Understanding the pulmonary shunt fraction (Qs/Qt) is crucial for assessing oxygenation defects in respiratory distress. Our free online tool helps clinicians and students quickly calculate the shunt fraction based on key hemodynamic and blood gas parameters, providing insight into lung efficiency and potential causes of hypoxemia.
Formula:
The pulmonary shunt fraction (Qs/Qt) is determined using the following formula, based on oxygen content in arterial, mixed venous, and capillary blood:
Qs/Qt = (CcO2 - CaO2) / (CcO2 - CvO2)
Where:
- Qs/Qt = Pulmonary Shunt Fraction (%)
- CcO2 = Capillary Oxygen Content (mL/dL)
- CaO2 = Arterial Oxygen Content (mL/dL)
- CvO2 = Mixed Venous Oxygen Content (mL/dL)
Each oxygen content value is further calculated:
- PAO2 (Alveolar Oxygen Partial Pressure) = (FiO2 × (Pb - PH2O)) - (PaCO2 / 0.8)
- CcO2 = (Hb × 1.34 × 1.0) + (PAO2 × 0.003)
- CaO2 = (Hb × 1.34 × (SaO2 / 100)) + (PaO2 × 0.003)
- CvO2 = (Hb × 1.34 × (SvO2 / 100)) + (PvO2 × 0.003)
Where:
- FiO2 = Fraction of Inspired Oxygen (decimal)
- Pb = Barometric Pressure (mmHg)
- PH2O = Water Vapor Pressure (47 mmHg at 37°C)
- PaCO2 = Arterial Partial Pressure of Carbon Dioxide (mmHg)
- Hb = Hemoglobin Concentration (g/dL)
- SaO2 = Arterial Oxygen Saturation (%)
- PaO2 = Arterial Partial Pressure of Oxygen (mmHg)
- SvO2 = Mixed Venous Oxygen Saturation (%)
- PvO2 = Mixed Venous Partial Pressure of Oxygen (mmHg)
- 1.34 = Oxygen carrying capacity of Hemoglobin (mL O2/g Hb)
- 0.003 = Solubility coefficient of Oxygen in plasma (mL O2/dL/mmHg)