Balance and fall risk in peritoneal dialysis patients

Abstract

BACKGROUND:

Vestibular, neurological and musculoskeletal functions are affected in patients with renal failure. These problems can in turn affect the balance system in peritoneal dialysis (PD) patients. Previously, postural balance changes were shown in hemodialysis patients. This is the first study that evaluates whether there are similar changes in patients with PD.

OBJECTIVE:

This study aimed to compare balance and fall risk between patients undergoing PD treatment and healthy subjects, and aimed to determine the correlation between biochemical parameters and fall risk and balance assessments in PD patients.

METHODS:

This controlled study included 58 patients receiving PD treatment (PD Group) and 75 healthy subjects (Control Group). The Berg Balance Scale (BBS) and Tetrax ${}^{\@setsize{\tiny}{6pt}{\vpt}{\@vpt}\textregistered}$ Interactive Balance System were used for the comparison of balance between groups. For patients in the PD Group, duration of PD, blood pressure, Kt/V ${}_{\text{urea}}$ (actual mass of urea removed via peritoneal dialysis), and serum biochemical parameters were recorded and correlation analysis was performed between these parameters and balance measurements.

RESULTS:

There were no statistically significant differences between groups in terms of demographics or BBS scores ( $p>$ 0.05). The fall risk of patients in the PD Group was significantly higher than those in the Control Group ( $p<$ 0.0001) according to Tetrax measurements. Female gender, older age, higher BMI, and higher blood glucose levels were negatively correlated with balance parameters of PD patients ( $r>$ 0.3). There was no statistically significant correlation between duration of PD, blood pressure, and Kt/V ${}_{\text{urea}}$ with balance parameters or fall risk.

CONCLUSIONS:

Balance was impaired in patients undergoing PD in comparison to healthy subjects. Fall risk may be evaluated using the Tetrax ${}^{\@setsize{\tiny}{6pt}{\vpt}{\@vpt}\textregistered}$ instead of BBS for this population. Serum glucose level, BMI and age appear to affect balance and fall risk. Therefore, optimization of body weight and normalization of serum glucose levels are important factors for improving balance. The duration of PD, blood pressure, and Kt/V ${}_{\text{urea}}$ do not affect balance system.

Keywords

Postural balance risk of fall peritoneal dialysis static posturography

1. Introduction

Balance is defined as the ability to maintain a position within the limits of stability or base of support and is therefore classified by the International Classification of Functioning, Disability and Health as an activity [1]. It is essential for optimal functioning of the locomotor system and the performance of many activities in daily life [2].

Many aspects of the human body, such as the central nervous system, somatosensorial system (e.g. proprioception), vestibular system, visual system, muscular strength, and cognitive functions are related to balance control. Pathologies of these functions may result in balance impairment and falling [3, 4]. Related health problems may result in severe physical, social, and psychological impairments, decreased ability to work, and high costs.

Neurological and musculoskeletal problems are some of the main quality of life limitations in patients with renal failure, in particular those treated with long-term maintenance dialysis [5]. Vestibular and visual systems, muscular strength, proprioception, and cognitive functions are also affected in patients with renal failure [6, 7].

There are few studies evaluating postural sway in hemodialysis (HD) patients. Those studies showed that the HD is associated with changes in postural sway, which objective hallmark of their functional abilities, in comparison to healty controls. That changes cause poorer physical function and higher accident falls than healthy population [8, 9, 10]. There is only one study evaluating balance before and after HD by electronic posturographic balance system. In that study the balance of ESRD patients before and after a routine session of hemodialysis treatment was evaluated. Fall Index scores were found to be lower in healthy controls than that of ESRD patients and was higher after hemodialysis, indicating a negative effect of hemodialysis on postural stability [10].

This study aimed to compare balance and fall risk between PD patients and healthy subjects. In addition, we aimed to determine whether there is a correlation between biochemical parameters and fall risk and balance assessments in PD patients. This is the first study that evaluates whether there are balance changes in patients with PD.

2. Methods

This controlled study was approved by the local ethics committee, and written informed consent was obtained from all participants. All procedures that involved human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Fifty-eight patients (23 females and 35 males) undergoing PD treatment were included in the PD Group and 75 healthy subjects (31 females and 44 males) not diagnosed with renal disease were included in the Control Group. A total of 20 patients undergoing PD treatment were excluded from the study because of limited cooperation with the balance measurements resulting in the inability to obtain proper measurements. The Control Group was selected from individuals in the hospital employee population and patients’ relative. Participants with neurologic or musculoskeletal disorders, diagnosis of renal osteodystrophy, visual or hearing pathologies, or severe bone or rheumatologic disease which might affect the balance system, were excluded from the study.

Age, gender, body mass index (BMI) (body weight [kg]/height ${}^{2}$ [m ${}^{2}$ ]) of all participants were recorded.

Primary renal disease, Kt/V ${}_{\text{urea}}$ (it relates to the actual mass of urea removed by peritoneal dialysis), blood pressure, and PD duration were recorded for patients in the PD Group. PD was performed either four times a day in sessions ranging from 6–8 hours in length during the day or as automated PD (8–10 hours at night). Patients were given Dianeal PD4 (Eczacibasi-Baxter Hospital Products, Istanbul, Turkey) with glucose concentration adjusted according to each patient’s need for ultrafiltration.

All PD patients’ charts were reviewed and the following laboratory parameters were recorded: HbA1C levels of diabetic patients, hemoglobin, C-reactive protein (CRP), serum levels of glucose, blood urea nitrogen, creatinine, calcium, phosphorus, sodium, potassium, alkaline phosphatase, albumin, intact parathyroid hormone (iPTH), ferritin, and serum iron levels and transferrin saturation index scores. Hemoglobin levels were determined using the Cell Dyn 3700 hematology analyzer (Abbott Laboratories, Abbott Park, IL, USA) and iPTH levels were measured via electrochemiluminescence immunoassay using the Modular analytics E170 (Roche Diagnostics GmbH, Mannheim, Germany). Other biochemical parameters were assessed via standard laboratory methods using the Roche Hitachi 902 chemistry analyzer (Roche Diagnostics Corporation, Indianapolis, IN, USA).

All participants were evaluated using the Berg Balance Scale (BBS) to measure dynamic and static balance and the Tetrax ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Interactive Balance System to measure static posturography.

3. Berg balance scale

The BBS is the gold standard clinical test widely used to assess dynamic and static balance in elderly patients. It is designed to measure balance during specific functional tasks which are common in everyday life. It includes 14 simple balance tasks scored on a 5-point ordinal scale (0, 1, 2, 3, and 4), with a maximum total score of 56 [11, 12]. Tasks require subjects to maintain positions of varying difficulty and perform specific tasks such as standing and sitting unsupported, transfers, turning to look over shoulders, picking up an object from the floor, turning 360 ${}^{\circ}$ , and placing alternate feet on a stool. BBS scores of 41–56 indicate a low fall risk, 21–40 a medium fall risk, and 0–20 a high fall risk [13, 14]. The reliability, validity, and transcultural adaptation of the Turkish version of the BBS has been shown by Sahin et al. [15].

4. Static posturography

Static posturography was measured using the Tetrax ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Interactive Balance System (Sunlight Medical Ltd., Ramat Gan, Israel). This system evaluates static postural balance by recording vertical pressure fluctuations on four different power plates with the subject standing barefoot on the device with their arms hanging freely next to the body. Hand pieces on both sides of the device provide stability when needed. Participants positioned their bare feet on the plates and stood in a comfortable position for this evaluation. Fall risk, stability index (SI), and Fourier index measurements were evaluated using the Tetrax ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Interactive Balance System.

Risk of fall is a numerical value between 0 and 100 (low fall risk, 0–35; moderate fall risk, 36–57; high fall risk, 58–100). This evaluation system provides a hypothetic risk value. The SI is a variable indicating the degree of postural sway and therefore tests the overall stability and ability to control and compensate for changes in posture. Higher SI and fall risk shows poorer postural performance. The Fourier index is a regression analysis of postural sway intensity through the Fourier transform, which shows a different frequency for each lesion that causes instability. Fluctuations of 0.01–0.1 Hz (F1) usually signify normal and comfortable posture and are related to visual control. Fluctuations of 0.1–0.5 Hz (F2-4) usually signify an abnormality in the vestibular organ or fatigue of the musculoskeletal system while those of 0.5–1 Hz (F5-6) show a high index when the subject has an impairment in the somatic sensory response due to a decline in motor functions of the spine and lower extremities. Fluctuations of more than 1 Hz (F7-8) indicate postural instability due to a central nervous system abnormality [3, 16].

Eight different postures can be evaluated with static posturography. For this study, the normal eyes opened (NO) posture with F1 fluctuation and the pillow with eyes closed (PC) posture with a foam-rubber pillow positioned on the floor of the Tetrax ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ at F2, F6, and F8 fluctuations were recorded. The duration of balance recording approximately took 5 minutes. The measurement duration for each position lasted 32 seconds and duration of recovery time between measures was 2–3 seconds.

Outcomes were assessed by the same assistant health staff (electromyography technician) using the same method.

4.1 Statistical analysis

Statistical analysis was performed using the statistical package SPSS (Version 17.0, SPSS Inc., Chicago, IL, USA). Normal continuous variables were described as the mean $\pm$ standard deviation ( $p>$ 0.05 in Kolmogorov-Smirnov test or Shapiro-Wilk ( $n<$ 30)), and non-normal continuous variables were described as the median. Comparisons between groups were applied using the Student T test for normally distributed data and the Mann-Whitney U test for data that were not normally distributed. The categorical variables between the groups were analyzed using the Chi-squared test. Correlations were tested using the Pearson’s correlation test and the correlation coefficients were interpreted as either excellent $r\geqslant$ 0.91; good 0.90 $\geqslant r\geqslant$ 0.71; fair 0.70 $\geqslant r\geqslant$ 0.51; weak 0.50 $\geqslant r\geqslant$ 0.31; or little or none $r\leqslant$ 0.3. A $p$ value of 0.05 was considered significant.

5. Results

Mean age of patients in the PD Group was 54.2 $\pm$ 12.2 years and 50.4 $\pm$ 12.1 in the Control group. Age, gender, BMI, and BBS were similar between groups. Characteristics of the study populations are summarized in Table 1.

Table 1
Clinical characteristics of the study population

	Peritoneal	Control	p
	dialysis	group
	group	(n: 75)
	(n: 58)
Age, (years), mean $\pm$ SD	54.2 $\pm$ 12.2	50.4 $\pm$ 12.1	0.084
Gender (female/male), n	23/35	31/44	0.086
Body mass index (kg/m ${}^{2}$ ),	27.2 $\pm$ 5.3	28.3 $\pm$ 5.6	0.74
mean $\pm$ SD
Berg balance scale,	55 $\pm$ 2.1	55.7 $\pm$ 0.6	0.101
mean $\pm$ SD

SD: standard deviation.

Table 2

Static posturography results (mean $\pm$ standard deviation)

Characteristics	Peritoneal		Control		p
	dialysis		group
	group		(n: 75)
	(n: 58)
Risk of fall	53.1	$\pm$ 31.2	34	$\pm$ 21.5	$<$ 0.0001
Stability index in NO	18.8	$\pm$ 9.1	14.1	$\pm$ 4.7	0.00018
posture
F1 fourier index in NO	17.1	$\pm$ 10.5	14.3	$\pm$ 7.3	0.07
posture
F2 fourier index in PC	19.2	$\pm$ 7.5	13.7	$\pm$ 4.7	0.00004
posture
F6 fourier index in PC	5.4	$\pm$ 2.3	4.3	$\pm$ 2.2	0.007
posture
F8 fourier index in PC	0.3	$\pm$ 0.1	0.2	$\pm$ 0.1	0.03
posture
Stability index in PC	35.8	$\pm$ 15.7	27.2	$\pm$ 10.2	0.0002
posture

NO: normal opened eyes; PC: pillow with eyes closed.

Table 3

Laboratory parameters of peritoneal dialysis patients ( $n=$ 58)

Parameter	Value (mean $\pm$ standard deviation)
Glucose	112.3	$\pm$ 43.9
Blood urea nitrogen	60.7	$\pm$ 14.2
Creatinine	8.3	$\pm$ 3.2
Sodium	137.4	$\pm$ 2.8
Potassium	4.4	$\pm$ 0.5
Calcium	8.9	$\pm$ 0.6
Phosphorus	4.9	$\pm$ 1.1
Albumin	3.7	$\pm$ 0.3
Alkaline phosphatase	120.4	$\pm$ 54.3
Iron	68.9	$\pm$ 20.9
Transferrin saturation index	30.8	$\pm$ 9.7
C-reactive protein	10.3	$\pm$ 12.7
Intact parathyroid hormone	579.7	$\pm$ 311.2
Ferritin	432.6	$\pm$ 315.6
Hemoglobin	10.8	$\pm$ 1.2
HbA1c	7.5	$\pm$ 1.8

Mean duration of PD was 63.35 $\pm$ 42.04 months. The major etiology of renal failure was hypertension in 19 patients, followed by diabetes mellitus (15 patients), glomerulonephritis (7 patients), polycystic kidney disease (4 patients), and amyloidosis (1 patient). Various other causes were responsible in 4 patients and the etiology was unknown in 8.

5.1 Comparisons of posturography results between groups

Fall risk was significantly higher in the PD Group than in the Control Group ( $p<$ 0.0001). SI and F2, F6, F8 measurements were higher in the PD Group than the Control Group ( $p<$ 0.05) while the F1 index was similar ( $p>$ 0.05) between groups. Static posturography results are shown in Table 2.

In addition, SI scores with NO posture and F8 fluctuations were higher in female patients (p: 0.033; p: 0.031, respectively).

5.2 Correlation analysis results of PD patients

BMI was correlated with risk of fall and BBS (r: 0.339; r: $-$ 0.362, respectively).

There was no statistically significant correlation between balance measurements and age, duration of PD, blood pressure or Kt/V ${}_{\text{urea}}$ , while there was a negative correlation between age and BBS (r: $-$ 0.433).

Fall risk, SI, and F8 scores were higher in diabetic patients than non-diabetics ( $p<$ 0.05).

Blood glucose level was correlated with fall risk, SI, and BBS score (r: 0.38; $-$ 0.63; 0.393, respectively). Other biochemical parameters were not correlated with balance measurements. Biochemical parameters of PD patients are given in Table 3.

6. Discussion

To the best of our knowledge this is the first study in the literature focusing on balance and biochemical parameters in PD patients. The main result of our study is that balance is impaired in patients undergoing PD in comparison to healthy subjects. Our findings demonstrate that patients undergoing PD have balance system pathologies but that these pathologies are not related with the duration of PD, blood pressure, Kt/V ${}_{\text{urea}}$ , or biochemical parameters, with the exception of glucose.

There are a number of measurement tools for the evaluation of balance impairments. In the present study, risk of fall, the stability index, and Fourier index measurements and the Berg Balance Scale were utilized. PD patients had a moderate fall risk while the healthy population had a low fall risk according to static posturography results. The SI and most Fourier measurements were significantly higher in subjects in the PD Group than in the healthy Control Group, revealing that patients undergoing PD treatment have balance impairments and a higher fall risk when compared to healthy individuals. In our study, F1 Fourier fluctuations in the NO posture were similar between the two groups, suggesting that PD patients’ posture was normal in comfortable postures. F2, F6, and F8 parameters were better in the healthy subjects. Balance pathologies related with F2, F6, and F8 may therefore be seen in PD patients even without any vestibular or neuromuscular disease. However, as these fluctuations were independent from the duration of PD, BMI, blood pressure, Kt/V ${}_{\text{urea}}$ , and biochemical parameters, more complicated pathophysiological mechanisms may affect F2, F6, and F8 fluctuations.

In previous studies only force plate has been used to evalute balance in ESRD patients. We also evaluated patients with berg balance scale. BBS was used as a measurement tool in this study as patients with renal failure have poor balance when compared to the healthy population of the same age. However, we were unable to find any difference between the two groups using the BBS, while fall risk was significantly higher in the PD Group than in the Control Group. For these reasons, we do not recommend BBS for the evaluation of balance impairment in routine outpatient clinical assessment. Static posturography using the Tetrax system appears to be a more useful evaluation tool than the BBS in PD patients. Despite its high reliability and validity, the BBS may not be the most appropriate test of mobility or balance. Because this clinical observational tool is scored on an ordinal scale, it may not be sufficiently sensitive to change, particularly in active adults with high levels of balancing ability [17]. Important limitations of the BBS such as the need for rescoring of the rating scale, a ceiling effect, and relatively low responsiveness have been reported in the literature. Moreover, dynamic balance (e.g. reacting to a perturbation, gait) is unexplored by the BBS [14].

According to the literature, control of standing balance is an important indicator of fall risk. It is well known that balance is impaired with increasing age with elderly individuals experiencing a loss in strength and sensorimotor processing, increased reaction times, and reduced vision [4, 18, 19]. Our results revealed that the age was correlated with BBS. In addition, SI score and F8 fluctuations were higher in the female population in the present study.

For the PD patients, blood glucose level were correlated with balance. Additionally, fall risk and SI and F8 scores were higher in diabetic patients than non-diabetic patients, suggesting that asymptomatic central nervous system abnormalities might affect postural stability in diabetics. However, as HbA1c was not associated with fall risk, the higher fall risk and SI and F8 scores may be associated with the presence of diabetes and its microvascular complications. In the present study as only the most recent HbA1c results were evaluated, we did not have any information regarding previous blood glucose regulation or the history of previously undetected micro and macrovascular complications which might have affected our results. In addition, spot blood glucose levels were found to affect postural stability. However, blood glucose fluctuations due to the glucose included in the PD solution may also have had an effect on our results.

Neurological complications due to the uremic state or its treatment contribute to morbidity and mortality in patients with renal failure. Despite continuous therapeutic advances, many neurological complications of uremia, such as uremic encephalopathy, peripheral or vestibulocochlear neuropathy, and myopathy fail to fully respond to dialysis [7]. These complications can affect the balance system of these patients. The presence of a variety of toxins such as potassium, calcium, urea, and iPTH contribute to the development of uraemic neuropathy [20, 21, 22]. In the present study, patients did not describe any neurological complications. In addition, the above mentioned biochemical parameters were not correlated with balance measurements, suggesting that more complicated mechanisms or other biochemical parameters not evaluated in this study may affect balance changes in the PD population. Another possible explanation is that asymptomatic neuronal pathophysiologic changes can be seen in the PD population and that these changes may increase the fall risk in this population.

Obesity may decrease static postural control. Cruz-Gómez et al. evaluated 180 patients and reported greater increases in sway in obese subjects than in overweight subjects [23]. In the present study, BMI was associated with fall risk and BBS scores in patients undergoing PD treatment. For this reason, weight management should be recommended to PD patients to improve postural stability.

Osteoarticular disorders such as bone and joint infections, arthropathy, pseudotumours, bone cysts, adynamic bone disease, and pathological fractures significantly limit the quality of long-term survival and can be seen in renal failure [24, 25, 26]. These pathologies can precipitate immobilization, decreased muscle strength, gait abnormalities, and postural instability. Patients in our study did not report the presence of such disorders in their medical history and were thus accepted as not having osteoarticular/neuromuscular problems and further investigation using radiology, computerized tomography (CT), magnetic resonance imaging (MRI), electroneuromoygraphy (ENMG) or scintigraphic assessments was not performed. For this reason, pathologies which may affect our results cannot be definitively excluded.

Limitations of our study included the small sample size and the reliance on the participant’s self-reporting for the exclusion of osteoarticular/neuromuscular problems. In addition, we did not directly evaluate the relationship between renal failure and physical functioning. The Tetrax ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ Interactive Balance System was used to calculate a hypothetic fall risk value. This fall risk value may not correlate with routine daily living activity however. Finally, the number of participants’ previous falls were not recorded.

7. Conclusion

It is important to identify balance pathologies and fall risk in PD patients. Proper identification may contribute to the development of treatment strategies to reduce fall risk and to improve balance in these patients. Fall risk may be evaluated using static posturography instead of BBS. Optimal body weight, and blood glucose level are important for the balance system. Additional studies featuring larger sample sizes would help verify our findings. In addition, radiological technics such as X-ray, CT, MRI, ENMG, or scintigraphic assessments can be used for the definitive exclusion of vestibular, osteoarticular, and neuromuscular problems in further studies.

Footnotes

Acknowledgments

The authors would like to thank Çağla Sarıturk for the statistical evaluation and Kevser Aydar for the evaluation of the balance measurements.

Conflict of interest

None to report.

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