Impedance cardiography in the estimation of hemodynamic and fluid status of coma patients during continuous venovenous hemodiafiltration

Introduction

Most ICU patients on continuous venovenous hemodiafiltration (CVVHDF) are in multisystem failure and require extensive monitoring [1]. Impedance cardiography (ICG) technology provides a measurement of fluid status using the thoracic fluid content (TFC), along with cardiac output (CO), cardiac index (CI) and systemic vascular resistance index (SVRI). NICCOMO^® (Medis, Germany), a noninvasive ICG device that provides trustworthy measures, could be a complementary monitor for CVVHDF, supporting fluid balance and helping avoid hemodynamic instability [2].

Methods

The study was an analysis of coma patients with acute renal failure while undergoing CVVHDF (Equasmart^®; Hemodec, Italy). By means of NICCOMO^® the TFC, CI, CO, mean arterial pressure and SVRI were constantly recorded. Employing the Pearson method, the percentage variations in each of the parameters during the CVVHDF treatment were correlated to the amount of fluid removed (FR), normalized to body weight.

Results

Ten patients were studied (six men and four women); the age range was 53.1 ± 15.2 years. A total of 16.6 l of fluid was removed during CVVHDF (830 ml/day over 20 treatment days). The median FR per day was 1,837 ml and the median hourly FR rate was 252 ml. TFC diminished in all patients at the end of CVVHDF treatment (average reduction 14.8 ± 9/kΩ), while all other hemodynamic parameters showed both increases and decreases. We found that the percentage TFC changes were closely and inversely related with those of FR (r = -0.68, P < 0.001); other hemodynamic parameters showed a moderate correlation with FR. The ICG device was helpful to promptly identify one patient who experienced hemodynamic instability and to prevent it.

Conclusion

TFC is a reliable and noninvasive method for evaluating the quantity of FR during CVVHDF. This parameter changed consistently with fluid subtraction and TFC measurements can guide the extent of FR. This compact ICG device provides safe and accurate readings and seems to be one of the best options for evaluation of basic hemodynamic parameters and TFC during hemodiafiltration.