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

Abstract

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. Randomized controlled animal study. University research department of experimental anesthesiology. Ten anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output. On different days, the dogs randomly received dopamine (2.5 and 5.0 microg x kg(-1) x min(-1), n = 10), dopexamine (0.5 and 1.0 microg x kg(-1) x min(-1)) without (n = 8) or with pretreatment with a selective beta2-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. We continuously measured microvascular hemoglobin saturation (mu-Hbo2) by light-guide spectrophotometry in the gastric mucosa. Dopexamine, but not dopamine, significantly increased gastric mucosal mu-Hbo2 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 mu-Hbo2 as well as on cardiac output and oxygen delivery were prevented by selective beta2-adrenoceptor-blockade. 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 beta2-adrenoceptors, which explains the superior effects of dopexamine to dopamine on mu-Hbo2. The regional effects of both catecholamines were not mirrored by systemic hemodynamics.