The Lack anaesthetic system. An assessment during spontaneous ventilation.

The Lack anaesthetic system is a coaxial modification of the Magill circuit. The resistance of the system was found to be unacceptably high. When air was administered through the system to spontaneously breathing trained volunteers, marked evidence of rebreathing was present when fresh gas flow equalled minute volume. It is suggested that a fresh gas glow equal to one and a half-times minute volume would be required to prevent rebreathing of alveolar gas.