A comparison of indirect methods for continuous estimation of arterial PCO2 in men

Abstract

Four different measures (PETCO2, PACO2, PADCO2, and PJCO2) for indirectly estimating arterial PCO2 (PaCO2) from respired gas at the mouth have been investigated. PETCO2 was the end-tidal PCO2. PACO2 was calculated using a reconstruction of the alveolar oscillation of PCO2 obtained from the end-tidal "plateau" in PCO2. PADCO2 was calculated as for PACO2 except that the effects of dead space were incorporated. PJCO2 was calculated from an empirical relationship involving PETCO2 and tidal volume. Six subjects were studied at rest and during cycle ergometry at 50 and 100 W while breathing a variety of gas mixtures. Arterial samples were drawn for determination of true PaCO2. The differences for each method between estimated and true PaCO2 at rest and at 50 and 100 W were as follows: PETCO2, -1.35 +/- 2.64, 1.67 +/- 2.31, and 2.67 +/- 2.02 (SD) Torr; PaCO2, -2.15 +/- 2.73, -0.80 +/- 2.18, and -0.35 +/- 2.31 (SD) Torr; PADCO2, -1.55 +/- 2.54, 0.25 +/- 2.16, and 0.63 +/- 2.26 (SD) Torr; and PJCO2, -1.41 +/- 2.30, 0.12 +/- 1.79, and 0.08 +/- 1.96 (SD) Torr. It is concluded that, at rest, all methods significantly underestimate true PaCO2 and during exercise PETCO2 significantly overestimates PaCO2, but no bias was detected for any of the other methods.

Overnight Changes in the Cerebral Vascular Response to Isocapnic Hypoxia and Hypercapnia in Healthy Humans

“…Small systematic differences may exist between arterial and end-tidal measurements that are dependent on factors such as body position. However, the magnitudes of such differences are maintained during hypercapnic stimulation, 28,29 and the used of P ET CO 2 in the present study would not be a significant confound.…”

Corrected End-Tidal PCO2 Accurately Estimates PaCO2 at Rest and During Exercise in Morbidly Obese Adults

“…Studies have shown that P jco 2 appears to be a good predictor of Pa co 2 during exercise in young adults. 3,4,8,9 In contrast to younger individuals, the use of the Jones equation in older subjects signifi cantly underestimated Pa co 2 at maximal exercise, whereas P etco 2 was a better estimator of Pa co 2 . 8 Aging is associated with changes in respiratory function, such as increased dead space (V d ) and ventilation-perfusion mismatch, which may alter the relationship between P etco 2 and Pa co 2 .…”

“…[1][2][3][4] Extreme obesity is associated with changes in respiratory mechanics and gas exchange properties that may disturb the relationship between Pa co 2 and P etco 2 . However, based on our fi ndings in morbidly obese subjects, the P( et 2 a) co 2 differences at rest and during exercise were small and well within the previously published ranges, [1][2][3][4] confi rming that although obesity places a substantial load on the respiratory system, which could affect gas exchange kinetics, it does not affect CO 2 clearance. 20 peak exercise) ( Fig 3 ), suggesting inadequate compensatory exercise hyperventilation.…”

“…To avoid the invasive procedure of placing arterial catheters for sampling arterial blood, partial pressure of end-tidal CO 2 (P etco 2 ) has been used as a noninvasive method to estimate Pa co 2 in young, healthy adults at rest and during exercise. [1][2][3][4] These studies have concluded that, although P etco 2 may slightly underestimate Pa co 2 at rest, P etco 2 is a good index of Pa co 2 during resting conditions. During exercise, the instantaneous P aco 2 fl uctuates cyclically with breathing, 5 and the P etco 2 is higher than the average P aco 2 over the complete breathing cycle.…”

Ventilatory chemoreflexes at rest following a brief period of heavy exercise in man.

“…Ventilatory volumes and flows were recorded using a turbine device (Howson, Khamnei, O'Connor & Robbins, 1986) (Weil & Zwillich, 1976), which may in turn lead to a reduced hypoxic sensitivity (Bascom, Clement, Cunningham, Painter & Robbins, 1990). Exposure to hyperoxia is known to speed recovery from HVD (Easton, Slykerman & Anthonisen, 1988 (Clement, Pandit, Bascom, Dorrington, O'Connor & Robbins, 1995 (Robbins, Conway, Cunningham, Khamnei & Paterson, 1990). The calculations used to derive pHa from these measured values have been described previously (Clement et al 1995); the magnitude of these calculated corrections to the measured arterialized venous Pco2 was generally small.…”