Mean cardiac output by thermodilution with a single controlled injection

Objective. A new method to estimate mean cardiac output by thermodilution with a single duration-controlled injection was evaluated in patients. Design. Prospective criterion standard study. Setting. University hospital cardiac surgical intensive care unit and cardiac operation room. Patients. Of 33 patients, 24 underwent coronary bypass graft surgery, four had a valve replacement, and five were treated in the intensive care unit. Interventions. Interventions consisted of thermodilution cardiac output measurements. One single duration-controlled injection of cold fluid was used to calculate cardiac output. This controlled injection was performed with a duration equal to one whole ventilation cycle of the ventilator. An algorithm adapted to this duration-controlled injection calculated cardiac output. Moreover, this algorithm has properties to reduce errors caused by artificial ventilation and thermal noise. Measurements and Main Results. In 33 patients, the averaged values of four measurements equally spread over the ventilatory cycle (phase-controlled) were compared with the values of two single duration-controlled measurements. The measurements were performed during periods of stable respiration and circulation. No significant difference was observed between the mean of four phase-controlled measurements and the mean of the two duration-controlled measurements. The cardiac output values in the intensive care patients were significantly higher compared with the two other patient groups (p < .05). The difference between the two methods could not be subdivided for the three patient groups (p > .05). The coefficient of variation of the single duration-controlled thermodilution measurements was significantly lower than the single phase-controlled measurements, 3% vs. 6% (p < .01). Conclusions. One single duration-controlled injection thermodilution measurement is as accurate and repeatable as the mean of four phase-controlled measurements and is clinically feasible.