Haemodynamics and electrolyte balance: a comparison between on-line pre-dilution haemofiltration and haemodialysis.

BACKGROUND: An important advantage of convective therapies is improved vascular reactivity. However, it is not well known whether the vascular response during convective therapies remains superior when compared to haemodialysis (HD) with an adjusted temperature of the dialysate. It has also been suggested that convective therapies may impair small electrolyte removal through an effect on the Donnan equilibrium. In the present study, we compared the haemodynamic response and small electrolyte removal between pre-dilution on-line haemofiltration (HF) and HD procedures. METHODS: Cardiac output (CO), central blood volume (CBV) and peripheral vascular resistance (PVR) were assessed, using the saline dilution technique, in 12 stable patients during HF and HD with two different temperatures of the dialysate [36.5 and 35.5 degrees C (HD(36.5) and HD(35.5))]. Balances for sodium, potassium, calcium and conductivity were assessed using total dialysate/filtrate collections. Target filtration volume for HF was 1.2 times body weight. The temperature of the infusate was 36.5 degrees C. RESULTS: The change (Delta) in CBV was less during HD with a dialysate temperature of 35.5 degrees C (-0.03+/-0.14 l; P<0.05) compared to HF (-0.16+/-0.05 l) and HD(36.5) (-0.11+/-0.14 l), but the other haemodynamic parameters did not differ between the studied techniques. DeltaPVR was significantly related to DeltaCBV (r = -0.46; P<0.01), whereas DeltaCBV was related to ultrafiltration rate (r = -0.34; P = 0.05). DeltaCO was related to DeltaCBV (r = 0.62; P<0.001). Solute balances did not differ between HF and HD. CONCLUSION: Using the saline dilution method, no difference in the change in CO and PVR was observed between on-line HF vs HD(36.5) and HD(35.5). Only CBV declined to a significantly lesser degree during HD(35.5), although absolute differences were small. Changes in the other haemodynamic variables appeared more dependent upon the degree and rapidity of fluid removal than upon the treatment modality. No difference in small electrolyte balance was observed between HF and HD, suggesting that ionic removal is not impaired during on-line HF.     

Effect of blood cooling on cuprophan-induced anaphylatoxin generation

We investigated whether cooling of the extracorporeal blood during hemodialysis could prevent anaphylatoxin generation and leukopenia caused by blood-cuprophan contact. After preliminary in vitro studies confirming the temperature dependence of C5a generation, we carried out hypothermic dialysis on nine patients by manipulating blood and dialysate temperature in such a way that blood temperature within the dialyzer averaged 25 degrees C. In comparison with the control procedure (blood temperature within the dialyzer 35 degrees C) hypothermic dialysis reduced peak C5a generation from 41.7 +/- 17 ng/ml to 9.7 +/- 3.4 ng/ml (P less than 0.01), and white blood cell fall from 72 +/- 15 to 25 +/- 20% (P less than 0.01). Arterial PO2 decreased less in hypothermic dialysis (-19 +/- 9% of pre-HD value) than in the control procedure (-30 +/- 11%) (P less than 0.05). We conclude that blood cooling attenuates cuprophan-induced anaphylatoxin generation and leukopenia.     

Thermal effects and blood pressure response during postdilution hemodiafiltration and hemodialysis: the effect of amount of replacement fluid and dialysate temperature

It has been suggested that the incidence of hypotensive episodes is less with hemodiafiltration (HDF) than with hemodialysis (HD). The aim of the present study was to assess the BP response during HD and postdilution HDF in relation to the thermal effects of these different treatment modalities by manipulating the dialysate temperature (Td) during HD and the amount of replacement fluid during HDF. In 12 patients, energy transfer rate (in watts) and maximal decline in mean arterial pressure during HD at Td 37.5 degrees C, HD at Td 35.5 degrees C, and postdilution HDF with amounts of replacement fluids infused at room temperature of 1 L/h and 2.5 L/h, respectively, were assessed. All measurements were done twice in each patient. Energy transfer rate was comparable between HD 35.5 degrees C (-26.61 +/- 5.33) and HDF 2.5 L/h (-25.25 +/- 7.91) and was significantly more negative compared with HD 37.5 degrees C (-3.53 +/- 6.44) and HDF 1 L/h (-15.88 +/- 6.94). The maximum decline in mean arterial pressure was significantly higher during HD 37.5 degrees C (-25.6 +/- 13.5) than during HD 35.5 degrees C (-15.1 +/- 13.8) and HDF 2.5 L/h (-19.2 +/- 17.7), whereas there was no significant difference with HDF 1 L/h (-23.0 +/- 14.0). In conclusion, thermal effects during postdilution HDF are dependent on the amount of replacement fluid. Also during HDF, the BP response is strongly related to thermal effects. The use of postdilution HDF with low or intermediate amounts of replacement fluids infused at room temperature seems to have no advantage in preventing hemodynamic instability, compared with HD 35.5 degrees C.     

Impact of sodium and ultrafiltration profiling on haemodialysis-related hypotension.

BACKGROUND: Symptomatic hypotension is the most frequent complication in patients receiving haemodialysis (HD). Previous studies have reported that the use of modulating dialysate sodium concentration or ultrafiltration (UF) rates, or the combination use of sodium profile and UF profile may better preserve blood volume and reduce the incidence of hypotensive episodes. The aim of this study was to evaluate the effects of sodium balance-neutral sodium profile and UF profile and their combination on preservation of blood volume, cardiac function and occurrence of hypotensive episodes. METHODS: Using Fresenius MC 4008S, eight stable HD patients underwent four treatments: (1) control, constant dialysate sodium concentration of 138 mmol/l with constant UF; (2) sodium profile, a linearly decreasing dialysate sodium concentration (148-131 mmol/l) with constant UF; (3) UF profile, a linearly decreasing UF rate with dialysate sodium concentration of 138 mmol/l; (4) sodium+UF profile, combination of sodium and UF profile. Each treatment was applied in 10 dialysis sessions. Relative blood volume (RBV), mean blood pressure (MBP), heart rate (HR), interior vena cava diameter (IVCD), stroke volume (SV), cardiac output (CO), plasma sodium concentration and the frequency of symptomatic hypotension were monitored. RESULTS: There were no significant differences in the IVCD, MBP, SV, CO and body weight before dialysis between the three profiles and the control. The total plasma protein, haemoglobin, and intradialytic sodium mass removal showed similar results. Compared with the control, better preservation of RBV and MBP at 4 and 5 h and a higher stability in SV variation, but larger UF volume were achieved during sodium+UF profile (P<0.05, respectively), the incidence of intradialytic hypotension was significantly reduced (P<0.05). CONCLUSIONS: With the similar intradialytic sodium removal, during sodium balance-neutral linearly decreasing sodium profile combined with linearly decreasing UF profile, greater intradialytic stability of the blood volume, blood pressure and cardiac function could be obtained, and hypotensive episodes were significantly reduced.     

Thermal effects of different dialysis techniques and blood pump speeds: an in vitro study

Thermal effects have a pivotal impact on hemodynamic stability during dialysis procedures. In contrast to conventional dialysis techniques, there are no data in the literature regarding the thermal energy balance during on-line techniques. Secondly, little data exist on the effect of extracorporeal blood pump speed (EBPS) on thermal energy balance. In this study we assessed, first, relative differences in energy transfer rate (ETR) over the extracorporeal circuit during on-line hemo(dia)filtration (H(D)F) procedures and hemodialysis (HD) at different dialysate temperatures during an in vitro procedure using a blood temperature monitor (BTM). Secondly, we assessed the thermal effects of different blood pump speed (BPS) rates during the various treatment modalities. ETR was different among all treatment modalities (p < 0.05) studied, except for HD at 36.5 degrees C vs. pre-dilution hemofiltration (HF) and post-dilution HDF vs. HD at 37.5 degrees C. ETR had the most negative result, indicating the largest energy loss, during HD at 35.5 degrees C (-58.5.2 +/- 2.6 W), whereas it was almost comparable between pre-dilution HF (-30.7 +/- 4.1 W) and HD at 36.5 degrees C (-35.1.2 +/- 2.4 W). Post-dilution HDF (-17.7 +/- 1.2 W) resulted in an ETR comparable to that of HD at 37.5 degrees C (-15.0 +/- 3.9 W). ETR during post-dilution HF was -43.8 +/- 1.3 W. The thermal effect of the BPS was more pronounced during the procedures with the more negative ETR. In conclusion, on-line techniques and BPS have widely varying effects on ETR during dialysis, which should be considered when the hemodynamic effects among different treatment modalities are compared.     

Temperature control by the blood temperature monitor

The rationale of temperature control during hemodialysis (HD) is to prevent heat accumulation, which increases body temperature and enhances hypotensive susceptibility. Treatments where thermal energy is neither delivered nor removed from the patient through the extracorporeal circulation (so-called extracorporeal thermoneutral treatments) lead to a marked increase in body temperature and to considerable heat accumulation during HD. Since this accumulation of heat cannot be explained by increased heat production, it must be related to reduced heat dissipation through the body surface. Peripheral vasoconstriction, and cutaneous vasoconstriction in particular, compensating for the ultrafiltration-induced decrease in blood volume is considered an important component in this setting. Therefore, to maintain temperature homeostasis, thermal energy has to be cleared from the patient by the extracorporeal system because cutaneous clearance of thermal energy is compromised intradialytically. The focus on dialysate temperature alone does not properly address the problem of controlled extracorporeal heat removal because dialysate temperature is only one of the variables involved in that process. These difficulties can be addressed by changing from the control of dialysate temperature to control of body temperature. Control of body temperature and temperature homeostasis is achievable by the physiologic feedback control system realized in the temperature control mode (T-mode) of the blood temperature monitor (BTM). The delivery of isothermic dialysis, that is, dialysis where body temperature is controlled to remain constant during the treatment, has impressively improved hemodynamic stability in hypotension prone patients.     

Haemodialysis with on-line monitoring equipment: tools or toys?

BACKGROUND: On-line monitoring of chemical/physical signals during haemodialysis (HD) and bio-feedback represents the first step towards a 'physiological' HD system incorporating adaptive and logic controls in order to achieve pre-set treatment targets. METHODS: Discussions took place to achieve a consensus on key points relating to on-line monitoring and bio-feedback, focusing on the clinical applications. RESULTS: The relative blood volume (BV) reduction during HD can be monitored by optic devices detecting the variations in concentration of haemoglobin/haematocrit. BV changes result from an equilibrium between ultrafiltration and the refilling capacity. However, BV reduction has little power in predicting intra-HD hypotensive episodes, while the combination of the patient-dialysate sodium gradient, the relative BV reduction between the 20th and 40th minute of HD, the irregularity of the profile of BV reduction over time and the heart rate decrease from the start to the 20th minute of HD predict intra-HD hypotension with a sensitivity of 82%, a specificity of 73% and an accuracy of 80%. A bio-feedback system drives the relative BV reduction according to desired values by instantaneously changing the ultrafiltration rate and the dialysate conductivity. This system has proved to reduce the incidence of intra-HD hypotension episodes significantly. Ionic dialysance and the patient's plasma conductivity can be calculated easily from on-line inlet and outlet dialysate conductivity measurements at two different steps of dialysate conductivity. Ionic dialysance is equivalent to urea clearance corrected for recirculation and is a tool for continuously monitoring the dialysis efficiency and detecting early problems with the delivery of the prescribed dose of dialysis. Given the strict and linear relationship between conductivity and sodium content, the conductivity values replace the sodium concentration values and this permits the development of a conductivity kinetic model, by means of which sodium balance can be achieved at each dialysis session. The conductivity kinetic model has been demonstrated to improve intra-HD cardiovascular stability in hypotension-prone patients significantly. Ionic dialysance is also a useful tool to monitor vascular access function, as it can be used to obtain serial measurements of vascular access blood flow. On-line urea monitors provide detailed information on intra-HD urea kinetics and delivered dialysis dose, but they are not in widespread use because of the costs related to the disposable materials (e.g. urease cartridge). The body temperature monitor measures the blood temperature at the arterial and venous lines of the extra-corporeal circuit and, thanks to a bio-feedback system, is able to modulate the dialysate temperature in order to influence the patient's core body temperature, which can be kept at constant values. This is associated with improved intra-HD cardiovascular stability. The module can also be used to quantify total recirculation. CONCLUSIONS: On-line monitoring devices and bio-feedback systems have evolved from toys for research use to tools for routine clinical application, particularly in patients with clinical complications. Conductivity monitoring appears the most versatile tool, as it permits quantification of delivered dialysis dose, achievement of sodium balance and surveillance of vascular access function, potentially at each dialysis session and without extra cost.     

The effect of sodium profiling and feedback technologies on plasma conductivity and ionic mass balance: a study in hypotension-prone dialysis patients.

BACKGROUND: Sodium profiling improves haemodynamic tolerance in haemodialysis (HD) patients but may also influence sodium homeostasis. Changes in blood volume and plasma conductivity (PC) during HD can be modelled by feedback technology, but their effects on sodium homeostasis are not widely studied. METHODS: This randomized crossover study compared PC and ionic mass balance (IMB) as surrogate markers of sodium balance between standard HD [dialysate conductivity (DC) 14.0 mS/cm], sodium profiling (DC 15.0-->14.0 mS/cm), blood volume (BV)-controlled and PC-controlled feedback (target: post-HD PC: 14.0 mS/cm) in 10 HD patients with frequent hypotension. RESULTS: 440 treatments were studied. Pre-dialytic PC was significantly higher during SP (14.4+/-0.2 mS/cm) compared to standard HD (14.2+/-0.3 mS/cm), and was not different between the other manoeuvres: PC-controlled (14.1+/-0.3 mS/cm), and BV-controlled feedback (14.2+/-0.2 mS/cm). Except for the first treatment, during which IMB was lower during the sodium profile, IMB did not differ significantly between the various manoeuvres and was strongly dependent upon ultrafiltration volume and the difference between pre-dialytic PC and DC. Symptomatic hypotensive episodes occurred least frequently during BV-controlled feedback (8%) compared to the other manoeuvres (standard HD, 16%; sodium profile, 14%; PC-controlled feedback, 17%), but differences were not significant. Inter-dialytic weight gain and pre-dialytic systolic blood pressure did not differ. CONCLUSIONS: Pre-dialytic PC increased during the sodium profile, and did not differ between BV- or PC-controlled feedback compared to standard HD. Thus, it appears that both BV- and PC-controlled feedback can be safely prescribed without substantial salt- and water-loading, at least in the short term. Analysis of IMB is useful to assess differences in sodium balance between single treatment sessions but appears of less value in a steady-state situation.     

Preventing dialysis hypotension: a comparison of usual protective maneuvers

BACKGROUND: Intradialytic hypotension (IH) is a common adverse event. Currently, there are several commonly utilized therapies of IH, but they have not been compared directly in the same group of patients. We performed the present study in order to learn which of these techniques is most effective so that a rational approach to treating IH could then be formulated. METHODS: A single-blinded, crossover study design of five different protocols was undertaken in 10 hemodialysis patients with a prior history of IH. Each patient first underwent one week (three dialyses) of standard dialysis (dialysate sodium 138 mEq/L). Then each patient was subjected to one week each (three dialyses) of the four test protocols, performed in random order in a blinded fashion. The specific protocols were as follows: high sodium dialysate, in which the patient was dialyzed using a dialysate sodium of 144 mEq/L; sodium modeling, during which the dialysate sodium declined from 152 to 140 mEq/L in the last half hour of dialysis; one hour of isolated ultrafiltration followed by three hours of isovolemic dialysis; and cool temperature dialysis in which the dialysate was cooled to 35 degrees C. RESULTS: Weight loss in each of the five protocols was essentially identical, varying between 2.9 and 3 kg. There were significantly fewer hypotensive episodes per treatment in the sodium modeling, high sodium, and cool temperature protocols as compared with the standard protocol (P < 0.05). Ultrafiltration followed by dialysis was associated with a significantly greater number of hypotensive episodes per treatment than any of the three test protocols (P < 0.05). Similarly, the number of nursing interventions required for IH per treatment was significantly greater in the standard dialysis and in the isolated ultrafiltration protocols compared with sodium modeling and cool temperature protocols (P < 0.05). The number of hypotensive signs and symptoms per treatment was also significantly reduced during the sodium modeling and cool temperature protocols compared with the standard protocol (P < 0.004 and P < 0.02, respectively). Again, the isolated ultrafiltration protocol resulted in significantly more hypotensive symptoms and signs than the three test protocols (P < 0.005). Finally, the nadir mean arterial pressures were significantly lower in the standard and isolated ultrafiltration protocols when compared with the three test protocols (P < 0.05). The upright postdialysis blood pressure was best preserved in the sodium modeling and cool temperature protocols compared with the standard and isolated ultrafiltration protocols (P < 0.05). CONCLUSION: This study supports the use of sodium modeling as a first step in combating IH. Also effective were the use of cool-temperature dialysate and a high-sodium dialysate. All three test protocols were well tolerated. As applied in this study, isolated ultrafiltration followed by isovolemic dialysis was notably less effective in reducing IH.     

Effect of cool temperature dialysate on the quality and patients' perception of haemodialysis.

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 degrees C) followed by another three sessions using a standard dialysate temperature (36.5 degrees 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.     

Effect of ultrafiltration on thermal variables, skin temperature, skin blood flow, and energy expenditure during ultrapure hemodialysis

The cause of the increase in core temperature (CT) during hemodialysis (HD) is still under debate. It has been suggested that peripheral vasoconstriction as a result of hypovolemia, leading to a reduced dissipation of heat from the skin, is the main cause of this increase in CT. If so, then it would be expected that extracorporeal heat flow (Jex) needed to maintain a stable CT (isothermic; T-control = 0, no change in CT) is largely different between body temperature control HD combined with ultrafiltration (UF) and body temperature control HD without UF (isovolemic). Consequently, significant differences in DeltaCT would be expected between isovolemic HD and HD combined with UF at zero Jex (thermoneutral; E-control = 0, no supply or removal of thermal energy to and from the extracorporeal circulation). During the latter treatment, the CT is expected to increase. In this study, changes in thermal variables (CT and Jex), skin blood flow, energy expenditure, and cytokines (TNF-alpha, IL-1 receptor antagonist, and IL-6) were compared in 13 patients, each undergoing body temperature control (T-control = 0) HD without and with UF and energy-neutral (E-control = 0) HD without and with UF. CT increased equally during energy-neutral treatments, with (0.32 +/- 0.16 degrees C; P = 0.000) and without (0.27 +/- 0.29 degrees C; P = 0.006) UF. In body temperature control treatments, the relationship between Jex and UF tended to be significant (r = -0.51; P = 0.07); however, there was no significant difference in cooling requirements regardless of whether treatments were done without (-17.9 +/- 9.3W) or with UF (-17.8 +/- 13.27W). Changes in energy expenditure did not differ among the four treatment modes. There were no significant differences in pre- and postdialysis levels of cytokines within or between treatments. Although fluid removal has an effect on thermal variables, no single mechanism seems to be responsible for the increased heat accumulation during HD.     

QTc dispersion increases during hemodialysis with low-calcium dialysate

BACKGROUND: The risk of ventricular arrhythmias is known to increase during hemodialysis (HD) treatment, but the cause of this phenomenon has remained unidentified. QT dispersion (= QTmax - QTmin) reflects heterogeneity of cardiac repolarization, and increased dispersion is known to predispose the heart to ventricular arrhythmias and sudden cardiac death. METHODS: We studied the effect of dialysate calcium concentration on cardiac electrical stability during HD treatment in 23 end-stage renal disease patients. Three HD treatments were applied with dialysate Ca++ concentrations of 1.25 mmol/L (dCa++1.25), 1.5 mmol/L (dCa++1.5), and 1.75 mmol/L (dCa++1.75). The QTc interval and QTc dispersion were measured before and after the three sessions. RESULTS: With the dCa++1.5 and dCa++1.75 dialyses, serum Ca++ increased and the QTc interval remained stable (dCa++1.5) or decreased (dCa++1.75), but no significant change was noted in QTc dispersion. With dCa++1.25 HD, serum Ca++ decreased (1.24 +/- 0.11 vs. 1.20 +/- 0.09 mmol/L, P < 0. 05), and both the QTc interval (403 +/- 27 vs. 419 +/- 33 ms, P < 0. 05) and QTc dispersion increased (38 +/- 19 vs. 49 +/- 18 ms, P < 0. 05). The change in the QTc interval correlated inversely with the change in serum Ca++ (r = -0.68, P < 0.0001). Except for serum Ca++ and plasma intact parathyroid hormone, predialysis and postdialysis values in other blood chemistry, blood pressure, heart rate, body weight, and total ultrafiltration were equal in the three dialysis sessions. CONCLUSION: This study is the first, to our knowledge, to demonstrate that HD increases QTc dispersion if a low-calcium (dCa++1.25) dialysate is used. This indicates that the use of low-calcium dialysate may predispose HD patients to ventricular arrhythmias and that perhaps it should be avoided, at least when treating patients with pre-existing cardiac disease.     

Hemodialysis with low-temperature dialysate: a long-term experience

The effect of cool dialysate in hemodialysis (HD)-induced symptoms was studied in a group of 8 patients, neither diabetic nor anephric, with a high incidence of HD-induced hypotension (20-90%). Patients were studied during two consecutive periods of 6 months, the first one with dialysate at 37 degrees C (598 sessions) and the second one at 35 degrees C (599 sessions). Dialysis at low temperature was associated with a decrease in symptomatic hypotension (SH) (47.4 vs. 33.9%, p less than 0.001), a greater loss of weight during HD (1.52 +/- 0.03 vs. 1.71 +/- 0.03 kg, p less than 0.001) and stabilization of predialysis systolic blood pressure (SBP) at a lower level (144 +/- 0.69 vs. 139 +/- 0.98 mm Hg, p less than 0.001). At 37 degrees C, SH was associated with a higher ultrafiltration (1.71 +/- 0.05 vs. 1.32 +/- 0.05 kg, p less than 0.001). There was an improvement of symptoms both taken as a whole (55.6 vs. 45.8%, p less than 0.01) or one by one, cramps were the only exception as they increased at 35 degrees C (2.7 vs. 10.9%, p less than 0.001) being related with a greater weight loss at both temperatures (1.47 +/- 0.04 vs. 2.04 +/- 0.25 kg at 37 degrees C, p less than 0.001; 1.76 +/- 0.03 kg vs. 2.23 = 0.10 kg at 35 degrees C, p less than 0.001). In spite of the increase in the frequency of cramps, 7 out of 8 patients experienced some amelioration of dialysis symptoms (range between 7 and 21.4%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Resting energy expenditure and thermal balance during isothermic and thermoneutral haemodialysis--heat production does not explain increased body temperature during haemodialysis.

BACKGROUND: During routine haemodialysis (HD) body temperature increases, which contributes to haemodynamic instability. The relative roles of increased heat production and/or incomplete heat transfer are not fully elucidated. Concomitant measurement of heat production and heat transfer may help to assess the factors determining thermal balance during HD. METHODS: Thirteen stable non-diabetic maintenance HD patients were investigated during two HD procedures (isothermic, dT = 0, no change of body temperature; thermoneutral, dE = 0, no energy transfer between blood and dialysate), using a blood temperature monitor (BTM) in active mode. Energy transfer, blood and dialysate temperature, and relative blood volume change (dBV) were continuously recorded, and resting energy expenditure (REE; Deltatrac Datex) was measured repeatedly during each procedure. Fourteen healthy persons served as controls for REE comparison. RESULTS: In isothermic HD, median energy removal was 218 kJ/4 h HD (= heat flow -15.1 W). This cooling correlated with dBV induced by ultrafiltration (rho = 0.731, P < 0.01). There was no difference in dBV between isothermic (7.7%) and thermoneutral (8.1%) HD. Predialysis REE was 82.8 W/1.73 m(2), not different from controls. No variation in REE during HD was observed, except a small and transient increase after a light meal (5 and 4%). In the time course of REE, no difference between the procedures was found. CONCLUSIONS: Our findings suggest that stable maintenance HD patients have REE not different from healthy controls, that HD procedure per se does not significantly increase REE and that neither isothermic nor thermoneutral regimen has any influence on metabolic rate. Therefore, body temperature elevation during routine HD may rather be due to decreased heat removal. With the use of BTM in active mode, body temperature can be kept stable (isothermic HD), which requires active cooling. This negative energy transfer is proportional to decrease in blood volume induced by ultrafiltration.     

Efficacy and safety of haemodialysis treatment with the Hemocontrol biofeedback system: a prospective medium-term study.

BACKGROUND: Hypovolaemia has been implicated as a major causal factor of morbidity during haemodialysis (HD). A model biofeedback control system for intra-HD blood volume (BV) changes modelling has been developed (Hemocontrol), Hospal Italy) to prevent destabilizing hypovolaemia. It is based on an adaptive controller incorporated in a HD machine (Integra), Hospal Italy). The Hemocontrol biofeedback system (HBS) monitors BV contraction during HD with an optical device. HBS modulates BV contraction rates by adjusting the ultrafiltration rate (UFR) and the refilling rate by adjusting dialysate conductivity (DC) in order to obtain the desired pre-determined BV trajectories. METHODS: Nineteen hypotension-prone uraemic patients (seven males, 12 females; mean age 64.5+/-3.0 SEM years; on maintenance HD for 80.5+/-13.2 months) volunteered for the present prospective study that compared the efficacy and safety of bicarbonate HD treatment equipped with HBS, as a whole, with the gold-standard bicarbonate treatment equipped with a constant UFR and DC (BD). The study included three phases: Medium-term studies started with one period of 6 months of BD and always had a follow-up period of HBS treatment ranging from 14 to 30 months (mean 24.0+/-1.6); short-term studies started in September 1999, when all patients went back to BD treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase A). Afterwards, they once again started HBS treatment for a wash-out period of 4 weeks and a short-term study period of a further 3 weeks (phase B). Every patient underwent acute studies during a single HD run, once during phase A and once in phase B. Resistance (R) and reactance (Xc) measurements were obtained utilizing a single-frequency (50 kHz) tetrapolar bioimpedance analysis (BIA). Extracellular fluid volume (ECV) was calculated from R, Xc, and height and body weight measurements using the conventional BIA regression equations. RESULTS: The overall occurrence of symptomatic hypotension and muscle cramps was significantly less in HBS treatment in both medium- and short-term studies. Self-evaluation of intra- and inter-HD symptoms (worst score=0, best score=10) revealed a statistically significant difference, as far as post-HD asthenia was concerned (6.2+/-0.2 in HBS treatment vs 4.3+/-0.1 in BD treatment, P<0.0001). No difference was observed between the two treatments when comparing pre- and post-HD lying blood pressure, heart rate, body weights and body weight changes in medium- and short-term studies. The residual BV%/ Delta ECV% ratio, expression of the vascular refilling, was significantly higher during HBS treatment in acute studies. CONCLUSIONS: HBS treatment is effective in lowering hypovolaemia-associated morbidity compared with BD treatment; this could be related to a greater ECV stability. Furthermore, HBS is a safe treatment in the medium-term because these results are not achieved through potentially harmful changes in blood pressure, body weight, and serum sodium concentration.     

Effects of acetate and bicarbonate dialysate in stable chronic dialysis patients

The effects of acetate and bicarbonate dialysate on the biochemical and clinical parameters of 16 stable chronic hemodialysis patients were investigated in a double-blind crossover study. A central delivery system was used for both types of dialysates with identical sodium concentrations (138 mEq/liter) and osmolality in a single-pass dialysate flow. The results indicate that dialysis with bicarbonate leads to significantly less hypoxemia (P less than or equal to 0.001) and hypotensive episodes (P less than or equal to 0.002) than with acetate. Pre- to post-dialysis blood pressure changes were also more marked during acetate dialysis. Older patients with recurrent hypotension on acetate benefit most from bicarbonate dialysate. This group of patients appears to metabolize acetate more slowly and has a significantly lower post-dialysis bicarbonate concentration (P less than or equal to 0.005) than asymptomatic patients during dialysis with acetate dialysate.     

The faster potassium-lowering effect of high dialysate bicarbonate concentrations in chronic haemodialysis patients.

BACKGROUND: Hyperkalaemia is common in patients with advanced renal disease. In this double-blind, randomized, three-sequence, crossover study, we compared the effect of three dialysate bicarbonate concentrations ([HCO3-]) on the kinetics of serum potassium (K+) reduction during a conventional haemodialysis (HD) session in chronic HD patients. METHODS: We studied eight stable HD patients. The choice of dialysate [HCO3-] followed a previously assigned treatment protocol and the [HCO3-] used were low bicarbonate (LB; 27 mmol/l), standard bicarbonate (SB; 35 mmol/l) and high bicarbonate (HB; 39 mmol/l). Polysulphone dialysers and automated machines provided blood flow rates of 300 ml/min and dialysis flow rates of 500 ml/min for each HD session. Blood samples were drawn at 0 (baseline), 15, 30, 60 and 240 min from the arterial extracorporeal line to assess blood gases and serum electrolytes. In three of the eight patients, we measured serum K+ 1 h post-dialysis as well as K+ removal by the dialysis. The same procedures were followed until the completion of the three arms of the study, with a 1 week interval between each experimental arm. RESULTS: Serum K+ decreased from 5.4+/-0.26 (baseline) to 4.96+/-0.20, 4.90+/-0.19, 4.68+/-0.13 and 4.24+/-0.15 mmol/l at 15, 30, 60 and 240 min, respectively, with LB; from 5.38+/-0.21 to 5.01+/-0.23, 4.70+/-0.25, 4.3+/-0.15 and 3.8+/-0.19 mmol/l, respectively, with SB; and from 5.45+/-0.25 to 4.79+/-0.17, 4.48+/-0.17, 3.86+/-0.16 and 3.34+/-0.11 mmol/l, respectively, with HB (P<0.05 for high vs standard and low [HCO3-] at 60 and 240 min). The decrease in serum K+ correlated with the rise in serum [HCO3-] in all but LB (P<0.05). Potassium rebound was 3.9+/-10.2%, 5.2+/-6.6% and 8.9+/-4.9% for LB, SB and HB dialysates, respectively (P=NS), while total K+ removal (mmol/dialysis) was 116.4+/-21.6 for LB, 73.2+/-12.8 for SB and 80.9+/-15.4 for HB (P=NS). CONCLUSIONS: High dialysate [HCO3-] was associated with a faster decrease in serum K+. Our results strongly suggest that this reduction was due to the enhanced shifting of K+ from the extracellular to the intracellular fluid compartment rather than its removal by dialysis. This finding could have an impact for those patients with life-threatening pre-HD hyperkalaemia.     

Thermal energy balance and body temperature: comparison between isolated ultrafiltration and haemodialysis at different dialysate temperatures.

BACKGROUND: Haemodynamic stability is better maintained during isolated ultrafiltration (i-UF) than during combined ultrafiltration/haemodialysis (UF + HD). This difference might be explained by differences in thermal energy balances. In this study we compared the thermal energy balance of i-UF with UF + HD at different dialysate temperatures (Td) and determined the Td at which the thermal energy balance during UF + HD is similar to the thermal energy balance during i-UF. METHODS: In the first part of the study, 10 chronic haemodialysis patients were compared during three different treatment sessions, i-UF, UF + HD at Td of 35.5 degrees C and UF + HD at Td of 37.5 degrees C. The second part of the study consisted of one session of 1 h of UF + HD (UF + HD ET-set) with a pre-set energy transfer (ET) at the same level of ET found for that particular patient during i-UF in the first part of the study. RESULTS: First part of the study: body temperature (BT) decreased significantly during i-UF (-0.25 +/- 0.25 degrees C, P<0.05) and UF + HD 35.5 degrees C (-0.24 +/- 0.18 degrees C, P<0.05) and increased significantly during UF + HD 37.5 degrees C (+0.18 +/- 0.19 degrees C, P<0.05). The differences between the change in BT during UF + HD 37.5 degrees C compared with the other treatments were significant (P<0.05). ET gave a significantly more negative value during i-UF (-30.8 +/- 3.1 W, P<0.05) than during UF + HD 35.5 degrees C (-23.6 +/- 4.1 W, P<0.05). A slightly positive ET was found during UF + HD 37.5 degrees C (+0.4 +/- 4.7 W, P=not significant). Second part of the study: there was a slight, but not significant, decrease in BT during UF + HD ET-set (-0.17 +/- 0.26 degrees C). The changes in BT did not differ significantly between i-UF and UF + HD ET-set. After 1 h of UF + HD ET-set, the mean Td was 34.75 degrees C (34.0-36.0 degrees C). The correlation between pre-dialysis BT and Td during UF + HD ET-set was significant (r=0.764, P<0.05). CONCLUSION: ET gives a more negative value during i-UF than during UF + HD 35.5 degrees C and than during UF + HD 37.5 degrees C. To obtain the same thermal ET during UF + HD as that achieved during i-UF, a mean Td of 34.75 degrees C is needed, depending on the pre-dialytic BT of the patient. The results of this study may be of relevance in relation to future clinical investigations which can elucidate whether differences in vascular response between i-UF and UF + HD are only related to differences in thermal balance.