[Systemic and coronary haemodynamic effects of dobutamine and norepinephrine during metabolic acidosis]

The effects of clinical doses of dobutamine (5 microgram/kg x min) and norepinephrine (0.2 microgram/kg x min) on systemic haemodynamics and coronary circulation were studied during normal pH and during metabolic acidosis (pH 7.0) induced by hydrochloric acid in 9 anaesthetized closed chest dogs. Metabolic acidosis per se failed to show any significant depression of cardiac function, indicating that animals with intact sympathoadrenal system are highly resistant to acidaemia. Our results further demonstrated that a significant circulatory response to clinical doses of dobutamine and norepinephrine was still present during metabolic acidosis. However, the increase in cardiac output, max dp/dt and mean arterial pressure after dobutamine was found to be significantly reduced at low pH-values, whereas the vasopressor response to norepinephrine was not affected. From these results it may be speculated that metabolic acidosis differently influences the responsiveness of alpha- and beta-adrenergic receptors. Finally our results show that metabolic acidosis did not compromise the coronary adjustment to catecholamine-induced increases in myocardial oxygen demand.