Admixture of Atmospheric Air in the T‐piece Used as a Weaning System

Abstract

Ayre's T-piece may be used for intubated, non-anaesthetized patients requiring an oxygen supplement or humidified gas mixtures. The system has the disadvantage that atmospheric air (VAD) enters through the expiratory leg when the inspiratory flow and therapeutic gas flow (TGF) are not equal. This admixture can be reduced in the simple T-piece by the addition of either a compliant inspiratory reservoir, or a compliant inspiratory reservoir and an expiratory unidirectional valve. These three systems have been studied in a model investigation using different tidal volumes (VT), respiratory frequencies, and therapeutic gas flow. VAD was measured using a pneumotachograph and the inspiratory tidal volume was measured with a Wright Respiratory Monitor. The ratio VAD/VT was employed as an expression of the admixture of atmospheric air during inspiration. The introduction of a compliant inspiratory reservoir to the simple T-piece results under all conditions in a considerable reduction in VAD/VT. A further reduction was obtained by introducing an expiratory unidirectional valve into the system - however, with the result that the previously open system is turned into a closed system. When selecting a weaning system, the risk to the patient of the discontinuation of the gas flow should therefore be weighed against the advantages obtained by a reduction of the admixture.

Distribution of Expiratory Gas and Rebreathing in a T‐piece Modification Combined with a PEEP Valve

“…The absence of an inspiratory compliant reservoir (ICR), i.e., a respiration bag, means that the FGF must be equal to or greater than the inspiratory peak flow. I n a situation with a FGF of less than the inspiratory peak flow, the fresh gas (FG) supply can only equal the inspiration if the system is provided with an ICR (6).…”