CARDIAC-OUTPUT MEASUREMENT BY TRANSPULMON ARY INDICATOR DILUTION TECHNIQUE - AN ALTERNATIVE TO THE PULMONARY-ARTERY CATHETER

Cardiac output measurements are often helpful in the management of cri tically ill patients and high risk-patients. In this study an alternat ive technique for measurement of cardiac output by the transpulmonary indicator dilution technique (TPID) was evaluated in comparison to con ventional thermodilution using a pulmonary artery catheter. With TPID, a thermistor-tipped catheter (the smallest available is 1.3 F) is pla ced 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 l ess invasive since the possible complications of the pulmonary cathete rs are avoided. We investigated the accuracy and reproducibility of tr anspulmonary 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 cir culatory shunt undergoing diagnostic heart catheterization. The patien ts were between 0.5 and 25.2 years old, their body surface between 0.3 5 and 1.89 m(2). Measurements were performed in duplicate with bolus i njections of ice-cold normal saline (0.15 ml/kg), randomly spread over the respiratory cycle. In total 48 thermodilution curves were measure d simultaneously in the pulmonary artery and in the aorta. Thermodilut ion curves were monoexponentially extrapolated for elimination of reci rculation and cardiac output was calculated with a standard Stewart Ha milton procedure. Results. The amplitude of the typical arterial therm odilution curve shows a smaller and more delayed course than the pulmo nary artery thermodilution curve. There was a very good correlation be tween the values found by pulmonary and TPID cardiac output measuremen ts (R=0.968). There was a slightly smaller cardiac output value measur ed 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 tech nique for measurement of cardiac output. We showed over a broad range in age and body surface very good correlation with thermodilution meas urements in the pulmonary artery. The slightly smaller values for TPID are explained by early recirculation, for clinical purposes the diffe rence is negligible. However, the reproducibility of a method is clini cally very important. Both methods showed in duplicate measurements ba sically the same reproduciblity. The disadvantage of TPID in being mor e sensitive to baseline alteration is counterbalanced by less respirat ory variability in comparison to the conventional thermodilution techn ique. However, by increasing the amount of injected indicator (i.e., 0 .2 ml/kg congruent to 15 ml in an adult) it is possible to reduce the effect of baseline alteration, By using fiberoptic catheters it is eve n possible to use TPID as double-indicator dilution technique to measu re intrathoracic blood volume (ITBV) and extravascular lung water (EVL W). We conclude that in many patients TPID might be an attractive, les s invasive and reliable alternative to conventional cardiac output mea surement by pulmonary artery catheter.