Effects of Two Different Dosages of Dobutamine on Pulmonary Artery Wedge Pressure, Systemic Arterial Blood Pressure and Heart Rate in Anaesthetized Horses

The purpose of the present study was to investigate the effects of two different dobutamine concentrations on pulmonary artery wedge pressure (PAWP) and on mean systemic arterial blood pressure (MAP) in horses anaesthetized with isoflurane, after induction of general anaesthesia with xylazine, ketamine and diazepam. Eight healthy warm-blood horses were included in the study. Each horse was subjected to general anaesthesia twice with two different dosages of dobutamine, 3 and 5 μg/kg bw/min, being infused over 15 min, starting 50 min after induction of general anaesthesia (T₀). The heart rate, the PAWP and the MAP were recorded after 10 min (T₁) and then every 5 min until 15 min after cessation of intravenous dobutamine administration (T₃-T₅). The PAWP was measured by a right heart catheter, which was positioned in the pulmonary capillaries. Mean systemic arterial blood pressure was monitored at the facial artery for the duration of general anaesthesia. All parameters increased at both dosage rates of dobutamine and decreased significantly when dobutamine administration ceased. The increase in heart rate was significantly higher after administration of 3 μg/kg bw/min dobutamine compared with the dosage of 5 μg/kg bw/min dobutamine. The increase in MAP was also higher at this dosage, but not significantly different to the dosage of 5 μg/kg bw/min dobutamine. During both dosages the MAP was above a value considered to be compatible with good peripheral circulation. The greater increase in PAWP was observed during administration of 5 μg/kg bw/min dobutamine, but PAWP was not significantly different with the dosage of 3 μg/kg bw/min dobutamine. In conclusion, the administration of dobutamine led to an increase in MAP and PAWP above a value considered to be compatible with a good peripheral circulation. The results of the present study indicate that dobutamine improves circulation, in addition to its well-known effect on the periphery.