Repeated USMLE Questions Step 1- 160

A 74-year-old man with a long history of emphysema presents to the office for a routine examination. He is complaining of fatigue and shortness of breath for 2 weeks. Physical examination is remarkable for scattered wheezes on both lung bases. Arterial blood gas is ordered for the patient.

Which one of these results reflects the shift of oxygen dissociation curve to the right?

A- pH 7.00, bicarbonate 15, Pco2 60 and Po2 90

B- pH 7.05, bicarbonate 15, Pco2 30 and Po2 90

C- pH 7.47, bicarbonate 15, Pco2 30 and Po2 90

D- pH 7.50, bicarbonate 24, Pco2 40 and Po2 90

E- pH 7.60, bicarbonate 24, Pco2 60 and Po2 90

Answer






This patient has a long history of emphysema and respiratory distress. He exhibits respiratory acidosis due to defective gas exchange and shortness of breath. This condition is associated with shifting oxygen dissociation curve to the right. Shift to the right is caused by low pH, high Pco2 and low Po2.

The correct answer is A