Continuous monitoring of cardiac output postoperatively using an implantable Doppler probe

The authors evolved a Doppler probe which can be attached to the ascending aorta intraoperatively. Using a pulsed echo Doppler flowmeter operating at 2 mHz, cardiac output was continuously measured during the first 2 days after open-heart surgery in 20 patients. The internal diameter of the aorta was assessed with ultrasound echo technique. The probe was fixed to the ascending aorta with a double suture through the adventitia. The suture was tightened by means of a long tourniquet which was passed through an infraxiphoid skin incision, between the two chest drains. A stable position providing adequate signals was achieved by use of probes with stabilizing "side flaps". In 8 cases the method was compared with the thermodilution technique using Swan-Ganz catheters. Analysis of 44 simultaneously performed measurements revealed a highly significant correlation between the two methods, and the results remained comparable throughout the 48-hour test period. There were no complications and all the probes could be easily removed.