Acute effects of furosemide on blood electrolytes and hemodynamics in dogs.

The effects of furosemide on the hemodynamics, blood electrolytes, and urinary output in 5 anesthetized dogs were studied. There were no significant changes in blood Na+ or Ca++ levels, but K+ decreased significantly after 15 minutes of furosemide treatment. There were no significant changes in the blood pressure, heart rate, left ventricular systolic pressure, index of left ventricular contractility [(dp/dt)/IIP], or systemic vascular resistance. Left ventricular dp/dt decreased for 30 to 60 minutes. Later the dp/dt and (dp/dt)/IIP of left ventricular pressure exceeded control values, although increases were not significant. Left ventricular work index and stroke volume decreased significantly between 30 and 90 minutes. The cardiac output and cardiac index also decreased. Left ventricular end-diastolic pressure decreased significantly only at 30 minutes. Cardiac function remained unchanged and consistent with the electrolytes changes. Although there was a marked diuresis, which normally must have significantly decreased the effective blood volume and hence the myocardial contractility, the cardiac function remained unchanged. These results suggests that furosemide might have a direct effect on the myocardium. Clinical improvement in patients might be the result of a direct effect on the myocardium aside from its effect due to diuresis.