The effect of dobutamine and bolus crystalloid fluids on the cardiovascular function of isoflurane anaesthetised horses

Reasons for performing study:

Hypotension is the most common cardiovascular complication encountered during equine inhalational anaesthesia, for which a dobutamine intravenous constant rate infusion (DCRI) is often the sole treatment. There is limited literature available on the combined use of crystalloid boluses and inotropic agents during equine hypotensive episodes.

Objectives:

To determine the cardiovascular effects of DCRI, alone and in combination with a crystalloid bolus (CB) during controlled ventilation in hypotensive, isoflurane anaesthetised horses.

Study design:

Prospective, randomised, cross-over experimental design of 6 healthy Standardbred horses aged 5–13 years weighing 464–578 kg.

Methods:

Horses were premedicated with intravenous acepromazine and xylazine. Anaesthesia was induced with intravenous ketamine and diazepam. Isofluorane was used to maintain anaesthesia and achieve a target mean arterial pressure (MAP) of 60 mmHg ± 5%. Sixty minutes post induction (T0) when a stable end tidal isoflurane percentage and target MAP had been achieved for ≥15 min one of 2 treatments was given. Treatment A (TA) was a DCRI, commencing at 0.5 μg/kg bwt/min and increasing in increments of 0.5 ug/kg bwt every 10 min as required to achieve a MAP of 80 mmHg ± 5% by 30 min following initiation of the DCRI. Treatment B (TB) was as for TA plus a 20 ml/kg bwt CB. Cardiac output, haemoglobin concentration, PaO2 and SaO2 were obtained at baseline (T0) and 30 min following initiation of the DCRI (T1). Data were analysed with a Wilcoxon matchedpairs signed rank test (P<0.05 considered significant), with data presented as median ± interquartile ranges.

Results:

Treatment A was associated with a significant (P = 0.03) increase in oxygen delivery index (DO2I) from baseline (T0 707.78 ± 159.73 ml/ min/m2 ; T1 1260.26 ± 184.56 ml/min/m2 ), while TB was not (P = 0.09).

Conclusions:

In an experimental model of isoflurane induced hypotension, DCRI results in increased DO2I, while the use of DCRI in combination with CB does not.