Qp/Qs Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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Respiratory numbers often become useful only after the right relationship is calculated. Qp/Qs Calculator focuses on the pulmonary measurements shown in this tool and turns them into the specific ratio, score, or estimate its engine supports.

What this calculator does

Qp/Qs Calculator uses Which method, RVOT diameter, RVOT VTI, LVOT diameter, LVOT VTI, Pulmonary venous O₂ saturation, and the remaining displayed fields to produce the qp/qs ratio used by this calculator. It only uses the fields shown in this calculator; it does not silently add tests, diagnoses, symptoms, or clinical variables that are absent from the interface. Mirrors Qp/Qs modes: RVOT/LVOT VTI geometry, Fick oxygen-saturation equation using PVO2/MVO2/PAO2, and direct Qp/Qs.

How to use it

Enter or select Which method, RVOT diameter, RVOT VTI, LVOT diameter, LVOT VTI, and the remaining displayed fields. Use measurements from the same respiratory assessment and confirm whether oxygen values are percentages, fractions, or pressures. If an input is unknown, it is better to leave the calculation unresolved than to invent a value.

How the calculation works

The calculator supports geometry, Fick oxygen-saturation, and direct-flow modes. The saturation form uses (systemic arterial O2 − mixed venous O2) ÷ (pulmonary venous O2 − pulmonary arterial O2); the geometry mode compares RVOT and LVOT cross-sectional area × VTI, and direct mode divides entered Qp by Qs.

Example

Using the calculator’s prefilled demonstration values, the primary output is 1.56, labeled “Qp/Qs ratio”; Qp is 98.175 and Qs is 62.832. That sample is useful for checking the calculation path, but real interpretation should use verified measurements from the same clinical or study context.

How to interpret the result

Read qp/qs ratio in the context of the pulmonary measurement or scoring system used. Trends, measurement quality, oxygen/ventilator settings, and the disease being evaluated usually matter more than an isolated decimal value.

Limitations and notes

Respiratory measurements depend on technique, calibration, oxygen/ventilator settings, altitude, timing, and the patient population in which a rule was validated. A single calculated value should be interpreted with symptoms, examination, serial measurements, imaging, and the clinical question that prompted the test.