Blood pressure variation and its correlates among patients undergoing hemodialysis for renal failure in Benin City, Nigeria.

BACKGROUND: Blood pressure (BP) variation is commonly encountered during hemodialysis (HD) procedure. Both intradialysis hypotension and hypertension have implications for outcome of treatment and overall morbidity and mortality of the patients.
METHODOLOGY: A retrospective study was carried out in the dialysis unit of a tertiary health institution in Benin City among patients who had HD for acute kidney injury (AKI) or chronic kidney disease (CKD) over a 3-year period. Data retrieved included age, gender, type of kidney disease, cause of kidney disease, systolic BP at onset of dialysis and at end of dialysis, and diastolic BP (DBP) at onset of and at end of dialysis.
RESULTS: Complete data were available for 217 patients. One hundred and seven patients (49.3%) had no significant change in BP; 30.9% had intradialytic hypertension (IDHT) while 19.8% had intradialytic hypotension (IDH). IDH was more prevalent among patients with diabetic kidney disease while IDHT was more common among patients with hypertensive nephropathy (P = 0.002). Female patients had higher mean BP parameters compared to male patients pre- and post-dialysis, but only changes in DBP were statistically significant (P = 0.029). Patients with CKD had higher mean BP parameters pre- and post-dialysis compared to patients with acute AKI and the differences were statistically significant.
CONCLUSION: Females had higher mean BP parameters than males. Patients with CKD had higher mean BP parameters compared with AKI patients. IDHT is a significant problem among patients on HD in our center. Measures to curtail this trend should be instituted with the goal of reducing morbidity and mortality.

Introduction

Hemodialysis (HD) is the commonly available modality of renal replacement therapy in Nigeria. It involves the use of an extracorporeal circuit to filter blood to remove excess water and metabolic waste products.

Blood pressure (BP) has a strong relationship with kidney disease. Hypertension may be a physical sign of kidney disease and can also be a cause of kidney disease. Hypotension, on the other hand, leads to decreased renal perfusion and may result in acute kidney injury (AKI). Chronic kidney disease (CKD) patients with concomitantly low or high systolic and diastolic BPs (DBPs) tend to have highest mortality rates.[1]

There is a strong association between BP and end-stage renal disease (ESRD). A good number of ESRD patients (about 84.1%) have hypertension.[2] The HD procedure is associated with fluctuations in BP which may manifest as hypotension or hypertension.

The decrease in blood volume which occurs at initiation of the dialysis procedure can result in hypotension. Intradialytic hypotension (IDH) refers to a fall in systolic BP >20 mmHg or a decrease in mean arterial BP >10 mmHg associated with symptoms[3] and occurs in 15%–25% of dialysis treatments.[4] Recurrent episodes of hypotension during HD, and hence organ hypoperfusion, may cause ischemic damage to the heart and brain manifesting as infarction, arrhythmia, stroke, or seizures.[5] The elderly and patients with compromised cardiovascular function are more prone to IDH due to the presence of structural and functional abnormalities of the heart and blood vessels.[6] In addition, hypotension, and its attendant hypoperfusion, increases the risk of vascular access thrombosis[7] and may also accelerate decline in residual renal function in ESRD patients.

Intradialytic hypertension (IDHT) refers to increased BP during or immediately after HD resulting in postdialysis hypertension.[8] The prevalence of IDHT is about 15% among patients on maintenance HD. Studies have shown that IDHT leads to poor clinical outcomes with affected patients having higher rates of hospitalization and death.[910] Several factors have been implicated in the pathogenesis of IDHT. These include hyperactivity of the sympathetic and renin angiotensin-aldosterone systems, volume overload, endothelial cell dysfunction, erythropoietin-stimulating agents, and removal of BP medications during the HD procedure.[8]

We sought to determine the pattern of BP variation during dialysis and associated correlates among patients who undergo dialysis in our center. This information may assist in patient management in terms of increasing our index of suspicion in certain patients which would bring about early preemptive action when necessary.

Methodology

This study was a retrospective survey that involved patients admitted to a HD unit in a tertiary hospital in Benin City, Nigeria. The period reviewed was January 2010 to December 2012. Permission was granted by the Research Ethics Committee of the hospital.

The case files of patients dialyzed in the unit during the period studied were retrieved. Patients who had <4 sessions of dialysis were excluded from the study to avoid confounding factors such as hypotension requiring inotropes and severe anemia in patients presenting late and very ill. Patients who failed to complete 4 h of dialysis in their 2nd, 3rd, and 4th dialysis sessions were also excluded from the study.

Variables obtained from the case files were age, gender, type of kidney disease, cause of kidney disease, systolic BP (SBP) at onset of dialysis and at end of dialysis, and DBP at onset of and at end of dialysis.

For each patient reviewed, we chose the 2nd, 3rd, and 4th sessions of dialysis for the study. The first dialysis session was avoided because the dialysis protocol of our unit is that the first dialysis session should run for 2 h.

Average predialysis SBP and DBP were determined by finding the average of the predialysis SBP and DBP of the three HD sessions studied while average postdialysis SBP and DBP were determined by finding the average of the postdialysis SBP and DBP of the three HD sessions studied.

BP variation during dialysis was determined by finding the difference between average pre-HD SBP and average post-HD SBP.

IDH was defined as a negative difference >20 mmHg between average pre-HD SBP and average post-HD SBP.[3]

IDHT was defined as a positive difference of ≥10 mmHg between average pre-HD SBP and average post-HD SBP.[8]

Patients whose change in average SBP pre- and post-dialysis did not meet the criteria for IDH or IDHT were considered not to have significant change in BP during dialysis.

Data obtained were analyzed using IBM SPSS software version 21 (IBM Inc., NY, USA). Data were presented as tables, pie charts, and bar charts. Continuous variables were expressed as means and standard deviations while categorical variables were expressed as frequencies and percentages. Means were compared using Student's t-test or analysis of variance where appropriate. Chi-square test was used to compare proportions. P < 0.05 was considered statistically significant.

Results

A total of 228 patients were dialyzed during the period of study, out of which 217 patients met the inclusion criteria and were recruited for the study. There were 139 males (64.1%) and 78 females (35.9%). Patients aged <40 years were 110 (50.7%) while the elderly (>60 years) were 42 (19.4%). Mean age of patients was 42.5 ± 17.4 years. Majority of the patients (84.8%) had CKD, and the most common cause of CKD was hypertension in 44 patients (25.7%) [Table 1].

Table 1

Baseline demographic and clinical characteristics of the study population (n=217)

Parameter	Frequency (%)/mean±SD
Mean age (years)	42.5±17.4
Age groups
≤40	110 (50.7)
41-60	65 (30.0)
>60	42 (19.4)
Gender
Male	139 (64.1)
Female	78 (35.9)
Nature of kidney disease
AKI	33 (15.2)
CKD	184 (84.8)
Etiology of CKD
Hypertension	44 (23.7)
Chronic glomerulonephritis	38.2 (71)
Diabetes mellitus	17 (9.1)
HIV associated	20 (10.8)
Obstructive nephropathy	14 (7.5)
Others	20 (10.5)

SD=Standard deviation, CKD=Chronic kidney disease, AKI=Acute kidney injury

The mean SBP, DBP, and mean arterial pressure (MAP) of the patients pre- and post-dialysis are shown in Table 2. Mean SBP and DBP were higher predialysis compared to values postdialysis but only postdialysis DBP was significantly lower than the predialysis value (P = 0.008).

Table 2

Comparison of mean blood pressure parameters pre- and post-dialysis (n=217)

Parameter	Predialysis	Postdialysis	P
SBP (mmHg)	151.9 (22.5)	152.0 (26.6)	0.982
DBP (mmHg)	96.2 (16.3)	93.5 (15.6)	0.008

SBP=Systolic blood pressure, DBP=Diastolic blood pressure

Female patients had higher mean SBP and DBP compared to male patients pre- and post-dialysis, but only DBP was significantly higher in females compared to male patients(P = 0.029) [Table 3].

Table 3

Blood pressure parameters according to gender

Parameter	Male (n=139)	Female (n=78)	P
Predialysis (mmHg)
SBP	151.2 (21.4)	153.1 (24.5)	0.565
DBP	94.4 (14.5)	99.4 (18.6)	0.029
Postdialysis (mmHg)
SBP	151.7 (26.2)	152.6 (27.6)	0.842
DBP	93.0 (16.1)	94.3 (14.5)	0.548

SBP=Systolic blood pressure, DBP=Diastolic blood pressure

Patients with CKD had higher mean SBP and DBP pre- and post-dialysis compared to patients with AKI. However, only postdialysis mean SBP and DBP were significantly higher in CKD patients compared to those with AKI [Table 4].

Table 4

Blood pressure parameters versus type of kidney disease

Parameter	AKI (n=31)	CKD (n=186)	P
Predialysis (mmHg)
SBP	143.7±24.1	153±22.1	0.029
DBP	91.1±22.1	96.8±14.9	0.07
Postdialysis (mmHg)
SBP	137.8±17.5	154.2±26.1	0.002
DBP	86.8±18.4	94.6±14.9	0.011

SBP=Systolic blood pressure, DBP=Diastolic blood pressure, AKI=Acute kidney injury, CKD=Chronic kidney disease

BP variation observed postdialysis using SBP was as follows: 107 (49.3%) patients had no significant change in SBP, 43 (19.8%) patients had IDH, while 67 (30.9%) had IDHT [Figure 1].

Figure 1

Postdialysis change in average systolic blood pressure of patients (n = 217)

IDH was more prevalent among patients with diabetic kidney disease while IDHT was more prevalent among patients with hypertensive nephropathy (P = 0.002), as shown in Table 5 and Figure 2.

Table 5

Blood pressure variation during dialysis versus etiology of chronic kidney disease (n=186)

Etiology	No significant change (%)	IDH (%)	IDHT (%)	P/χ2
Hypertensive nephropathy	14 (31.8)	12 (27.3)	18 (40.9)	0.002/20.740
Chronic glomerulonephritis	46 (64.8)	5 (7.0)	20 (28.2)
Diabetic nephropathy	5 (29.4)	7 (41.2)	5 (29.4)
Others	28 (50.9)	12 (21.8)	15 (27.3)

IDHT=Intradialytic hypertension, IDH=Intradialytic hypotension

Figure 2

Postdialysis change in average systolic blood pressure versus etiology of chronic kidney disease (n = 217)

Discussion

The population of dialysis patients studied consisted of 64% of males. Male gender has been reported to be associated with progression of CKD compared to female gender.[11] Men also have more economic power in Nigeria and hence were more likely to afford dialysis therapy if required, compared to women.

Patients aged <40 years made up half of the study population. This finding agrees with the epidemiology of CKD in Nigeria. Studies on CKD in Nigeria have shown that young-to-middle-aged adults make up the bulk of the dialysis population.[12] This is opposed to what obtained in the developed countries where the elderly constitute the bulk of patients on dialysis therapy.[13] The most common causes of CKD among the patients were hypertensive nephropathy, chronic glomerulonephritis, and diabetic nephropathy. This finding agrees with previous works on CKD patients in Nigeria.[14]

Predialysis mean BP values (SBP and DBP) of patients were significantly higher than postdialysis BP values. The effect of pooling blood into the extracorporeal circuit could account for this finding. Furthermore, ESRD patients may not have residual renal function, thus requiring high volume ultrafiltration which contributes to the drop in BP values.

Patients with AKI had lower BP values compared to those with CKD. Hypertension is strongly associated with CKD such that up to 80% of CKD patients have hypertension. On the other hand, AKI may have resulted from sepsis and hypovolemia which are usually associated with low BP values.

The prevalence of IDH in this study was 19.8%. IDH is known to occur in 15%–55% of HD sessions.[15] The prevalence of IDH varies from study to study because there is no unified definition of IDH. The European Best Practice Guidelines (EBPG) defined IDH as a decrease in SBP ≥20 mmHg or a decrease in MAP ≥10 mmHg with clinical symptoms.[3] Other definitions of IDH include decrease in SBP >10% of pre-HD value or SBP <100 mmHg with clinical symptoms[16] and as a decrease in SBP ≥40 mmHg of decrease in DBP ≥20 mmHg.[17] Kuipers et al. looked at 3818 HD sessions in 124 patients prospectively over a 3-month period and found a prevalence of 8.5% after considering patients who required intervention for IDH in addition to meeting the EBPG BP recommendation.[18] Our study was retrospective and we looked at BP changes without considering the presence or absence of clinical symptoms of hypotension. This may explain the higher prevalence of 19.8% in the 217 patients reviewed.

IDH was more prevalent among patients with diabetic nephropathy compared to those with hypertensive nephropathy or chronic glomerulonephritis. A possible reason for this finding is autonomic dysfunction. Autonomic neuropathy is a common chronic complication of diabetes. The presence of autonomic neuropathy prevents the normal compensatory vascular response to ultrafiltration during dialysis. The presence of comorbid conditions such as cardiac disease with systolic or diastolic dysfunction also contributes to increased risk of IDH in diabetics on HD.

IDHT occurred in 30% of the patient population studied and was more prevalent among patients with hypertensive nephropathy compared to patients with diabetic nephropathy or chronic glomerulonephritis. The prevalence of IDHT in our study cannot be directly compared to that found in other studies because IDHT has not been systematically studied in large dialysis populations and there is no unified definition for it. However, workers from varying studies reported a prevalence that ranges from 5 to 30%.[192021] Fluid overload is a recognized possible cause of IDHT.[22] This could be one of the factors contributing to IDHT in our patients. Patients in our center are unable to dialyze as frequently as required due to financial constraints, and as a result, they present fluid overloaded. Ojeh-Oziegbe et al.[23] had earlier reported the high cost of dialysis and its effect on dialysis therapy in our region. Furthermore, inadequate use of antihypertensive medications for the treatment of hypertension due to poor funding may have also contributed to the high prevalence of IDHT observed in this study. Several antihypertensive drugs are removed extensively during dialysis and this may contribute to increased incidence of IDHT.[19]

IDHT can be managed through proper control of intravascular volume, interdialytic weight gain, blockade of the sympathetic nervous system, and the reticular activating system with appropriate drugs. BP medication minimally removed by dialysis should be favored and dialysis frequency must be optimized.

This study was limited by its retrospective nature such that the presence or absence of symptoms of IDH during HD could not be ascertained. In addition, being a single-center experience, there is a need to apply caution in generalizing our findings. Despite this limitation, this study is one of the first studies in Nigeria that assessed BP variation and its correlates among the increasing population of dialysis-requiring renal failure patients, hence the strength of the study. More studies are needed from other hospitals to corroborate or, otherwise, further discuss these findings.

Conclusion

IDH and IDHT are prevalent among ESRD patients on chronic HD in our center. IDH and IDHT are known risks for increased morbidity and mortality in this set of patients. We recommend individualization of patients with respect to management of these conditions. Routine proper determination of target dry weight by diet and fluid intake counseling, medication adjustment, and correction of anemia are some measures that aid in the prevention and treatment of IDH.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.