Einfluss verschiedener Katecholamine auf die Mikroperfusion und Oxygenierung des Gastrointestinaltraktes beim Pferd in Allgemeinanästhesie

The aim of this study was to evaluate the influence of different cardiovascular active drugs with different adrenoreceptor affinity on both systemic and local tissue perfusion characteristics.   Ten horses underwent general anaesthesia with isoflurane in dorsal recumbancy and were subjected to a median laparotomy. Anaesthesia induction was achieved with i.v. ketamin (2.2 mg/kg BW) and midazolam (0.05 mg/kg BW), after xylazine (0.8 mg/kg BW) as premedication. All horses were mechanically ventilated. After 90 min. of equilibration, every horse was subjected to a continuous rate infusion of three different doses (μg/kg/min) of dobutamine (0.5/1/3), dopamine (1/2/5), norepinephrine (0.1/0.2/0.5) and phenylephrine (0.5/1/3), each infused for 15 min. in a randomized order. In between every individual catecholamine, a wash out period of 45 min. was set. At the end of every dose rate and wash out period, the microvascular bloodflow and tissue oxygen saturation of the jejunum, stomach and colon were measured using a combination of Laser-Doppler-Flowmetry and white light remission spectrophotometry. Simultaneously cardiac output (CO) was measured by thermodilution, and heart rate (HR), mean arterial pressures (MAP) and respiratory rate (RR) were recorded. At the same time points both arterial and mixed venous blood gas samples were taken and analyzed.   Influence of drug and dose was analyzed by 1-way-ANOVA for repeated measurements (p < 0.05).   Dobutamine dose-dependently increased CO, HR and MAP and the gastrointestinal blood flow with a significant increase up to +47.6 ± 26.3% for the jejunum and up to +29.9 ± 15.4% in the colon (mean ± SD). Dopamine significantly decreased the local blood flow in its high dose, both in the small and large intestines (-35.7 ± 17% and -39.8 ± 21.7%, respectively). Also tissue oxygen saturation significantly fell below baseline values (89.9 ± 5.7%), most prominently in the small intestines with the high dose of dopamine (75.7 ± 7.3%). Globally CO increased, while SVR and MAP decreased. Norepinephrine had no significant influence on the gastrointestinal circulation, but significantly increased MAP and SVR in a dose related manner. The high dose of phenylephrine caused a significant decrease in blood flow in the small and large intestines and the stomach, of up to -31.2 ± 32.0%, -44.1 ± 21.1% and -28.0 ± 19.2%, respectively. Tissue oxygen saturation was also decreased, most prominently at the colon measurement site with a value of 74.8 ± 3.2% vs. a baseline measurement of 90.9 ± 5.0%. The MAP and SVR significantly increased in a dose dependent fashion, while CO and HR were significantly decreased.   Dobutamine improved both global and local perfusion characteristics, so it remains the most suitable catecholamine to treat hypotension in horses under general anaesthesia. Dopamine negatively impacted microcirculatory blood flow in the gastrointestinal tract, despite a significant increase in CO. Phenylephrine produced the most intense decrease in both systemic and local circulation, whilst norepinephrine increased MAP and SVR without negatively affecting the mesenteric blood flow, which could make it a suitable vasopressor for use in equine colic surgery.