Effect of lower limb compression devices on thermodilution cardiac output measurement

OBJECTIVE: The aim of this study was to determine whether lower limb (calf) sequential compression devices (SCDs) have a significant effect on thermodilution cardiac output measurements using a pulmonary artery catheter. DESIGN: Prospective clinical investigation. SETTING: Surgical and neurosurgical intensive care units in a university hospital. PATIENTS: A total of 43 patients with pulmonary artery catheters and bilateral lower limb SCDs. MEASUREMENTS AND MAIN RESULTS: Cardiac output was measured (average of three) when the SCDs were off (T1), during the first 2-4 secs of the inflation cycle (T2), during seconds 4-8 of the inflation cycle (T3), and when the SCDs were off again (T4). Cardiac output measurements were consistently lower when measured during the SCD inflation cycle. The decrease in cardiac output ranged from 7.58% to 49.5%, with a mean reduction of 24.51% in the first 2-4 seconds and 20.61% during seconds 4-8 (p < .001). Two patients displayed an increase in cardiac output during the inflation cycle; one patient had an increase of 2.78% and the other an increase of 13.5%. In 11 patients, measurements were also made using a pulse contour-analysis cardiac output device, but no changes in pulse contour-analysis cardiac output were observed during the same time period. CONCLUSIONS: Thermodilution cardiac output measurements via a pulmonary artery catheter should not be done during the inflation cycle of lower limb SCDs because they produce a falsely low cardiac output.