PaO2: temperature correction

As the temperature of blood decreases, the solubility of O₂ and CO₂ increases, which consequently lowers their partial pressures (decreases PaO₂ and PaCO₂). This especially becomes important during cold cardiopulmonary bypass.

PaCO₂ decreases by approximately 2 mm Hg and PaO₂ decreases by approximately 5 mm Hg per °C below 37°C. Therefore if an ABG at 37°C showed a PaCO₂ of 40 mmHg and a PaO₂ of 100 mm Hg, at 27°C it would be approximately a PaCO₂ of 20 mm Hg and a PaO₂ of 50 mm Hg.

There are many long and complicated formulas for making this correction, one of the easier ones is taken from J Appl Physiol 9: 201-204, 195: Calculations based on the known temperature factors for blood gases suggest that a 1°C fall in the temperature of blood sealed in an anaerobic environment will lower the CO₂ tension 4.4% and the O₂ tension 6%. This tension change is approximately exponential, and is computed from the formula Pb/Pm = 10f(b–m) to correct values from temperature of measurement (m) to that of the body (b). In the normal range, ‘f’ is 0.0247 for oxygen and 0.0185 for carbon dioxide.