Transpulmonary thermodilution assessments: precise measurements require a precise procedure.

When incorporating the values of a hemodynamic parameter into the care of patients, the precision of the measurement method should always be considered. A prospective analysis in the previous issue of Critical Care showed that the precision of transpulmonary thermodilution (TPTD) allows for reliable mean values if a standardised procedure is used. The present finding has a physiological basis, as TPTD requires a more prolonged transit time, which in turn reduces the effects that airway pressure and arrhythmia have on venous return-cardiac output steady states. Moreover, this result suggests that the current accepted threshold value of a 15% increase in cardiac output to identify a positive response to a fluid challenge could be reduced in the future. Indeed, this value is mainly related to the precision of the pulmonary artery catheter.