The effect of artificial ventilation on functional residual capacity and arterial oxygenation. II. Comparison of spontaneous respiration and artificial ventilation at similar arterial carbon dioxide tensions, tidal volumes and inspiratory gas flow rates.

We have compared cardiac output, gas exchange and pulmonary mechanics during spontaneous breathing and artificial ventilaton under conditions which kept PaCO2 within the normal range and maintained constant tidal volume and inspired gas flow rate. In dogs anaesthetized with pentobarbitone and ventilated with air, artificial ventilation increased VD/VT but did not reduce Q angstrom, FRC, or CL. PaO2 increased and A-aDO2 decreased during aritificial ventilation, perhaps because of a small increase in Q angstrom and a small decrease in oxygen consumption. It appears that many of the reported deleterious effects of artificial ventilation may be due to the use of other anaesthetic agents and patterns of ventilation, and to changes in PaCO2.