Estimation of respiratory functions by analysis of expired gas and blood gas during artificial ventilation and general anesthesia

: One-hundred and seven patients undergoing elective surgery were studied to analyze the correlations between preoperative spirometric values and respiratory parameters during general anesthesia. They were grouped according to 3 criterions; preoperative %VC of less than 80%, FEV1.0% of less than 70%, V50/V25 exceeding 4.0. Following the induction of general anesthesia and of mechanical ventilation, expiratory flow (VE), FECO2, PaCO2 and PaO2 were measured to calculate respiratory parameters including VCO2-SR, VD/VT-Bohr, VD/VT-physiological (phys), a-ETDCO2, Volume Pressure Index (VPI) and A-aDO2. Six respiratory parameters were compared between the groups, and correlations between preoperative spirometric values were studied. Those with lower %VC had higher values in VCO2-SR and in VPI, and those with lower FEV1.0% had higher values in VCO2-SR, in VD/VT-phys and in a-ETDCO2. Significant correlations were also observed between these parameters. Preoperative V50/V25 and A-aDO2 during general anesthesia did not correlate with any of the parameters studied. We conclude that VCO2-SR, VD/VT-phys, a-ETDCO2 and VPI during general anesthesia are useful to detect the patients with restrictive and/or obstructive lung dysfunction, although they are not sensitive enough to detect those with small airway disease.