LUNG DENSITY FOR ASSESSMENT OF HYDRATION STATUS IN HEMODIALYSIS-PATIENTS USING THE COMPUTED TOMOGRAPHIC DENSITOMETRY TECHNIQUE

The density of the lung reflects the total mass of fluid, air, and dry lung tissue per unit volume of the lung. Lung density can be measured by evaluation of attenuation of an electron beam with computed tomogr aphy (CT). This technique has been shown to be sufficiently reliable a nd sensitive to distinguish normal from abnormal lung water. The aim o f this study was to find out whether lung density properly reflects th e hydration status in hemodialysis patients in comparison with other s tandard methods. Fourteen hemodialysis patients, with an ultrafiltrati on ranging from 0.3 to 4.5 liters per session, underwent CT measuremen ts of lung density, ultrasonographic measurements of the the diameter of the inferior vena cava after quiet expiration (IVCe) and quiet insp iration (IVCi), and measurements of the hematocrit and plasma levels o f the biochemical hydration markers cyclic guanosine monophosphate (cG MP) and atrial natriuretic peptide (ANP). These measurements were perf ormed before and 3.5 to 4 hours after termination of dialysis. Quantit ative estimates of lung density were obtained within pixels with CT nu mbers ranging between -1000 and -100 Hounsfield Units (HU), and compar ed with normal data from 18 normal controls. In normal controls, the l ung density ranged from -800 to -730 HU. In hemodialysis patients, lun g density was significantly higher than normal before dialysis (-678 /- 96 HU, P < 0.01) and significantly decreased after dialysis (-706 /- 92 HU, P < 0.05), indicating a decrease in fluid content of the lun g. The density was normalized in 5 patients. A significant correlation was found between lung density and IVCe both before and after dialysi s (r = 0.8, P < 0.01 for both). Change in density was significantly co rrelated to amount of ultrafiltration (r = 0.67, P < 0.01) and percent change in blood volume (r = 0.63, P < 0.05), indicating that lung den sity is greatly affected by changes in the extracellular fluid volume. mainly the intravascular volume. In conclusion, lung water reflects t he hydration status in hemodialysis patients and can be monitored by m easuring the lung density by CT. Accordingly, normalization of lung de nsity can help to achieve a proper dry weight in these patients.