From the Guidelines
No, a pulmonary embolism (PE) does not always present with hypoxemia or low oxygen saturation. While hypoxemia is a common finding in PE, occurring in approximately 70-80% of patients, some individuals with PE may maintain normal oxygen levels, as noted in the study by 1. This is particularly true in smaller, peripheral emboli that affect a limited portion of the pulmonary vasculature. The degree of hypoxemia typically correlates with the size and location of the embolism, with larger, more central clots causing more significant oxygen desaturation.
Other classic symptoms of PE include:
- Dyspnea
- Pleuritic chest pain
- Tachycardia
- Tachypnea though the presentation can be highly variable. Some patients may even be asymptomatic. This variability in presentation makes PE diagnosis challenging and is why clinicians should maintain a high index of suspicion for PE in at-risk patients, even when oxygen saturation appears normal, as suggested by 1 and 1. The pathophysiology behind this involves ventilation-perfusion mismatch, where blood flow is blocked to certain lung areas while ventilation continues, but if the affected area is small enough, compensatory mechanisms can maintain adequate oxygenation.
According to the most recent guidelines, administration of supplemental oxygen is indicated in patients with PE and SaO2 <90%, as stated in 1. Further oxygenation techniques should also be considered, including high-flow oxygen and mechanical ventilation in cases of extreme instability. Patients with RV failure are frequently hypotensive or are highly susceptible to the development of severe hypotension during induction of anaesthesia, intubation, and positive-pressure ventilation. Consequently, intubation should be performed only if the patient is unable to tolerate or cope with non-invasive ventilation.
In terms of management, the use of supplemental oxygen and careful consideration of ventilation techniques is crucial in patients with PE, as emphasized by 1. The goal is to maintain adequate oxygenation while minimizing the risk of further hemodynamic compromise. By prioritizing the patient's oxygenation and hemodynamic status, clinicians can improve outcomes and reduce the risk of morbidity and mortality associated with PE.
From the Research
Presentation of Pulmonary Embolism (PE)
- A pulmonary embolism (PE) is characterized by occlusion of blood flow in a pulmonary artery, typically due to a thrombus that travels from a vein in a lower limb 2.
- The diagnosis of PE is determined by chest imaging, and the clinical probability of PE can be assessed using a structured score or clinical gestalt 2.
Oxygen Saturation in PE
- Oxygen saturation is one of the criteria used in the simplified Pulmonary Embolism Severity Index (sPESI) to identify patients eligible for outpatient treatment 3.
- However, a saturation of 90% or greater does not always exclude hypoxemic respiratory failure, and a target saturation of 91.5% may be more optimal for excluding respiratory failure 3.
- Adding oxygen saturation to the 2014 ESC risk stratification strategy can improve the discriminatory power for 30-day mortality and PE-related death 4.
Hypoxemia in PE
- Not all patients with PE present with hypoxemia, and some may have normal oxygen saturation levels 5.
- In patients with intermediate-risk PE, supplemental oxygen therapy may improve echocardiographic parameters, but its effect on mortality is uncertain 5.
- Thrombolytic therapy may be beneficial in reducing death and recurrence of PE, but it may also increase the risk of major and minor hemorrhagic events, including hemorrhagic stroke 6.
Key Findings
- PE does not always present with hypoxemia, and oxygen saturation levels can vary among patients 2, 4, 3, 5.
- Oxygen saturation is an important factor in risk stratification and management of PE, but it should be considered in conjunction with other clinical factors 2, 4, 3.
- Further research is needed to determine the optimal management of PE, including the use of supplemental oxygen therapy and thrombolytic therapy 5, 6.