Dopexamine but not dopamine increases gastric mucosal oxygenation during mechanical ventilation in dogs

Objective: 

To compare the effects of dopamine and dopexamine on gastric mucosal oxygenation during mechanical ventilation without and with positive end-expiratory airway pressure (PEEP) and after compensation of the PEEP-induced hemodynamic suppression.

Design:

Randomized controlled animal study.

Setting:

University research department of experimental anesthesiology.

Subjects: 

Ten anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

Interventions: 

On different days, the dogs randomly received dopamine (2.5 and 5.0 mug(.)kg(-1.)min(-1), n = 10), dopexamine (0.5 and 1.0 mug(.)kg(-1.)min(-1)) without (n = 8) or with pretreatment with a selective beta(2)-adrenoceptor antagonist (ICI 118,551, n = 7), or saline (control, n = 7). To simulate common clinical situations, these interventions were performed during different ventilation modes: during mechanical ventilation without and with high levels of PEEP, and after compensation of the PEEP-induced systemic hemodynamic suppression by titrated volume resuscitation with hydroxyethyl starch.

Measurements and Main Results: 

We continuously measured microvascular hemoglobin saturation (muHbo(2)) by light-guide spectrophotometry in the gastric mucosa. Dopexamine, but not dopamine, significantly increased gastric mucosal muHbo(2) by about 20%, regardless of the dose and the ventilation mode, Both catecholamines dose-dependently increased cardiac output and oxygen delivery by up to 75% without effects on systemic oxygen saturation. The effects of dopexamine on muHbo(2) as well as on cardiac output and oxygen delivery were prevented by selective beta(2)-adrenoceptor-blockade.

Conclusions:

Dopexamine but not dopamine improved gastric mucosal oxygenation in dogs. This effect was independent of the dosage and the ventilation mode. Thus, dopexamine may reverse a decrease in splanchnic oxygenation induced by ventilation with PEEP. The dopexamine-induced increase in gastric mucosal oxygenation was mediated by beta(2)-adrenoceptors, which explains the superior effects of dopexamine to dopamine on muHbo(2). The regional effects of both catecholamines were not mirrored by systemic hemodynamics.