Calculate the Qp/Qs ratio from cardiac catheterization oxygen saturations to quantify intracardiac shunts. Assess ASD, VSD, and PDA hemodynamic significance.
The pulmonary-to-systemic flow ratio (Qp/Qs) is the gold standard for quantifying intracardiac shunts. Measured during cardiac catheterization using oxygen saturation data from multiple cardiac chambers, this ratio determines whether a shunt is hemodynamically significant and helps guide decisions about surgical or percutaneous closure.
A Qp/Qs of 1.0 indicates equal pulmonary and systemic blood flow (no shunt). Ratios above 1.5 are generally considered hemodynamically significant for left-to-right shunts (ASD, VSD, PDA), while ratios below 1.0 indicate right-to-left shunting (as in cyanotic congenital heart disease).
This calculator uses the Fick principle with oxygen saturation data from the pulmonary veins, pulmonary artery, aorta, SVC, and IVC. It computes mixed venous oxygen saturation using the Flamm formula, derives the Qp/Qs ratio, and estimates absolute pulmonary and systemic flows when hemoglobin and oxygen consumption are provided. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case.
Accurate Qp/Qs determination is essential for surgical decision-making in congenital heart disease. Under-estimation may lead to missed opportunities for closure, while over-estimation may result in unnecessary procedures. This calculator automates the multi-step Fick calculation, reducing arithmetic errors during catheterization data review and providing immediate clinical interpretation. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain.
Mixed Venous O₂ = (3 × SVC O₂ + IVC O₂) / 4 (Flamm formula) Qp/Qs = (Aortic O₂ − Mixed Venous O₂) / (Pulmonary Vein O₂ − PA O₂) Qp = VO₂ / (1.36 × Hb × 10 × (PV O₂ − PA O₂) / 100) L/min Qs = VO₂ / (1.36 × Hb × 10 × (Ao O₂ − MV O₂) / 100) L/min
Result: Qp/Qs = 1.09 — No significant shunt
Mixed venous O₂ = (3×70 + 76)/4 = 71.5%. Qp/Qs = (95 − 71.5) / (98 − 75) = 23.5/23 = 1.02. With a ratio near 1.0, there is no hemodynamically significant intracardiac shunt.
Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.
Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use. ## Practical Notes
Use this for repeatability, keep assumptions explicit. ## Practical Notes
Track units and conversion paths before applying the result. ## Practical Notes
Use this note as a quick practical validation checkpoint. ## Practical Notes
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Use as a sanity check against edge-case outputs. ## Practical Notes
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A Qp/Qs > 1.5:1 is generally considered hemodynamically significant for left-to-right shunts. For ASD closure, most guidelines recommend intervention at Qp/Qs ≥ 1.5:1 with evidence of right heart volume overload.
The SVC and IVC have different oxygen saturations due to varying tissue oxygen extraction. The Flamm formula (3×SVC + 1×IVC)/4 weights the SVC more heavily because it better represents myocardial oxygen saturation and avoids falsely elevated values from renal blood return in the IVC.
Yes, cardiac MRI and echocardiography can estimate Qp/Qs. MRI uses phase-contrast velocity mapping of the aorta and pulmonary artery. Echo uses Doppler-derived stroke volumes. However, catheterization remains the gold standard.
A ratio below 1.0 indicates predominant right-to-left shunting, meaning deoxygenated blood is bypassing the lungs and entering the systemic circulation. This causes cyanosis and is seen in conditions like Tetralogy of Fallot and Eisenmenger syndrome.
VO₂ is needed for absolute Fick flow calculations (Qp and Qs in L/min) but does NOT affect the Qp/Qs ratio itself, which depends only on oxygen saturation differences. However, inaccurate VO₂ will affect the absolute flow values.
Eisenmenger syndrome occurs when a long-standing left-to-right shunt causes irreversible pulmonary hypertension, eventually reversing the shunt direction to right-to-left. At this stage, shunt closure is contraindicated because the shunt serves as a pressure relief valve.