CONTINUOUS MEASUREMENT OF CARDIAC-OUTPUT USING PULSE CONTOUR ANALYSIS

Pulse contour cardiac output (PCCO) is an easily applicable method for continuous measurement of cardiac output in critically ill patients. Calculation of stroke volume is possible by analysing the area under t he systolic part of the arterial pulse pressure waveform together with an individual calibration factor (Zao) to account for the individuall y variable vascular impedance. Since vascular impedance is potentially affected by altered vascular tone, it was the aim of the present stud y to examine the validity of PCCO in ICU patients receiving various do sages of a variety of vasoactive drugs. Patients aad methods. Continuo us cardiac output was measured in 20 ICU patients for a total of 110 h using the pulse contour method. The precision of PCCO was determined in comparison with its calibration reference, the thermodilution metho d (TDCO): (1) during administration of vasoactive drugs at a constant rate and (2) during conditions with altered vascular tone and haemodyn amics elicited by changes in vasoactive drug dosage. For this purpose, the patients received varying dosages of vasoactive drugs (dopamine, dobutamine, epinephrine, norepinephrine, nitroglycerin, prostacycline and urapidil). Results. A total of 165 data sets was obtained, each co nsisting of the average of four capnometrically triggered TDCO measure ments and the corresponding PCCO values. The relative difference betwe en methods (+/-2 SD) was +/-23.9% (SD 0.851 . min(-1); r=0.93) if a si ngle calibration at the beginning of measurement series was performed (Fig. 2). The bias of the mean cardiac output values of both methods w as -0.091 . min(-1). The precision of PCCO improved to +/-15.7% by add itional calibrations (SD 0.56 . min(-1); r=0.96; bias 0.0031 . min(-1) ). Data of two patients showed that recalibration may be necessary aft er extreme haemodynamic changes due to septic shock or cooling. Altera tion of vascular tone by clinically used dosage of vasoactive drugs, h owever, had no destabilizing effect on the pulse contour method. Concl usions. It could be demonstrated that PCCO provides a valuable method for continuous cardiac output measurement in the intensive care settin g with a precision comparable to that of thermodilution.