified. The direct effects of pentobarbital on left ventricular function were measured by employing an isolated canine heart preparation with a blood oxygenator. Seven hearts were perfused with blood, dextran, and perfluorochemical artificial blood. Ventricular function was evaluated using the slope of the end-systolic pressure-volume relationship (E_es) and the maximal rate of pressure development (dP/dt_max) in ventricles contracting isovolumically in control, after a low dose (13 μg/ml), and after a high dose (48 μg/ml) of pentobarbital. These concentrations represent one-half and two times the typical value (25 μg/ml) found to produce anesthesia in canines (assessed by tail clamp or blink reflex). The low dose of pentobarbital did not produce clear-cut depression in contractile function. The high dose of pentobarbital produced significant reductions of E_es, and dP/dt_max:E_es decreased 29%, from a control of 4.30 ± 0.84 to 3.05 ± 0.49 mmHg/ml and dP/dt_max decreased 24%, from a control of 909 ± 148 to 695 ± 173 mmHg/s. Thus, the threshold for the direct depressant effect of pentobarbital on ventricular function falls within the range of half to double the typically-reported anesthetic concentrations.