Pulmonary/Systemic Flow Ratio

Enter hemoglobin and oxygen saturations obtained during catheterization to estimate Qp/Qs and characterize shunt direction.

Hemoglobin (g/dL)

Systemic arterial saturation (%)

Pulmonary artery saturation (%)

Mixed venous saturation (%)

Pulmonary venous saturation (%)

Results

Systemic oxygen content (CaO₂)

18.97 mL O₂/dL

Mixed venous oxygen content (CvO₂)

13.26 mL O₂/dL

Pulmonary venous oxygen content (Cpvo₂)

18.97 mL O₂/dL

Pulmonary artery oxygen content (CpaO₂)

14.59 mL O₂/dL

Qp/Qs ratio

1.30

Left-to-right shunt (Qp > Qs) – assess magnitude and clinical significance.

Clinical guidance:

Qp/Qs >1.5 often indicates significant left-to-right shunt warranting intervention.
Qp/Qs <1 suggests right-to-left shunt; assess for cyanosis and hemodynamic compromise.

How to Use This Calculator

During catheterization, measure oxygen saturations in systemic artery, pulmonary artery, mixed venous blood (RA/SVC), and pulmonary veins (or assume 98–100%). Use co-oximetry for accuracy. Oxygen content calculations require hemoglobin. Use simultaneous lab value to minimize error. Combine ratio with pressure data, imaging, and clinical status to determine need for shunt closure or further evaluation.

Formula

Oxygen content (mL O₂/dL) = (1.36 × Hb × SaO₂/100) + (0.0031 × PaO₂).

Frequently Asked Questions

Use left atrial or pulmonary capillary wedge saturation if accessible; otherwise assume 98–100% for fully oxygenated blood. Mixed venous sampling (e.g., from PA) accounts for systemic venous admixture. Use true mixed venous values for accuracy. Dissolved oxygen contributes minimally. Hemoglobin-bound oxygen dominates content, so specifying PaO₂ is optional. Pulse oximetry is insufficient—arterial blood gases or co-oximetry are recommended for precise saturation measurement. Low hemoglobin reduces oxygen content, potentially exaggerating calculated shunt ratios. Interpret alongside clinical context.