Study on the Repeatability of Cardiac Output Measurements Dependence of Temperature of Injectate

Device: Pulmonary artery catheter
Four series of cardiac output measurements, each series consists of eight measurements using cold and eight measurements using tepid injectate. Randomized order of temperature at first series and crossover design.
Other Name: Baxter

Bolus thermodilution cardiac output measurements by means of a pulmonary artery catheter have been a mainstay of monitoring critically ill patients for more than thirty years. Recent studies have questioned wether the traditional practice of averaging measurements from tree room temperature thermal indicator injections give sufficient precision.

This study tests the number of indicator injections necessary to be within 5 % of the "true" cardiac output (taken as the average of 16 injections) when the injection is synchronized with the respiration. The reliability of the thermodilution measurements are tested A) in sedated, artificially ventilated cardiac surgical patients and B) in the same patients when postoperatively awake and spontaneously breathing. We further compare the use of room temperature and iced thermal indicator injections.

The study hypothesis is that when injections are synchronized with the respiration, only three injections at room temperature are needed to achieve the desired precision in mechanically ventilated patients.

Only patients receiving a pulmonary artery catheter according our institution standard procedure of care will be included.