Increased postdialysis systolic blood pressure is associated with extracellular overhydration in hemodialysis outpatients
2014; Elsevier BV; Volume: 87; Issue: 2 Linguagem: Inglês
10.1038/ki.2014.276
ISSN1523-1755
AutoresArkom Nongnuch, Neil Campbell, Edward P. Stern, Sally El‐Kateb, L Fuentes, Andrew Davenport,
Tópico(s)Hemodynamic Monitoring and Therapy
ResumoRecently, intradialytic hypertension was reported to be associated with increased mortality for hemodialysis patients. To determine whether volume status plays a role in dialysis-associated hypertension, we prospectively audited 531 patients that had volume assessments measured by multiple-frequency bioelectrical impedance during their midweek dialysis session. Mean pre- and postdialysis weights were 73.2 vs 71.7 kg, and systolic blood pressures (SBPs) 140.5 vs. 130.3mmHg, respectively. Patients were divided into groups based on a fall in SBP of 20mmHg or more (32%), an increased SBP of 10mmHg or more (18%), and a stable group (50%). There were no differences in patient demographics, dialysis prescriptions, predialysis weight, total body (TBW), and extracellular (ECW) and intracellular water (ICW). However, the change in weight was significantly less in the increased blood pressure group (1.01kg vs. stable 1.65, and 1.7 hypotensive). The ratio of ECW to TBW was significantly higher in the increased blood pressure group, particularly post dialysis (39.1 vs. stable 38.7% and fall in blood pressure group 38.7%). ECW overhydration was significantly greater in the increased blood pressure group post dialysis (0.7 (0.17 to 1.1) vs. stable 0.39 (-0.2 to 0.95) and fall in blood pressure group 0.38 (-0.19 to 0.86) liter). We found that patients who had increased blood pressure post dialysis had greater hydration status, particularly ECW. Thus, patients who increase their blood pressure post dialysis should have review of target weight, consideration of lowering the post-dialysis weight, and may benefit from increasing dialysis session time or frequency. Recently, intradialytic hypertension was reported to be associated with increased mortality for hemodialysis patients. To determine whether volume status plays a role in dialysis-associated hypertension, we prospectively audited 531 patients that had volume assessments measured by multiple-frequency bioelectrical impedance during their midweek dialysis session. Mean pre- and postdialysis weights were 73.2 vs 71.7 kg, and systolic blood pressures (SBPs) 140.5 vs. 130.3mmHg, respectively. Patients were divided into groups based on a fall in SBP of 20mmHg or more (32%), an increased SBP of 10mmHg or more (18%), and a stable group (50%). There were no differences in patient demographics, dialysis prescriptions, predialysis weight, total body (TBW), and extracellular (ECW) and intracellular water (ICW). However, the change in weight was significantly less in the increased blood pressure group (1.01kg vs. stable 1.65, and 1.7 hypotensive). The ratio of ECW to TBW was significantly higher in the increased blood pressure group, particularly post dialysis (39.1 vs. stable 38.7% and fall in blood pressure group 38.7%). ECW overhydration was significantly greater in the increased blood pressure group post dialysis (0.7 (0.17 to 1.1) vs. stable 0.39 (-0.2 to 0.95) and fall in blood pressure group 0.38 (-0.19 to 0.86) liter). We found that patients who had increased blood pressure post dialysis had greater hydration status, particularly ECW. Thus, patients who increase their blood pressure post dialysis should have review of target weight, consideration of lowering the post-dialysis weight, and may benefit from increasing dialysis session time or frequency. Although a fall in blood pressure remains the commonest complication associated with routine outpatient hemodialysis treatments,1.Caplin B. Kumar S. Davenport A. Patients’ perspective of haemodialysis-associated symptoms.Nephrol Dial Transplant. 2011; 26: 2656-2663Crossref PubMed Scopus (121) Google Scholar,2.Davenport A. Intradialytic complications during haemodialysis.Hemodial Int. 2006; 10: 162-167Crossref PubMed Scopus (128) Google Scholar a minority of patients become hypertensive either toward or at the end of dialysis or shortly after completion of the dialysis session. Although a recognized complication of hemodialysis,3.Levin N.W. Intradialytic hypertension: I.Semin Dial. 1993; 6: 370-371Crossref Scopus (10) Google Scholar,4.Fellner S.K. Intradialytic hypertension: II.Semin Dial. 1993; 6: 371-373Crossref Scopus (23) Google Scholar it is only relatively recently that intradialytic hypertension has been recognized as an independent risk factor for both more frequent hospital admissions and also decreased patient survival.5.Inrig J.K. Oddone E.Z. Hasselblad V. et al.Association of intradialytic blood pressure changes with hospitalization and mortality rates in prevalent ESRD patients.Kidney Int. 2007; 71: 454-461Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar,6.Inrig J.K. Patel U.D. Toto R. et al.Association of blood pressure increases during haemodialysis with 2-year mortality in incident haemodialysis patients: a secondary analysis of the Dialysis Morbidity and Mortality Wave 2 Study.Am J Kid Dis. 2009; 54: 881-890Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar The definition of intradialytic hypertension has varied over the years,3.Levin N.W. Intradialytic hypertension: I.Semin Dial. 1993; 6: 370-371Crossref Scopus (10) Google Scholar, 4.Fellner S.K. Intradialytic hypertension: II.Semin Dial. 1993; 6: 371-373Crossref Scopus (23) Google Scholar, 5.Inrig J.K. Oddone E.Z. Hasselblad V. et al.Association of intradialytic blood pressure changes with hospitalization and mortality rates in prevalent ESRD patients.Kidney Int. 2007; 71: 454-461Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar, 6.Inrig J.K. Patel U.D. Toto R. et al.Association of blood pressure increases during haemodialysis with 2-year mortality in incident haemodialysis patients: a secondary analysis of the Dialysis Morbidity and Mortality Wave 2 Study.Am J Kid Dis. 2009; 54: 881-890Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar, 7.Mees D. Rise in blood pressure during hemodialysis-ultrafiltration: a "paradoxical" phenomenon?.Int J Artif Organs. 1996; 19: 569-570PubMed Google Scholar but most clinical studies now report intradialytic hypertension as an increase in systolic blood pressure (SBP) during dialysis of greater than 10mmHg above the predialysis blood pressure measurement.5.Inrig J.K. Oddone E.Z. Hasselblad V. et al.Association of intradialytic blood pressure changes with hospitalization and mortality rates in prevalent ESRD patients.Kidney Int. 2007; 71: 454-461Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar,6.Inrig J.K. Patel U.D. Toto R. et al.Association of blood pressure increases during haemodialysis with 2-year mortality in incident haemodialysis patients: a secondary analysis of the Dialysis Morbidity and Mortality Wave 2 Study.Am J Kid Dis. 2009; 54: 881-890Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar Intradialytic hypertension has been reported to occur in about 21% of hemodialysis sessions, affecting more than 15% of patients,8.Van Buren P.N. Kim C. Toto R.D. et al.The prevalence of persistent intradialytic hypertension in a hemodialysis population with extended follow-up.Int J Artif Organs. 2012; 35: 1031-1038Crossref PubMed Scopus (31) Google Scholar and it is more frequently reported in older patients, those prescribed more antihypertensive medications, and those with lower serum creatinine.9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar Although intravascular volume is typically reduced during dialysis, changes in relative blood volume do not necessarily closely mirror changes in blood pressure,10.Booth J. Pinney J. Davenport A. Do changes in relative blood volume monitoring correlate to hemodialysis-associated hypotension?.Nephron Clin Pract. 2011; 117: c179-c183Crossref PubMed Scopus (61) Google Scholar and this has led to the hypothesis that intradialytic hypertension is more likely to be due to changes in vascular tone.11.Inrig J.K. Van Buren P. Kim C. et al.Probing the mechanisms of intradialytic hypertension: a pilot study targeting endothelial cell dysfunction.Clin J Am Soc Nephrol. 2012; 7: 1300-1309Crossref PubMed Scopus (53) Google Scholar The cause of intradialytic hypertension remains to be determined, with different authors speculating on increased renin and angiotensin release and sympathetic nervous system activation in response to ultrafiltration, elimination of antihypertensive medications in patients with established hypertension, increased viscosity and hematocrit following ultrafiltration, and high dialysate calcium concentrations.3.Levin N.W. Intradialytic hypertension: I.Semin Dial. 1993; 6: 370-371Crossref Scopus (10) Google Scholar,4.Fellner S.K. Intradialytic hypertension: II.Semin Dial. 1993; 6: 371-373Crossref Scopus (23) Google Scholar However, as there is a link between sodium balance and hypertension in hemodialysis patients,12.Shah A. Davenport A. Does a reduction in dialysate sodium improve blood pressure control in haemodialysis patients?.Nephrology (Carlton). 2012; 17: 358-363Crossref PubMed Scopus (30) Google Scholar,13.Davenport A. Audit of the effect of dialysate sodium concentration on inter-dialytic weight gains and blood pressure control in chronic haemodialysis patients.Nephron Clin Pract. 2006; 104: c120-c125Crossref PubMed Scopus (54) Google Scholar we speculated that patients with intradialytic hypertension could also potentially have an expanded extracellular volume to account for the rise in blood pressure during dialysis. We therefore reviewed the dialysis records of 531 patients who had volume assessments measured by multiple-frequency bioelectrical impedance to determine whether volume status had a role in dialysis-associated hypertension. Multifrequency bioelectrical impedance assessments were made on 531 stable adult patients attending for their midweek hemodialysis session; the mean age was 60.3±16.5 years, 62.0% were male, 37.3% were diabetic, 42.2% were Caucasoid, and the median dialysis vintage was 42.0 (23.7–48.5) months. Predialysis weight was 73.2±18.0kg, and postdialysis weight was 71.7±17.7kg. Predialysis SBP was 140.5±26.5mmHg with a diastolic blood pressure of 71.7±17.7mmHg, and postdialysis systolic pressure was 130.3±26.3mmHg with a diastolic blood pressure of 71.8±15.2mmHg. Predialysis hemoglobin was 112.6±15.2g/l, median glucose was 6.2 (5.2–8.3)mmol/l, serum albumin was 38.6±6.2g/l, and median C-reactive protein was 5 (2–12)mg/l. A total of 67 patients were not included in the audit as bioimpedance was not performed, because 14 patients had pacemakers/defibrillators, 15 were unable to stand owing to amputations or active foot ulceration, 12 were recent starters, 6 had recent hospital in-patient stays, and the remaining 20 patients had a variety of metallic prosthetic implants—hips and knees—or were unable to stand. As such bioimpedance measurements were made on 89% of patients attending for their midweek dialysis session. Patients were divided into three groups, those in whom the blood pressure decreased during dialysis by ≥20mmHg,14.Kooman J. Basci A. Pizzarelli F. et al.EBPG guideline on haemodynamic instability.Nephrol Dial Transplant. 2007; 22: ii22-ii44PubMed Google Scholar n=171 (32.2%), those in whom the SBP increased by ≥10mmHg,5.Inrig J.K. Oddone E.Z. Hasselblad V. et al.Association of intradialytic blood pressure changes with hospitalization and mortality rates in prevalent ESRD patients.Kidney Int. 2007; 71: 454-461Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar n=96 (18.1%), and 264 patients (49.7%) in whom the SBP did not meet the definitions of intradialytic hypotension or hypertension, from here on termed the ‘stable’ group (Supplementary Figure online). These three groups did not differ in demographics, or cardiac history and medications (Supplementary Table S1 online), although those with a fall in blood pressure with dialysis were of an older dialysis vintage (46 (15–74) months) compared with both those with ‘stable’ (27 (9–64) months) and those with an increase in SBP post dialysis (23 (5–63.6) months), P<0.05 (Supplementary Table S1 online); in addition, the ‘stable’ blood pressure group had fewer diabetics (30.7%) compared with the fall in SBP (45%) group and with the increased blood pressure group (41.7%). There were no differences in dialysis prescription (Supplementary Table S2 online). Download .jpg (.04 MB) Help with files Supplementary Figure 1 Download .jpg (.04 MB) Help with files Supplementary Figure 2 A total of 17 nursing interventions were recorded during the dialysis sessions; 10 patients had their ultrafiltration rate reduced or stopped (six in the fall in blood pressure group and four in the stable group), and seven patients were given a bolus of intravenous fluid (two in the fall in blood pressure group and four in the stable group); the mean SBP for these patients was 111.2±10.4mmHg. Predialysis hemoglobin and serum biochemistries did not differ between the groups, nor did dialysate composition or dialysis modality (Supplementary Table S2 online). Similarly, there was no difference in the dialysate to serum sodium gradient, and also when corrected for glucose effect, or between the preserum and postserum sodium (Supplementary Table S2 online). Urea reduction ratios were marginally, but statistically significantly, greater in the stable cohort compared with those who increased their blood pressure post dialysis, 74.8±7.2 vs. 71.4±8.5% (P=0.032), but there was no difference between the group with a fall in SBP with dialysis, 74.4±7.1%. Postdialysis SBP differed between the groups (Figure 1). However, the predialysis SBP was higher in those patients who were documented to have a fall in SBP of ≥20mmHg, and it was lower in those who had a rise in SBP of ≥10mmHg (Figure 1). Predialysis diastolic blood pressures showed a similar pattern to predialysis SBP, but the difference after dialysis was limited to those groups that had decreased and increased blood pressures post dialysis, respectively (Figure 2).Figure 2Predialysis and postdialysis diastolic blood pressure according to groupings. Patients with a fall in systolic blood pressure ≥20mmHg between predialysis and postdialysis systolic blood pressure recordings (hypotensive), patients with an increase in systolic blood pressure of ≥10mmHg (hypertensive), and those patients with systolic blood pressure change <10mmHg to -19mmHg. Values expressed as mean±s.d., **P<0.01 vs. hypertensive group.View Large Image Figure ViewerDownload (PPT) Neither weight, total body water (TBW), nor extracellular water (ECW) and intracellular water (ICW) differed between the groups before or after dialysis (Table 1). However, the change in absolute weight was less for the group in which blood pressure increased post dialysis (1.01±1.2 vs. stable 1.65±1.4, and 1.7±1.0 fall in blood pressure group, P<0.05), as was the percentage weight loss of 1.47±1.5 for the group in which blood pressure increased post dialysis (2.3±1.8 in the stable group and 2.3±1.5 in the fall in blood pressure group, respectively, P 0.05Male (%)59.161.464.6>0.05Caucasoid (%)43.939.446.9>0.05Medical history (%) Hypertension (%)80.780.780.2>0.05 IHD (%)15.822.319.8>0.05 Valvular disease (%)9.49.58.3>0.05 BP meds (%)52.647.757.3>0.05 Hemoglobin, g/l114.0±14.9113.0±15.8110±14.2>0.05 Albumin, g/l39.4±7.438.6±8.237.2±9.2>0.05 CRP, mg/l5.0 (2.0–11.0)5.0 (2.0–14.0)4.0 (2.0–14.0)>0.05 Sodium, mmol/l139.2±3.2138.7±8.4139.2±3.5>0.05 Glucose, mmol/l6.6 (5.2–8.8)5.9 (5.0–7.7)6.8 (5.4–9.1)>0.05 Weight before dialysis, kg74.1±18.273.1±17.572.1±18.1>0.05 Weight after dialysis, kg72.5±18.271.4±17.171.3±18.5>0.05 SBP before dialysis, mmHg152.6±25.1136.1±25.1130.7±25.1<0.001 SBP after dialysis, mmHg119.3±22.1130±24.7151.1±24.5 0.05 ECW before dialysis, l14.4±3.214.8±3.615.2±3.6>0.05 ICW before dialysis, l22.1±5.223.0±6.022.8±5.2>0.05 ECW/TBW before dialysis39.5±1.339.2±2.339.9±1.40.006 TBW after dialysis, l34.9±7.736.1±10.135.9±7.8>0.05 ECW after dialysis, l13.5±2.913.8±3.314.1±2.9>0.05 ICW after dialysis, l21.5±4.922.1±5.822.1±4.8>0.05 ECW/TBW after dialysis38.7±1.538.6±2.239.1±1.40.027Abbreviations: BP, blood pressure; CRP, C-reactive protein; ECW, extracellular water; ICW, intracellular water; IHD, ischemic heart disease; SBP, systolic blood pressure; TBW, total body water.Patients with a fall in systolic blood pressure ≥20mmHg between predialysis and postdialysis systolic blood pressure recordings (hypotensive), patients with an increase in systolic blood pressure of ≥10mmHg (hypertensive), and those patients with systolic blood pressure change of <10mmHg to -19mmHg (stable). Ischemic heart disease (myocardial infarction, coronary artery bypass surgery, or coronary artery stenting), valvular heart disease (valvular disease), peripheral vascular disease (PVD), cerebrovascular disease (CVD), and percentage of patients prescribed antihypertensive drugs (BP meds). Multifrequency bioelectrical impedance assessments. TBW, ECW, and ICW, all reported in liters. Values are expressed as mean ±s.d., median (interquartile range), or percentage. P-values between hypertensive and hypotensive groups. Open table in a new tab Download .jpg (.04 MB) Help with files Supplementary Figure 3Figure 4Postdialysis systolic blood pressure according to predialysis tertile of extracellular water (ECW) to total body water (TBW), analyzed by multivariable multilevel modeling, adjusted for predialysis systolic blood pressure of 129.5mmHg and for sex, age, and diabetes. ***P<0.001 vs. lowest tertile.View Large Image Figure ViewerDownload (PPT) Abbreviations: BP, blood pressure; CRP, C-reactive protein; ECW, extracellular water; ICW, intracellular water; IHD, ischemic heart disease; SBP, systolic blood pressure; TBW, total body water. Patients with a fall in systolic blood pressure ≥20mmHg between predialysis and postdialysis systolic blood pressure recordings (hypotensive), patients with an increase in systolic blood pressure of ≥10mmHg (hypertensive), and those patients with systolic blood pressure change of <10mmHg to -19mmHg (stable). Ischemic heart disease (myocardial infarction, coronary artery bypass surgery, or coronary artery stenting), valvular heart disease (valvular disease), peripheral vascular disease (PVD), cerebrovascular disease (CVD), and percentage of patients prescribed antihypertensive drugs (BP meds). Multifrequency bioelectrical impedance assessments. TBW, ECW, and ICW, all reported in liters. Values are expressed as mean ±s.d., median (interquartile range), or percentage. P-values between hypertensive and hypotensive groups. A fall in SBP remains the most common complication of routine outpatient hemodialysis treatments,2.Davenport A. Intradialytic complications during haemodialysis.Hemodial Int. 2006; 10: 162-167Crossref PubMed Scopus (128) Google Scholar and we observed a fall of 20mmHg or greater in 32.2% of our patients attending their midweek dialysis session. On the other hand, an increase in SBP of 10mmHg or greater was documented in 18.1% of dialysis sessions, in keeping with more recent previous reports.8.Van Buren P.N. Kim C. Toto R.D. et al.The prevalence of persistent intradialytic hypertension in a hemodialysis population with extended follow-up.Int J Artif Organs. 2012; 35: 1031-1038Crossref PubMed Scopus (31) Google Scholar,9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar Earlier reports on intradialytic hypertension suggested that it was more common in older patients and in those prescribed more antihypertensive medications.9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar We did not find any differences in age or the number of patients prescribed antihypertensive medications and the number of different antihypertensive drugs prescribed to patients. It has been suggested that, as activation of the renin–angiotensin system may have a role in intradialytic hypertension, angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may help prevent this condition.3.Levin N.W. Intradialytic hypertension: I.Semin Dial. 1993; 6: 370-371Crossref Scopus (10) Google Scholar,4.Fellner S.K. Intradialytic hypertension: II.Semin Dial. 1993; 6: 371-373Crossref Scopus (23) Google Scholar However, we found a similar number of patients prescribed ACEIs among the groups, and if anything more patients with increased blood pressure post dialysis were prescribed ARBs or ACEIs and ARBs than the stable blood pressure group. This would suggest that in our patient cohort, prescription of ACEIs/ARBs did not significantly affect intradialytic hypertension. Activation of the sympathetic nervous system has also been proposed as a cause of intradialytic hypertension,4.Fellner S.K. Intradialytic hypertension: II.Semin Dial. 1993; 6: 371-373Crossref Scopus (23) Google Scholar,9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar but we did not observe any differences between the groups in terms of the prescription of beta-blockers or central sympathetic nervous system blockers, such as moxonidine. Other reports have raised the possibility that high concentrations of calcium in dialysates could be associated with intradialytic hypertension.3.Levin N.W. Intradialytic hypertension: I.Semin Dial. 1993; 6: 370-371Crossref Scopus (10) Google Scholar,9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar However, we found no association with either dialysate electrolyte composition or temperature, or dialysis modality14.Kooman J. Basci A. Pizzarelli F. et al.EBPG guideline on haemodynamic instability.Nephrol Dial Transplant. 2007; 22: ii22-ii44PubMed Google Scholar and whether patients had an increase in blood pressure post dialysis. An increased dialysate to serum sodium concentration gradient has also been reported to lead to hypertension, but again we could find no difference in the dialysate to serum sodium gradient,15.Pinney J.H. Oates T. Davenport A. Haemodiafiltration does not reduce the frequency of intradialytic hypotensive episodes when compared to cooled high-flux haemodialysis.Nephron Clin Pract. 2011; 119: c138-c144Crossref PubMed Scopus (31) Google Scholar or differences in the predialysis to postdialysis serum sodium between the groups. In keeping with previous reports, we noted that those patients who had a fall in SBP of ≥20mmHg started dialysis with higher SBPs, and those who had a ≥10mmHg increase in postdialysis SBP had lower initial blood pressures.8.Van Buren P.N. Kim C. Toto R.D. et al.The prevalence of persistent intradialytic hypertension in a hemodialysis population with extended follow-up.Int J Artif Organs. 2012; 35: 1031-1038Crossref PubMed Scopus (31) Google Scholar,9.Inrigg J.K. Intradialytic hypertension: a less-recognized cardiovascular complication of haemodialysis.Am J Kidney Dis. 2010; 55: 580-589Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar However, other studies have reported that although patients with intradialytic hypertension had lower predialysis blood pressures, they had similar 24-h blood pressures compared with those with either intradialytic hypotension or stable intradialytic blood pressure.16.Van Buren P.N. Toto R. Inrig J.K. Interdialytic ambulatory blood pressure in patients with intradialytic hypertension.Curr Opin Nephrol Hypertens. 2012; 21: 15-23Crossref PubMed Scopus (15) Google Scholar This highlights the difficulties of assuming that predialysis blood pressure can be used as a guide to intradialytic blood pressure control, and developing clinical guidelines based on predialysis blood pressure measurements.17.Davenport A. Cox C. Thuraisingham R. Achieving blood pressure targets during dialysis improves control but increases intradialytic hypotension.Kidney Int. 2008; 73: 759-764Abstract Full Text Full Text PDF PubMed Scopus (165) Google Scholar Although TBW and both ICW and ECW volumes were similar between the groups, this was probably because of the large variation in patient size18.Davenport A. Differences in prescribed Kt/V and delivered haemodialysis dose—why obesity makes a difference to survival for haemodialysis patients when using a 'one size fits all' Kt/V target.Nephrol Dial Transplant. 2013; 28: iv219-iv223Crossref PubMed Scopus (41) Google Scholar and different ethnicities.19.Kumar S. Khosravi M. Maasart A. et al.The effects of racial differences in body composition and total body water measured by multifrequency bioelectrical impedance analysis affect delivered Kt/V dialysis dosing.Nephron Clin Pract. 2014; 124: 60-66Crossref Scopus (27) Google Scholar As water content of tissues, in particular fat and muscle, differs, we chose to compare patients using the ratio of ECW/TBW.20.Van der Kerkhof J. Hermans M. Beerenhout C. et al.Reference values for multifrequency bioimpedance analysis in dialysis patients.Blood Purif. 2004; 22: 301-306Crossref PubMed Scopus (56) Google Scholar Those patients who had a rise in blood pressure post dialysis had higher ECW/TBW before dialysis, had lower weight loss during dialysis, and higher ECW/TBW post dialysis, suggesting that these patients were more volume overloaded than patients who had either a fall in SBP or stable blood pressure during dialysis. As a raised ECW/TBW ratio can also be caused by inflammation and a loss in ICW, we looked at predialysis albumin and CRP concentrations, but found no differences. We estimated the relative ECW to ICW as recommended by the European Society of Parenteral Nutrition, and this showed that those patients who increased their postdialysis blood pressure had ECW overhydration both before and after dialysis compared with the other groups. As such our study would suggest that patients who had increased blood pressure post dialysis are most likely to be volume overloaded, and downward revision of their target weight should be considered. Our study does not exclude changes in the vascular response to volume overload.11.Inrig J.K. Van Buren P. Kim C. et al.Probing the mechanisms of intradialytic hypertension: a pilot study targeting endothelial cell dysfunction.Clin J Am Soc Nephrol. 2012; 7: 1300-1309Crossref PubMed Scopus (53) Google Scholar We only analyzed predialysis and postdialysis blood pressures rather than changes in intradialytic blood pressure. However, the number of patients requiring nursing interventions was modest at 3.2%, with only 1.3% of patients requiring intravenous fluids for treating symptomatically low blood pressure during dialysis. As such the risk of misclassifying patients between the groups was small. We chose to measure bioimpedance before and then after the midweek dialysis session, and, as patient weight gains and volume status changes during the course of the dialysis week, it would be interesting to serially follow up patients to determine whether they change the group according to differences in volume status. Our study has a number of limitations. First, we only included a single hemodialysis session for each patient, and a more robust approach would be to classify changes in blood pressure with hemodialysis over time. However, we did not have the serial bioimpedance data to perform this analysis. Blood pressure was recorded in the dialysis centers using integral blood pressure and stand-alone blood pressure machines. Although the stand-alone blood pressure machines are regularly serviced and calibrated, the integral blood pressure devices were calibrated by the dialysis machine manufacturer. We have internal audit data looking at the reliability of both integral and stand-alone blood pressure devices in our dialysis centers, and this does not show any systematic bias between the various devices. As our bioimpedance device passes electrical currents through the body, we were unable to perform bioimpedance measurements in all patients, excluding those with pacemakers, metallic implants, and those with amputations and active foot ulceration. Even so, with more than 80% of the dialysis population evaluated, we feel that our data are robust. Our study does support other reports that, after intradialytic hypotension, intradialytic hypertension is a relatively common complication of routine outpatient dialysis treatments. Patients with intradialytic hypertension have been reported to have an increased mortality risk,5.Inrig J.K. Oddone E.Z. Hasselblad V. et al.Association of intradialytic blood pressure changes with hospitalization and mortality rates in prevalent ESRD patients.Kidney Int. 2007; 71: 454-461Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar,6.Inrig J.K. Patel U.D. Toto R. et al.Association of blood pressure increases during haemodialysis with 2-year mortality in incident haemodialysis patients: a secondary analysis of the Dialysis Morbidity and Mortality Wave 2 Study.Am J Kid Dis. 2009; 54: 881-890Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar and our study would suggest that this increased risk of death is associated with persistent volume overload. As such patients with postdialysis hypertension should have their target weight reviewed and may benefit from longer or more frequent dialysis sessions. The bioimpedance records of 531 prevalent adult hemodialysis outpatients who had attended their routine midweek dialysis session were audited. Multifrequency bioelectrical impedance analysis measurements were made before and then approximately 20min after dialysis (InBody 720 Body Composition Analysis, Biospace, Seoul, South Korea)21.Davenport A. Negative dialysate to sodium gradient does not lead to intracellular volume expansion post haemodialysis.Int J Artif Organs. 2010; 33: 700-705PubMed Google Scholar using a direct segmental multifrequency bioelectrical impedance analysis method with tetrapolar 8-point tactile electrodes. A total of 30 impedance measurements were taken by using six frequencies (1–1000kHz) at each of five segments (right arm, left arm, trunk, right leg, and left leg), and reactance by 15 impedance measurements using three frequencies (5–250kHz) at each of the five segments.22.Fürstenberg A. Davenport A. Comparison of multifrequency bioelectrical impedance analysis and dual-energy X-ray absorptiometry assessments in outpatient haemodialysis patients.Am J Kidney Dis. 2010; 57: 123-129Abstract Full Text Full Text PDF PubMed Scopus (131) Google Scholar ECW volume excess or ECW overhydration was estimated according to the method recommended by the European Society for Parenteral and Enteral Nutrition.23.Kyle U.G. Bosaeus I. De Lorenzo A.D. et al.Composition of the ESPEN Working GroupBioelectrical impedance analysis—part I: review of principles and methods.Clin Nutr. 2004; 23: 1226-1243Abstract Full Text Full Text PDF PubMed Scopus (1820) Google Scholar Patients with cardiac pacemakers, implantable defibrillators, amputees, and those unable to stand on the bioimpedance machine were excluded from study. Similarly 18 patients who had either recently started on dialysis who had not achieved their clinically determined target weight or established hemodialysis patients recently discharged from hospital due to recent illness requiring emergency admission who had not re-established a stable target weight were excluded. All patients were dialyzed using Fresenius F4000H or 5000H dialysis machines (Fresenius, Bad Homburg, Germany), Braun Dialog+ (B. Braun, Melsungen, Germany) with integrated blood pressure monitoring, and polysulfone high-flux dialyzers (Nipro, Osaka, Japan),24.Vernon K. Peasegood J. Riddell A. et al.Dialyzers designed to increase internal filtration do not result in significantly increased platelet activation and thrombin generation.Nephron Clin Pract. 2011; 117: c403-c408Crossref PubMed Scopus (54) Google Scholar with ultrapure quality dialysis water at a modal temperature of 35°C and anticoagulated with a tinzaparin bolus (Leo Laboratories, Princes Risborough, UK).25.Davenport A. Low-molecular-weight heparin as an alternative anticoagulant to unfractionated heparin for routine outpatient haemodialysis treatments.Nephrology (Carlton). 2009; 14: 455-461Crossref PubMed Scopus (106) Google Scholar Delivered dialysate sodium was regularly checked by both flame photometry and ion electrophoresis methods.26.Sandhu E. Crawford C. Davenport A. Weight gains and increased blood pressure in outpatient hemodialysis patients due to change in acid dialysate concentrate supplier.Int J Artif Organs. 2012; 35: 642-647Crossref PubMed Scopus (29) Google Scholar Predialysis and postdialysis blood samples were measured using a standard laboratory autoanalyzer (Roche Integra, Roche Diagnostics, Lewes, UK), with an indirect ion-selective electrode technique for sodium, and predialysis serum sodium was also corrected for glucose interference.27.Davenport A. Interdialytic weight gain in diabetic haemodialysis patients and diabetic control as assessed by glycated haemoglobin.Nephron Clin Pract. 2009; 113: c33-c37Crossref PubMed Scopus (24) Google Scholar Serum albumin was determined by the bromcresol green method and hemoglobin by autoanalyzer (XE-2100 Sysmex, Kobe, Japan). Blood pressure was taken in a standardized manner both immediately before starting dialysis and after dialysis in the nonfistula arm while in the sitting position using the hemodialysis machine integrated electronic blood pressure monitor. In cases of dialysis machines without functioning integral blood pressure measuring devices, blood pressure was measured using a Dinamap (Dinamap Pro100, Critikon, Tampa, FL). Blood pressure devices were regularly serviced and calibrated by the medical physics department at the Royal Free Hospital. All patients received dietetic advice to reduce dietary sodium intake. Patients did not receive intravenous iron or erythropoietin-stimulating agents during their midweek dialysis session. Ethics approval for this retrospective audit fulfilled the UK National Health Service audit and clinical service development guidelines. Results are expressed as mean±s.d., or median and interquartile range, or percentage. Statistical analysis was by χ2-analysis, corrected for small numbers by Yates’ correction, Students’ t-test for parametric data, and the Mann–Whitney U-test for nonparametric data, with Bonferroni correction for multiple analyses where appropriate, and by analysis of variance or Kruskall–Wallis test with Tukey’s or Dunn’s post hoc correction, as appropriate, as well as by backward logistic regression analysis, excluding variables that were not statistically relevant unless they improved model fit. In addition, to analyze the effect of predialysis and postdialysis SBP, multivariable multilevel regression random intercept analysis was undertaken adjusted for age, sex, and diabetes. Statistical analysis used Graph Pad Prism version 6.0 (Graph Pad, San Diego, CA), SPSS version 20 (University Chicago, IL), and Stata version 10a (StataCorp, College Station, TX). Statistical significance was taken at or below the 5% level. We thank D Nitsch and B Caplin for statistical advice and statistical analysis. This work was funded by Royal Free Hospital. Figure S1. Scatter plot of pre and post dialysis systolic blood pressures for the 3 groups, patients with a fall in systolic blood pressure ≥20mmHg between pre and post dialysis systolic blood pressure recordings (hypotensive), patients with an increase in systolic blood pressure of ≥10mmHg (Hypertensive) and those patients with systolic blood pressure change of 20 mmHg, intradialytic hypertension (Hypertensive) systolic blood pressure rose by >10 mmHg, and those patients with no hypertension or hypotension (Stable). Table S2. Patients divided into 3 groups: intradialytic hypotension (Hypotensive) fall in systolic blood pressure >20 mmHg, intradialytic hypertension (Hypertensive) systolic blood pressure rose by >10 mmHg, and those patients with no hypertension or hypotension (Stable). Table S3. Sensitivity analysis comparing those patients who had an increase of systolic blood pressure of 10mmHg or greater compared to those patients who had an increase in systolic blood pressure of up to 9mmHg or a fall in systolic blood pressure post dialysis. Supplementary material is linked to the online version of the paper at http://www.nature.com/ki Download .doc (.08 MB) Help with doc files Supplementary Tables
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