A new equation to estimate temperature‐corrected P a CO 2 from P ET CO 2 during exercise in normoxia and hypoxia

• Published in: Scandinavian journal of medicine & science in sports Vol. 26; no. 9; pp. 1045 - 1051
• Main Authors: González Henríquez, J. J., Losa‐Reyna, J., Torres‐Peralta, R., Rådegran, G., Koskolou, M., Calbet, J. A. L.
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• ISSN: 0905-7188; 1600-0838
• DOI: 10.1111/sms.12545

End‐tidal PCO 2 ( P ET CO 2 ) has been used to estimate arterial pressure CO 2 ( P a CO 2 ). However, the influence of blood temperature on the P a CO 2 has not been taken into account. Moreover, there is no equation validated to predict P a CO 2 during exercise in severe acute hypoxia. To develop a new equation to predict temperature‐corrected P a CO 2 values during exercise in normoxia and severe acute hypoxia, 11 volunteers (21.2 ± 2.1 years) performed incremental exercise to exhaustion in normoxia ( N ox, P I O 2 : 143 mmHg) and hypoxia ( H yp, P I O 2 : 73 mmHg), while arterial blood gases and temperature ( ABT ) were simultaneously measured together with end‐tidal PCO 2 ( P ET CO 2 ). The J ones et al. equation tended to underestimate the temperature corrected (tc) P a CO 2 during exercise in hypoxia, with greater deviation the lower the P a CO 2 tc ( r  = 0.39, P  < 0.05). The new equation has been developed using a random‐effects regression analysis model, which allows predicting P a CO 2 tc both in normoxia and hypoxia: P a CO 2 tc  = 8.607 + 0.716 ×  P ET CO 2 [ R 2  = 0.91; intercept SE  = 1.022 ( P  < 0.001) and slope SE  = 0.027 ( P  < 0.001)]. This equation may prove useful in noninvasive studies of brain hemodynamics, where an accurate estimation of P a CO 2 is needed to calculate the end‐tidal‐to‐arterial PCO 2 difference, which can be used as an index of pulmonary gas exchange efficiency.