A 77 year old presents with symptoms and signs that suggest pneumonia after recent return from Bali
Mixed respiratory alkalosis and (normal anion gap) metabolic acidosis and elevated A-a gradient.
Significant respiratory alkalosis (pCO2 = 24). Expect a pH higher than 7.5.
Expected HCO3 for acute compensated respiratory alkalosis would be 21, actual HCO3 is 18.6 which suggests an additional metabolic acidosis. The low CO2 suggests this an acute respiratory disorder, with a chronic respiratory alkalosis you would expect a CO2 closer to normal with a near normal pH. It is unlikely a patient would have a very rapid respiratory rate for a prolonged period.
A-a gradient = 40, expected in this age group = 24 (age/4 + 4), is elevated suggesting VQ mismatch which is also suggestive of consolidation in lung (?pneumonia).