Ventilatory effects of oxygen-enriched mixtures in the dog under althesin anaesthesia.

In six dogs anaesthetized with Althesin, minute ventilation, respiratory rate, tidal volume, PaO2 and PaCO2 were measured while breathing air (F/O2 = 0.21), and then after correction of hypoxaemia (F/O2 = 0.35), and again while breathing 100% oxygen (F/O2 = 1.00). The administration of 35% oxygen corrected the hypoxaemia (PaO2 = 8.98 +/- 0.76 kPa in air; PaO2 = 16.39 +/- 1.59 kPa with 35% oxygen), but produced a significant and sustained depression of ventilation. The administration of 100% oxygen induced a further significant and sustained decrease in ventilation. It is concluded that hypoxaemia is not necessary for the ventilatory depressant action of oxygen in the anaesthetized dog and that, under Althesin anaesthesia, peripheral arterial chemoreceptors are active up to high PaO2 values.