SELECTIVE MECHANICAL VENTILATION OF DEPENDENT LUNG REGIONS IN THE ANAESTHETIZED HORSE IN DORSAL RECUMBENCY

The effects of selective mechanical ventilation of dependent lung regions were studied in anaesthetized horses (mean weight 486 kg) in dorsal recumbency. Blood-gas measurements were performed with the horse in the lateral position during spontaneous breathing (before selective intubation) and in dorsal recumbency during spontaneous breathing, general mechanical ventilation, and spontaneous breathing +selective mechanical ventilation. Arterial oxygen tension (Pa O 2 ) was 32.3 kPa in the lateral position during spontaneous breathing with a high inspired oxygen fraction (Fl O 2 >92%). In dorsal recumbency Pa O 2 decreased to 10.9 kPa during spontaneous breathing and was not significantly affected by general mechanical ventilation (Pa O 2 12.6 kPa). The institution of selective mechanical ventilation with a selective positive end-expiratory pressure (PEEP) of 20 cm H 2 O caused a marked increase in Pa O 2 to an average of 35.3 kPa. It is concluded that selective intubation of dependent regions in the diaphragmatic lobes is a feasible procedure and that selective mechanical ventilation with PEEP markedly improves arterial oxygenation in the anaesthetized horse in dorsal recumbency.