The circle system without absorber. Use with controlled ventilation.

An investigation is described into the performance of two types of circle system used without a carbon dioxide absorber in both the laboratory and in the operating theatre with controlled ventilation. The newer system was found to be more efficient than the old but in both types of system the tidal volume was found to be very important, a large tidal volume resulted in increased efficiency. The possibility of predicting arterial blood carbon dioxide using this system is briefly discussed, and rules are suggested for the use of the system.