Correct!
2. Right to left shunting

Although not 100% diagnostic, inhalation of 100% oxygen raises the PaO2 minimally in right to left shunting because the venous blood shunted to the arterial circulation is not or only modestly oxygenated.

Shunt fraction is calculated by the following formula:

            Qs/Qt=(CcO2-CaO2)/(CcO2-CvO2)

Where

• Qs=blood flow through the shunt
• Qt=total cardiac output
• CcO2=pulmonary end-capillary O2 content. Generally held to be the same as the alveolar O2 content
• CaO2=arterial oxygen content
• CvO2=mixed venous O2 content
• v=venous

Normally there is 4-10% shunt due to Thebesian and bronchial veins which drain deoxygenated blood into the arterial circulation.

Which of the following would be the next most appropriate step in the patient's evaluation? (Click on the correct answer to proceed to the fourth of six panels)

1. Chest CT scan
2. Complete pulmonary function testing
3. Echocardiogram
4. Pulmonary angiogram
5. Ventilation-perfusion lung scan

Home/Critical Care