TFC (thoracic fluid content): a new parameter for assessment of changes in chest fluid volume.

Clinical assessment of cardiac status can be difficult and incomplete without an assessment of fluid volume status, especially of the lungs. Now, a new parameter is available, thoracic fluid content (TFC). It is an indicator of total fluid volume, both intracellular and extracellular. Because it is measured noninvasively using impedance cardiography (ICG), it could be a welcome addition to the physician's assessment. An evaluation of TFC was performed beginning with 1) an examination of chest impedance (Z) as an accurate means of following fluid changes, 2) the relationship of TFC to Z using both loop and spot electrodes, and 3) clinical applications of TFC. In 1) 12 dogs, Z was superior (r = 0.935, P < 0.006) to 10 traditional hemodynamic and gas transfer parameters in trending a lactated Ringer's infusion; 2) a plastic model, changes in TFC values derived from Z measurements using both loop and spot electrodes were virtually identical and paralleled infused saline (r = 0.999, P < 0.001); 3) the clinical setting, TFC trended fluid changes well. From these results, we conclude that TFC is a reliable measurement of chest fluid status and of changes in that fluid. Along with cardiac index (CI), also provided by the ICG monitor, TFC can be very helpful to the clinician.

Impedance cardiography: the next vital sign technology?

OBJECTIVE: To evaluate the following: (1) the intramethod variability of impedance cardiography (ICG) cardiac output (CO) measurements via the latest generation monitor and thermodilution CO measurements (CO-TDs); (2) the intermethod comparison of ICG CO and CO-TD; and (3) comparisons of the intergeneration ICG CO equation to CO-TD, using the latest ICG CO equation, the ZMARC (CO-ICG), and the predecessor equations for measuring the ICG CO of Kubicek (CO-K), Sramek (CO-S), and Sramek-Bernstein (CO-SB). DESIGN: Prospective study. SETTING: A cardiovascular-thoracic surgery ICU in a community university-affiliated hospital. PATIENTS: Post-coronary artery bypass graft patients (n = 53) in whom 210 pairs of CO measurements were made. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The CO-ICG was determined simultaneously while the nurse was performing the CO-TD. Variability within the monitoring method was better for CO-ICG compared to CO-TD (6.3% vs 24.7%, respectively). The correlation, bias, and precision of the CO-ICG was good compared to CO-TD (r(2) = 0.658; r = 0.811; bias, -0.17 L/min; precision, 1.09 L/min; CO-ICG = 1.00 x CO-TD - 0.17; p < 0.001). A steady improvement in agreement of the previous ICG methodologies compared to CO-TD was observed as follows: (1) CO-K: r(2) = 0.309; r = 0.556; bias, -1.71 L/min; precision, 1.81 L/min; CO-K = 0.78 x CO-TD - 0.45; p < 0.001; (2) CO-S: r(2) = 0.361; r = 0.601; bias, -1.46 L/min; precision, 1.63 L/min; CO-S = 0.80 x CO-TD - 0.36; p < 0.001; and (3) CO-SB: r(2) = 0.469; r = 0.685; bias, -0.77 L/min; precision, 1.69 L/min; CO-SB = 1.03 x CO-TD - 0.95; p < 0.001. The CO-ICG demonstrated the closest agreement to CO-TD. CONCLUSION: The latest ICG technology for determining CO (CO-ICG) is less variable and more reproducible in an intrapatient sense than is CO-TD, it is equivalent to the average accepted CO-TD in post-coronary artery bypass graft patients, and showed marked improvement in agreement with CO-TD compared to measurements made using previous generation ICG CO equations.