The pulmonary vascular effects of dopamine, dobutamine, and isoproterenol in unilobar pulmonary edema in dogs.

Although catecholamine inotropic drugs are often used to support the circulation of critically ill patients with hypoxemic respiratory failure, their effect on the pulmonary circulation and on gas exchange is incompletely understood. In order to improve our understanding of the effects of these drugs on the pulmonary circulation, we made measurements of total and regional intrapulmonary shunt (Qs/Qt), distribution of pulmonary blood flow, and pulmonary hemodynamics before and after infusions of dopamine (n = 6, 5 micrograms/kg/min), dobutamine (n = 6, 10 micrograms/kg/min), isoproterenol (n = 6, 0.1 micrograms/kg/min), or saline in dogs with unilobar oleic acid-induced pulmonary edema. In addition to permitting determination of the overall hemodynamic and gas exchange effects of these drugs, this preparation allowed measurement of changes in distribution of pulmonary blood flow between normal and edematous lung. In 6 dogs given dobutamine, mean cardiac output (CO) increased by 1 liter/min, while pulmonary arterial pressure (PPA) increased by 2 mm Hg with no change in pulmonary vascular resistance (PVR) or distribution of pulmonary blood flow. There was a 5% increase in mean Qs/Qt which, because of the lack of evidence of pulmonary vasoactivity, was attributed to time or to increased CO. Isoproterenol produced a similar increase in CO, but reduced PPA and PVR indicating pulmonary vasodilator activity. Pulmonary vasodilation was most prominent in edematous lung, resulting in an increase in relative blood flow to the edema lung lobe and a substantial increase in Qs/Qt, exceeding the increase in all other groups. Dopamine, similarly increasing CO, did not change overall PVR but reduced fractional blood flow to the edema lobe by 3.4% of CO. Neither Qs/Qt nor PaO2 changed significantly in this group. The differing effects of these agents on pulmonary hemodynamics, intrapulmonary blood flow distribution, and gas exchange have potentially significant implications affecting the choice of drug used for circulatory support in hypoxemic respiratory failure.