What is the proper workup for a patient experiencing hypoxemia (low oxygen saturation)?

From the Guidelines

The proper workup for a patient who is desaturating oxygen should begin with immediate assessment of airway, breathing, and circulation while providing supplemental oxygen to maintain saturation above 90%, with a target saturation range of 94-98% for acutely ill patients not at risk of hypercapnic respiratory failure, as recommended by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The initial evaluation includes vital signs, physical examination focusing on respiratory and cardiovascular systems, and auscultation of lung fields.

• Laboratory tests should include arterial blood gas analysis to assess pH, PaO2, PaCO2, and bicarbonate levels, complete blood count to identify anemia or infection, and basic metabolic panel.
• Imaging studies are essential, starting with chest X-ray to identify pneumonia, pulmonary edema, pneumothorax, or pleural effusions, potentially followed by CT chest for more detailed evaluation.
• Electrocardiogram and cardiac enzymes should be obtained to rule out cardiac causes.
• Additional tests may include D-dimer if pulmonary embolism is suspected, echocardiogram to assess cardiac function, and pulmonary function tests for underlying respiratory disease.
• Continuous pulse oximetry monitoring is necessary throughout the workup, with adjustments to oxygen therapy as needed to maintain the target saturation range, and consideration of alternative oxygenation techniques such as high-flow oxygen or mechanical ventilation in cases of severe hypoxemia or respiratory failure, as recommended by the 2019 ESC guidelines for the diagnosis and management of acute pulmonary embolism 1. The comprehensive approach is critical because oxygen desaturation can result from various pathologies including ventilation-perfusion mismatch, diffusion limitations, hypoventilation, or right-to-left shunting, and prompt identification of the underlying cause is essential for appropriate treatment.
• For patients not at risk of hypercapnic respiratory failure who have saturation below 85%, treatment should be started with a reservoir mask at 15 L/min, as recommended by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.
• For most patients with known chronic obstructive pulmonary disease (COPD) or other known risk factors for hypercapnic respiratory failure, a target saturation range of 88-92% is suggested pending the availability of blood gas results, as recommended by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.

From the Research

Proper Workup for a Patient Desaturating Oxygen

• The first step in managing a patient who is desaturating oxygen is to assess the severity of hypoxemia and determine the underlying diagnosis 2.
• Oxygen therapy can be delivered by variable or fixed rate devices, and non-invasive ventilation may be considered if patients deteriorate 2.
• High-flow nasal cannula (HFNC) oxygen therapy is being increasingly used to prevent post-extubation hypoxemic respiratory failure and reintubation, and has been shown to be non-inferior to non-invasive ventilation (NIV) in preventing post-extubation treatment failure in COPD patients 3, 4.
• The American Association for Respiratory Care (AARC) recommends aiming for an oxygen saturation range of 94-98% for most hospitalized patients, and 88-92% for those with COPD 5.
• HFNC has been shown to be comparable to NIV in preventing reintubation after extubation in COPD patients, and may produce improved tolerance, comfort, and less complications such as airway care interventions 4.

Treatment Options

• HFNC oxygen therapy may be considered as an alternative to NIV for previously intubated COPD patients, especially those at high risk for extubating failure 3, 4.
• Non-rebreather face mask oxygen therapy may also be considered, especially in patients with mild carbon monoxide poisoning 6.
• Early critical care team involvement is a key part of the management pathway for patients with hypoxemia, and specialist treatments for severe hypoxemia can only be undertaken on an intensive care unit 2.

Monitoring and Escalation

• Patients with hypoxemia should be closely monitored, and oxygen therapy should be titrated to achieve the desired oxygen saturation range 5, 2.
• If patients deteriorate, they may require escalation to non-invasive ventilation or tracheal intubation and mechanical ventilation 2.
• A clear escalation plan should be in place, and each new scenario should be approached in a structured manner with an open diagnostic mind 2.