SP294HYDRATION STATUS ASSESSMENT IN CHRONIC KIDNEY DISEASE - COMPARISON OF DIFFERENT TECHNIQUES

Abstract

Introduction and Aims: Volume overload, even subclinical, is often present in chronic kidney disease (CKD) and, if left untreated, it leads to a poor control of hypertension and thus to a significant risk of cardiovascular disease. The accurate assessment of volume load is a daily challenge. The aim of our study was to determine the hydration status by using three different techniques: physical examination to assess edema, measurement of inferior vena cava (IVC) diameter by ultrasound and multifrequency bioelectrical impedance analysis (MF-BIA). Methods: During september-december 2014 we performed a prospective study. Overt edema of the lower limbs was detected through physical examination by two different physicians and further classified into mild, moderate and severe. On the day of the evaluation, a blood sample was drawn and the serum creatinine and sodium levels were determined. All the ultrasound measurements were performed by the same physician, different from the ones who evaluated the edema or who used the bioimpedance device. Body fluid distribution was assessed by MF-BIA using InBody S10 analyzer. MF-BIA estimated the extracellular water (ECW) to total body water (TBW) ratio, which represents edematous state if higher than 0.39. Patients were categorized into stages 1 to 5 according to CKD staging in the NKF-K/DOQI guidelines. Results: 62 patients were included (29F, 33M, mean age 59.6+/-14.5). Overt edema was present in 27 patients (43.5%): 12 had mild, 10 moderate and 5 severe edema. Incidence of overt edema was significantly higher in stage 5 CKD (56%) compared to stages 1-4 (44%, p=0.03). The IVC diameter in patients without overt edema was significantly lower than the IVC diameter in patients with edema (17.1+/-2 mm vs 21.2 +/-3.5 mm, p<0.01). ECW/TBW measured by MF-BIA identified 38 patients (61.3%) with volume overload. Patients with overt edema had ECW/TBW significantly higher than those without edema (0.411+0.016 vs 0.389+/-0.008, p<0.001). Subjects with mild overt edema had ECW/TBW significantly lower compared with those with moderate and severe edema (0.398+/-0.011 vs 0.419+/-0.013, respectively 0.426+/-0.010, p<0.001). Out of the 35 patients without overt edema, 12 (34%) were diagnosed with subclinical edema according to MF-BIA: 9 had mild volume overload, 3 had important volume overload (ECW/TBW>0.4). The IVC diameter in patients with normal ECW/TBW was significantly lower compared with patients with increased ECW/TBW (16.9+/-2.4 mm vs 20.2+/-3.4 mm, p<0.001). Incidence of poor controlled hypertension was higher in patients with volume overload. From the 27 patients with overt edema, 23 (85%) had high blood pressure compared with 8 (23%) from the 35 patients without edema ( p<0.001). It was found a positive, but weak, correlation between systolic blood pressure and IVC diameter (Pearson coefficient 0.266, p=0.03), respectively ECW (Pearson coefficient 0.253, p=0.04). No difference was found regarding sodium levels between patients with volume overload and those with normal volume status. Conclusions: Our study proves that evaluation of hydration status by MF-BIA is a reliable measure of fluid status in CKD. Subclinical edema is often present in CKD, before its detection by physical exam. Incidence of poor controlled hypertension is higher in patients with volume overload. An isolated systolic arterial hypertension, an IVC diameter higher than 20 mm or an ECW/TBW ratio higher than 0.39 must raise awareness regarding a possible fluid overload requiring prompt management.