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

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Abstract
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 (PaO2) was 32.3 kPa in the lateral position during spontaneous breathing with a high inspired oxygen fraction (FlO2 >92%). In dorsal recumbency PaO2 decreased to 10.9 kPa during spontaneous breathing and was not significantly affected by general mechanical ventilation (PaO2 12.6 kPa). The institution of selective mechanical ventilation with a selective positive end-expiratory pressure (PEEP) of 20 cm H2O caused a marked increase in PaO2 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.