adjust DLCO to altitude

Pao2 affects the measurement of Dlco because oxygen competes with CO for hemoglobin binding sites. At altitude the Pao2 is lower and thus more CO can be taken up by hemoglobin. Dlco thus rises with altitude by approximately 0.53% for each 100 m of altitude. An equation to adjust the Dlco at altitude to its equivalent value at a standard pressure of 760 mm Hg is: Dlco[PBadjusted] ≈ Dlco[measured] × (0.505 + 0.00065 PB).

In the patient in this scenario, the measured Dlco of 18.1 is only a 10% reduction from 20.1. However, in Aspen, at a PB of 570 mm, a measured Dlco of 18.1 is equivalent to 18.1 × (0.505 + 0.00065 × 570), or 15.84, at a standard pressure of 760 mm Hg, approximating Los Angeles at sea level. This represents a real 21% reduction in Dlco and chemotherapy should be held according to protocol and evaluated further (choice B correct; choice A is incorrect).