HZV-Bestimmung mittels transpulmonaler Thermodilution Eine Alternative zum Pulmonaliskatheter?

Zusammenfassung

Die Messung des Herzzeitvolumens (HZV) ist zur Überwachung und Therapiesteuerung von Risikopatienten und Schwerstkranken häufig hilfreich. Die vorliegende Untersuchung beschreibt die HZV-Bestimmung mittels transpulmonaler Thermodilution (TPID) und vergleicht sie mit der herkömmlichen pulmonalarteriellen Thermodilution, wie sie unter Verwendung eines Pulmonaliskatheters klinisch breit angewendet wird. Bei sehr guter Übereinstimmung zwischen pulmonalarteriellem und transpulmonalem HZV (Bias=−4,7%±1,5% sem) über den gesamten untersuchten Altersbereich (0,5 bis 25,2 Jahre), besteht bei Doppelbestimmung auch eine vergleichbare Reproduzierbarkeit für die beiden Verfahren (SD=10.9% vs. 11,7%). Der geringeren Beeinflussung der HZV-Messung mittels TPID vom respiratorischen Zyklus steht die etwas größere Anfälligkeit gegenüber spontanen Temperaturschwankungen des Patienten entgegen. Im Gegensatz zur respiratorischen Abhängigkeit der pulmonalarteriellen Thermodilution kann die Anfälligkeit der TPID gegenüber diesen Temperaturschwankungen jedoch durch eine höhere Indikatordosierung weiter reduziert werden. Die zusätzlichen Einsatzmöglichkeiten in der pädiatrischen Anästhesie und Intensivmedizin, die prinzipiell geringere Invasivität und niedrigere Kosten sind Vorteile dieser Methode. Sie kann aber nicht bei allen klinischen Fragestellungen den Pulmonaliskatheter ersetzen.

Abstract

Cardiac output measurements are often helpful in the management of critically ill patients and high risk-patients. In this study an alternative technique for measurement of cardiac output by the transpulmonary indicator dilution technique (TPID) was evaluated in comparison to conventional thermodilution using a pulmonary artery catheter. With TPID, a thermistor-tipped catheter (the smallest available is 1.3 F) is placed in the aorta via a femoral artery introducer. Thus, TPID can also be used in very small children in whom placement of a pulmonary artery catheter may be difficult or even impossible. In principle, TPID is less invasive since the possible complications of the pulmonary catheters are avoided. We investigated the accuracy and reproducibility of transpulmonary thermodilution in patients over a broad range in age and body surface.

Methods. Following approval by the ethics committee and written consent, the data were obtained from 21 patients without a circulatory shunt undergoing diagnostic heart catheterization. The patients were between 0.5 and 25.2 years old, their body surface between 0.35 and 1.89 m². Measurements were performed in duplicate with bolus injections of ice-cold normal saline (0.15 ml/kg), randomly spread over the respiratory cycle. In total 48 thermodilution curves were measured simultaneously in the pulmonary artery and in the aorta. Thermodilution curves were monoexponentially extrapolated for elimination of recirculation and cardiac output was calculated with a standard Stewart Hamilton procedure.

Results. The amplitude of the typical arterial thermodilution curve shows a smaller and more delayed course than the pulmonary artery thermodilution curve. There was a very good correlation between the values found by pulmonary and TPID cardiac output measurements (R=0.968). There was a slightly smaller cardiac output value measured by the TPID (Bias=−4.7±1.5% sem) The reproducibility of duplicate measurements with the two methods were nearly the same, the standard deviation of the difference was 10.9% for the pulmonary thermodilution method and 11.7% for TPID.

Discussion. TPID gives an alternative technique for measurement of cardiac output. We showed over a broad range in age and body surface a very good correlation with thermodilution measurements in the pulmonary artery. The slightly smaller values for TPID are explained by early recirculation, for clinical purposes the difference is negligible. However, the reproducibility of a method is clinically very important. Both methods showed in duplicate measurements basically the same reproduciblity. The disadvantage of TPID in being more sensitive to baseline alteration is counterbalanced by less respiratory variability in comparison to the conventional thermodilution technique. However, by increasing the amount of injected indicator (i.e., 0.2 ml/kg≅15 ml in an adult) it is possible to reduce the effect of baseline alteration. By using fiberoptic catheters it is even possible to use TPID as double-indicator dilution technique to measure intrathoracic blood volume (ITBV) and extravascular lung water (EVLW). We conclude that in many patients TPID might be an attractive, less invasive and reliable alternative to conventional cardiac output measurement by pulmonary artery catheter.