Lung density for assessment of hydration status in hemodialysis patients using the computed tomographic densitometry technique

Abstract

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 tomography (CT). This technique has been shown to be sufficiently reliable and sensitive to distinguish normal from abnormal lung water. The aim of this study was to find out whether lung density properly reflects the hydration status in hemodialysis patients in comparison with other standard methods. Fourteen hemodialysis patients, with an ultrafiltration ranging from 0.3 to 4.5 liters per session, underwent CT measurements of lung density, ultrasonographic measurements of the diameter of the inferior vena cava after quiet expiration (IVCe) and quiet inspiration (IVCi), and measurements of the hematocrit and plasma levels of the biochemical hydration markers cyclic guanosine monophosphate (cGMP) and atrial natriuretic peptide (ANP). These measurements were performed before and 3.5 to 4 hours after termination of dialysis. Quantitative estimates of lung density were obtained within pixels with CT numbers ranging between -1000 and -100 Hounsfield Units (HU), and compared with normal data from 18 normal controls. In normal controls, the lung density ranged from -800 to -730 HU. In hemodialysis patients, lung 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 lung. The density was normalized in 5 patients. A significant correlation was found between lung density and IVCe both before and after dialysis (r = 0.8, P < 0.01 for both). Change in density was significantly correlated 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 density is greatly affected by changes in the extracellular fluid volume, mainly the intravascular volume. In conclusion, lung water reflects the hydration status in hemodialysis patients and can be monitored by measuring the lung density by CT. Accordingly, normalization of lung density can help to achieve a proper dry weight in these patients.

Monitoring cardiovascular changes during hemodialysis in children

“…A number of new techniques have been introduced to determine the ideal or "true" postdialytic dry weight of dialysis patients. These include, among others, lung density assessment using dual X-ray and computerized tomographic densitometry [21,22], echography of the caval vein [4,23], continuous optical hemoglobin monitoring [24], conventional and vector analysis of bioimpedance [25], and the measurement of the basal thoracic impedance [21]. Continuous cardiovascular monitoring during dialytic fluid withdrawal is essential for better understanding and control of the adaptation process.…”

Disorders of Respiration and Sleep-Disordered Breathing in Patients with Chronic Renal Failure

“…Patients with CRF, even in the absence of cardiopulmonary symptoms, accumulate interstitial pulmonary fluid, which is removed by haemodialysis [26,27]. Thus, in the study of Wallin et al, despite normal gas exchange, central blood volume and cardiac output at the start of dialysis, extravascular lung water before HD was found increased by 33% compared to controls, while after HD there was an almost 20% decrease.…”

“…Increased lung density before dialysis was also demonstrated with CT densitometry. Lung density reflected changes in intravascular volume and significant reductions or even normalization of lung density could be seen after dialysis [27,28]. Decreases in lung density were paralleled by improvement in lung volumes [28].…”

Characterization of pulmonary microcirculation according to hemodynamic changes with computed tomography

“…Thin-section Computed tomography (CT) can visualize vessels with up to 300µm small diameter, and the background density of lung parenchyma represents vascular density with smaller diameter than 300µm. However, the background density can be easily affected by volume of air, interstitial thickness, and body fluid [1][2][3][4][5][6][7] . Microfocal angiography is an accurate method for evaluation of regional blood flow, but not applicable in clinical practice [8][9] .…”