Objective: By means of a Swan-Ganz catheter cardiac output is calculated using the Stewart-Hamilton thermodilution equation. Assuming the body as a thermally isolated inert system, this equation theoretically always results in zero cardiac output.
Methods: Using the first and second law of thermodynamics together with a few lines simple analysis this statement is proven.
Conclusion: It is at least a necessary condition for the application of the Stewart-Hamilton equation, that core body temperature is kept constant in a thermo- regulatory steady state.