Mean alveolar gases and alveolar-arterial gradients in pulmonary patients

Abstract

In view of uncertainties about the best way to estimate mean alveolar gases in patients with ventilation-perfusion inequalities, three different methods were evaluated on 54 patients. 1) O2 and CO2 were recorded by mass spectrometer on an O2 (x)-CO2 (y) diagram. The coordinates at the intersect of the expiratory record with the mixed expired R line (RE) ives the mean alveolar values (PAo2 and PAco2. 2)pa'co2 was calculated with the Bohr equation using a predicted anatomic dead space and PA'o2 was derived with the alveolar equation. 3) End-tidal (ET) P02 were averaged over 1 min at rest in steady state. Mean RET calculated from 3 was identical with RE. Mean values for PAco2, PA'CO2. and PETco2 differed by less that 1 Torr, but the variance was least with the end-tidal method. There was a highly significant correlation between delta aAPco2 using PETco2 and VD/VT, better than with either of the other methods. The end-tidal measurement appears to give the best approximation of mean alveolar gas in pulmonary patients.

Noninvasive Monitoring of Arterial Blood Gases

“…The C02 concentration in the sample is measured either by means of a mass spectrometer or by an infrared analyzer. 20 ' 21 In clinical practice, on the other hand, a major problem arises in identifying the alveolar gas sample in the expired gas in patients with abnormalities in the distribution of ventilation. For end-tidal sampling, the alveolar gas sample is taken beginning %of the time after the start of exhalation.…”

Measurement of expired carbon dioxide, oxygen and volume in conjunction with pretest probability estimation as a method to diagnose and exclude pulmonary venous thromboembolism

“…The major novelty of the present work, compared with previous studies is the addition of the exhaled pO 2 measurement to allow visual plot of the CO 2 -O 2 relationship on the alveolar CO 2 -O 2 curve. However, more contemporaneous work by Luft et al suggested that the optimal method to estimate alveolar gases was the end-tidal method, even in patients with chronic obstructive lung disease (Luft et al, 1979). Prior work has provided concept framework suggesting that end-tidal CO 2 decreases and end-tidal O 2 increases in rats subjected to experimental PE, and in humans diagnosed with pulmonary thromboembolism (Paoletti et al, 1986;Jones et al, 2003).…”

“…In particular, we sought to determine if the expired pCO 2 /pO 2 is more useful as a diagnostic tool when measured from either forced, deep exhalations, or from averaged end-tidal measurements obtained during quiescent breathing (Bock et al, 1929;Riley et al, 1946;Hatle & Rakseth, 1974;Luft et al, 1979;Kline et al, 2004). However, no prior study has reported the diagnostic utility of the expired pCO 2 /pO 2 in consecutive patients, and the most feasible, reproducible and accurate technique to collect expired pCO 2 and pO 2 for diagnostic study remains unknown.…”