How the model works
Method readouts can differ from true modeled flow for a stated teaching reason.
Modeled forward flow drives the circulation. The Fick and thermodilution panels are observations of that state, not alternative inputs that silently replace it. Entering a manual Fick value changes the calculation result, not the patient’s pressure/flow model.
The simulator includes selected measurement-error examples. Their magnitudes and directions are deliberate demonstrations, not universal correction factors for sepsis, shock, TR or low flow.
Fick CO = VO₂ / [1.34 × Hb × (SaO₂ − SvO₂)/100 × 10], with VO₂ in mL/min and Hb in g/dL. This panel uses Hb-bound oxygen only. Default estimated Fick assumes VO₂ 250 mL/min and Hb 14 g/dL; synthetic venous saturation is constructed from the actual modeled flow and the selected metabolic assumption.
Some examples use a different actual VO₂, demonstrating bias from assuming 250. Invalid saturation differences, nonpositive flow or an oxygen balance requiring negative venous saturation produce no valid result. The detailed ventilator gas model has separate fixed assumptions and includes dissolved oxygen; the two teaching modules are not a single measured metabolic system.
An idealized 10 mL cold injection produces a delayed gamma-shaped temperature curve. The numerator uses 37°C blood, 0°C injectate and an illustrative thermal factor 1.08. The curve is normalized over a 30-second window and numerically integrated; calculated flow is inversely related to its area.
The result appears only after the simulation clock completes the recording, even if the graph is hidden. Severe TR illustrates a broadened curve with a chosen 20% under-reading; a low-flow example illustrates 12% over-reading. These are not clinical correction rules: real TR/low-flow bias can vary or be absent.
Shunts use the synthetic Fick Qs where valid and withhold conventional thermodilution Qp/Qs interpretation. V-A ECMO makes conventional systemic Fick/thermodilution ambiguous because oxygen and indicator transit involve the circuit; those readouts are withheld.
Impella’s flow path is distinguished from native stroke volume. Whenever a method’s assumptions no longer fit the selected network, the explanation takes precedence over a reassuring numeric result.
