Role of Dialysis Sodium Gradient on Intradialytic Hypertension: An Observational Study
Authors: Movilli Ezio , Camerini Corrado , Gaggia Paola , Zubani Roberto , Feller Paolo , Poiatti Patrizia , Pola Alessandra , Carli Orsola , Valzorio Brunella , Cancarini Giovanni 
Published: November 2013

<b><i>Introduction:</i></b> The causes of intradialytic hypertension (IDHyper) are not well understood and this condition can complicate the clinical management of hemodialysis (HD) patients. <b><i>Aim:</i></b> To evaluate the potential role of intradialytic sodium gradient (NaG) on blood pressure values and IDHyper during HD. <b><i>Patients and Methods:</i></b> 206 prevalent HD patients on 3 times weekly HD treatment for at least 6 months (dialytic vintage 6-240 months) followed at our institution were studied. Mean age was 68 ± 14 years, 129 were men. For 2 consecutive months (24 HD sessions) after the start of observation, the following variables were evaluated in predialysis after the long interdialysis interval: pre-HD plasma sodium (pNa, mmol/l) and potassium (pK, mmol/l) concentrations (mean value of 8 determinations), pre- and post-HD systolic (SBP, mm Hg) and diastolic (DBP, mm Hg) blood pressure, dry body weight (dBW, kg), interdialytic weight gain (IDWG, kg), ultrafiltration rate (UFR, ml/kg/h), dialysis dose (Kt/V), protein catabolic rate (PCRn, g/kg/day), hemoglobin (Hb, g/dl). SBP, DBP, IDWG, UFR are the mean values of the 24 HD sessions. 76% of patients were on antihypertensive therapy, 171 patients were on bicarbonate HD, and 35 on HDF. Dialysate Na concentration was set at 140 mmol/l in all patients. Duration of HD and the blood and dialysate flow rate were kept constant during observation. <b><i>Statistical Analysis:</i></b> Data are expressed as mean ± SD; linear and multiple regression analysis and t test for unpaired data were employed. Significant differences were defined as p < 0.05. <b><i>Results:</i></b> Pre-HD pNa was 138.1 ± 2.3 mmol/l, pK 5.0 ± 0.4 mmol/l, dBW 67 ± 14 kg, IDWG 2.9 ± 0.8 kg, UFR 11.2 ± 3.7 ml/kg/h, Kt/V 1.43 ± 0.18, PCRn 1.13 ± 0.17 g/kg/day, and Hb 11.2 ± 0.8 g/dl. Pre- and post-HD SBP values were 139 ± 13 and 134 ± 12 mm Hg (p < 0.0001); pre- and post-HD DBP did not change significantly. A dialysis Na gradient (NaG) (dialysate Na - pre-HD pNa) was calculated, as well as the delta of SBP (&#x0394;SBP) (post-HD SBP - pre-HD SBP). IDHyper was defined as &#x0394;SBP >0. A significant direct correlation was found between NaG and &#x0394;SBP (p < 0.0001) and multiple regression analysis with &#x0394;SBP as dependent variable confirmed the strong correlation with NaG (p < 0.00001). According to &#x0394;SBP behavior, 171 patients (83%) had a decrease or no change in post-HD SBP (group 1; no IDHyper); 35 patients (17%) increased their post-HD SBP (group 2; IDHyper). NaG values were significantly greater in patients in group 2 (group 1: 1.5 ± 2.2 vs. group 2: 3.3 ± 2.5, p < 0.0001). <b><i>Conclusions:</i></b> This study shows that the intradialytic &#x0394;SBP is independently and strongly associated with the dialytic NaG. The more positive the NaG (net intradialytic Na gain), the more positive the &#x0394;SBP and IDHyper.