• 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 7 Answers

A 57 year-old woman presents with 2 days of fevers, dyspnea and a cough productive of rust-colored sputum. Her room air oxygen saturation in the emergency room is found to be 85% and the intern decides to obtain a room air arterial blood gas while they are waiting for the chest x-ray to be done. The blood gas reveals: pH 7.54, PCO₂ 25, PO₂ 65, HCO₃- 22, Base excess -1

Acid-base status:

• The patient has a high pH (alkalemia)
• The PCO₂ is low (respiratory alkalosis). The high pH in conjunction with the low PCO₂ tells us that the respiratory alkalosis is the primary process.
• Although the bicarbonate is on the low side, the base excess of -1 tells us that the patient does not have a metabolic acidosis. The patient, therefore, has not mounted a compensatory response yet.
• Summary: Acute, uncompensated respiratory alkalosis   

Alveolar-arterial oxygen difference:

The alveolar-arterial oxygen difference is 54 mmHg. This value is elevated and tells us that the patient’s hypoxemia is due to either shunt or areas of low V/Q.

Explanation for the clinical picture:

The patient has a history suggestive of pneumonia. The pneumonia has led to areas of shunt and/or low V/Q that have led to her arterial hypoxemia. The arterial hypoxemia will, in turn, lead to the hypoxic ventilatory response that is responsible for her hyperventilation and respiratory alkalosis. Because the hypoxemia may have only been present for a short time, there has not been adequate time for metabolic compensation to occur.

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