• SOM 4th Yr Curriculum

• CLERKSHIP INFORMATION
• Introduction / Goals and Objectives
• Rotations
  • HMC
  • UWMC
  • VAMC
• Seminars
• Faculty Only
• PULMONARY EDUCATION
• Pulmonary Med Library
• Arterial Blood Gases
• Cardiopulmonary Exercise Testing
• Mechanical Ventilation
• Pulmonary Function Testing
• Pleural Effusion
• Radiology

Arterial Blood Gas

Case 2 Answers

A 60 year-old man with amyotrophic lateral sclerosis is brought into clinic by his family who are concerned that he is more somnolent than normal. On further history, they report that he has been having problems with morning headaches and does not feel very refreshed when he wakes up. An arterial blood gas is performed and reveals: pH 7.37, PCO₂ 57, PO₂ 70, HCO₃- 32

Acid-base status:

• The patient has a low pH (acidemia)
• The PCO₂ is high (respiratory acidosis) and the bicarbonate is high (metabolic alkalosis). The low pH in combination with the high PCO₂ tells us that the respiratory acidosis is the primary process.
• The metabolic alkalosis is the compensatory process.
• Summary: A chronic respiratory acidosis with a compensatory metabolic alkalosis.

Alveolar-arterial oxygen difference:

The alveolar-arterial oxygen difference is 9 mmHg, a normal value, which tells us that the hypoxemia is entirely due to hypoventilation.

Explanation for the clinical picture:

The patient has a respiratory acidosis with a compensatory metabolic alkalosis. The respiratory acidosis tells us that the patient is hypoventilating while the compensatory metabolic alkalosis tells us that this is a chronic process. The patient is likely hypoventilating due to progression of his amyotrophic lateral sclerosis, a neurodegenerative disorder associated with progressive muscle weakness that eventually involves the muscles of respiration.

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