Nephrology Dialysis Transplantation 2007 22(Supplement 7):vii119-vii137; doi:10.1093/ndt/gfm333
© The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Factors which may influence cardiovascular disease in dialysis and transplant patients—blood pressure (Chapter 10)
Janice Harper1,
Alex Hodsman2,
Julie Gilg2,
David Ansell2 and
Andrew J. Williams3
1Royal Liverpool University Hospital, Liverpool, 2UK Renal Registry, Bristol and 3Morriston Hospital, Swansea
Correspondence and offprint requests to: Dr J Harper, Royal Liverpool University Hospital, Liverpool, UK. Email: janice.harper{at}rlbuht.nhs.uk
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Abstract
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Many renal units still fail to return blood pressure data to
the Renal Registry. In England, Northern Ireland and Wales,
the percentage of HD patients achieving the combined blood pressure
standard (<140/90 pre-dialysis) averages 43% (inter unit
range 16–60%) and post-dialysis (<130/80) average 48%
(range 22–66%). On average 27% (range 12–48%) of
PD patients achieve the standard of <130/80 and 26% of renal
transplant patients (range 16–40%).
Over the last 8 years there has been no significant change in systolic or diastolic blood pressure achievement.
Better comorbidity data returns are required by the Registry to perform blood pressure survival analyses.
Keywords: blood pressure; chronic kidney disease; dialysis; end stage renal disease; epidemiology; haemodialysis; peritoneal dialysis; registry; transplant
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Introduction
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International and UK blood pressure guidelines [
1,
2,
3,
4] recommend
a target blood pressure below 130/80 mmHg for patients with
chronic kidney disease (CKD), diabetes and established atherosclerosis.
The intention is to reduce cardiovascular complications and
progression to renal failure. So far, clinical trials involving
CKD patients have all been designed to assess low blood pressure
on renal progression as the primary endpoint. Cardiovascular
data from these trials are inconclusive and were reviewed in
some detail in last year's report. Blood pressure guidelines
take no account of epidemiological data that describe a U-shaped
relationship between baseline systolic blood pressure (SBP)
and 1 year mortality. Several reports show higher cardiovascular
mortality for haemodialysis patients with baseline pre- and
post-SBP <110 mmHg [
5,
6]. The UK Renal Registry has also
shown increased all-cause mortality at 1 year for incident haemodialysis
patients with baseline pre- and post-SBP <120 mmHg [
7]. This
raises concern that achieving lower blood pressure targets may
be detrimental for some dialysis patients. In 2006, two studies
of USA haemodialysis patients analysed the changing relationship
of blood pressure with mortality over several years. In the
first, hazard ratios for 3-year all-cause mortality for 56 338
incident patients were 2.5 for a baseline SBP <120 mmHg and
1.4 for baseline SBP 120–139 mmHg [
8]. Hazard ratios were
5.5 and 1.9, respectively when blood pressure variability was
included in the analysis. In the second study [
9] the hazard
ratio for 2 year all-cause mortality for 16 959 incident patients
was 1.7 for baseline SBP 110–119 mmHg. Interestingly,
the hazard ratio fell to 0.8 and 0.7 for the third and fourth
year, respectively. This is the first data to suggest that achieving
low blood pressure guidelines may be beneficial for dialysis
patients. In the same study a baseline SBP >170 mmHg was
only associated with increased all-cause mortality after 3 years.
Intuitively one would expect early deaths to affect patients
with established heart failure as hypertension precedes cardiac
failure by many years but neither study included comorbidity
data to delineate causal associations. Finally, data from the
Irbesartan Diabetic Nephropathy Trial [
10] showed improved renal
function and patient survival down to a SBP of 120 mmHg. Below
this, all-cause mortality increased (relative risk 1.25) for
both patients with and without pre-existing cardiovascular disease.
It will be difficult to prove whether low blood pressure may
be beneficial as poor health is a common confounding factor
in renal patients.
Last year less than one-third of patients on RRT in England and Wales achieved the blood pressure standard. However, the renal unit at York consistently achieves the best blood pressure results across all treatment modalities suggesting a rational approach to monitoring and therapy. Their patients are sent to a dietician for salt restriction initially. Then patients achieve dry weight by ultrafiltration or diuretics. Finally, antihypertensive medication is increased. Several publications in the last year support this strategy. An audit of 469 prevalent haemodialysis patients dialysing in seven different centres in the UK compared blood pressure control with varying dialysate sodium concentration [11]. All patients were advised to restrict salt intake to 5 g/day. Patients dialysing with sodium concentration 137–139 mmol/l had significantly lower pre- and post-SBP compared to those dialysed against 140 mmol/l. They also had lower interdialytic weight gains and were prescribed fewer antihypertensive drugs. Intradialytic hypotension correlated with age rather than dialysate sodium concentration. Similarly, a prospective study of 46 prevalent peritoneal dialysis patients in Turkey showed reduced salt intake and use of hypertonic solutions could maintain blood pressure below 130/85 mmHg over a 2-year period without antihypertensive medication [12]. Left ventricular hypertrophy was detected in only 8% of patients after 2 years. No patient lost residual renal function, ultrafiltration rate or dialysis adequacy during the study. The published evidence suggests salt and water balance is important to achieve blood pressure standards in dialysis patients.
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Blood pressure control
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The RA standards for control of hypertension were established
in August 2002:
Pre-haemodialysis blood pressure <140/90 mmHg.
Post-haemodialysis, peritoneal dialysis and renal transplant blood pressure <130/80 mmHg.
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Methods
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The Registry extracts quarterly blood pressure data electronically
from UK renal units. Data from Northern Ireland is included
for the first time this year. A single blood pressure reading
is extracted for each patient, the last BP recorded in quarter
four. If this is not available, the last BP from quarter three
is taken. Patients with no blood pressure data for the last
two quarters of 2005 are excluded. All patients with data are
included in the statistical analysis. Renal units with sparse
data for a given treatment modality (data for <50% of patients
or less than 20 patients) are omitted from renal unit level
results/figures. This approach is taken because small numbers
do not skew the data but do give unreliable estimates at the
renal unit level.
Each year a number of analyses are performed for the prevalent cohort on RRT (see Appendix at the end of the chapter for definition of prevalent cohort). This report presents data for 2005.
- Completeness of data is analysed at renal unit and national level for patients on haemodialysis, peritoneal dialysis and renal transplant recipients.
- Distributions of SBP, diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse pressure (PP) are defined for different treatment modalities. Maximum and minimum values are recorded and average values (mean and median), standard deviations and quartiles calculated. The data are presented as caterpillar plots showing median values and quartile ranges for renal units and nations. Data were also analysed by primary diagnosis. The number preceding each centre name indicates the percentage of patients with missing data at that centre.
- Where applicable, the percentage achieving Renal Association or other surrogate standard is also calculated and represented as caterpillar plots with 95% confidence intervals. For the percentage achieving standards,
2 testing is used to identify significant variability between centres and countries. Data are also analysed by primary diagnosis.
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Results
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Data returns
Poor returns (<50%) were obtained from 20 centres for HD
data, 31 centres for PD data and 35 centres for Tx data (
Table 10.1).
For most renal units, the problem is in transferring the clinical
data to their renal IT systems. For a few units, the data may
not be extracted from the correct database table within their
renal IT system, in which case they should contact the Registry
directly.
Overall the completeness of returns is improving but still remains
poor for transplant patients. Northern Ireland is omitted from
the figures for PD as data is available for only 12 patients.
Distribution of blood pressure by modality
Figures 10.1 and 10.2 show histograms of systolic and diastolic blood pressure, for pre-HD data. Blood pressure distributions for post-HD, PD and Tx are also approximately normal. Peaks above the curve indicate digit bias. Figure 10.3 shows systolic, diastolic and PP distributions for each modality (post-HD data is shown).
The median blood pressure pre-HD, post-HD, PD and Tx is 143/75,
128/69, 136/80 and 136/79 mmHg. Median PP for each group is
66, 59, 57 and 57 mmHg, respectively. The HD population has
the widest spread for blood pressure. Standard deviations (SBP/DBP)
pre-HD, post-HD, PD and Tx are 26/15, 25/14, 23/13 and 19/11,
respectively. This compares to 18/10 for a hypertensive population.
Last year in a single centre study of 317 prevalent HD patients,
the Registry showed blood pressure was significantly higher
at the start of the dialysis week. The wider blood pressure
distribution for HD may partially therefore reflect the random
timing of readings and influence of fluid overload.
Achievement of combined systolic and diastolic standard
Figures 10.4–10.7
show a wide variation between renal units achieving the combined blood pressure standard for each modality. In England, Northern Ireland and Wales, the percentage of HD patients achieving the standard pre-dialysis averages 43% (range over renal units 16–60%) and post-dialysis averages 48% (range 22–66%). Only 27% of PD patients (range 12–48%) and 26% of Tx patients (range 16–40%) achieve the standard. Chi squared testing indicates the variation between centres for HD and Tx is significant (P < 0.001) but not for PD. The variation between nations is also significant for HD and Tx (P 
0.008) but not for PD. The results are similar to last year and show control of hypertension remains inadequate across all treatment modalities but is significantly better in the HD population.
Systolic pressure alone
Figures 10.8–10.15 show wide variation between renal units
achieving the SBP standard. In England, Northern Ireland and
Wales, the percentage of HD patients achieving the standard
pre-dialysis averages 45% (range 19–62%) and post-dialysis
averages 51% (range 30–69%). On average 37% of PD patients
(range 12–59%) and 35% of Tx patients (range 24–55%)
achieve the standard. Chi squared testing indicates that the
variation between centres is significant for each treatment
modality (
P 0.003). The variation between nations is significant
for HD (
P 0.005) and Tx (
P = 0.029) but not for PD. Median
SBP for pre-HD, post-HD, PD and Tx is 143, 128, 136 and 136
mmHg, respectively.
Diastolic pressure alone
Figures 10.16–10.23 show wide variation between renal
units achieving the DBP standard. In England, Northern Ireland
and Wales, the percentage of HD patients achieving the standard
pre-dialysis averages 84% (range 69–96%) and post-dialysis
averages 77% (range 59–90%). On average 47% of PD patients
(range 27–61%) and 52% of Tx patients (range 30–74%)
achieve the standard. Chi squared testing indicates the variation
between centres for HD and Tx is significant (
P < 0.001)
but not for PD. The variation between nations is significant
for pre-HD and Tx (
P < 0.001) but not for post-HD or PD.
The median DBP for pre-HD, post-HD, PD and Tx is 75, 69, 80
and 79 mmHg, respectively. The median and lower quartile for
Tx DBP in Northern Ireland are both 70 mmHg. These values are
the same because there are only 81 observations and there is
evidence of digit bias. The data shows approximately half (50.6%)
of the observations recorded as exactly 70 mmHg. It is not clear
whether DBP is lowest post-HD because HD patients are older
(DBP falls after 60 years of age in the general population due
to increasing arterial stiffness) or because of the synergistic
effect between ultrafiltration and antihypertensive medication.
Mean arterial pressure
Figures 10.24–10.31 show wide variation between renal units achieving the desired MAP. MAP is calculated as DBP plus one-third of the PP. In England, Northern Ireland and Wales, the percentage of HD patients achieving the standard pre-dialysis averages 72% (range 43–89%) and post-dialysis averages 69% (range 43–80%). On average 48% of PD patients (range 32–68%) and 48% of Tx patients (range 34–74%) achieve the standard. Chi squared testing indicates that there is significant variation between centres for HD and Tx (P < 0.001). The variation is less marked for PD and is only of borderline significance (P = 0.052). The variation between nations is significant for pre-HD (P = 0.001) and Tx (P < 0.001) but not for post-HD or PD. The median MAP for pre-HD, post-HD, PD and Tx is 98, 89, 98 and 97 mmHg, respectively.
Pulse pressure
Figures 10.32–10.35 show the variation between renal units
for PP. PP is calculated as SBP minus DBP. The median PP for
pre-HD, post-HD, PD and Tx is 66, 59, 57 and 57 mmHg, respectively.
A high SBP accounts for the wider PP in HD patients pre-dialysis.
Blood pressure by primary diagnosis
Figures 10.36–10.43 show the variation in blood pressure
control by primary diagnosis for each treatment modality (post-HD
data is shown). Each year in the Registry Report, the data have
shown a similar pattern. SBP is highest in patients with macrovascular
disease (diabetes and renovascular disease), lower in patients
with glomerulonephritis and still lower in patients with tubular
disorders (PCKD and pyelonephritis).
Diabetics have the poorest blood pressure control of all the
diagnostic groups. While salt intake correlates with water intake
in non-diabetics, hyperglycaemia accounts for 50% of water intake
by diabetics on HD [
13] so may exacerbate hypertension. Blood
pressure control is significantly better on HD for all diagnostic
groups (
P < 0.0001 for all groups). Combining groups, the
percentage of patients achieving the BP standard on HD compared
to PD or Tx are 42%
vs 24% for macrovascular disease, 49%
vs 26% for glomerulonephritis and 53%
vs 26% for tubular disorders
(
P < 0.0001 for each comparison). This may be due to more
frequent monitoring and intervention in the HD population. If
so, nephrologists will need to devise more effective strategies
for monitoring blood pressure control in out-patient populations.
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Future direction
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The UK Renal Registry needs improved returns of comorbidity
data for each patient to perform adjusted survival analyses.
The question of whether achieving blood pressure standards is
beneficial for all patients receiving RRT can then be addressed.
The Registry requests that blood pressure data is logged every
session for HD patients so it can assess blood pressure variability
during the dialysis week.
Conflict of interest statement. None declared.
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Appendix
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Definition of the cohort for blood pressure analyses
Defining the cohort
- Analysis of prevalent patients.
- Prevalent patients are defined as all patients (including the incident cohort for that year) alive on 31st December for that year.
- Data set called Qtreat.
Qtreat
- Usual UKRR checking programs run on data set.
- Exclusion criteria applied to create data set Qtemp.
Exclusion criteria are:
- Patients who had died before the first day of the quarter.
- Patients on dialysis with a treatment centre of elsewhere (not identified).
- Patients receiving treatment at a non-Registry site.
- Patients with no date of starting ERF treatment.
- Patients who had been receiving treatment for a negative number of days i.e. incorrect starting dates or incorrect patient number on data sent in.
- Patients who had recovered before the start of the quarter.
- Where data on a patient are submitted from more than one centre, only data from the primary centre are used.
Qtemp
- Further exclusion criteria applied to Qtemp to create data set called Quarter.
Exclusion criteria are:
- Patients who have transferred out of the centre (qhcent) by the end of the quarter.
- Patients who had not yet transferred in to the centre (qhcent) by the end of the quarter.
- Patients who had recovered by the end of the quarter.
- Patients who had stopped treatment by the end of the quarter.
- Patients who had died by the end of the quarter.
- Patients who were lost to follow up by the end of the quarter.
Quarter
- Further exclusion criteria applied to quarter to create data set called Bichem.
Exclusion criteria are:
- Patients who had been on ERF treatment for 90 days at the end of the quarter.
- Patients who changed treatment modality in the quarter.
- Patients who transferred into the centre (qhcent) at some time in the quarter.
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References
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- Chobanian AV, Bakris GL, Black HR, et al. The seventh report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure: the JNC 7 report. JAMA (2003) 289:2560–2572.[Abstract/Free Full Text]
- National Kidney Foundation: K/DOQI clinical practice guidelines on hypertension and hypertensive agents in chronic kidney disease. Am J Kidney Dis (2004) 43:S1–S290.[Medline]
- European Society of Hypertension - European Society of Cardiology Guidelines Committee. 2003 European Society of Hypertension - European Society of Cardiology guidelines for the management of arterial hypertension. J Hypertens (2003) 21:1011–1053.[CrossRef][ISI][Medline]
- British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary Care Cardiovascular Society, Stroke Association. JBS 2: Joint British Societies’ guidelines on prevention of cardiovascular disease in clinical practice. Heart (2005) 91(Suppl. 5):v1–52.[Free Full Text]
- Zager PG, Nikolic J, Brown RH, et al. "U" curve association of blood pressure and mortality in hemodialysis patients. Kidney Int (1998) 54:561–569.[CrossRef][ISI][Medline]
- Port FK, Hulbert-Shearon TE, Wolfe RA, et al. Predialysis blood pressure and mortality risk in a national sample of maintenance hemodialysis patients. Am J Kidney Dis (1996) 33:507–517.
- UK Renal Registry Report 2003.
- Li Z, Lacson E, Lowrie EG, et al. The epidemiology of systolic blood pressure and death risk in hemodialysis patients. Am J Kidney Dis (2006) 48:606–615.[CrossRef][ISI][Medline]
- Stidley CA, Hunt WC, Tentori F, et al. Changing relationship of blood pressure with mortality over time among hemodialysis patients. J Am Soc Nephrol (2006) 17:513–520.[Abstract/Free Full Text]
- Pohl MA, Blumenthal S, Cordonnier DJ, et al. Independent and additive impact of blood pressure control and angiotensin II receptor blockade on renal outcomes in the Irbesartan Diabetic Nephropathy Trial: clinical implications and limitations. J Am Soc Nephrol (2005) 16:3027–3037.[Abstract/Free Full Text]
- 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–c125.[CrossRef][ISI][Medline]
- Asci G, Ozkahya M, Duman S, et al. Volume control associated with better cardiac function in long-term peritoneal dialysis patients. Perit Dial Int (2006) 26:85–88.[Abstract/Free Full Text]
- Ramdeen G, Tzamaloukas AH, Malhotra D, et al. Estimates of interdialytic sodium and water intake based on the balance principle: differences between non diabetic and diabetic subjects on hemodialysis. ASAIO J (1998) 44:812–817.[ISI][Medline]
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Abstract
Introduction
