Variation in the arterial to end-tidal PCO2 difference during one-lung thoracic anaesthesia.
We have measured the arterial to end-tidal PCO2 difference (PaCO2-PE'CO2) in 22 patients undergoing pulmonary resection in the lateral thoracotomy position during two-lung ventilation (TLV) and after transition to one-lung ventilation (OLV). With OLV for each patient, the practice of correcting the estimate by an initial measurement of (PaCO2-PE'CO2) was evaluated by subtracting the initial (PaCO2-PE'CO2) from subsequent values measured at 10-min intervals. Net (uncorrected) and corrected differences during OLV were analysed using ANOVA. (PaCO2-PE'CO2) values during TLV and OLV were similar: mean (SD) 1.3 (0.6) kPa and 1.2 (0.7) kPa, respectively (ns). Mean (PaCO2-PE'CO2) varied in the range 0.2-2.5 kPa, while maximum (PaCO2-PE'CO2) was 0.3-2.8 kPa. The mean (SD) of 133 pairs of measurements with OLV was 1.1 (0.7) kPa. Even after correction, mean (PaCO2-PE'CO2) varied in the range -0.7 to 0.8 kPa; individual extreme values were from -1.3 to 1.7 kPa. Variation between patients was found to be greater than variation within patients for both net and corrected differences (F ratio = 37.0 and 10.9, respectively), although calculating a corrected difference did reduce variation between patients from a mean square value of 2.44 to 0.61. The wide variation in (PaCO2-PE'CO2) suggests that the accuracy of estimation of PaCO2 by monitoring PE'CO2, although improved by the use of a corrected difference, remains questionable during OLV.
Ip Yam
P C
PC
University Department of Anaesthesia, Royal Liverpool University Hospital.
Innes
P A
PA
Jackson
M
M
Snowdon
S L
SL
Russell
G N
GN
D000328:Adult; D000368:Aged; D000768:Anesthesia, General / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood*; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008175:Lung Neoplasms / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial; D013990:Tidal Volume
D002245:Carbon Dioxide