THE USE OF INFERIOR VENA CAVA SONOGRAPHY AND BIOELECTRIC IMPEDANCE ANALYSIS FOR THE FOLLOW UP OF DRY WEIGHT

Dry.weight (DW), could be defined as the postHD weight where the patient is in a state of normohydration. We evaluated the clinical relevance of bioelectric impedance analysis (BIA) and inferior vena cava (IVC) sonography for the assessment of DW and we investigated the relationship between DW and hypertension. We studied 19 chronic HD patients (12M/7F; median age: 46, R [20-74]) in two consecutive studies. In study I, a formal examination was performed on all patients including a chest x-ray. BIA indexes (resistance; Rz, reactance; Xc, phase angle; PA) were measured three times (preHD, postHD, 150 mn after HD) by using a single frequency (50 kHz) current. IVC diameter was determined 120-150 mn after HD. In study II, 9 (4M/5F) hypertensive patients from first study were investigated. Their DW was reduced over a period of 4-8 week, by %3 if clinical hydration status was normal (n=6) and by %5 if clinically overt overhydration was present (n=3). After the reduction of dry weight these patients were reevaluated with BIA and IVC sonography. For obtaining normal references of BIA indexes, we performed BIA in 79 (35M /44F) healthy adults. In study I; the fluid removal during HD resulted in significant reduction in body weight (BW) and rise in all BIA indexes. The changes in BW and BIA indexes were significantly (p<0.05) correlated (Pearson's r values: Rz/h: ^0.685; Xc/h: -0.694; PA: -0.478, p=0.001 for all three variables). BIA measurements were significantly lower in clinically overhydrated patients than clinically normohydrated patients. IVC measurements were not different between the two groups. In study II, after DW reduction, both pre and postHD mean arterial pressure readings were significantly reduced. All BIA indexes increased significantly, and preHD measurements became similar with the control group. However IVC measurements didn 't differ significantly from the first measurements. BIA seems more useful than VCI measurements especially for the follow up of the dry weight. BIA analysis could provide an objective method for the follow up of dry weight changes over the time.