Qp Qs Ratio Calculator - Cardiac Cath Oximetry Run

A qp qs ratio calculator is a bedside tool for an oximetry run during a right and left heart catheterization, and it returns a single dimensionless number that compares pulmonary and systemic blood flow to detect and quantify an intracardiac shunt. The reading is 1.0 when the two flows are matched, climbs above 1.0 with a left-to-right shunt, and drops below 1.0 with a right-to-left shunt. The calculator needs four blood oxygen saturation samples from the same catheterization and pairs the number with the 1.5 and 2.0 cut points from the 2020 ACC/AHA adult congenital heart disease guideline.

• • Read a recent right and left heart cath at the bedside: paste the four saturations from the report and see the ratio and the band before the team conversation.
• • Worked example for teaching: run Ao 95, SVC 65, PV 97, PA 87 to confirm the 3.0 reading that the standard textbook example returns.
• • Repeat scoring after a vasodilator or balloon trial: re-enter the post-intervention saturations to see whether the number falls below 1.5.

The four saturations should come from the same catheterization report. Mixing a post-vasodilator pulmonary artery sample with a baseline aortic sample produces a misleading reading, so the result is a triage prompt rather than a stand alone diagnosis.

A second catheterization pattern that uses the same right heart inputs to surface a pulmonary pressure problem is the PVR Calculator, which turns mean PAP, left atrial pressure, and cardiac output into pulmonary vascular resistance in dynes and Wood units for the same hemodynamics workup.

The calculator subtracts the SVC saturation from the aortic saturation to get the systemic flow numerator, subtracts the pulmonary artery saturation from the pulmonary vein saturation to get the pulmonary flow denominator, and divides the numerator by the denominator to return the ratio.

• aoSat: Aortic oxygen saturation percent from the systemic artery sample.
• svcSat: SVC or mixed venous oxygen saturation percent drawn from the SVC or right atrium.
• pvSat: Pulmonary vein oxygen saturation percent, drawn from a wedged pulmonary vein or assumed at 98 percent when sampling is not feasible.
• paSat: Pulmonary artery oxygen saturation percent drawn from the main pulmonary artery.
• qpQs: Pulmonary to systemic flow ratio, a dimensionless number that equals 1.0 when no shunt is present.

The result panel shows the ratio with two decimal places, a band label, the closest published threshold, and a one-sentence clinical guidance string.

According to 2020 ACC/AHA Guideline for the Management of Adults With Congenital Heart Disease, the oximetry Fick equation is the standard hemodynamic variable used to detect and quantify an intracardiac shunt during cardiac catheterization.

A second hemodynamic tool that uses the same right and left heart catheterization inputs to surface a valve area is the Aortic Valve Area Calculator, which turns mean gradient, peak velocity, and left ventricular ejection time into a single aortic valve area for the same hemodynamics workup.

Four concepts drive the result. Naming them keeps the calculator from being read as a stand alone diagnosis.

The shunt ratio is one half of the modern congenital workup. The other half is the pulmonary vascular resistance, which the PVR calculator turns into Wood units for the same catheterization.

A second catheterization tool that turns arterial blood gas inputs into a single pulmonary function number is the AA Gradient Calculator, which applies the alveolar gas equation to alveolar and arterial oxygen tensions for the same pulmonary workup.

The form takes four catheterization saturations and returns the ratio with a published band. Each saturation should come from the same cardiac catheterization report.

1. 1 Enter the aortic saturation: type the Ao sat from the catheterization summary.
2. 2 Enter the SVC or mixed venous saturation: use the SVC sat from the right heart sample.
3. 3 Enter the pulmonary vein saturation: type the PV sat from a wedged pulmonary vein, or use 98 percent as a textbook assumption when sampling is not feasible.
4. 4 Enter the pulmonary artery saturation: type the PA sat from the main pulmonary artery sample.
5. 5 Read the ratio and band: the result panel shows the number with two decimals, a band label, the closest published threshold, and a one-sentence clinical guidance string.
6. 6 Compare the band to the 1.5 closure threshold: if the band is at or above 1.5 and right heart imaging shows chamber enlargement, the 2020 ACC/AHA guideline supports a closure review.

A patient with an atrial septal defect has Ao 95, SVC 65, PV 97, and PA 87 on a recent cardiac catheterization. The calculator returns 3.00 with a large left-to-right shunt band, well above the 2.0 cut point.

A second bedside score that uses vital signs and mental status to surface a sepsis triage band is the Q SOFA Calculator, which turns blood pressure, respiratory rate, and Glasgow Coma Scale into a published sepsis triage number for the same emergency department workflow.

Using this calculator offers several practical advantages over mental math and a separate shunt lookup table.

• • Standardized dimensionless ratio: the calculator returns a single dimensionless number, the convention used in modern cardiac catheterization reports and in the 2020 ACC/AHA guideline.
• • No oxygen consumption or hemoglobin required: the saturation-only form of the Fick formula is the published bedside shortcut, so the result is available as soon as the four saturations are drawn.
• • Built-in 1.5 closure threshold: the result panel pairs the number with the 1.5 closure threshold from the 2020 ACC/AHA guideline, so the next step is implied by the same number.
• • Direct band assignment: the band label maps the reading to a published clinical category from no shunt through large left-to-right and right-to-left.

The same dimensionless ratio and band convention are used in the catheterization lab, the congenital clinic, and the pre-operative planning meeting, giving the cath team, the imaging cardiologist, and the surgeon a shared language.

A lab-to-single-number pattern that pairs naturally with the ratio in an inpatient workup is the Arterial Blood pH Calculator, which applies the Henderson-Hasselbalch equation to PaCO2 and HCO3 for the same cardiopulmonary workflow.

The result depends on the four catheterization saturations and on the patient. Small changes in any saturation can move the reading across a band boundary.

• • The result is a screening number for an intracardiac shunt, not a stand alone diagnosis. A full cardiac catheterization with a step-up, step-down, and a contrast or bubble study is required before any defect-specific therapy is started.
• • Patients with bidirectional shunting, Eisenmenger syndrome, or pulmonary vascular disease can have readings below 1.0 with pulmonary pressures above systemic pressures.

The ratio sits inside a published hemodynamic workup. The 2020 ACC/AHA guideline pairs the 1.5 closure threshold with chamber enlargement and a pulmonary vascular resistance below 5 Wood units, which is why the ratio never stands alone.

According to 2020 ACC/AHA Guideline for the Management of Adults With Congenital Heart Disease, a Qp/Qs ratio of 1.5 or above with chamber enlargement is a class IIa trigger for closure of an atrial septal defect.

According to Medscape Atrial Septal Defect overview, a right-to-left ratio below 1.0 is uncommon in isolation and usually points to Eisenmenger syndrome or a coexisting pulmonary vascular problem.

A catheterization tool that turns cuff pressures plus heart rate into a mean arterial pressure is the Blood Pressure Calculator, which gives the cath team a single number to compare against the direct catheterization pressures on the same report.