| Abstract|| |
Cooling the dialysate below 36.5°C is an important factor that contributes to hemodynamic stability in patients during hemodialysis (HD). In this study, the effect of dialysate temperature on hemodynamic stability, patients' perception of dialysis discomfort and post dialysis fatigue were assessed in a group of patients on HD. A total of 50 patients, all of whom were on 3-times-perweek dialysis regimen, were studied. Patients were assessed during six dialysis sessions; in three sessions, the dialysate temperature was normal (37°C) and in three other sessions, the dialysate temperature was low (35°C). Specific scale questionnaires were used in each dialysis session, to evaluate the symptoms during the dialysis procedure as well as post-dialysis fatigue, and respective scores were noted. The results showed that usage of low dialysate temperature was associated with the following: higher post dialysis systolic blood pressure (P< 0.05) and lower post dialysis heart rate (P< 0.01), with similar ultrafiltration rates, better intra-dialysis symptoms score and post-dialysis fatigue scores (P< 0.001, and P < 0.001, respectively), shorter post-dialysis fatigue period (P< 0.001) as well as higher urea removal (P< 00001) and Kt/V (P< 0.0001). Patients' perceptions were measured by a questionnaire, which showed that 76% of them felt more energetic after dialysis with cool dialysate and requested to be always dialyzed with cool dialysate. Low temperature dialysate is particularly beneficial for highly symptomatic patients, improves tolerance to dialysis in hypotensive patients and helps increase ultrafiltration while maintaining hemodynamic stability during and after dialysis.
Keywords: Cool Dialysate, Hemodynamic Stability, Hypotensive Episodes, Standard Dialysate, Urea Reduction Ratio, Equilibrated Kt/V, Post dialysis fatigue
|How to cite this article:|
Azar AT. Effect of dialysate temperature on hemodynamic stability among hemodialysis patients. Saudi J Kidney Dis Transpl 2009;20:596-603
|How to cite this URL:|
Azar AT. Effect of dialysate temperature on hemodynamic stability among hemodialysis patients. Saudi J Kidney Dis Transpl [serial online] 2009 [cited 2020 Feb 18];20:596-603. Available from: http://www.sjkdt.org/text.asp?2009/20/4/596/53247
| Introduction|| |
Many studies have shown that cool dialysate improves cardiovascular tolerance among hemodialysis (HD) patients and reduces hypotensive episodes during HD. ,,,,, During standard dialysis and ultrafiltration, the combination of low blood volume and loss of peripheral vascular resistance causes hypotension. Blood cooling has been used to stabilize blood pressure (BP) during very high efficiency HD with high ultrafiltration rate, and helps to maintain BP without compromising the efficacy of HD. ,, The increase in BP associated with cool dialysate is due largely, if not entirely, to increased total peripheral resistance and increased venous tone.  The use of cooler dialysate improves left ventricular contractility, independently of pre-load and after-load.  The aim of this study was to assess the impact of dialysate temperature on hemodynamic stability, patients' perception of dialysis quality and on the post-dialysis fatigue syndrome in patients on maintenance HD. This study also aims at studying the effect of using cool dialysate on dialysis efficacy. The study was carried out on a sample of patients selected randomly and compared the response at two bath temperatures: 37°C as the usual temperature, and 35°C as the low temperature. We chose the latter temperature because several studies have shown that this degree of cooling produces the least variations in core body temperature.  ,,,
| Subjects and Methods|| |
The study was carried out on 50 clinically stable patients after obtaining informed consent to participate. There were 23 males and 27 female patients, with ages ranging between 28 and 73 years (48 ± 13, mean and SD), and dialysis therapy duration ranging between 6 and 96 months (32 ± 28). The etiology of renal failure was chronic glomerulonephritis (11 patients), vascular nephropathy (9 patients), diabetic nephropathy (11 patients), hypertension (7 patients), chronic interstitial nephropathy (5 patients), unknown cause (4 patients), and others (3 patients). The study was carried out between August and October 2007. The vascular access used was a native arteriovenous fistula in 45 patients, and a permanent jugular catheter in five patients. Seven patients were taking antihypertensive medicines, which were told to be omitted on the day of HD. Regular medications for the selected sample included phosphate binders. Patients had dialysis three times a week, in 3-4 hour sessions, with arterial blood flow of 300-350 mL/min, and dialysate flow of 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. All patients used hollow fiber dialyzers with high-permeability biocompatible membrane; 1.8 m 2 polysulphone with an ultrafiltration coefficient of 18 mL/hour/mmHg. The dialysis technique was conventional HD on all patients; no patient was on hemodiafiltration. The adjustable parameters during a HD session were kept constant throughout the study. Fluid removal was calculated as the difference between the patients' weight before and after a dialysis session. Pre-dialysis body weight, blood pressure, pulse rate and axillary temperature were measured before ingestion of food and drink. Blood pressure was determined with a digital electronic sphygmomanometer with the patient in sitting position, and axillary temperature was measured with a mercury thermometer with glass support. In patients having an arteriovenous fistula, the contralateral arm was used for both BP measurements. The BP, pulse rate, arterial line pressure, venous line pressure, blood flow rate, transmembrane pressure and fluid loss were all checked 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. Mean arterial pressure was calculated as the diastolic pressure plus onethird of the pulse pressure. The urea reduction ratio (URR) was calculated using the formula: urea pre-urea post/urea pre × 100%.  Dialysis dose was measured by equilibrated Kt/V (Kt/ V eq ).  The single pool Kt/V (Kt/V sp ) was determined from the Daugirdas second generation formula.  The method of research utilized was single subject multiple probes across participants in each group, over six HD sessions. During the first three sessions, patients continued having their dialysis with the usual dialysate temperature at 37°C; the data of this week were considered as baseline values. During the subsequent three sessions, the dialysate temperature was decreased to 35°C. During the study weeks, the ultrafiltration rate in each dialysis session (expressed in mL and in percentage of lean weight) was noted. The average of the three weekly values was calculated for each patient. The room temperature was controlled and was 23°C at low air movement. The number of hypotensive events the patients had during HD as well as the other symptoms and complications they might have developed were registered. A hypotensive event was defined according to the criteria established by the DOQI guidelines which refers to a decrease in systolic BP of > 20 mmHg associated with symptoms.  To assess the patients' perception on the symptoms they had during the HD session, a modified version of the questionnaire designed by Cruz et al was used.  At the end of each dialysis session, during the study weeks, a questionnaire was given to each patient with the following questions: Have you had any discomfort during the dialysis session? Which one? What level of discomfort have you noticed?
If the patient recovered rapidly, the discomfort was considered as being mild, if it persisted for longer than half an hour it was considered moderate, and if it persisted throughout the whole session, it was considered as severe. To assess the post-dialysis fatigue syndrome, the modified Sklar et al questionnaire was used.  Before each dialysis session, the patient was asked the following: how long did it take to recover from the last dialysis session? Which was the main complaint he/she had? What level of discomfort did he/she experience? The discomfort was considered mild if it did not prevent the patient from doing his/her usual activity, moderate if his/her activity was limited but he/she did not have to take bed-rest, or severe if he/she had to take bed-rest to recover. At the end of the second study week, each patient was asked his/her preference regarding dialysate temperature [normal (37°C) or low (35°C)]. For the subsequent four weeks, each patient was dialyzed using his/her preferred dialysate temperature, and during the last week all the previous parameters were collected again including the questionnaires. All questionnaires were evaluated by the same individual. Statistical analysis was performed using SPSS 14.0 and NCSS 2007 software packages. Mean errors relative to reference values were compared by one way ANOVA test. The Student's t test was used for both paired and non paired data. P values < 0.05 were considered as statistically significant.
| Results|| |
The change noted in clinical parameters by decreasing the dialysate temperature are shown in [Table 1].
There was no change in the post-dialysis axillary temperature with the use of dialysate at 37°C, but it decreased with the use of bath at 35°C (P< 0.001). The mean arterial pressure post dialysis was significantly higher in patients dialyzed with cool dialysate compared with those dialyzed with normal dialysate (P= 0.01). The BP decreased after dialysis with both cool and normal temperature dialysate (P< 0.05 for SBP with both dialysates, P< 0.05 for DBP at 37°C, and P= 0.07 for DBP at 35°C). The heart rate increased with bath temperature at 37°C (P< 0.001) and was not altered with bath temperature at 35°C. The main discomfort experienced by the patients during the HD session was lightheadedness; this symptom being the one that most conditioned the "Symptomatology Index" during HD. Other reported symptoms included the following: with bath temperature at 37°C, three patients reported feeling hot and uncomfortable, and one patient had cramps; with bath temperature at 35°C, three patients had chills, and two patients had cramps. Two patients had vomiting with both bath temperatures. The main problem experienced by the patients post-dialysis was fatigue, followed by light headedness. One patient complained of post dialysis headache with bath temperature at 37°C, and one other had cramps with bath temperature at 35°C. The improvement in patients' perception of symptoms and in the number of hypotensive events after decreasing the dialysis bath temperature was particularly relevant in patients who had poor tolerance to HD with dialysate bath temperature of 37°C. At the end of the second study week, the patients were asked their preference regarding the dialysate bath temperature: the conventional 37°C or, the new 35°C (low temperature). Thirty eight patients (76%) preferred the 35°C dialysate, seven (14%) preferred the 37°C dialysate while no specific preference was indicated by the remaining five patients (10%). The vast majority of respondents reported feeling more energetic and having a dramatic improvement in their general health following dialysis with cool dialysate. The results from the questionnaire are summarized in [Table 2]. As indicated in [Table 3], the difference in Kt/V eq values with the use of cool dialysate (35°C) and normal dialysate (37°C) was statistically significant (P< 0.0001). Usage of cool dialysate resulted in increased ultrafiltration, while maintaining hemodynamic stability compared with normal dialysate (37°C) (P< 0.0001). Also, there was a statistically significant difference in the URR between HD using cool dialysate and normal dialysate (P< 0.0001). [Figure 1] and [Figure 2] illustrate the comparison of Kt/V eq and URR between the two dialysate temperatures.
| Discussion|| |
In a non-selected HD population, reduction of the dialysate temperature increases hemodynamic stability, decreases subjective symptomatology during dialysis, and improves post dialysis fatigue syndrome. By decreasing dialysate temperature from 37 to 35°C, patients complete the dialysis session with higher systolic blood pressure and lower heart rate, with the same degree of ultrafiltration.  , , , The decrease in dialysate temperature increases vascular reactivity  and achieves better preservation of cardiac output and central blood volume,  facilitating the hemodynamic response to prevent hypotensive episodes. To evaluate the level of discomfort experienced by the patients during the HD session, the modified questionnaire by Cruz et al was used,  that allows for a quantification by means of a symptomatology index. Hemodialysis with low dialysate temperature was accompanied by a decrease of this index in the study patients. Other studies analyzing the patient perception of dialysis quality have also obtained similar results.  , Post-dialysis fatigue is a frequent complication that limits activity and quality of life among patients in the period immediately following the HD session. It is a poorly understood syndrome in which, the influence of dialysate temperature has never been studied as a possible cause.  In our study, we found that post-dialysis fatigue syndrome is related to dialysate temperature and reduction of the latter, decreases the perception of its severity and duration. It may not be true that all symptoms in all patients improve by decreasing the dialysate temperature. For instance, the incidence of cramps increases, as has been observed in a previous study.  We observed that the patients benefiting with the use of low dialysate temperature are those who show poor tolerance with the usual dialysate temperature. Patients with more than one episode of hypotension per week and those with higher discomfort perception during HD, or those with a more severe post-dialysis syndrome were the ones who benefited most with dialysate temperature of 35°C. In the remaining patients, no major change was observed in the analyzed parameters or the subjective perception of symptoms during HD with the use of cool dialysate.
Fine et al,  suggested the dialysate temperature should be reduced only in patients whose body temperature was low, since they represent the group of patients who are likely to improve with this measure. In our study, the post dialysis body temperature was significantly lower in patients who were dialyzed with cool dialysate. Other studies have not been able to find such correlation between cool dialysate HD and body temperature.  Skin temperature does not help in identifying the group of patients that may benefit from reducing the dialysate temperature.
With the current available data, the role of dialysate temperature in HD is an issue that is not sufficiently explained. The rationale for using a dialysate temperature of 37°C is empirical and is based on the body temperature. This figure is being revised in the general population.  On the other hand, it is a well known fact that the temperature in dialysis patients is lower than that of the healthy population.  According to these data, the mean pre-dialysis axillary temperature during the first two weeks of our study were 36 and 36.1°C, respectively. These figures are lower than the mean values of 36.3°C reported in the literature for a healthy population.  Therefore, it is probably better to define the thermal aspects of HD with regard to the physiologic effects on the patient. During the HD session, there is an increase of heat production associated with a negative energy balance.  In order to achieve a neutral energy balance (thermoneutral dialysis), the body core temperature has to be raised using dialysate temperatures of about 37.5°C. Also, in order to keep the body core temperature steady (isothermal dialysis), it is required to increase energy loss by using dialysate with temperature of about 35.5°C or even lower, depending on the ultrafiltration rate.  , ,
The increase in body core temperature is an important factor causing hemodynamic instability and thus, isothermal dialysis is better tolerated than thermoneutral dialysis.  Body core temperature, that of the blood coming out of the heart, is the one that controls the thermoregulatory mechanisms. In recent clinical studies, tympanic temperature has been used as the reference method to measure core temperature in dialyzed patients.  , , , , In a preliminary study in our patients, we have noted that tympanic temperature is 0.2-0.4°C higher than axillary temperature. In the present study, we used axillary temperature because it is the one usually measured in HD units. Moreover, although axillary temperature is lower than core temperature, the temperature of arterial blood reaching the dialyzer through an arteriovenous fistula is even lower. 
For measuring Kt/V and URR, the secondgeneration formula was used because, it eliminated the overestimation of Kt/V compared with the first formula. 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 significant differences in the Kt/V eq values between dialysis with cool dialysate and standard dialysate. Contrary to earlier studies,  we found that cool dialysate had a beneficial effect on urea removal (P< 0.0001) and equilibrated Kt/V (P< 0.0001). Also, using of cool dialysate in this study resulted in achieving an increased ultra-filtration rate compared with normal dialysate (P< 0.0001).
| Conclusion|| |
This study shows that cool dialysate improves tolerance to HD and is an important factor in stabilizing BP during HD, without compromising the efficacy of dialysis. In general, this study also shows that usage of cool dialysate helps in achieving higher ultrafiltration while maintaining hemodynamic stability during and after dialysis. At the same time, the URR and Kt/V eq values were also increased. Using of cool dialysate is a simple, useful and economical procedure, especially for highly symptomatic patients. Not all patients may benefit from it and we should not forget that it creates a negative energy balance, the clinical implication of which remains to be determined. Individualization of bath temperature by means of thermal sensors may be one of the clinical goals of HD in the years to come.
| Acknowledgement|| |
The author thanks all medical staff at the nephrology department in the Ahmad Maher Teaching Hospital, Cairo, Egypt for their invaluable support during the course of this study.
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Ahmad Taher Azar
Menoufeya, Menouf Ahmad Orabi Square Azar Building
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]