From the Guidelines
Yes, a patient with a pulmonary embolism (PE) can have a good oxygen saturation (SpO2) reading. This is an important clinical point because normal oxygen levels do not rule out PE. In fact, studies suggest that approximately 30-40% of patients with confirmed PE maintain normal oxygen saturation levels (≥95%) at presentation 1.
Key Points to Consider
- The body has compensatory mechanisms, including increased respiratory rate and heart rate, that can maintain adequate oxygenation despite partial blockage of pulmonary blood flow.
- If the PE affects a small portion of the lung or if collateral circulation develops, gas exchange may remain relatively preserved.
- Clinicians should not rely solely on oxygen saturation to rule out PE but should instead consider the entire clinical picture, including risk factors (such as recent surgery, immobility, cancer, or hormonal therapy), symptoms (like sudden dyspnea, chest pain, or syncope), and other diagnostic tests such as D-dimer, CT pulmonary angiography, or ventilation-perfusion scanning when PE is suspected, even when SpO2 readings appear normal.
Management of Oxygen Therapy in PE
According to the BTS guideline for oxygen use in adults in healthcare and emergency settings, in pulmonary embolism, aim at an oxygen saturation of 94–98% (or 88–92% if the patient is at risk of hypercapnic respiratory failure) (grade D) 1.
Clinical Implications
It is crucial to consider the clinical context and not solely rely on SpO2 readings when evaluating a patient for PE. A normal SpO2 reading does not exclude the diagnosis of PE, and further diagnostic testing should be considered based on clinical suspicion.
From the Research
Oxygen Saturation in Pulmonary Embolism
- A patient with a pulmonary embolism (PE) can have a good oxygen saturation (SpO2) reading, as the relationship between PE and SpO2 is not straightforward 2.
- The clinical probability of PE can be assessed using a structured score or clinical gestalt, and in patients with a low probability of PE, an oxygen saturation level of >94% is one of the factors that identifies patients at very low risk of PE 2.
- However, it is essential to note that SpO2 readings can be normal or near-normal in some patients with PE, especially if they have a small clot or are not experiencing significant respiratory distress 3, 4.
- The diagnosis of PE is typically determined by chest imaging, and SpO2 readings should be considered in conjunction with other clinical factors, such as symptoms, medical history, and laboratory results 2, 5.
Factors Influencing Oxygen Saturation in PE
- The size and location of the clot can affect oxygen saturation, with larger clots or those located in more proximal pulmonary arteries potentially causing more significant hypoxemia 5, 4.
- The patient's underlying respiratory and cardiovascular function can also influence SpO2 readings, with patients having pre-existing conditions such as chronic obstructive pulmonary disease (COPD) or heart failure potentially experiencing more severe hypoxemia 3, 6.
- Treatment of PE, including anticoagulation and thrombolysis, can also impact oxygen saturation, with improvements in SpO2 readings potentially occurring as the clot is resolved 2, 5, 4, 6.