Impedance cardiography: can it replace thermodilution and the pulmonary artery catheter?

Clinical assessment of cardiac output (CO) is inaccurate, yet the use of the pulmonary artery catheter (PAC) for thermodilution (TD) measurement of CO (CO(TD)) has declined significantly. Can noninvasive impedance cardiography (ICG) now be used to measure CO (CO(ICG)) in place of CO(TD)? A literature review of recent CO(ICG) correlations with CO(TD) (r = 0.73-0.92) were similar to ours, r = 0.81. A search for conditions interfering with CO(ICG) revealed no serious problems with patient position, cardiac or pulmonary assist devices, "wet lungs," body mass index > or = 30, or age > or = 70 years. A prospective randomized study was initiated beginning with a record of physician assessment of CO as high, normal, or low; concordance was 57%. Data from ICG was revealed only in the study group, resulting in a 49 per cent change in treatment compared with 29 per cent in the control group. Length of stay was shorter in the study than the control group in the intensive care unit (2.4 +/- 8.8 vs 3.3 +/- 7.3 days) and on the floor (9.8 +/- 10.6 vs 15.7 +/- 19.0 days). In conclusion, ICG is comparable with TD, is easily, accurately, and safely performed, enhances clinical assessment of CO, and improves care in hemodynamically compromised patients.

Impedance cardiography: a potential monitor for hemodialysis.

BACKGROUND: Impedance cardiography (ICG) technology has improved dramatically, and at least one device now can give a measurement of fluid status by using thoracic fluid content (TFC), along with cardiac output (CO) and cardiac index (CI). With a built-in sphygmomanometer cuff, it can also provide blood pressure (BP) and systemic vascular resistance index (SVRI). A currently available small portable ICG that provides reliable measures of fluid status could be an ideal noninvasive monitor for hemodialysis (HD), with the potential of helping avoid significant hemodynamic instability during HD. METHODS: A case series of patients with chronic renal failure was studied while undergoing HD using ICG (BioZ, CardioDynamics, Int. Corp., San Diego, CA). Parameters recorded at 15-min intervals included TFC, CI, BP (systolic, diastolic, and mean arterial), SVRI, and heart rate. Using the Pearson method, the percentage changes in each of the parameters during the HD session were correlated to the amount of fluid removed (FR), normalized to body weight. RESULTS: Forty-one patients were enrolled, but six patients were excluded due to incomplete data; therefore, 35 patients (13 men and 22 women) formed the basis of the analysis. The age range was 28 to 87 (mean 55.1 +/- 16.1) years. The amount of FR was 2.88 +/- 1.13 L (37.3 +/- 14.6 ml/kg). TFC decreased in all patients during the HD session (average reduction 12.7 +/- 8 kohms(-1)); whereas all other hemodynamic parameters showed both increases and decreases. The correlation of change in TFC with FR was moderate (r = 0.579, P = 0.0003); other hemodynamic parameters showed a poor correlation with FR. Neither the standard hemodynamic parameters nor the ICG device's special parameters were able to identify the five patients in this series who experienced significant hemodynamic instability or intradialytic hypotension. CONCLUSION: TFC, measured easily and noninvasively using ICG, correlates with the amount of fluid removed during HD. In comparison with the other hemodynamic parameters measured, TFC changed most consistently with fluid removal. Whether or not serial TFC measurements in a given patient at different HD sessions can guide the extent of FR will require additional study. This compact, easily operated, and nonobtrusive ICG device with the capability for continuously providing the standard hemodynamic parameters plus CO, TFC, and standard limb lead electrocardiography could replace current monitoring systems.

Cardiopulmonary assessment: is improvement needed?

Clinical parameters alone have repeatedly been proven unreliable in assessing cardiopulmonary status, especially in hemodynamically unstable patients. To learn if we had a diagnostic problem in our hospital, we compared physician assessment of cardiac index (CI) and thoracic fluid content (TFC) to values obtained using impedance cardiography (ICG). We selected the newest available ICG monitor, the BioZ, which employs this noninvasive technology. For CI measurements we have shown it to be equivalent to thermodilution and to be more reproducible (variability: 6.3% vs. 24.7%). Physician assessment of CI and TFC (high, normal, or low) was compared to the BioZ monitor's results in 186 patients, considered to be hemodynamically unstable, from the emergency room, the intensive care units, and the floors. Normal values were defined for CI (2.5-4.2 L/min m(2)) and for TFC (males: 30-50 kohm(-1) and females: 21-37 kohm(-1)). The concordance between physician assessment and the BioZ was 51% for CI with Kappa of 0.14 and 58% for TFC with Kappa of 0.19. Attendings did slightly better than the surgical residents with CI (52% vs. 48%) but slightly worse with TFC (57% vs. 61%). The potentially serious conditions of low CI and high TFC were misdiagnosed 42% and 46% of the time, respectively, by all physicians. Analysis of the data revealed that physician use of clinically available objective hemodynamic data, such as heart rate, blood pressure, and pulse pressure index, would not have been helpful. Furthermore, assistance from the pulmonary artery catheter (PAC) is often not available in our hospital, which has experienced a 90% decrease in its utilization over the past six years. Considering the increasing acuity of our aging patient population, accurate assessment of cardiopulmonary status is needed. The use of ICG could be a valuable addition to the physician's armamentarium.

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.

Through-the-knee amputation: an improved technique.

Through-the-knee amputation (TKA) is an excellent lower extremity treatment for the ischemic extremity when revascularization is not feasible and a prosthesis is not practical. Over the past 8 years 185 major amputations have been performed at our hospital of which 63 were of the TKA type. In 61 of these an improved technique was used that resulted in nonischemic, strong, and aesthetic stumps with 100 per cent primary healing. Our technique consists of removing the distal 2 cm of the femoral head with the two condyles and allowing the patella to ankylose to the new distal femoral end. In comparison with the other major amputations the TKA with this technique had significant advantages over the above-knee amputation and often was found to be superior to the below-knee amputation especially when rehabilitative ambulation with a prosthesis was not possible.