A comparison of the hemodynamic effects of inotropic agents

This experimental study was conducted to compare and contrast the cardiovascular effects of the drugs most commonly used to alleviate low-cardiac-output syndrome. Twenty-five adult mongrel dogs were infused with sodium pentobarbital (60 mg/min) until their cardiac output fell to 50+/-5% of the average control values determined by thermodilution technique prior to pentobarbital infusion. The dogs were then divided into six groups, and one of the following agents or combinations of agents was administered to each group: isoproterenol, glucagon, dopamine, dobutamine, levarterenol and phentolamine, or levarterenol and nitroprusside. All drugs, except for glucagon and the combination of levarterenol and nitroprusside, produced an increase in cardiac output above the nonfailure baseline values. However, this increase was accompanied by an undesirable, pronounced tachycardia except when levarterenol was used simultaneously with phentolamine. Both dopamine and the combined infusion of levarterenol and phentolamine proved the most effective in restoring systemic arterial pressure to near baseline values, and both were able to increase renal blood flow above the failure baseline values. While renal blood flow remained elevated with all dosages of levarterenol and phentolamine, it tended to decrease with larger doses of dopamine. These experiments demonstrate that there are major advantages in the use of simultaneously infused levarterenol and phentolamine for control of low-cardiac-output syndrome: increased cardiac output without elevated peripheral vascular resistance, restoration of systemic arterial pressure and consequent improved coronary flow, absence of tachycardia, and augmented renal blood flow.