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 should include vital signs, physical examination focusing on respiratory and cardiovascular systems, and pulse oximetry monitoring.

• Laboratory tests should include:
  • Arterial blood gas analysis to assess pH, PaO2, PaCO2, and bicarbonate levels
  • Complete blood count to identify anemia or infection
  • Basic metabolic panel
• Imaging studies should start with a chest X-ray to identify pneumonia, pulmonary edema, pneumothorax, or pleural effusions, potentially followed by CT chest if more detail is needed.
• Additional tests may include:
  • Electrocardiogram to assess for cardiac causes
  • Echocardiogram if heart failure is suspected
  • D-dimer with possible CT pulmonary angiogram if pulmonary embolism is a concern
• Bronchoscopy may be considered for airway obstruction or to obtain samples. Throughout the workup, it's essential to treat the underlying cause while providing appropriate respiratory support, which may range from supplemental oxygen to non-invasive ventilation or intubation with mechanical ventilation depending on severity, as suggested by the 2019 ESC guidelines for the diagnosis and management of acute pulmonary embolism 1. 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. The choice of oxygen therapy device and flow rate should be adjusted to achieve the target saturation range, with consideration of the patient's underlying condition and risk factors for hypercapnic respiratory failure, as outlined in the BTS guideline 1.

From the Research

Proper Workup for a Patient Desaturating Oxygen

• The proper workup for a patient desaturating oxygen involves assessing the patient's respiratory status and determining the underlying cause of desaturation 2, 3, 4.
• High-flow nasal cannula (HFNC) oxygen therapy has been shown to be effective in preventing post-extubation hypoxemic respiratory failure and reintubation in patients with chronic obstructive pulmonary disease (COPD) 2, 3.
• HFNC has also been compared to non-invasive ventilation (NIV) in patients at high risk for extubation failure, with studies suggesting that HFNC is comparable to NIV in preventing reintubation and may have improved tolerance and comfort 2, 3.
• In patients with mild carbon monoxide poisoning, HFNC has been shown to rapidly reduce blood carboxyhemoglobin levels and may be a potential oxygen therapy method for clinical treatment 5.
• The use of HFNC has also been compared to standard oxygen face masks in post-extubation intensive care unit patients, with studies suggesting that HFNC may be more effective than standard oxygen supply devices for oxygenation in the post-extubation period 4.

Key Considerations

• When assessing a patient desaturating oxygen, it is essential to consider the patient's underlying medical condition, respiratory status, and oxygen therapy requirements 2, 3, 4.
• The choice of oxygen therapy device, such as HFNC or NIV, should be individualized based on patient characteristics and clinical needs 2, 3.
• Pulse oximetry-based surveillance monitoring can be used effectively for patients on supplemental oxygen and for those on room air to detect deterioration and prevent adverse events 6.

Respiratory Rate and Desaturation

• Studies have shown that respiratory rate does not differ significantly between patients receiving supplemental oxygen and those breathing room air, either overall or during desaturation events 6.
• The speed of desaturation, magnitude, and duration of desaturation events have also been found to be similar between patients receiving supplemental oxygen and those breathing room air 6.