CO2 rebreathing of T-piece system in patients during recovery phase from acute respiratory failure.

Eight respiratory parameters which might affect the amount of carbon dioxide rebreathing were assessed in seven patients who were breathing spontaneously from large-bore T tube system during the recovery phase from acute respiratory failure. With multivariate regression analysis, the absolute amount of rebreathed CO2 at the connector of endotracheal tube (VINSPCO2) were approximately estimated by using relatively small number of parameters, including minute volume (VEXP), fresh gas inflow to T piece system (VFGI) and preferably by additional parameters concerning CO2 output of the patients.CO2 rebreathing ratio, VINSPCO2 divided by gross outward flux of CO2 at the connector (VEXPCO2), was predicted with simple regression equation by using (VEXP/VFGI) as follows,(VINSPCO2)/(VEXPCO2) = 0.405 + 0.33 x ln (VEXP/VFGI)The maximum (VEXP/VFGI) ratio to prevent rebreathing of CO2 at the connector was 0.30, whereas the ratio to prevent CO2 accumulation due to rebreathing was 0.45.