Disturbances of cardiopulmonary function in anaesthetised horses

Oxygenation of pulmonary vein blood in conscious and anaesthetised ponies

Catheters were implanted through the left atrium into large veins drawing blood from regions of the diaphragmatic lobes in five ponies. Measurement of oxygen and carbon dioxide tensions in blood samples drawn through these catheters showed that in laterally recumbent conscious and anaesthetised animals the function of the lowermost lung is progressively impaired while in the supine position the function of both lungs is adversely affected.

Radiographic evidence of impaired pulmonary function in laterally recumbent anaesthetised horses

Studies in conscious and anaesthetised ponies demonstrated that starvation, anaesthesia and changes in body position influence the radiographic appearance of the lungs in the lateral and dorsoventral views. Radiographic appearances could not be closely correlated with blood gas values, but they suggested that the volume of the lowermost lung of the laterally recumbent animal is greatly reduced.

Recovery from anaesthesia in ponies: a comparative study of the effects of isoflurane, enflurane, methoxyflurane and halothane

The duration and quality of recovery after separate 2 hour anaesthetic periods with equipotent alveolar concentrations of isoflurane, enflurane, halothane and methoxyflurane were evaluated in experimental ponies. Recovery was shortest after isoflurane anaesthesia, followed by enflurane, halothane and finally methoxyflurane, although standing was achieved more rapidly after enflurane than after isoflurane. This sequence of recovery times was compatible with the respective solubilities of the 4 agents. The smoothest recovery was obtained after isoflurane anaesthesia, followed by methoxyflurane, halothane and then enflurane. The isoflurane recovery was characterized by very quiet and prolonged sternal recumbency with excellent coordination upon standing. The chief difficulties with halothane recovery were shivering and delayed coordination upon standing. Enflurane anaesthesia was followed by a very brief period of sternal recumbency but there was considerable shivering and incoordination upon standing. This may have been due to central nervous stimulation during anaesthesia producing a residual excitatory effect. On the basis of this investigation, isoflurane was considered to be the most satisfactory volatile anaesthetic for the horse.

Ventilation and cardiovascular studies during mechanical control of ventilation in horses

Eleven out of 12 horses were underventilating while breathing spontaneously during halothane anaesthesia with high arterial carbon dioxide tensions. In addition, large alveolar to arterial oxygen tension gradients were found to be present. Mechanically, controlled ventilation with an intermittent positive pressure of 20-30 cm H2O reduced arterial carbon dioxide levels to normal. The alveolar to arterial oxygen gradients did not increase and in some cases decreased. These (A - a) Po2 gradients were due mainly to true shunt of the order of 30 per cent and not to ventilation perfusion inequality.