Dopamine under α₁-blockade, but not dopamine alone or fenoldopam, increases depressed gastric mucosal oxygenation

Objective: To compare the effects of dopamine, both in the presence and absence of α₁-blockade, and fenoldopam on microvascular gastric mucosal oxygenation and systemic oxygen transport under compromised circulatory conditions, both without and with fluid resuscitation. Design: Randomized controlled animal study. Setting: University department of anesthesiology. Subjects: Eight anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output. Interventions: On different days, the dogs received in random order either dopamine (2.5 and 5.0 μg·kg^-1 ·min^-1, with or without α₁-blocker pretreatment), the selective DA₁-agonist fenoldopam (0.1 and 1.0 μg·kg^-1·min^-1, with and without DA ₁-blocker pretreatment), or saline (control). These interventions were performed under compromised cardiocirculatory conditions (induced by ventilation with positive end-expiratory pressure [PEEP] of 10 cm H ₂O), both without and with fluid resuscitation. Measurements and Main Results: We continuously measured regional microvascular hemoglobin saturation (μHbO₂) in gastric mucosa by reflectance spectrophotometry and systemic oxygen transport (ḊO₂). Ventilation with PEEP significantly decreased ḊO₂ (from 19 ± 2 to 9 ± 1 mL·kg^-1·min^-1, mean ± SEM) and gastric mucosal μHbO₂ (from 57 ± 2% to 37 ± 3%). Fluid resuscitation restored ḊO₂ back to baseline (from 9 ± 1 to 19 ± 2 mL·kg^-1 ·min^-1) but only partially restored μHbO₂ (from 37 ± 3% to 50 ± 4%). Under both conditions, dopamine with and without α₁-blockade significantly increased ḊO ₂ (by about 5 mL·kg^-1·min^-1 in the nonresuscitated state and 10 mL·kg^-1·min ^-1 in the fluid resuscitated state, respectively), but only dopamine in the presence of α₁-blockade also significantly increased gastric mucosal μHbO₂ (by 5 ± 1% and 7 ± 2% in the nonresuscitated and fluid resuscitated states, respectively). Fenoldopam under all study conditions did not significantly affect ḊO₂ or μHbO₂, either in the presence or absence of DA₁- blockade. Conclusions: During compromised cardiocirculatory conditions, α₁-receptor activation during dopamine infusion prevented an increase in gastric mucosal oxygenation. Furthermore, selective DA ₁-stimulation (by fenoldopam) was insufficient to overcome the PEEP-induced depression of μHbO₂. The responses of gastric mucosal oxygenation did not parallel changes in systemic oxygen transport. These findings were independent of fluid resuscitation.