NONINVASIVE MEASUREMENT OF CARDIAC-OUTPUT BY AN ACETYLENE UPTAKE TECHNIQUE AND SIMULTANEOUS COMPARISON WITH THERMODILUTION IN ICU PATIENTS

A simple, accurate, and noninvasive method of cardiac output measureme nt can be an extremely useful tool for the clinician and researcher. T his study used the acetylene gas uptake technique to measure the absor ption of acetylene into the pulmonary circulation during a constant ex halation, which is proportional to the pulmonary capillary blood flow and to the cardiac output, assuming no anatomic shunts. We compared ca rdiac output measured simultaneously by this and by the standard therm odilution (TD) technique in 21 patients in the ICU with a variety of m edical and surgical conditions and a wide range of cardiac outputs, Mi e also compared the two techniques in 19 ambulatory patients with a 2- h interval between the invasive and noninvasive test to assess variabi lity over time, The two tests had an excellent correlation when done s imultaneously with a correlation coefficient of 0.89 (p < 0.001), With a 2-h interval between the two tests, the correlation coefficient was 0.66 (p = 0.0018), Nine patients in the simultaneous group had cardio myopathy. When they were excluded, the correlation coefficient increas ed to 0.96, Most of these patients had documented tricuspid regurgitat ion (TR), which may underlie the greater difference between acetylene uptake and TD values, with consistently higher TD values in these pati ents, This study confirms the correlation between the acetylene uptake and the standard invasive TD techniques in sick patients with various medical and surgical conditions and a wide range of cardiac outputs, Furthermore, me believe this would be a more accurate method for measu ring cardiac output in patients with cardiomyopathy and TR because it is based only on pulmonary capillary blood flow.