CARDIOPULMONARY EFFECTS OF DESFLURANE IN PONIES, AFTER INDUCTION OF ANESTHESIA WITH XYLAZINE AND KETAMINE

Cardiopulmonary parameters were measured in 12 ponies (small horses) b efore anaesthesia and, following induction with xylazine and ketamine, during maintenance of anaesthesia with desflurane, In six of the poni es (group A) anaesthesia was maintained for three hours with desfluran e at an end-tidal concentration of 7.4 per cent, In the other six poni es (group B), anaesthesia was maintained in the same way for one hour and then the effects of end-tidal desflurane concentrations of 7.4 per cent and 9.6 per cent with and without artificial ventilation were in vestigated, In group A ponies the arterial blood pressure and the syst emic vascular resistance index (SVRI) decreased significantly during t he first 45 minutes of anaesthesia but recovered with time, The cardia c index and heart rates were unchanged throughout the measurement peri od but arterial carbon dioxide tensions increased significantly, In gr oup B ponies, with either mode of ventilation, increasing desflurane c oncentration resulted in decreases in arterial blood pressure, cardiac index and mixed venous oxygen tension, although the changes were not always statistically significant, There were marked individual differe nces in the cardiovascular responses to the high desflurane concentrat ions, the minimum mean arterial blood pressure ranging from 35 to 62 m m Hg, and the cardiac index from 23 to 50 ml/kg/min, The study conclud es that during maintenance of anaesthesia with end tidal concentration s of desflurane of 7.4 per cent, cardiac index is well maintained and the initial fall in arterial blood pressures results from a fall in SV RI, However, increasing the concentration of desflurane causes a fall in blood pressure due to cardiac depression.