A nurse is caring for a 45-year-old patient with a history of deep vein thrombosis who presents with sudden dyspnea and chest pain, suspected of pulmonary embolism. Which assessment finding would be the MOST critical priority requiring immediate intervention?

Oxygen saturation of 78% indicates severe hypoxemia, a life-threatening emergency requiring immediate oxygen therapy and respiratory support. Other findings (leg swelling, chest pain, tachycardia) are important but less critical.

Clinical Priority in Suspected Pulmonary Embolism

The most critical assessment finding requiring immediate intervention is oxygen saturation of 78% on room air with severe dyspnea. In the context of a suspected pulmonary embolism (PE), this finding represents a state of severe hypoxemia, indicating that the patient’s gas exchange is critically compromised. The immediate physiological threat is end-organ damage, including irreversible brain injury, due to inadequate oxygen delivery to tissues.

The prioritization of this finding is rooted in the physiological progression of a high-risk PE. A large embolic burden obstructs pulmonary blood flow, creating a ventilation-perfusion (V/Q) mismatch. Blood continues to perfuse non-ventilated lung units, resulting in a shunt-like effect where deoxygenated blood returns to the systemic circulation. Simultaneously, the sudden increase in pulmonary vascular resistance causes acute right ventricular (RV) pressure overload. The RV dilates and fails, reducing left ventricular preload and systemic cardiac output ^[3]. This dual insult of V/Q mismatch and low cardiac output leads to profound oxygen desaturation. An SpO2 of 78% is a sentinel sign of this decompensation, falling on the steep portion of the oxyhemoglobin dissociation curve where small further drops in partial pressure of oxygen result in massive desaturation. Evidence-based summaries on perioperative hypoxemia management emphasize that severe hypoxemia is a direct threat to life and demands the most urgent intervention, which in this case is immediate high-flow oxygen or positive pressure ventilation to support oxygenation while definitive treatment is initiated ^[4].

While the other options are clinically significant findings associated with deep vein thrombosis and PE, they do not represent the same immediate threat to life. Unilateral leg swelling with a positive Homan’s sign (Option 2) is a classic but unreliable finding for the source of the thrombus and does not indicate the current severity of the cardiopulmonary crisis. Chest pain that worsens with deep inspiration (Option 3) is characteristic of pleural irritation from a pulmonary infarction and, while distressing, is not an immediate life threat. A heart rate of 110 bpm with mild anxiety (Option 4) reflects a compensatory sinus tachycardia and sympathetic response to pain, anxiety, and reduced cardiac output. This finding requires monitoring but is an expected compensatory mechanism, not the primary decompensation. The nurse’s immediate priority, guided by the airway, breathing, circulation (ABC) framework, is to correct the life-threatening hypoxemia that is rapidly depriving vital organs of oxygen .