Comparison between continuous and intermittent thermodilution measurement of the cardiac output during coronary bypass surgery.

purpose of the study: Continuous recording of cardiovascular parameters ranks high in cardio-anaesthesia. Various methods to measure the cardiac output have been developed within a period of a few years. We compared the bolus thermodilution method (COI), which has been internationally adopted as ''gold standard'' method, with the continuous thermodilution method (CCO) for measuring the cardiac output by means of the CCO Vigilance Monitor. Our aim was to find out whether cardiac output can be determined with valid results during coronary artery bypass surgery when using CCO. Method: A flow-directed catheter was used (8 Fr. IntelliCath(TM) CCO PA) in 98 patients during coronary artery bypass surgery after initiation of anaesthesia, introducing the catheter via the right V. jugularis interna, for continuous measurement of the cardiac output via the CCO Vigilance Monitor. The same equipment was also used to measure the cardiac: output via the bolus thermodilution method (COI mode) at the following stages: after abandoning the CCO mode 10 minutes subsequent to beginning the operation before sternotomy; 10 minutes after sternotomy before connecting to the heart-lung machine; 15 minutes after disconnecting the heart-lung machine before closing the thorax; and 10 minutes after closing the thorax. As a corresponding comparative value of the CCO method, we used the average cardiac output value calculated for each of the four times of measurement for the last three minutes before applying the boli. Results: In regression analysis we chose the linear model CCO=b x COI with gradient b=1 and zero point ordinate a=0. The identity measures, Spearman's rank correlation coefficients, and linear regression coefficients calculated for the four times of measurement, showed good agreement. Scatter of the paired differences between both methods (CCO - CCI) did not have any deterministic structure at all times of measurement. The average bias at the 4 times of measurement was 0.10 l/min, -0.12 l/min, -0.1 l/min, and -0.03 l/min, respectively, with a precision=2xs of 1.17 l/min, 1.36 l/min, 1.69 l/min and 1.50 l/min, respectively. The average relative error (100 x [CCO -COI]/COI) with standard deviation was calculated for the 4 times of measurement as 3.2% (s=15.4%), - 1.6% (s=15.3%), -0.9% (s=13.9%) and -0.3% (s=12.0%), respectively. Conclusion: Literature references show that the continuous thermodilution method is not only valid for intensive-care long-term measurement of cardiac output with approximately stationary haemodynamics, but also - as our results prove - valid if haemodynamics are not usually stationary, such as during coronary artery bypass surgery. The pros of the continuous thermodilution method are that no additional equipment is required apart from the standard equipment used in intensive-care medicine and cardio-anaesthesiology; that there is no stress caused by volume; and that manipulation is safe because no calibration routine is needed and also because measurement and analysis techniques are fully automated. Hence, we are of the opinion that the intraoperative use of this cardiac output measurement technique during open heart surgery is clinically indicated.