Descending aortic blood flow and cardiac output: A clinical and experimental study of continuous oesophageal echo-Doppler flowmetry

Background: Several studies have demonstrated that perioperative optimisati on of oxygen delivery and haemodynamics can reduce mortality and morbidity for high-risk surgical patients. To optimise cardiac output, reliable, cont inuous and "less invasive" methods for measuring cardiac output are urgentl y needed. Methods: Eight landrace pigs were studied during experimental repeated card iac tamponade and 14 patients during liver transplantation. Aortic blood fl ow was measured by using transoesophageal echo-Doppler technique. A total o f 91 paired measurements of aortic blood flow and cardiac output with diffe rent techniques were performed in the pigs and 124 paired measurements in t he patients. Results: Transoesophageal echo-Doppler did provide continuous real-time mon itoring of the rapid and dramatic haemodynamic changes occurring during car diac tamponade and during liver transplantation, while only intermittent in formation was obtained from the bolus thermodilution technique. Changes in haemodynamics were more difficult to detect with the "continual" cardiac ou tput thermodilution technique. Changes in aortic blood flow closely followe d changes in cardiac output determined by the bolus thermodilution techniqu e both in pigs (r=0.89) and in patients (r=0.80). In patients, aortic blood flow constituted about 70% of cardiac output determined by the bolus therm odilution technique. Conclusions: A combined echo-Doppler technique can be valuable for continuo us monitoring of haemodynamic changes in the perioperative setting, and cha nges in aortic blood flow agree well with corresponding changes in cardiac output intermittently obtained by thermodilution cardiac output measurement s. With the combined echo-Doppler technique a proper position of the Dopple r beam is greatly facilitated by the M-mode echo visualisation of the aorti c wall and aortic cross-sectional area is continuously measured.