What is the workup for hypoxia?

From the Guidelines

The workup for hypoxia should start with assessing the patient's oxygen saturation using pulse oximetry and obtaining a medical history to identify potential causes of hypoxia, such as pneumonia, pulmonary embolism, or exacerbation of chronic conditions like COPD or heart failure 1.

Initial Assessment

• Assess oxygen saturation using pulse oximetry and record the result
• Take a medical history to identify potential causes of hypoxia
• Perform a physical examination to look for signs of specific diagnoses, such as heart failure or pleural effusion
• Consider blood gas assessment in patients with unexplained confusion and agitation, as this may be a presenting feature of hypoxaemia and/or hypercapnia 1

Oxygen Therapy

• If the patient is hypoxaemic, provide oxygen therapy using nasal cannulae at 2-6 L/min or simple face mask at 5-10 L/min, unless the saturation is below 85% (use reservoir mask) or if the patient is at risk from hypercapnia 1
• The recommended initial target saturation range is 94-98%, unless the patient has COPD or other risk factors for hypercapnic respiratory failure, in which case aim for a saturation of 88-92% pending blood gas results 1

Monitoring and Adjustment

• Continuously monitor the patient's oxygen saturation and adjust the oxygen therapy as needed to maintain the target saturation range
• Recheck blood gases after 30-60 minutes to adjust the oxygen therapy and ensure that the patient is not at risk of hypercapnia 1

Special Considerations

• In patients with myocardial infarction or acute coronary syndromes, oxygen therapy may not be necessary and may even be harmful if the patient is not hypoxaemic 1
• In patients with stroke, oxygen therapy may be harmful if the patient is not hypoxaemic, and should be used with caution 1
• In patients with poisoning or drug overdoses, oxygen therapy should be used with caution and the patient should be monitored closely for signs of hypercapnia or other complications 1

From the Research

Workup for Hypoxia

The workup for hypoxia involves several steps to establish the presence of hypoxemia, identify the underlying cause, and guide management. The following are the key components of the workup:

• Establish the presence of hypoxemia with measurements of arterial blood gases 2
• Search for signs of tissue hypoxia 2
• Assign a physiologic cause for hypoxemia, which can include:
  • Alveolar hypoventilation
  • Ventilation/perfusion mismatches
  • Diffusion disorders
  • True shunts
  • Decrease in the partial pressure of inspired oxygen 3, 4
• Begin oxygen therapy by a method appropriate to the underlying pathophysiologic mechanism 2
• Repeat arterial blood gas measurements to assure adequate reversal of hypoxemia 2
• Treat any underlying disease(s) 2

Pathophysiological Mechanisms

Five pathophysiological mechanisms should be assessed in the presence of hypoxemia:

• Alveolar hypoventilation
• Ventilation/perfusion mismatches
• Diffusion disorders
• True shunts
• Decrease in the partial pressure of inspired oxygen 3 These mechanisms can lead to tissue hypoxia, which requires a prompt diagnostic approach to guide management.

Diagnostic Approach

A diagnostic approach for evaluating hypoxemia should include:

• Assessing the main etiologies of hypoxemia based on respiratory pathophysiology 3
• Evaluating the patient's oxygen delivery (DO2) and oxygen content (CaO2) 5
• Considering the patient's ability to compensate for hypoxemia, including changes in 2-3-DGP erythrocytic activity, reduction in oxygen uptake by non-vital organ systems, and expression of hypoxia-resistant iso-enzymes 5