Electrical impedance tomography to measure pulmonary perfusion: is the reproducibility high enough for clinical practice?

A possible clinical application of electrical impedance tomography (EIT) might be to monitor changes in the pulmonary circulation, provided the reproducibility of the EIT measurement is adequate. The purpose of this study was threefold: the intra- and inter-investigator variability of repeated measurements was investigated. Three different regions of interest (ROI) were analysed to assess the optimal ROI. Twenty-four healthy subjects and six patients were included. The Sheffield applied potential tomograph (DAS-01P, IBEES, Sheffield, UK) was used. Electrodes were attached by investigator A, and duplicate EIT measurements were performed. After detachment and 45 min of rest, the protocol was repeated by another investigator B, and afterwards by the initial investigator A. Three ROIs were analysed: whole circle, 'inner half circle' and contour. The mean difference in impedance changes between observers is presented in arbitrary units (AU) +/- SD. Finally, the influence of age, body composition and sex on the EIT result was examined. For the contour ROI, the mean difference for the intra-investigator situation was -1.44 x 10(-2) +/- 18.45 x 10(-2) AU (-0.7 +/- 9.0%), and was 5.46 x 10(-2) +/- 21.66 x 10(-2) AU (2.7 +/- 10.8%) for the inter-investigator situation. The coefficient of reproducibility of the intra- and inter-investigator reproducibility varied between 0.89 and 0.97 for all ROIs (P < 0.0001). There is a relation between impedance change and age (correlation coefficient r = -0.63, P < 0.01 for contour ROI), and between impedance change and body mass index (BMI) (r = -0.53, P < 0.05). We found a significant difference in mean impedance change between groups of males and females. In conclusion, EIT results are highly reproducible when performed by the same investigator as well as by two different investigators.

Hemodialysis (HD) versus peritoneal dialysis (PD): latent overhydration in PD patients?

Data on the difference in fluid status between hemodialysis (HD) and peritoneal dialysis (PD) patients are scarce. Bio-electrical impedance analysis (BIA) is able to detect total body water (TBW) and its distribution in intracellular (ICW) and extracellular water (ECW). Echographic determination of the diameter of the inferior caval vein (VCD) provides information about the intravascular space (IVS). Nineteen PD-patients and 20 HD-patients in stable clinical condition were studied. In HD-patients a significant decrease in VCD, mean arterial pressure (MAP), TBW and ECW was noted due to ultrafiltration. Both ratios of VCD to ICW/ECW and of VCD to ECW/TBW decreased. No significant differences were found in these variables between PD-patients and HD-patients before HD. In both patient groups the measured variables pointed towards overhydration and the increased ratios both of VCD to ICW/ECW and VCD to ECW/TBW towards the storage of surplus of fluid in the intravascular space. It can be concluded that both PD-patients and HD-patients before HD have a surplus of fluid in the extracellular compartment, predominantly stored in the intravascular space.

The effect of profiled hemodialysis on intradialytic hemodynamics when a proper sodium balance is applied.

BACKGROUND: Profiled hemodialysis (HD) has been claimed to ameliorate intradialytic complications such as hypotension. Frequently, these profiles are based on providing the patient with an accumulating sodium load. This increases the risk of interdialytic complications, such as hypertension and increased weight gain. The present study investigated the effect of profiled HD, without an accompanying sodium loading, on intradialytic hemodynamics in stable HD patients. METHODS: In eight stable HD patients a standard hemodialysis (S-HD) was compared to a decreasing Na(+)-profiled hemodialysis (Na-HD), and an ultrafiltration profiled hemodialysis (UF-HD). Care was taken to have the sodium balances similar during these sessions. The patients were monitored non-invasively during dialysis with respect to their cardiac performance by means of electrical impedance cardiography, their variation in blood volume by means of an on-line optical measurement, and their hydration state by means of body impedance analysis. RESULTS: Sodium balance and mean arterial sodium concentrations were similar in the three treatments. Intradialytic hemodynamics during UF-HD were similar to those of S-HD. However, Na-HD improved blood pressure preservation, remarkably without significant blood volume preservation, due to a better stroke volume preservation in the first hour of dialysis. CONCLUSION: Sodium-balanced, Na-profiled HD improves blood pressure preservation in stable HD patients without providing the patients with a sodium load. This effect is due to a better stroke volume preservation early in dialysis, without a significant reduction in blood volume decrease. UF-HD, as mono-therapy, has no beneficial effect on intradialytic hemodynamics in stable patients.

Epoprostenol-induced pulmonary vasodilatation in patients with pulmonary hypertension measured by electrical impedance tomography.

Electrical impedance tomography (EIT) has been proposed as a method to monitor dynamic changes in the pulmonary vascular bed. In this study we examined the validity of EIT in the measurement of pulmonary vasodilatation in eight patients with primary and secondary pulmonary hypertension when given the vasodilating agent epoprostenol (Flolan). Therefore, catheterization of the pulmonary artery was performed in the ICU and the cardiac output was measured by means of the Fick method. The pulmonary vascular resistance (PVR) and mean pulmonary arterial pressure (mPAP) were determined. Epoprostenol was given in increasing doses to test reversibility of pulmonary hypertension. The maximum test dose was 12 ng kg(-1) min(-1). During each step simultaneous EIT (DAS-01 P Portable Data Acquisition System, Sheffield, England) measurements were performed with the 16 electrodes equidistantly positioned in the third intercostal space. The maximal systolic impedance change, relative to end-diastole, deltaZperf, was chosen as a measure of pulmonary perfusion. The impedance change between baseline and highest tolerable epoprostenol concentration was compared with the change in PVR. The mean PVR (dyn s/cm5) decreased from 636 (+/-399) to 366 (+/-242); p < 0.01. DeltaZperf (in arbitrary units) for the whole patient group increased from 901 (+/-295) x 10(-3) to 1082 (+/-472) x 10(-3) (p<0.05). Only one patient showed a reduction in pulmonary artery pressure >20%, which is defined as significant vasodilatation. A strong relationship was found between the impedance changes and the change in PVR and mPAP in the patient with a significant vasodilatation on epoprostenol. From these results we conclude that EIT is a reliable method to measure blood volume changes due to pharmacologically induced vasodilatation in the pulmonary bed.