Use of an Extracorporeal Arteriovenous Tubing Loop to Measure Cardiac Output in Intensive Care Unit Patients by Ultrasound Velocity Dilution

Thermodilution cardiac output (CO) measurement requires heart catheterization and is known as a risk factor. The existing cannula in the radial artery in intensive care unit (ICU) patients can be used to measure CO by ultrasound dilution (COus). An arteriovenous shunt between the radial artery and cubital vein was created using a 25 cm tubing loop. An ultrasound flow dilution sensor was clamped on the tubing and connected to a modified HD01 monitor (Transonic Systems, Inc., Ithaca, NY). Calibration injections of 1 ml 0.9% NaCl were injected into the tubing. An intravenous bolus injection consisted of 10-20 ml 0.9% NaCl. Simultaneously, CO was measured by thermal dilution (COth; MI 166A, Hewlett Packard, Andover, MA). Each value for COth or COus was based on the average of three to five injections. Blood flow through the shunt was 10 to 26 ml/min. The comparison was made on 14 patients. In 33 measurements, the regression equation was COth = -0.08 + 1.02 COus (r = 0.97). In 22 cases, the difference between COth and COus was less than 5%, in 9 cases it was in the range of 5-10%, and in 2 cases it was in the range of 10-20%. The presence of arterial and venous lines in an ICU setting obviates the need for cardiac catheterization for the determination of CO.