Clinical Resources

Qp:Qs Shunt Calculator

Pulmonary to Systemic Blood Flow Ratio

%
%
From PA catheter, or calculated as (3 × SVC + IVC) / 4
%
Often assumed 98% if not directly measured
%

Results

Qp:Qs Ratio —
Interpretation —
Enter oxygen saturation or Doppler data above.

Clinical Use

Qp:Qs quantifies the ratio of pulmonary to systemic blood flow and is essential for evaluating intracardiac shunts in atrial septal defect (ASD), ventricular septal defect (VSD), and patent ductus arteriosus (PDA). It is the primary hemodynamic criterion for determining whether a shunt is significant enough to warrant intervention.

Significance Thresholds

  • <1.0: Right-to-left shunt (cyanotic physiology)
  • 1.0: No shunt
  • 1.0–1.5: Small left-to-right shunt — typically no intervention
  • 1.5–2.0: Moderate shunt — consider intervention
  • >2.0: Large shunt — intervention typically indicated

Limitations

The oximetry method assumes a single shunt site and stable hemodynamics. Mixed venous saturation can be difficult to estimate accurately, especially in the presence of an ASD (where SVC/IVC saturations may be preferable). The assumed SpvO2 of 98% may be inaccurate in patients with lung disease. Doppler-based Qp:Qs may be less reliable in the presence of significant valvular regurgitation or irregular rhythms.

References

  1. Baim DS, Grossman W. Grossman's Cardiac Catheterization, Angiography, and Intervention. 8th ed. Lippincott Williams & Wilkins; 2014.
  2. Baumgartner H, De Backer J, Babu-Narayan SV, et al. 2020 ESC Guidelines for the management of adult congenital heart disease. Eur Heart J. 2021;42(6):563-645. doi:10.1093/eurheartj/ehaa554
  3. Stout KK, Daniels CJ, Perloff JK, et al. 2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease. J Am Coll Cardiol. 2019;73(12):e81-e192. doi:10.1016/j.jacc.2018.08.1029