Comparative effects of isoproterenol and dopamine on myocardial oxygen consumption, blood flow distribution and total body oxygen consumption in conscious lambs with and without an aortopulmonary left to right shunt

Objectives. We sought to study the effects of catecholamines on myocardial oxygen consumption ((V) over dot O-2)), regional blood flows and total body (V) over dot O-2, in lambs with circulatory congestion.

Background. Catecholamines are often used to support cardiovascular function in children with circulatory congestion because they increase contractility as well as heart rate. However, these changes increase myocardial oxygen demand and thus can lead to a mismatch between myocardial oxygen supply and demand. Catecholamines can also change regional blood hows and (V) over dot O-2 unfavorably.

Methods. We infused isoproterenol (0.1 mu g/kg body weight per min) and dopamine (10 mu g/kg per min) and measured myocardial and total body iio, and regional blood flows in chronically instrumented 7-week old lambs with and without a left to right shunt.

Results. Isoproterenol increased myocardial (V) over dot O-2, parallel to the increase in heart rate. However, myocardial blood flow and, consequently, oxygen supply also increased. This increase out-weighed the increase in myocardial (V) over dot O-2 so that myocardial oxygen extraction decreased, Isoproterenol did not change blood flow distribution. Isoproterenol increased total body (V) over dot O-2; however, systemic oxygen supply increased even more, so that oxygen extraction decreased and mixed venous oxygen saturation increased. In contrast, dopamine had no or little effect on myocardial (V) over dot O-2 or blood how distribution.