A new equation to estimate temperature‐corrected PaCO₂ from P_ETCO₂ during exercise in normoxia and hypoxia

Abstract

End-tidal PCO2 (PET CO2 ) has been used to estimate arterial pressure CO2 (Pa CO2 ). However, the influence of blood temperature on the Pa CO2 has not been taken into account. Moreover, there is no equation validated to predict Pa CO2 during exercise in severe acute hypoxia. To develop a new equation to predict temperature-corrected Pa CO2 values during exercise in normoxia and severe acute hypoxia, 11 volunteers (21.2 ± 2.1 years) performed incremental exercise to exhaustion in normoxia (Nox, PI O2 : 143 mmHg) and hypoxia (Hyp, PI O2 : 73 mmHg), while arterial blood gases and temperature (ABT) were simultaneously measured together with end-tidal PCO2 (PET CO2 ). The Jones et al. equation tended to underestimate the temperature corrected (tc) Pa CO2 during exercise in hypoxia, with greater deviation the lower the Pa CO2 tc (r = 0.39, P < 0.05). The new equation has been developed using a random-effects regression analysis model, which allows predicting Pa CO2 tc both in normoxia and hypoxia: Pa CO2 tc = 8.607 + 0.716 × PET CO2 [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 Pa CO2 is needed to calculate the end-tidal-to-arterial PCO2 difference, which can be used as an index of pulmonary gas exchange efficiency.

Cerebral blood flow, frontal lobe oxygenation and intra-arterial blood pressure during sprint exercise in normoxia and severe acute hypoxia in humans

“…65 Therefore, it is reasonable assuming that the diameter of the MCA was not changed in Study I by the 6 mmHg decrease and increase in P ET CO 2 , during the sprint and recovery, respectively, assuming that P ET CO 2 is a good surrogate of PaCO 2 . 31…”

“…Part of the results on oxygen transport and pulmonary gas exchange obtained during the invasive experiments has been reported. 26,31,32 Since 7 ml (kg body mass) −1 of carbon monoxide (CO) was administered at exhaustion during the last incremental exercise test, a small amount of CO was present in blood at the start of the Wingate test. 26…”

Hypercapnia in diving: a review of CO2 retention in submersed exercise at depth

“…(1) P a CO 2tc = 8.607 + 0.716 x P ET CO 2 [33]. The relationship between P a CO 2 and P ET CO 2 under dive conditions was examined in a study by Mummery, et al, which found that in a dry hyperbaric chamber at 2.8 ATA, the end-tidal arterial PCO 2 difference was smaller at depth versus the surface under both resting and exercising conditions.…”

Total intravenous anesthesia produces outcomes superior to those with combined intravenous–inhalation anesthesia for laparoscopic gynecological surgery at high altitude

“…Some clinical investigations have demonstrated that P ET CO 2 can indirectly reflect P a CO 2 . 11,12 Under normal conditions, P ET CO 2 is lower than P a CO 2 by 3-6 mmHg. 13 At an altitude of 3000 m, the atmospheric pressure of our hospital is 532 mmHg and the P a CO 2 is 34 mmHg, resulting in a calculated P ET CO 2 of 28-31 mmHg.…”