A Universal Valve for Anaesthetic Circuits.

Intermittent positive pressure respiration (IPPR) is best accomplished with a completely closed system during the inspiratory phase, so that all gas squeezed out of the reservoir bag will go to the patient's lungs. Under these conditions ventilation is volume-controlled. A low pressure in the system during the expiratory and resting phases will have least adverse effect on the patient; however, that pressure must be slightly higher than the collapsing pressure of the reservoir bag in order that the latter may remain adequately filled (Mushin and Mapleson, 1954). When a non-rebreathing valve with automatic exit closure mechanism (Fink, 1954; Ruben, 1955; Lewis, 1956; Frumin et al., 1959; Sykes, 1959) is used for intermittent positive pressure respiration, it is most desirable to have a pressure buffering mechanism in the system to obviate increasing pressure in the bag, thus eliminating the danger of obstruction or occlusion of the exhalation valve with resulting increased resistance to expiration and the risk of rupturing lung tissue.