A patient under general anesthesia with hypothetical core body temperature 35°C has a PaO2 of 77 mm Hg. The corrected PaO2 would be closest to which value?

A patient under general anesthesia with hypothetical core body temperature 35°C has a PaO2 of 77 mm Hg. The corrected PaO2 would be closest to which value?

• A. 68 mm Hg
• B. 72 mm Hg
• C. 77 mm Hg
• D. 86 mm Hg

Answer: (A)

The key idea is that PaO2 reflects the amount of oxygen dissolved in plasma, which is influenced by temperature. Oxygen is more soluble in blood at lower temperatures, so a given PaO2 measured at a cooler core temperature (35°C) will be higher than what you’d get at normal body temperature (37°C). When you correct that value back to 37°C, the dissolved portion drops. In this scenario, a 2°C decrease in temperature from 37°C to 35°C would lower the PaO2 when adjusted to 37°C, bringing it from 77 mm Hg down toward the mid-to-high 60s. The closest value is about 68 mm Hg. So the corrected PaO2 is lower than the measured 77, reflecting the reduced solubility of oxygen at normothermia.

The key idea is that PaO2 reflects the amount of oxygen dissolved in plasma, which is influenced by temperature. Oxygen is more soluble in blood at lower temperatures, so a given PaO2 measured at a cooler core temperature (35°C) will be higher than what you’d get at normal body temperature (37°C). When you correct that value back to 37°C, the dissolved portion drops. In this scenario, a 2°C decrease in temperature from 37°C to 35°C would lower the PaO2 when adjusted to 37°C, bringing it from 77 mm Hg down toward the mid-to-high 60s. The closest value is about 68 mm Hg.

So the corrected PaO2 is lower than the measured 77, reflecting the reduced solubility of oxygen at normothermia.