What would an arterial blood gas (ABG) analysis reveal in a patient with a pulmonary embolism (PE)?

From the Guidelines

If you had a pulmonary embolism, your arterial blood gas (ABG) results would likely show hypoxemia, which is a low level of oxygen in the blood, characterized by reduced PaO2 and normal or low PaCO2 1. Specifically, you may see a low partial pressure of oxygen (PaO2) and a low oxygen saturation (SaO2). The ABG results might look like this:

• pH: slightly alkalotic (around 7.45-7.50) due to hyperventilation 1
• PaO2: low (around 60-80 mmHg) indicating hypoxemia
• PaCO2: low (around 25-30 mmHg) due to hyperventilation
• SaO2: low (around 85-90%) indicating hypoxemia
• Base excess: may be slightly elevated due to respiratory alkalosis It's essential to note that ABG results can vary depending on the severity of the pulmonary embolism and the individual's underlying health status, with the degree of hypoxia roughly correlating with the extent of the embolism 1. In terms of management, oxygen therapy would be initiated to improve oxygenation, and anticoagulation therapy with medications would be started to prevent further clot formation.

From the Research

Arterial Blood Gas Analysis in Pulmonary Embolism

• An arterial blood gas (ABG) analysis in a patient with a pulmonary embolism (PE) may reveal hypoxemia, which is a common finding in PE patients 2, 3, 4, 5, 6.
• The degree of hypoxemia can vary, with some studies showing a range of pO2 values from 32 to 97 mm Hg (average 60.5 +/- 13 mm Hg) 2.
• Hypocapnia and alkalosis may also be present, particularly in patients with severe embolism 2, 3.
• However, hypoxemia and hypocapnia are not specific findings in PE, as they can also be present in other conditions, such as cardiovascular disease or pulmonary disease 2, 3, 6.

Correlation with Severity of Embolism

• A significant correlation was found between the severity of hypoxemia and the degree of cyanosis and ECG changes 2.
• A pO2 of under 50 mm Hg was always associated with a severe embolism with amputation of over 40% of the pulmonary vascular bed 2.
• The severity of hypoxemia was also correlated with the extent of vascular obstruction, with more severe obstruction resulting in more severe hypoxemia 5.

Diagnostic Value of ABG Analysis

• ABG analysis is of limited value in the diagnostic work-up of PE if not interpreted in conjunction with clinical and other laboratory tests 6.
• A normal P(A-a)O2 gradient and a normal PaCO2 obtained in a patient during room air breathing can be used as evidence against the presence of pulmonary emboli 4.
• However, normal values of paO2 and paCO2 do not rule out the presence of pulmonary embolism 3, 6.