We studied the effects of the beta2-adrenoceptor and DA1-receptor agonist dopexamine on ventilation perfusion (V(A)/Q) distribution in anesthetized, paralyzed patients (n = 17) undergoing major abdominal surgery. Intrapulmonary shunt (Q(S)/Q(T)) (percentage of cardiac output [CO]), perfusion of low V(A)/Q areas (percentage of CO), ventilation of high V(A)/Q areas (percentage of total ventilation [V(E)]), and dead space ventilation [percentage of V(E)]) were calculated from the retention/excretion data of six inert gases. In the control state, Q(S)/Q(T) was 11% +/- 9% (mean +/- SD) and little perfusion of low V(A)/Q areas (3% +/- 4%) was observed. Infusion of 1.0 microg kg(-1) x min(-1) dopexamine had no effect on Q(S)/Q(T) and low V(A)/Q areas despite an increased CO (7.7 +/- 2.2 L/min versus 6.2 +/- 1.2 L/min; P < 0.01). Pao2 increased from 15.5 +/- 5.6 kPa (116 +/- 42 mm Hg) to 17.3 +/- 6.3 kPa (130 +/- 47 mm Hg) (P < 0.05). Infusion of 2.0 microg x kg(-1) x min(-1) dopexamine further increased CO to 8.4 +/- 2.7 L/min (P < 0.01) without alterations of Q(S)/Q(T), perfusion of low V(A)/Q areas, and Pao2. We concluded that dopexamine (1.0 microg x kg(-1) x min(-1) and 2.0 microg x kg(-1) x min(-1)) has no adverse effects on V(A)/Q relationships and Q(S)/Q(T) in anesthetized, paralyzed patients. CONCLUSIONS The I.V. administration of vasoactive drugs can improve oxygen delivery to different organ systems but may impair pulmonary gas exchange. In anesthetized, paralyzed patients, we studied the effects of beta2-adrenoceptor and DA1-receptor agonist dopexamine on ventilation perfusion distribution. Dopexamine (1.0 microg x kg(-1) x min(-1) and 2.0 microg x kg(-1) min(-1)) improved cardiac output and oxygenation without alterations of intrapulmonary shunt.