Abstract
Controlling blood pressure in hemodialysis patients is crucial but not always easy. The most common blood pressure measurement method is peri-dialysis measurement, but due to interdialytic blood pressure fluctuations, we are unsure if it is the proper way for evaluating blood pressure. Some studies have shown the superiority of 24-h ambulatory blood pressure monitoring over peri-dialysis blood pressure measurement. We aimed to compare the consistency of these methods in determining hypertension among hemodialysis patients. We studied 50 patients (mean age: 55.8 years) on regular hemodialysis in Imam Khomeini University Hospital, Tehran, Iran. Peri-dialysis blood pressure and interdialytic 24-h ambulatory blood pressure monitoring were recorded for each patient. Patients’ demographic data and peri-dialysis weight were recorded too. All data were analyzed using the PASW Statistics 18.0, SPSS Inc. (Chicago, IL). There was a significant difference between pre-dialysis mean systolic blood pressure (146.1 ± 23.3 mmHg) and mean systolic blood pressure recorded by ambulatory blood pressure monitoring (135.3 ± 19.3 mmHg) (p = 0.001). There was also a significant difference between pre-dialysis mean diastolic blood pressure (83 ± 14 mmHg) and mean diastolic blood pressure recorded by ambulatory blood pressure monitoring (77.3 ± 10 mmHg) (p = 0.003). But the frequencies of hypertension measured with both methods were significantly consistent and the Kappa agreement coefficient was 0.525 (p = 0.001). Considering ambulatory blood pressure monitoring as the gold standard for blood pressure measurement, our recommendation for the best cutoff point to diagnose hypertension, with the highest sensitivity and specificity would be 135/80 mmHg for pre-dialysis blood pressure and 115/70 mmHg for post-dialysis blood pressure.
Introduction
Hypertension (HTN) is one of the traditional risk factors for cardiovascular diseases. Especially because of its direct relation with left ventricular hypertrophy, HTN has a major role in developing cardiovascular morbidity and mortality in hemodialysis patients.Citation1,Citation2
The mortality of patients undergoing hemodialysis is 20% in the first year and 70% after 5 years and cardiovascular diseases are the major cause for this mortality.Citation3,Citation4 Thus, controlling blood pressure (BP) in hemodialysis centers is fundamental in patients’ treatment.Citation1
Managing HTN in hemodialysis patients is a challenge for nephrologists. Because of the interdialytic BP changes and lack of standard global criteria for definition and management of HTN in hemodialysis patients, management of HTN in these patients is almost confusing.Citation5
The most common BP measurement method is measuring BP before and after dialysis, but due to interdialytic BP fluctuations and the extent of accuracy and reproducibility of this method, many doubts that this would be the proper way for evaluating BP in hemodialysis patients.Citation5,Citation6 Some studies comparing Ambulatory BP Monitoring (ABPM) and peri-dialysis BP measurement have shown that pre-dialysis exam estimates both systolic and diastolic BPs higher than ABPM.Citation6–8 A 24-h ABPM can detect nighttime HTN and nighttime HTN is a stronger predictor of cardiovascular events compared to daytime.Citation9 Perloff et al.Citation10 showed that ABPM can predict cardiovascular events in hypertensive patients better than measuring BP in the clinic. This superiority was later proved in other studies which evaluated general population, treated and untreated hypertensive patients, refractory HTN, the patients with isolated systolic HTN, and the elderly.Citation11,Citation12
Ambulatory BP Monitoring interpretation is done by measuring the average of repeated BP measurements and this would be a better representative of patient’s BP. The ABPM technique can analyze the amplitude, periodicity, time to peak, and trough of BP.Citation11,Citation13,Citation14 Unlike clinic BP monitoring, ABPM makes it possible to observe the dipping status, morning surge, BP variability and duration of drug effects.Citation13 Also the sleep–awake cycle can only be observed using ABPM.Citation11,Citation15 Patients fall into four groups according to their day–night BP variationCitation15 ().
Table 1. Categorization of patients according to dipping phenomenon (15).
Some studies show that being a non-dipper and having a pulse pressure >53 mmHg are independent risk factors of cardiovascular events.Citation16,Citation17
The present situation of evaluating BP in hemodialysis patients by peri-dialysis measurement in most of the countries including Iran, may provide a quality sense from BP, but is unable to represent patients’ interdialytic BP.Citation18
Accurate diagnosis of HTN as a cardiovascular risk will enable us in more effective patient management and reducing future morbidity and mortality. This study aims to compare two methods of BP measurement in hemodialysis patients and evaluate their agreement.
Patients and methods
In this cross-sectional study, 50 patients on regular hemodialysis in Imam Khomeini University Hospital, Tehran, Iran were studied. The inclusion criteria were age of 18 years or more and having been on regular hemodialysis for at least 3 months. The exclusion criteria were pregnancy, having diabetes, dementia, and severe cardiac or hepatic failure.
This study was approved by committee of research ethics of Nephrology Research Center of Tehran University of Medical Sciences. The patients gave their written informed consent before entering the study.
Clinical history and demographic information were recorded on separate forms. A trained nurse measured and recorded each patient’s BP and weight before and after dialysis. Peri-dialysis BP was measured using digital Omron® sphygmomanometer made by Omron® Health Care (Kyoto, Japan) under the following conditions: (1) The patient had reached to the dialysis ward at least 30 min earlier and (2) had rested on the dialysis bed for at least 5 min.
For evaluating the agreement of the two devices, the pre-dialysis BP was measured by both Omron® and ABPM device with an interval of 5 min. After the dialysis session, the patients were referred to measure their BP for the next 24 h. The ABPM device was Ambulo™ 2400 made by Tiba Medical Inc. (Portland, OR) and the same trained nurse set the device for every patient. Ambulatory BP was recorded every 15 min during the day (7 a.m.–11 p.m.) and every 30 min during the night (11 p.m.–7 a.m.). All data were recorded in separate sheets, stratified by Microsoft Access Software, and analyzed using the PASW Statistics 18.0, SPSS Inc. (Chicago, IL).
Results
Fifty patients were evaluated in this study. Demographic data and characteristics of the patients are presented in . Most of the patients had a BMI between 19 and 25 (). shows patients’ BP measured before and after a dialysis session and shows their 24-h ABPM. There was a significant difference between pre-dialysis mean systolic BP and mean systolic BP measured by ABPM (p = 0.001). There was also a significant difference between pre-dialysis mean diastolic BP and ABPM mean diastolic BP (p = 0.003).
Table 2. Patients characteristics.
Table 3. BMI of the patients.
Table 4. Patients’ BP measured before and after a dialysis session.
Table 5. The results of 24-h ABPM of the patients.
On the basis of patients’ pre-dialysis BP measurement and considering HTN as BP >140/90 mmHg, 62% of the patients were hypertensive. The post-dialysis measurement showed 28% of patients as hypertensive.
On the basis of patients’ 24-h ABPM and considering HTN as mean BP >130/80 mmHg, 66% of the patients were hypertensive and if we consider HTN as mean nighttime BP >120/70 mmHg, 74% of the patients were hypertensive.
According to the ABPM, the average of mean arterial pressure among patients was 96.7 ± 12.2 mmHg.
Patients’ status of dipping is shown in .
Table 6. Patients status of dipping.
Sixty percent of patients had a pulse pressure >53 mmHg and 40% had a pulse pressure ≤53 mmHg. The frequency of HTN did not have a significant difference between the dipper and non-dipper groups of patients. In fact, among the dippers, 33.3% were hypertensive, while among non-dippers, 47.2% were hypertensive (p = 0.4).
No significant relationship was detected between mean intradialytic weight loss and BP decrease. Our findings also showed that interdialytic weight gain and interdialytic increase in BP were not significantly related.
Considering ABPM as the gold standard for BP measurement, our recommendation for the best cutoff point to diagnose HTN with pre-dialysis BP, with the highest sensitivity and specificity would be 135/80 mmHg ( and ).
Table 7. Recommended cutoff point for systolic BP in pre-dialysis measurement, according to ABPM as gold standard.
Table 8. Recommended cutoff point for diastolic BP in pre-dialysis measurement, according to ABPM as gold standard.
Considering ABPM as the gold standard for BP measurement, our recommendation for the best cutoff point to diagnose HTN with post-dialysis BP, with the highest sensitivity and specificity would be 115/70 mmHg. Our recommendations of peri-dialysis cutoff points according to ABPM as gold standard are summarized in .
Table 9. Our recommendations for cutoff points for diagnosing HTN with peri-dialysis BP measurement.
Comparing two methods of pre-dialysis measurement and ABPM revealed that the frequencies of HTN measured with both methods were significantly consistent and the Kappa agreement coefficient calculated for them was 0.525 (p = 0.001).
compares the frequency of HTN in both methods of measurement.
Table 10. The frequency of HTN by each method of measurement.
According to , 7 (14%) of the patients were shown hypertensive in pre-dialysis measurement, while ABPM showed them as non-hypertensive. This phenomenon can be explained as white coat HTN. Also, 3 (6%) of the patients who have been shown as non-hypertensive in pre-dialysis measurement have been shown as hypertensive in ABPM. This can be explained as masked HTN (high blood pressure at home and normal blood pressure in the clinic).
Discussion
The prevalence of HTN among hemodialysis patients is 70–90% in most of the literature.Citation19 The study of Nemati et al.Citation20 on patients from five major cities of Iran, showed that considering a BP of 140/85 mmHg as HTN cutoff point, the prevalence of HTN among hemodialysis patients is 58% and 29% according to pre-dialysis and post-dialysis BP measurements, respectively. Considering a BP of 140/90 mmHg as HTN cutoff point, the prevalence of HTN in our study was 62% and 28% according to pre-dialysis and post-dialysis BP measurements, respectively. These values are similar to Nemati’s study, and a little lower than non-Iranian studies. In our study, we were able to compare different cutoff points for HTN and two different BP measurement methods. Reducing the cutoff point of HTN with pre-dialysis BP measurement to 135/80 mmHg will result in considering a higher percentage of our patients as hypertensive (66%) which is higher than Nemati’s study but nearer to non-Iranian ones. Also, if we consider the cutoff point of 130/80 mmHg with ABPM, which we have suggested in our study, 66% of patients will be hypertensive. More studies are required to verify these ratios and determine the prevalence of HTN among Iranian hemodialysis patients.
Hypertension due to white coat effect, which has a prevalence of ∼30%Citation11,Citation21 was observed only in 14% of our patients. Masked HTN which is reported to have a prevalence of 8–20% in general population,Citation22,Citation23 was observed in 3 (6%) of our patients, one of which was a smoker. Smoking is a risk factor for masked HTN and it is also different among patients according to age, gender, and obesity.Citation22 Regarding that only three patients showed masked hypertension, we are unable to compare various contributing factors between them and patients of other studies.
Some studies show that having a pulse pressure >53 mmHg is independent risk factor of cardiovascular events.Citation16,Citation17 Sixty percent of our patients had a pulse pressure >53 mmHg.
Similar studies have shown that interdialytic weight gain increases BPCitation24,Citation25 which seems reasonable because interdialytic volume overload can increase patient’s weight and BP. However, our findings failed to show such a relationship. To explain this fact we should note to three points: first, this relation has not been proven in previous studies on Iranian patients, as the study by Nemati et al. did not find a significant association between interdialytic weight gain and pre-dialysis HTN either. Second, most of the studies showing this relation have used ABPM for 44 h rather than 24 h. Our study used 24-h ABPM. And third, the little sample size limits us in generalizing the results and therefore, there might still be a relation that our study has not been able to prove because of its limited number of subjects. More studies are necessary to clarify this relationship.
Dipping phenomenon is reported to have a prevalence of ∼16–57% among different populationsCitation11,Citation26 and some studies show that the reproducibility of this phenomenon is questionable in chronic kidney disease and hemodialysis patients.Citation8,Citation11,Citation27,Citation28 In our study, 24% of the patients were dipper and 76% non-dipper, which agree with other studies.
In another study on chronic kidney disease patients, it was shown that nighttime blood pressure can better predict cardiovascular events than daytime blood pressure.Citation9 In our study, 74% of the patients had nighttime HTN.
Conion et al.Citation29 showed that systolic/diastolic BP measured before dialysis is related with mean 24-h systolic/diastolic BP and 4.7/3.7 mmHg higher than that. Our study confirmed this relationship too, but the pre-dialysis BP was only 10.8/5.6 higher than mean 24-h BP which is almost half of the difference reported in Conion’s study.
In their study on 70 patients, Agarwal et al. showed that comparing with ABPM standard for diagnosing HTN:
Pre-dialysis BP of >150/85 mmHg has >80% sensitivity.
Post-dialysis BP >130/75 mmHg has >80% sensitivity.
Pre-dialysis BP of >160/90 mmHg has >80% specificity.
Post-dialysis BP >140/80 mmHg has >80% specificity.Citation5
Our study’s ABPM and peri-dialysis BP measurement showed that:
Comparing with ABPM gold standard of 130/80:
Pre-dialysis BP of >135/80 mmHg can predict HTN with 80% sensitivity and near 70% specificity.
Post-dialysis BP of >115/70 mmHg can predict HTN with 75% sensitivity and near 70% specificity.
These results lead us to recommend the cutoff point of 135/80 mmHg for defining HTN in pre-dialysis measurement instead of the currently used cutoff point of 140/90 mmHg. Of course we recommend this finding to be confirmed by other Iranian studies too.
On the basis of our findings we recommend further studies on Iranian hemodialysis patients to:
Confirm the cutoff point for HTN diagnosis in pre-dialysis measurement.
Determine the prevalence of HTN according to ABPM.
Determine the prevalence of white coat HTN.
Determine the relation between interdialytic weight gain and BP rise.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
References
- Sarnak MJ, Levey AS, Schoolwerth AC, et al. Kidney disease as a risk factor for development of cardiovascular disease: a statement from the American Heart Association Councils on Kidney in Cardiovascular Disease, High Blood Pressure Research, Clinical Cardiology, and Epidemiology and Prevention. Hypertension. 2003;42(5):1050–1065
- Zoccali C, Mallamaci F, Tripepi G, et al. Prediction of left ventricular geometry by clinic, pre-dialysis and 24-h ambulatory BP monitoring in hemodialysis patients: CREED investigators. J Hypertens. 1999;17(12 Pt 1):1751–1758
- U.S. Renal Data System, USRDS 2005 Annual Data Report: Atlas of End-Stage Renal Disease in the United States, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD; 2005
- Rayner HC, Pisoni RL, Bommer J, et al. Mortality and hospitalization in hemodialysis patients in five European countries: results from the Dialysis Outcomes and Practice Patterns Study (DOPPS). Nephrol Dial Transplant. 2004;19(1):108–120
- Agarwal R, Lewis RR. Prediction of HTN in chronic hemodialysis patients. Kidney Int. 2001;60(5):1982–1989
- da Silva GV, de Barros S, Abensur H, Ortega KC, Mion D Jr. Home blood pressure monitoring in blood pressure control among hemodialysis patients: an open randomized clinical trial. Nephrol Dial Transplant. 2009;24(12):3805–3811
- Agarwal R, Peixoto AJ, Santos SF, Zoccali C. Pre- and postdialysis blood pressures are imprecise estimates of interdialytic ambulatory blood pressure. Clin J Am Soc Nephrol. 2006;1(3):389–398
- Peixoto AJ, Santos SF, Mendes RB, et al. Reproducibility of ambulatory blood pressure monitoring in hemodialysis patients. Am J Kidney Dis. 2000;36(5):983–990
- Dolan E, Stanton A, Thijs L, et al. Superiority of ambulatory over clinic blood pressure measurement in predicting mortality: the Dublin outcome study. Hypertension. 2005;46(1):156–161
- Perloff D, Sokolow M, Cowan R. The prognostic value of ambulatory blood pressures. JAMA. 1983;249(20):2792–2798
- Agarwal R, Peixoto AJ, Santos SF, Zoccali C. Out-of-office blood pressure monitoring in chronic kidney disease. Blood Press Monit. 2009;14(1):2–11
- Kikuya M, Ohkubo T, Asayama K, et al. Ambulatory blood pressure and 10-year risk of cardiovascular and noncardiovascular mortality: the Ohasama study. Hypertension. 2005;45(2):240–245
- Pickering TG, Shimbo D, Haas D. Ambulatory blood-pressure monitoring. N Engl J Med. 2006;354(22):2368–2374
- Rodby RA, Vonesh EF, Korbet SM. Blood pressures in hemodialysis and peritoneal dialysis using ambulatory blood pressure monitoring. Am J Kidney Dis. 1994;23(3):401–411
- O’Brien E, Sheridan J, O’Malley K. Dippers and non-dippers. Lancet. 1988;2(8607):397
- Ohkubo T, Hozawa A, Yamaguchi J, et al. Prognostic significance of the nocturnal decline in blood pressure in individuals with and without high 24-h blood pressure: the Ohasama study. J Hypertens. 2002;20(11):2183–2189
- Verdecchia P, Schillaci G, Borgioni C, Ciucci A, Pede S, Porcellati C. Ambulatory pulse pressure: a potent predictor of total cardiovascular risk in HTN. Hypertension. 1998;32(6):983–988
- Santos SF, Mendes RB, Santos CA, Dorigo D, Peixoto AJ. Profile of interdialytic blood pressure in hemodialysis patients. Am J Nephrol. 2003;23(2):96–105
- Agarwal R, Nissenson AR, Batlle D, Coyne DW, Trout JR, Warnock DG. Prevalence, treatment, and control of HTN in chronic hemodialysis patients in the United States. Am J Med. 2003;115(4):291–297
- Nemati E, Ghanbarpour F, Taheri S, Einollahi B. Prevalence of HTN among Iranian hemodialysis patients and associated risk factors: a nationwide multicenter study. Pak J Biol Sci. 2008;11(6):910–914
- Andersen MJ, Khawandi W, Agarwal R. Home blood pressure monitoring in CKD. Am J Kidney Dis. 2005;45(6):994–1001
- Bobrie G, Clerson P, Menard J, Postel-Vinay N, Chatellier G, Plouin PF. Masked HTN: a systematic review. J Hypertens. 2008;26(9):1715–1725
- Waeber B. What stands behind masked HTN? J Hypertens. 2008;26(9):1735–1737
- Agarwal R, Light RP. Arterial stiffness and interdialytic weight gain influence ambulatory blood pressure patterns in hemodialysis patients. Am J Physiol Renal Physiol. 2008;294(2):F303–F308
- Kelley K, Light RP, Agarwal R. Trended cosinor change model for analyzing hemodynamic rhythm patterns in hemodialysis patients. Hypertension. 2007;50(1):143–150
- Staessen JA, Bieniaszewski L, O’Brien E, et al. Nocturnal blood pressure fall on ambulatory monitoring in a large international database. Hypertension. 1997;29(1):30--39
- Elung-Jensen T, Strandgaard S, Kamper A-L. Longitudinal observations on circadian blood pressure variation in chronic kidney disease stages 3–5. Nephrol Dial Transplant. 2008;23(9):2873–2878
- Tripepi G, Fagugli RM, Dattolo P, et al. Prognostic value of 24-hour ambulatory blood pressure monitoring and of night/day ratio in nondiabetic, cardiovascular events-free hemodialysis patients. Kidney Int. 2005;68(3):1294–1302
- Conion PJ, Walshe JJ, Heinle SK, Minda S, Krucoff M, Schwab SJ. Predialysis systolic blood pressure correlates strongly with mean 24-hour systolic blood pressure and left ventricular mass in stable hemodialysis patients. J Am Soc Nephrol. 1996;7(12):2658–2663