Dialysis

Effect of cool temperature dialysate on the quality and patients' perception of haemodialysis Abdelbasit Ayoub1 and Mary Finlayson2 1Renal Dialysis Unit, Waikato Hospital, Hamilton and 2School of Nursing, University of Auckland, Auckland, New Zealand Correspondence and offprint requests to: Abdelbasit Ayoub, Renal Dialysis Unit, Waikato Hospital, Hamilton, New Zealand. Email: abdelbasit87@hotmail.com

Abstract Top

Abstract

Introduction

Subjects and methods

Results

Discussion

References

Background. The effects of cool dialysate on the urea reduction ratio (URR) in high efficiency haemodialysis have not been completely studied. After reviewing the literature, it appeared that patients' perceptions of cool dialysis have not been studied. Since patients' perception have an impact on patient satisfaction, this motivated the authors to research this area of practice. Methods. This study was designed to determine whether a high URR and haemodynamic stability could be achieved by using cool dialysate in two groups of patients. The first group of five patients were known to have hypotension episodes during dialysis, and the second group of five patients were documented as having stable blood pressure (BP) during and after dialysis, after excluding vascular access recirculation and any other problems. Each patient was dialysed for three sessions using cool dialysate (35°C) followed by another three sessions using a standard dialysate temperature (36.5°C). All other dialysis session parameters were maintained. Results. The results show that the dialysate cooling resulted in an increased ultrafiltration in the low BP group (P = 0.05). Cool dialysis had neither an adverse nor a beneficial effect on urea removal in the two groups (P = NS). The mean arterial pressure post- and intra-dialysis was significantly higher in dialysis with cool dialysate in the low BP group (P < 0.01 and P < 0.007, respectively). The mean arterial pressure in the stable BP group remained unchanged when cool dialysate was used (P = NS). The intra-dialytic pulse rates in the low and stable BP groups were similar. A total of seven episodes of symptomatic hypotension were observed in the low BP group, but none in the stable BP group (P < 0.0001). Patients' perceptions about cool dialysate were measured by a questionnaire which showed that 80% of them felt more energetic after dialysis and requested to be always dialysed with cool dialysate. Conclusion. Cool dialysate improves tolerance for dialysis in hypotensive patients and helps increase ultrafiltration while maintaining haemodynamic stability during and after dialysis. Patients' perceptions were positive, as most of the selected sample felt more energetic and generally well during and after dialysis, and this had a positive impact on their activities of daily living. Keywords: cool dialysate; haemodynamic stability; hypotensive episodes; standard dialysate; urea reduction ratio

Introduction Top

Abstract

Introduction

Subjects and methods

Results

Discussion

References

Cooling dialysate below 36.5°C has been recognized as an important factor contributing to haemodynamic stability of patients during haemodialysis [1-5]. Many studies show that cool dialysate improves cardiovascular tolerance of haemodialysis and reduces hypotension episodes during haemodialysis [2,6-8]. During standard dialysis and ultrafiltration, the combination of low blood volume and loss of peripheral vascular resistance causes hypotension [9]. Blood cooling is used to stabilize blood pressure (BP) during very high efficiency haemodialysis with a high ultrafiltration rate, and helps to maintain BP without compromising the efficacy of haemodialysis [10]. A number of studies have shown that the use of cool dialysate resulted in fewer hypotensive episodes [11,12,13]. Increased BP associated with cool dialysate is due largely, if not entirely, to increased total peripheral resistance and increased venous tone [14]. Cooler temperature dialysate improves left ventricular contractility, independently of pre-load and after-load [11]. A lower dialysate temperature during routine haemodialysis might be justified as an intervention in treating the hypotension episodes during haemodialysis [15]. Moreover, the groups who appear to benefit most from cool dialysate are women, patients over 55 years of age, patients with low body surface area and patients with cardiovascular disease [16]. The aim of this research was to study the effect of using cool dialysate on the urea reduction ratio (URR) and on haemodynamic parameters in two groups of patients being dialysed in the InCentre Hemodialysis Unit at Waikato Hospital. The study was designed to determine whether a high URR and haemodynamic stability could be achieved by body temperature cooling during haemodialysis. The experiment involved dialysing the selected sample of patients randomly using either a standard dialysate temperature (36.5°C) or a cool temperature dialysate (35°C) for three dialysis sessions each. Patients were informed about the temperature of each dialysis session, as they can feel the cool dialysis. Moreover, patients were told what they may experience during the study as explained on the information sheet which was given to them in order to gain consent for the study.

Subjects and methods Top

Abstract

Introduction

Subjects and methods

Results

Discussion

References

The Waikato Ethics Committee approved the research project, and informed consent was obtained from each patient. Patients who met the criteria for the study were selected from a chronic dialysis population of 50 patients in the Incentre Hemodialysis Unit. A total of 10 haemodialysis patients ranging in age from 38 to 72 years (mean 59.8 ± 5.5) were selected. One group (hypotension-prone, n = 5) was characterized by having episodes of hypotension during dialysis, a systolic pressure of 90 mmHg accompanied by any of the following symptoms: nausea, vomiting, muscle cramps, dizziness or fainting. The second group of patients (n = 5) had stable BP during dialysis. The 10 patients were selected after excluding recirculation or vascular access problems. Patients were not eligible for participation in the study if they had experienced recent surgical intervention, severe anaemia, problems related to vascular access, coronary artery disease, acute renal failure or recent illnesses. The study was initiated in April 2002 and finished in June 2002. Each patient was used as a control for him/herself. The aetiology of renal failure in the patients selected for this study included diabetes mellitus (four), hypertension (two), glomerulonephritis (two), uncertain aetiology (one) and polycystic kidney disease (one). Five patients were taking antihypertensive medicines; these were not routinely taken on the day of haemodialysis. Regular medications for the selected sample included phosphate binders. Design and procedure

The experimental design was single-subject multiple probes across participants in each group, over six haemodialysis sessions. In three sessions, the dialysate temperature was normal (36.5°C) and in the other three sessions the dialysate temperature was low (35°C). The dialysate temperature was set as per the Fresenius machine manual; no extra devices such as a blood temperature monitor were used. Apart from changing the temperature to 35°C, all other dialysis parameters remained the same during the study. In each session, an F8HPS disposable dialyser with an ultrafiltration coefficient of 11.1 ml/h/mmHg composed of polysulfone was used. The dialysate flow rate was set at the desired level according to the manufacturer's guidelines at 500 ml/min. The dialysate consisted of the following constituents: sodium 141 mmol/l, potassium 2.0 mmol/l, calcium 1.3 mmol/l, magnesium 0.2 mmol/l, chloride 108.0 mmol/l, acetate 3.0 mmol/l and bicarbonate 35.0 mmol/l. A Fresenius model 4008B or 4008S dialysis machine equipped with a volumetric ultrafiltration control system was used in each dialysis. Fluid removal was calculated as the difference between the patients' weight before dialysis and their target dry weight. Blood flow rates were maintained constant for standard temperature and cool dialysis for each patient. Pre-dialysis body weight, blood pressure, pulse rate and oral temperature were measured before ingestion of food and drink. BP (measured by an electronic digital sphygmomanometer), pulse rate, arterial line pressure, venous line pressure, blood flow rate, trans-membrane pressure and fluid loss were all measured hourly during dialysis. Weight, BP, pulse rate and temperature were recorded post-dialysis. Blood flow during dialysis was slowed to 100 ml/min before collecting post-dialysis blood samples for urea, and the samples were analysed in Waikato Hospital's biochemistry laboratory. The URR was calculated using the formula: (urea pre - urea post/urea pre x 100%). Mean arterial pressure was calculated as the diastolic pressure plus one-third of the pulse pressure. Dialysis dose was measured by equilibrated Kt/V (Kt/Veq). The single-pool Kt/V (Kt/Vsp) was determined from the Daugirdas second-generation formula [17]. Kt/Veq = (1 - 0.47/t) x Kt/Vsp + 0.02. and Kt/Vsp = -In(R -0.008 x t) + (4 - 3.5 x R) x UF/W, where R = urea post/urea pre (in fractions of 1); UF = ultrafiltration volume in kg; T = treatment time in h; and W = body weight in kg. Patient's perceptions about their experiences of the cool temperature dialysate were measured after completion of the six dialysis sessions. A questionnaire, using both a closed question and two open-ended questions, was given to the patients. The questions were: How did you feel while being dialysed on cool temperature? Compared with normal temperature dialysis of 36.5°C, did you feel any differences while being dialysed on cool temperature? If yes, what were the differences? Would you like to continue cool temperature dialysis? The data were sorted and entered into Microsoft Excel then analysed using the analysis of variance (post hoc ANOVA) test. A probabilty of <0.05 was assumed to be significant.

Results Top

Abstract

Introduction

Subjects and methods

Results

Discussion

References

Low BP group

As the data in Table 1 show, the difference in Kt/Veq values in cool dialysate (35°C) and neutral dialysate (36.5°C) is statistically insignificant. The dialysate cooling resulted in an increased ultrafiltration compared with neutral dialysate (36.5°C) while maintaining haemodynamic stability and achieving target dry weight (P = 0.05). There was no statistically significant difference in the URR between the use of cool dialysate and neutral dialysate. During dialysis using the cool dialysate, the mean intra-dialytic arterial pressure was noticeably higher than during dialysis using a neutral dialysate (P = 0.007). The average intra- and post-dialysis pulse rates with a cool dialysate compared with a standard dialysate were similar.
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Table 1. The average results of the low BP group

The mean arterial pressure post-dialysis was significantly higher in the patients dialysed with cool dialysate compared with those dialysed with neutral dialysate (P = 0.01). The change in oral temperature post-dialysis for the cool dialysate patients was significantly lower than that of standard temperature dialysate patients (P = 0.001). There were seven episodes of symptomatic hypotension in the neutral dialysate patients compared with none for the cool dialysate patients. Stable BP

Data from Table 2 show that the Kt/Veq values are almost the same in cool and neutral dialysate patients. Dialysate cooling had no significant effect on achieved ultrafiltration or URR when compared with neutral dialysate. Pre-, intra- and post-dialytic pulse rates and BP were similar for cool and standard temperature dialysis in this group of patients.
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Table 2. The average results of the low urea reduction rate (URR) group who had stable BP

The post-dialysis temperature change for cool dialysis was significantly lower than for the standard temperature dialysis. It was 0.4°C in cool dialysate compared with 0.8°C in standard dialysate in the stable BP group. None of the patients in this group had episodes of systematic hypotension. The patients' perceptions

The vast majority of respondents reported feeling more energetic and having a dramatic improvement in their general health following dialysis with cool dialysate. The vast majority also indicated their preference for always being dialysed with cool dialysate. Twenty percent reported feeling cold during dialysis using cool dialysate. The results from the questionnaire are summarized in Table 3.
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Table 3. Patients' perceptions of the cool dialysate

Discussion Top

Abstract

Introduction

Subjects and methods

Results

Discussion

References

Kt/V and URR

The second-generation formula was used to calculate the dialysis dose because it eliminated the overestimation of Kt/V compared with the first formula (Kt/V = 1.2). Also, the total error (absolute value percentage error + 0.02 SD) was reduced with the second-generation formula. The calculation of the P-values shows that there were no significant differences in the Kt/Veq values between cool dialysate and standard dialysate in both groups. Also it shows that Kt/Veq values were >1.2, and it reflects that patients had good clearance when dialysed in the two treatment modules. As in earlier studies [4], we found cool dialysis had neither an adverse nor a beneficial effect on urea removal in the two groups. Ultrafiltration, BP, pulse and post-dialysis temperature

The cool dialysate in this study resulted in an increased ultrafiltration rate compared with neutral dialysate (P < 0.05). The ultrafiltration rate was calculated as the difference between the patients' weight before dialysis and the patients' dry weight. A similar study [11] showed that patients with large intra-dialytic weight gains could be dialysed on cool temperature dialysate (35°C), without the patients having hypotension episodes during dialysis. However, the ultrafiltration volume remained relatively unchanged in the stable BP group. In a prospective study done on 11 patients, Cruz et al. found that a cool dialysate (35.5°C) significantly increased the lowest intra- and post-dialysis BP, and significantly reduced the number of nursing interventions, as well as the volume of saline infused for treating intra-dialytic hypotension [18]. These findings were replicated in this study. As in the low BP group, the mean arterial pressure post- and intra-dialysis was significantly higher with the cool dialysate than with the standard dialysate. However, cool dialysate did not make any significant statistical difference in the stable BP group. The stability of BP during cool dialysis could be attributed to preservation of central blood volume and cardiac output [19]. The intra- and post-dialytic pulse was relatively lower in both groups, but this difference was not statistically significant. A study has found that cool dialysis increases left ventricular contractility in haemodialysis patients, which may be a potential mechanism whereby haemodynamic tolerance to the dialysis procedure can be improved [12]. A rise of 0.7°C body temperature in the low BP group and 0.4°C in the stable BP group has been observed in this study. Similar findings were noticed in a study where body temperature changed by 0.51°C when cool dialysate was used [4]. Episodes of symptomatic hypotension and patients' perception

A total of seven episodes of symptomatic hypotension requiring nursing intervention in which blood pressure was <90 mmHg were observed in the low BP-prone group, but none in the stable BP group. Hence, there were no episodes of symptomatic hypotension during the 35°C temperature haemodialysis treatment. This finding is supported by a study in which 18 symptomatic hypotension episodes were noted during dialysis using a dialysate at 37°C [11]. The patients' perceptions of being dialysed with cool dialysate reflected a very positive response and one that could be investigated further with a larger sample. Conclusion

This study shows that cool dialysate was tolerated well and proved to be an important factor in stabilizing BP during haemodialysis, without compromising the efficacy of haemodialysis with respect to low molecular weight molecules such as urea. Cool dialysate improves tolerance to dialysis in hypotensive patients. In general, this study shows that a cool dialysate helps increase ultrafiltration while maintaining haemodynamic stability during and after dialysis. At the same time, the URR and Kt/Veq values remained unchanged in the stable BP group and were relatively better in the low BP group. In other words, the cool dialysate was more beneficial for the low BP group. The use of cool dialysate is a simple, useful and economical procedure, especially for highly symptomatic patients. Patients' perceptions were positive as most of the selected sample felt more energetic and generally well during and after dialyses, and found it had a positive impact on their activities of daily living. Moreover, 80% requested to be dialysed using cool temperature dialysate in the future. Recommendations

Because the majority of the sample felt an improvement in their general health and requested to be always dialysed on cool dialysate, cool dialysate should be offered as an option to patients who usually have hypotensive episodes during dialysis, as it helps to increase the haemodynamic tolerance to haemodialysis. Further studies need to be done to study the relationship between cool dialysate and URR and the effect of cool dialysate on the heart rate during and post-dialysis. Also, a larger study of patients' perceptions of cool dialysate should be undertaken, as this would appear to be the first research of its type in this area of practice.

Acknowledgments

The authors thank Dr Daniel Schneditz for his help in analysis of the data, and appreciate the support of the renal physicians Drs Maggie Fisher and Peter Sizeland, Steve Holmes from the Clinical Audit Unit, Pani Weiland RN, and Nikola Hagan, clinical nurse leader, and the patients in the renal dialysis unit at Waikato Hospital, Hamilton, New Zealand. Conflict of interest statement. None declared.