Shunt Fraction Index (Qp:Qs) Calculator

Shunt Fraction Index (Qp:Qs Ratio): Explanation and Clinical Context The Qp:Qs ratio, also known as the Shunt Fraction Index, is used to quantify the magnitude of left-to-right cardiac shunts. It is defined as the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs). A Qp:Qs ratio of 1 indicates no shunt, while values above 1 indicate a left-to-right shunt, with higher values reflecting larger shunts.

Clinical decision-making often relies on this ratio: small shunts (<1.5) usually do not require intervention, moderate shunts (1.5–2.0) require careful monitoring, and large shunts (>2.0) typically need surgical or catheter-based closure. This calculation can be derived from invasive cardiac catheterization measurements or non-invasively using echocardiography with Doppler data. Accurate measurement helps guide timing for intervention and assess the risk of complications such as pulmonary hypertension or ventricular volume overload.