ObjectiveTo determine the systemic, pulmonary, mesenteric, and renal hemodynamic effects of short and prolonged infusions of dobutamine.DesignProspective randomized unblinded study.SettingUniversity research laboratory.SubjectsThirteen newborn (1-3 days old) piglets.InterventionsPiglets were instrumented and studied 48 hrs later. Fifteen-minute infusions of dobutamine at 5, 10, 20 and 50 [micro sign]g/kg[center dot]min were randomly given with 15-min rests between the doses. After a 1-hr hiatus, a dose of 10 [micro sign]g/kg[center dot]min was continuously administered for 2 hrs.Measurements and Main ResultsSystemic and pulmonary arterial pressures, cardiac index (thermodilution), and superior mesenteric and renal artery flows were measured. Vascular resistance values were calculated.Main ResultsFifteen-minute infusions: Dobutamine dose-dependently increased cardiac index with tachycardia but not stroke volume (from 187 +/- 43 to 238 +/- 51 mL/kg[center dot]min at baseline and 50 [micro sign]g/kg[center dot]min, respectively, p < .05; values expressed as mean +/- SD). Systemic, but not pulmonary, vascular resistance decreased, resulting in a significant decrease in systemic to pulmonary arterial pressure ratio (from 3.8 +/- 0.8 at baseline to 3.2 +/- 1.0 at 50 [micro sign]g/kg[center dot]min). Superior mesenteric and renal flows were not affected. Two-hour infusion at 10 [micro sign]g/kg[center dot]min: Cardiac index progressively increased from 173 +/- 34 to 240 +/- 58 mL/kg[center dot]min at baseline and 120 mins, respectively, (p < .05). The initial tachycardia was transient, and stroke volume was significantly increased at 60 mins and thereafter. Although systemic and pulmonary vascular resistance values fell simultaneously, systemic to pulmonary arterial pressure ratio decreased significantly to 3.4 +/- 0.9 at 120 mins from 3.9 +/- 0.7 at baseline. Superior mesenteric and renal artery flows increased significantly with vasodilation after 60 mins.ConclusionsShort infusions of dobutamine dose-dependently increase cardiac output due to tachycardia, without significant effect on mesenteric and renal blood flows. Prolonged infusion of dobutamine at 10 [micro sign]g/kg[center dot]min progressively increases cardiac output and stroke volume with transient tachycardia, and increases mesenteric and renal blood flows. Caution is required in the treatment of critically ill neonates with dobutamine, which could also reduce systemic to pulmonary arterial pressure ratio. (Crit Care Med 1999; 27:558-564)