Carbon dioxide and oxygen partial pressure in expiratory water condensate are equivalent to mixed expired carbon dioxide and oxygen.

This study was to determine whether the PCONCO2 and PCONO2 which collect in the expiratory trap of a ventilator circuit are equivalent to PECO2 and PEO2. Fifty studies were performed in 34 mechanically ventilated male patients. Five milliliters of condensate fluid were collected and PECO2 and PEO2 were measured. Exhaled gases were collected simultaneously with condensate fluid for 5 min in a meteorologic balloon and FECO2 and FEO2 were measured; PECO2 and PEO2 were then calculated. The mean PECO2 was not significantly different from PCONCO2 nor was the PCONO2 significantly different from the condensate PCONO2. There was a high correlation between mixed expired PECO2 and PCONCO2 as well as PEO2 and PCONO2. These data indicate expiratory PCONCO2 and PCONO2 provide a valid reflection of PECO2 and PEO2. The PCONCO2 and PCONO2 measured in a clinical blood gas analyzer are accurate and may be used in calculation of VD/VT and in metabolic assessments.