In a left-to-right shunt, oxygenated blood recirculates through the lungs, so pulmonary flow exceeds systemic flow. A Qp/Qs above 1.5 usually indicates a significant shunt that may need closure; below 1 indicates net right-to-left flow.
How to use the Qp/Qs Ratio Calculator
- Systemic arterial saturation
- Mixed venous saturation (SVC/IVC)
- Pulmonary venous saturation
- Pulmonary arterial saturation
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the four oxygen saturations from the catheter study.
Inputs explained
| Field | What to enter |
|---|---|
| Systemic arterial saturation | In % |
| Mixed venous saturation (SVC/IVC) | In % |
| Pulmonary venous saturation | In % |
| Pulmonary arterial saturation | In % |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Qp/Qs = (SaO₂ − SvO₂) ÷ (SpvO₂ − SpaO₂)
SaO₂ systemic arterial · SvO₂ mixed venous · SpvO₂ pulmonary venous (≈ SaO₂ or 98% if not measured) · SpaO₂ pulmonary arterial
Worked example
Inputs — Systemic arterial saturation: 96 %; Mixed venous saturation (SVC/IVC): 70 %; Pulmonary venous saturation: 98 %; Pulmonary arterial saturation: 82 %.
Results — Qp/Qs = 1.63.
Key terms
- Qp/Qs
- Pulmonary-to-systemic flow ratio.
Frequently asked questions
What Qp/Qs is significant?
Above 1.5:1, especially with right heart enlargement.
Why measure mixed venous saturation carefully?
It is often calculated as (3 × SVC + IVC) ÷ 4 because of streaming.
Can echo estimate Qp/Qs?
Yes – from flow in the pulmonary and aortic outflow tracts.