A comparison of the T-piece, Venturi T-piece and T-bag for emergence with the laryngeal mask.

We have compared the performance of a standard T-piece, a Venturi T-piece and a T-bag (T-piece with a small reservoir bag) for emergence with the laryngeal mask airway in 20 awake volunteers. FiO2, ETCO2 and FiCO2 were measured at oxygen flow rates of 2, 4 and 6 l.min-1 during three different breathing patterns: normal tidal volume, respiratory rate 12 .min-1; normal tidal volume, respiratory rate 20 .min-1; high tidal volume, respiratory rate 12 .min-1. The T-piece and T-bag delivered a higher overall average FiO2 than the Venturi T-piece (P < 0.00001). Compared with normal breathing, FiO2 was reduced at the higher respiratory rate and tidal volume with the T-piece and T-bag but was not reduced with the Venturi T-piece. FiO2 increased with increasing flow rates for all devices except the Venturi T-piece during normal breathing. ETCO2 was higher during normal breathing (4.4 +/- 0.8%) compared with higher respiratory rate (3.7 +/- 0.9%) and tidal volume (3.4 +/- 0.7%) for all devices. There were no differences in overall ETCO2 between devices. The FiCO2 was never higher than 0.2% in any subject. We conclude that the T-piece and T-bag are more effective oxygen enrichment devices than the Venturi T-piece. The T-bag provides a useful visual signal about depth and frequency of respiration.