RLHC Calculator (Age > 3 Years)

RLHC Calculator (Age > 3 Years) Right and Left Heart Catheterization Calculator: Clinical explanation and context Overview Right and left heart catheterization is a procedure performed to measure intracardiac pressures and blood oxygen saturations for the purpose of calculating pulmonary and systemic blood flows and resistances. The calculations in this tool use the Fick principle to estimate pulmonary flow and systemic flow and then derive resistances from measured pressure gradients and calculated flows. The results assist clinicians in assessing the presence and severity of intracardiac shunts, pulmonary vascular disease, and the hemodynamic response to oxygen administration.

Physiologic principle The Fick principle states that the rate of oxygen uptake by the lungs is equal to cardiac output multiplied by the arteriovenous oxygen content difference. When applied to the whole circulation, pulmonary blood flow equals oxygen consumption divided by the pulmonary arteriovenous oxygen content difference. In practice oxygen content is estimated from hemoglobin concentration and oxygen saturation.

Use measured oxygen consumption when available. If oxygen consumption is not directly measured use clinically appropriate estimates documented for the patient population. Key formulas used in the calculator Formula for body surface area uses the Mosteller method.

Pulmonary flow Qp and systemic flow Qs are calculated from the Fick principle using oxygen consumption, hemoglobin concentration and the appropriate saturation differences for pulmonary and systemic circulations. Pulmonary arterial resistance is computed as the transpulmonary pressure gradient divided by pulmonary flow. Systemic vascular resistance is computed as the systemic pressure gradient divided by systemic flow.

Indexed pulmonary arterial resistance is calculated by dividing pulmonary arterial resistance by body surface area. These calculations are standard for hemodynamic assessment during cardiac catheterization. Mixed venous saturation and practical notes on sampling Accurate estimation of mixed venous saturation is essential.

When true mixed venous blood from the pulmonary artery is not available use a clinically validated method to approximate mixed venous saturation from central venous and inferior vena cava saturations. This calculator implements an averaged approach to approximate mixed venous saturation consistent with methods described in the hemodynamic literature. Always interpret calculated flows in light of the sampling method used.

Clinical interpretation Qp divided by Qs near one indicates balanced pulmonary and systemic flow. A Qp to Qs ratio at or above one point five is commonly regarded as hemodynamically significant and is frequently used in decision making for closure of left to right shunts when right heart volume overload is present. Assess Qp to Qs together with chamber size, symptoms and pulmonary vascular resistance to determine management.

Pulmonary vascular resistance and operability guidance Normal pulmonary vascular resistance is in the low Wood unit range. A pulmonary vascular resistance near or above three Wood units is consistent with pulmonary vascular disease in adults. For pediatric patients pulmonary vascular resistance indexed for body surface area is commonly used.

Expert consensus and guideline reports frequently use indexed thresholds to guide operability. Many centers consider an indexed pulmonary vascular resistance below approximately four Wood units per square meter as supportive of operability with biventricular repair. Indexed pulmonary vascular resistances substantially above eight Wood units per square meter are often associated with poor likelihood of reversibility and require careful multidisciplinary review before considering corrective surgery.

Clinical decision making must integrate patient age, anatomy, response to pulmonary vasodilator testing and the overall clinical picture. Practical caveats and measurement accuracy Measurement error in oxygen saturations, inaccuracies in assumed oxygen consumption, hemoglobin measurement timing and sampling site selection can all affect calculated flows and resistances. When possible measure oxygen consumption directly and ensure accurate matched sampling for arterial and venous saturations.

Reproducible sampling techniques and standardized calculation methods improve the reliability of trends and comparisons such as rest versus post oxygen measurements. Interpret absolute numbers together with clinical context and, when results are borderline, consider further testing including pharmacologic vasoreactivity testing or repeat catheterization with careful measurement of oxygen consumption. How to use rest and post oxygen results The rest dataset provides baseline hemodynamics.

The post oxygen dataset is used to assess reversibility of pulmonary vasoconstriction by observing changes in pulmonary flows pressures and calculated resistances. A decrease in pulmonary vascular resistance with oxygen indicates at least partial vasoreactivity and may support operability in selected patients. Compare the rest and post oxygen parameters using the output table to assess direction and magnitude of change.

Limitations of numeric thresholds There is no single numerical threshold that alone determines management in complex congenital or acquired cardiac disease. Thresholds for Qp to Qs and pulmonary vascular resistance provide guidance but should never replace multidisciplinary clinical judgment. Patient specific factors include age anatomy prior therapy comorbidities and response to vasodilators.

Use the calculator to inform but not replace comprehensive clinical assessment. References StatPearls. Fick principle.

National Library of Medicine. 2024. AHA guideline for management of adults with congenital heart disease.

Circulation. 2018. Pulmonary vascular resistance index literature review and consensus sources.

Pulm Circ and related reviews. 2019 to 2021. Pediatric pulmonary vascular disease and operability discussions.

European and specialty reviews. 2014 to 2024. ThoracicKey Cardiac Outputs and Shunts.

Clinical physiology reference. 2025.