Qp/Qs Calculator - Pulmonary to Systemic Flow Ratio

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Fick uses oxygen saturation measurements from catheterization. Echo/Doppler uses outflow-tract diameters and velocity time integrals from echocardiography.
Oxygen saturation measured from a systemic artery (e.g., aorta or radial artery) during catheterization.
%
Mixed venous oxygen saturation from the pulmonary artery or calculated as (3 x SVC + IVC) / 4.
%
Oxygen saturation in the pulmonary vein. Often assumed to be 98-100% in the absence of pulmonary disease; can be measured directly during catheterization.
%
Oxygen saturation in the main pulmonary artery, measured during right heart catheterization.
%
Qp/Qs ratioMild L-to-R shunt
1.47

Pulmonary-to-systemic blood flow ratio

Net shunt fraction32.1%
Shunt classificationMild left-to-right shunt
1.47
Severe R-to-L<0.5Moderate R-to-L0.5-0.8Mild R-to-L0.8-0.9Normal0.9-1.1Mild L-to-R1.1-1.5Moderate L-to-R1.5-2Large L-to-R2+

Qp/Qs = 1.47 - Mild left-to-right shunt

  • Pulmonary flow exceeds systemic flow by a ratio of 1.47:1, meaning approximately 32.1% of pulmonary flow is recirculated shunt blood.
  • The Fick method depends on accurate oxygen saturation sampling from all four sites; errors in mixed venous saturation have the largest impact on the result.

Next stepCorrelate with clinical symptoms, echocardiographic chamber dilation, and right-heart pressure estimates before deciding on management.

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