RESUMEN
Its is known that positive pressure mechanical ventilation (PPMV) decreases diuresis and increases extravascular water, thereby impairing pulmonary gas exhange. Sympathomimetic amines are commonly used to relieve these effects. To compare the effects of dobutamine (DT) and dopamine (DP) on renal and pulmonary function, we studied 30 patients submitted to continuous PPMV for a least 72 h. All were in stable hemodynamic conditions.patients had pulmonary insufficiency of different etiology. The drugs were randomly administered by continuous intravenous infusion at the dose of 4 to 6 *g kg-1 min-1 for 3 h. An interval of 60 min was allowed to elapse between treatments. A significant increases in arterial pressure and heart rate occurred with both drugs (P,0.05). DP increased urinary flow by 93.7% (1.6ñ0.1 to 3.1 ñ0.4 ml/min; P,0.05) and Na excretion fraction (NaEF) by 35.5% (P,0.05).In contrast, DT reduced NaEF by 58.9%(P,0.05) and had effect on urinary flow. Neither drug altered cretinine clearance.The alveolo-arterial O2 difference (a-aO2D), which was 370ñ20 mmHg during the control period, increased to 394 ñ 20 mmHg after DP and decreased to 355 ñ 22 mmHg after DT, the difference being statistically significant (P,0.05). Pulmonary shunt (%) and the venous pO2 (mmHg) did not change during the infusion of DP or DT.In conclusion, an acute increase in salt and water excretion does not necessarily lead to an immediate reduction in pulmonary "shunt". DT deserves further investigation since it may increase paO2 in the absence of ventricular failure