Calculates Qp:Qs from oxygen saturations using the Fick principle.
Pulmonary-to-Systemic Flow Ratio: Clinical Guide
Browse Knowledge HubCalculates Qp:Qs from oxygen saturations using the Fick principle.
Overview
Calculates Qp:Qs from oxygen saturations using the Fick principle.
Clinical Significance
Estimates the pulmonary-to-systemic flow ratio in shunt assessment. Saturation sampling and assumptions about pulmonary venous saturation are critical.
When to Use
- Use when the required measurements are available, reliable and clinically relevant.
How It Is Calculated
- Qp/Qs = (SaO₂ − SvO₂) / (SpvO₂ − SpaO₂).
Interpretation
- Estimates the pulmonary-to-systemic flow ratio in shunt assessment. Saturation sampling and assumptions about pulmonary venous saturation are critical.
Worked Example
Enter valid values in the displayed units. MedicalC then applies: Qp/Qs = (SaO₂ − SvO₂) / (SpvO₂ − SpaO₂).
Limitations
- The result does not establish a diagnosis or mandate treatment.
- Measurement error may be more important than arithmetic precision.
- Published thresholds may differ between populations and settings.
Clinical Pearls
- Document the source values and units with the final result.
- Review trends rather than isolated values where appropriate.
Common Mistakes
- Using the wrong unit.
- Combining values from different time points.
- Applying the result outside the intended measurement or clinical context.
Frequently Asked Questions
What does this calculator provide?
Calculates Qp:Qs from oxygen saturations using the Fick principle.
What formula is used?
Qp/Qs = (SaO₂ − SvO₂) / (SpvO₂ − SpaO₂).
Can the result be used alone?
No. It must be interpreted with the full clinical assessment and appropriate investigations.
What is the main limitation?
The result depends on accurate source measurements, correct units and appropriate clinical applicability.
References
- Standard Fick principle for intracardiac shunt quantification. — Primary, supporting or authoritative reference for the implemented relationship.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026
Clinical Disclaimer
MedicalC calculators and clinical tools are intended to support healthcare professionals. They do not replace clinical judgement, individual patient assessment, local guidance or specialist advice.
Results should always be interpreted in the context of the patient’s history, examination, investigations, current clinical condition and applicable professional guidance.