[Acute renal replacement therapy in the intensive care unit]

On the intensive care department the most frequently used acute renal replacement techniques are intermittent haemodialysis and continuous haemofiltration. Although continuous techniques appear to have distinct advantages in the treatment of critically ill patients, no consistent differences in mortality have been found between continuous and intermittent treatment modalities. Due to uncertainty in this area, the use of unmodified cellulose membranes is probably best avoided. No good randomised studies are available with regard to the starting time of renal replacement techniques in critically ill patients. However, generally speaking a 'late' start should be avoided. With continuous techniques, the filtration volume should not be below 35 ml/kg/h. Although continuous (high-volume) filtration techniques may contribute to an improvement in the haemodynamics, the mechanisms behind this phenomenon remain unclear. At present, no randomised studies are available which have shown a beneficial effect of continuous techniques on the survival of critically ill patients without manifest renal insufficiency being demonstrated.

Optimizing dialysis dose by increasing blood flow rate in patients with reduced vascular-access flow rate

Dialysis efficacy indexed by Kt/V can generally be augmented by increasing the dialyzer blood flow rate. However, increasing the dialyzer blood flow rate may lead to vascular-access recirculation (AR) in patients with a compromised vascular-access flow rate. This can have an attenuating effect on dialysis efficacy. The aim of the present study is to investigate the effect of dialyzer blood flow rates of 200, 300, and 400 mL/min on AR and Kt/V in 8 patients with low (<600 mL/min) and 13 patients with normal (>600 mL/min) vascular-access flow rates. AR and vascular-access flow rate were determined using an ultrasound saline dilution technique, and session-delivered Kt/V was computed using an on-line dialysate urea monitor. AR was minor and only observed in 4 patients in the low vascular-access flow rate group (0.9% +/- 0.6%) at dialyzer blood flow rates of 200 mL/min (1 patient), 300 mL/min (2 patients), and 400 mL/min (3 patients) and 4 patients in the normal vascular-access flow rate group (1.2% +/- 1.1%) at dialyzer blood flow rates of 200 mL/min (3 patients) and 300 mL/min (1 patient). Kt/V increased with increasing dialyzer blood flow rates in both groups, and in individual cases, there was no decrease in Kt/V at greater dialyzer blood flow rates in either group. Also in those patients with minor AR, Kt/V increased at greater dialyzer blood flow rates, except in 1 patient in the low-flow group, in whom Kt/V remained unchanged at a change in dialyzer blood flow rate from 300 to 400 mL/min, whereas AR increased. From this study, it is concluded that even in patients with low access flow, increasing dialyzer blood flow rate in general leads to an increase in delivered Kt/V regardless of vascular access flow rate.

The influence of increasing dialysis treatment time and reducing dry weight on blood pressure control in hemodialysis patients: a prospective study

A good blood pressure control can be achieved with long hemodialysis sessions (dialysis center of Tassin, France). However, it is not well known whether a higher dialysis dose or a lower dry weight is responsible for this phenomenon. In a preliminary study, 21 hypertensive dialysis patients, dialyzed three times a week for 3-5 h, were randomized into three groups during a 3-month study period. In 6 patients, the dialysis treatment time was increased by 2 h, and the dry weight was gradually decreased (group 1). In 7 patients the dialysis treatment time was increased by 2 h without a change in dry weight (group 2). In 8 patients the dry weight was gradually lowered without changing the dialysis treatment time (group 3). Before and after the study, cardiac index and left ventricular mass index (echocardiography) and forearm vascular resistance (strain gauge plethysmography) were determined on a middialytic day. The blood pressure was assessed by 48-hour ambulatory monitoring. The antihypertensive medication was reduced when the postdialytic blood pressure became <130/80 mm Hg. The dry weight was reduced by 2.6 +/- 1.4 kg in group 1 and by 2.3 +/- 0.8 kg in group 3 (p < 0.05). The number of classes of antihypertensive medication was reduced from 3.3 to 1.8 in group 1 (NS), from 2.4 to 1.7 in group 2 (NS), and from 3.1 to 1.3 in group 3 (p < 0.05). The dose of the remaining antihypertensive drugs was reduced by 50% in group 1 (p < 0.05), by 32% in group 2 (NS), and by 72.2% in group 3 (p < 0.05). The interdialytic systolic blood pressure decreased significantly after increasing the dialysis time without changing the dry weight (group 2: 7 +/- 5 mm Hg; p < 0.05). The systolic blood pressure was also lower in the other patients groups: group 1: 13 +/- 26 mm Hg, group 3 : 7 +/- 16 mm Hg (NS). The pulse pressure decreased significantly in group 2 (7 +/- 5 mm Hg; p < 0.05) and in group 3 (6 +/- 7 mm Hg; p < 0.05) and tended to decrease in group 1 (11 +/- 12 mm Hg; p = 0.08). The diastolic blood pressure and the day-night blood pressure difference did not change significantly, nor did cardiac index and left ventricular mass index. The forearm vascular resistance tended to decrease in the patients on long dialysis sessions. This preliminary study suggests that the dialysis treatment time might have an independent beneficial effect on blood pressure control.

Role of bioimpedance spectroscopy in assessment of body water compartments in hemodialysis patients

Bioimpedance spectroscopy (BIS) has been advocated as a tool to assess fluid status in hemodialysis (HD) patients. However, uncertainty remains about the reliability of BIS in patients with abnormalities in fluid status. Aims of the study are to assess the agreement between total-body water (TBW) and extracellular volume (ECW) measured by BIS and tracer dilution (deuterium oxide [D(2)O] and sodium bromide [NaBr]), the influence of the relative magnitude of water compartments (expressed as TBW(D(2)O) and ECW(NaBr):body weight) on the agreement between BIS and tracer dilution, and the ability of BIS to predict acute changes in fluid status. BIS and tracer dilution techniques were performed in 17 HD patients before a dialysis session. Moreover, the relation between BIS and gravimetric weight changes was assessed during both isolated ultrafiltration and HD. Correlation coefficients between TBW and ECW measured by BIS and tracer dilution were r = 0.71 and r = 0.71, respectively. Mean differences (tracer-BIS) were 6.9 L (limits of agreement, -1.5 to 21.6 L) for TBW and 2.3 L (limits of agreement, -1.7 to 9.7 L) for ECW. There was a significant relationship between the relative magnitude of TBW and ECW compartments and disagreement between BIS and tracer dilution (r = 0.65 and r = 0.77; P < 0.05). During both isolated ultrafiltration and HD, there was a significant relation between gravimetric changes and change in ECW(BIS) (r = 0.83 and r = 0.76; P < 0.05), but not with change in TBW(BIS). In conclusion, agreement between BIS and tracer dilution techniques in the assessment of TBW and ECW in HD patients is unsatisfactory. The discrepancy between BIS and dilution techniques is related to the relative magnitude of body water compartments. Nevertheless, BIS adequately predicted acute changes in ECW during isolated ultrafiltration and HD, in contrast to changes in TBW.

A comparison between office and ambulatory blood pressure measurements in renal transplant patients with chronic transplant nephropathy

Hypertension is an important risk factor for chronic transplant nephropathy. Therapy is usually based on casual office blood pressure (BP) measurements. However, it is not well known how casual BP predicts 24-hour BP in this population. The main focus of this study is to compare casual office BP with 24-hour ambulatory BP monitoring in renal transplant recipients with signs of chronic transplant nephropathy. Moreover, in this group, the day-night BP profile was assessed. In 36 renal transplant recipients with incipient or progressive proteinuria or an increase in serum creatinine level greater than 20%, 24-hour ambulatory BP was performed. Patients were defined as a nondipper if the mean BP decreased by less than 10% during the nighttime period. The correlation between single office and 24-hour ambulatory BPs was 0.61 for systolic BP and 0.55 for diastolic BP (P < 0.001). The mean difference between 24-hour ambulatory and single office BPs was -4.2 +/- 18.6 mm Hg (range, -44 to 36 mm Hg) for systolic BP and -1.1 +/- 10.7 mm Hg (range, -34 to 27 mm Hg) for diastolic BP; 94.5% of patients were classified as nondippers. There was a significant relation between the nightly decline in mean arterial pressure and calculated creatinine clearance (r = 0.34; P < 0.05). In conclusion, in renal transplant recipients with chronic transplant nephropathy, a large difference between office and ambulatory BPs is present, with both overestimation and underestimation of 24-hour BP by office BP measurements. Moreover, a severely disturbed day-night BP rhythm was observed. In transplant recipients with compromised graft function, office BP may not reflect 24-hour BP adequately, and ambulatory BP measurements should be considered.

Effects of a venous cuff at the venous anastomosis of polytetrafluoroethylene grafts for hemodialysis vascular access

INTRODUCTION AND METHODS

The most frequent complication of polytetrafluoroethylene (PTFE) arteriovenous grafts for hemodialysis is thrombotic occlusion due to stenosis caused by intimal hyperplasia. This complication is also known for peripheral bypass grafts. Because the use of a venous cuff at the distal anastomosis improves the patency of peripheral bypass grafts, we considered that it might also improve the patency of PTFE arteriovenous grafts. Therefore, a randomized multicenter trial was carried out to study the effect of a venous cuff at the venous anastomosis of PTFE arteriovenous grafts on the development of stenoses and the patency rates.

RESULTS

Of the 120 included patients, 59 were randomized for a venous cuff. The incidence of thrombotic occlusion was lower in the cuff group (0.68 per patient-year) than in the no-cuff group (0. 88 per patient-year; P =.0007). However, the primary and secondary patency rates were comparable. The cuff group tended to have fewer stenoses at the venous and arterial anastomoses when examined with duplex scan. Graft failure was higher in patients with an initial anastomosing vein diameter smaller than 4 mm (7 of 18 [39%]) than in those with a vein diameter of 4 mm or larger (16 of 88 [18%]; P =. 052). Local edema, skin atrophy, and obesity yielded a higher risk on graft failure (23% vs 11%).

CONCLUSION

A venous cuff at the venous anastomosis of PTFE arteriovenous grafts for hemodialysis reduced the incidence of thrombotic occlusions; stenosis at the venous anastomosis was reduced. However, this did not result in a better patency rate. Therefore, the venous cuff should not be used routinely. Initial vein diameter and local problems (edema, obesity, or skin atrophy) appear to be the most important risk factors for graft failure.

Blood pressure control and hemodynamic changes in patients on long time dialysis treatment

In dialysis patients blood pressure can be well controlled with long dialysis (3 times a week for 8 h) in contrast to a more common short dialysis regime (3 times a week for 4 h). We studied whether the good blood pressure control in patients on long dialysis as compared to patients on short dialysis was associated with a decrease in extracellular fluid volume. Two-day interdialytic ambulatory blood pressure monitoring was performed in 26 non-diabetic patients on long dialysis, in 22 patients on short dialysis, matched for the years they were on dialysis treatment, and during 24 h in 19 healthy volunteers. After full equilibration, 24 h after dialysis, echography of the inferior caval vein was performed to determine fluid state. Cardiac dimensions and stroke index were measured by echocardiography. A blood sample was drawn for the determination of electrolytes and vasoactive hormones. 73% of the patients on short dialysis were using antihypertensive medication in contrast to none of the patients on long dialysis. However, blood pressure was significantly lower in patients on long dialysis (115 +/- 21/67 +/- 11 mm Hg) when compared to patients on short dialysis (143 +/- 26/81 +/- 16 mm Hg). Indexed caval vein diameter, left ventricular diameter index, and atrial natriuretic peptide were not significantly different in patients on long dialysis compared to patients on short dialysis. Also the cardiac index was comparable in patients on long and short dialysis. However, the total peripheral resistance index was significantly lower in patients on long dialysis compared to the patients on short dialysis and normal controls. The left ventricular mass index was increased in both patients on long and short dialysis compared to controls. We conclude that patients on long dialysis have adequate blood pressure control that seems mainly to be caused by a low total peripheral resistance. These data also suggest that factors other than a lower fluid state contribute to the good blood pressure control in patients on long dialysis.

Strategies for improving hemodynamic stability in cardiac-compromised dialysis patients

In hemodialysis patients, structural changes at all levels of the cardiovascular system are common. The presence of these cardiovascular changes is a risk factor for the development of intradialytic hypotension. This explains the clinical observation that the incidence of symptomatic hypotension is high in elderly hemodialysis patients, who often have a history of long-standing hypertension and atherosclerosis, and in hemodialysis patients with cardiovascular disease. With an increasing number of cardiovascular compromised dialysis patients, special attention should be given to this group of patients. As the age of patients on hemodialysis increases steadily, it is a challenge to provide comfortable treatment in these patients by reducing the incidence of symptomatic hypotensive periods. This article describes the use of relatively new and simple clinical maneuvers to reduce the incidence of symptomatic hypotension.

[Hypotensive periods during hemodialysis]

Hypotensive periods occur frequently during a haemodialysis session. The pathogenesis of intradialytic hypotension is multifactorial. The initiating factor is a decline in blood volume. Important contributory factors are inadequate vascular reactivity during haemodialysis and structural cardiovascular abnormalities. Compared with 'standard' haemodialysis, vascular reactivity is clearly increased during isolated ultrafiltration, haemodialysis with lowered fluid temperature (e.g. 36 degrees C), and haemofiltration. The single most important factor explaining these differences in vascular response is the thermal energy balance during the various treatment modalities. With a critical reduction of cardiac filling, the Bezold-Jarish reflex may occur, leading to paradoxical vasodilation and bradycardia.

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.

Haemodialysis vascular access and fistula surveillance methods in The Netherlands

INTRODUCTION

As the mean age of haemodialysis patients is increasing, fewer patients will have suitable blood vessels for the creation of a Brescia-Cimino fistula and an increased use of graft implants is to be expected.

METHODS

To assess the change in vascular access and the use of surveillance techniques, all haemodialysis centres in The Netherlands received a questionnaire regarding the types of vascular accesses and surveillance techniques used in their department on 31 December, 1996. The results were related to a comparable study done in 1987, shown between brackets.

RESULTS

The response of the haemodialysis staff was 96%, of the vascular surgeons this was 91%. Sixty-two per cent (70%) of the patients had Brescia-Cimino fistulas, 21% (13%) Polytetrafluoroethylene (PTFE) graft fistulas, 17% (17%) other vascular accesses. Scheduled surveillance for stenosis detection was done by recirculation measurements in 6%, venous pressure measurements in 31%, Duplex scanning in 11% and angiography in 11% of the centres. When access problems occurred, 79% of the physicians performed recirculation measurements, 38% venous pressure measurements, 79% Duplex scanning and 100% angiography. In 46% of the centres PTA was done occasionally, and in 46% routinely for the treatment of stenotic complications in arteriovenous fistulas.

CONCLUSIONS

The use of PTFE grafts and other types of vascular accesses has increased at the expense of BC fistulas. Recirculation and venous pressure measurements are primarily done when problems occur and not according to a standard surveillance schedule. For visualization of failing fistulas, 79% of the centres uses Duplex ultrasound analysis and 100% angiography. The popularity of PTA has increased from 46 to 92% of the centres.

Effect of intravenous saline, albumin, or hydroxyethylstarch on blood volume during combined ultrafiltration and hemodialysis

It is generally advocated to use saline or albumin infusions during symptomatic hypotension during dialysis. However, because of their side effects and/or costs, they are of limited use. Hydroxyethylstarch (HES), a synthetic colloid with a long-standing volume effect, is used in the management of hypovolemia. In this study, the efficacy of three fluids (isotonic saline [0.9%], albumin [20%], and HES [10%]) was assessed during three treatment sessions with combined ultrafiltration and hemodialysis, which differed in the type of fluid given intravenously. Changes in relative blood volume (BV), systolic BP (SBP), and vascular reactivity (venous tone [VT]) were compared. An intravenous infusion of 100 ml of fluid was given when the decrease in BV versus baseline was more than 10% as measured by a continuous optical reflection method. The ultrafiltration was continued. BV decreased significantly versus baseline independent of the intravenous fluid administration in all three treatment sessions. However, when we compared BV values at the end of the dialysis session with those at the time of infusion, BV continued to decrease significantly with saline (change in BV -4.56 +/- 2.75%; P < 0.05) and albumin (change in BV -2.13 +/- 2.51%; P < 0.05), but not with HES (change in BV -0.15 +/- 2.17%; NS). Between albumin and HES there were no significant differences in changes in BV (NS), whereas between HES and saline (P < 0.05) and between albumin and saline (P < 0.05) the differences in BV changes were significant. SBP remained unchanged within each session. Although SBP tended to decrease more with saline compared to albumin and HES, the difference was not significant. The higher decrease in BV and SBP with saline was counterbalanced by a significantly higher increase in VT, while VT remained unchanged in the other two sessions. It is concluded that HES is a promising fluid in preserving blood volume, comparable to albumin, but superior to saline.

Effect of dialysate temperature on energy balance during hemodialysis: quantification of extracorporeal energy transfer

An impaired vascular response is implicated in the pathogenesis of dialysis-induced hypotension, which is at least partly related to changes in extracorporeal blood temperature (Temp). However, little is known about changes in core Temp and differences in energy balance between standard and cool dialysis. In this study, core Temp and energy transfer between extracorporeal circuit and patient, as well as the blood pressure response, were assessed during dialysis with standard (37.5 degrees C) and cool (35.5 degrees C) Temp of the dialysate. Nine patients (4 men, 5 women; mean age, 69 +/-10 [SD] years) were studied during low- and standard-Temp dialysis, each serving as his or her own control. Bicarbonate dialysis and hemophane membranes were used. Energy transfer was assessed by continuous measurement of Temp in the arterial (Tart) and venous side (Tven) of the extracorporeal system according to the formula: c. rho.Qb*(Tven - Tart)*t, where c = specific thermal capacity (3.64 kJ/kg* degrees C), Qb = extracorporeal blood flow, rho = density of blood (1,052 kg/m3), and t = dialysis time (hours). Core Temp was also measured by Blood Temperature Monitoring (BTM; Fresenius, Bad Homburg, Germany). Core Temp increased during standard-Temp dialysis (36.7 degrees C +/- 0.3 degrees C to 37.2 degrees C +/- 0.2 degrees C; P < 0.05) despite a small negative energy balance (-85 +/- 43 kJ) from the patient to the extracorporeal circuit. During cool dialysis, energy loss was much more pronounced (-286 +/- 73 kJ; P < 0.05). However, mean core Temp remained stable (36.4 degrees C +/- 0.6 degrees C to 36.4 degrees C +/- 0.3 degrees C; P = not significant), and even increased in some patients with a low predialytic core Temp. Both during standard and cool dialysis, the increase in core Temp during dialysis was significantly related to predialytic core Temp (r = 0.88 and r = 0.77; P < 0.05). Systolic blood pressure (RR) decreased to a greater degree during standard-Temp dialysis compared with cool dialysis (43 +/- 21 v 22 +/- 26 mm Hg; P < 0.05), whereas diastolic RR tended to decrease more (15 +/- 10 v 0 +/- 19 mm Hg; P = 0.07). Core Temp increased in all patients during standard-Temp dialysis despite a small net energy transfer from the patient to the extracorporeal system. Concluding, Core Temp remained generally stable during cool dialysis despite significant energy loss from the patient to the extracorporeal circuit, and even increased in some patients with a low predialytic core Temp. The change in core Temp during standard and cool dialysis was significantly related to the predialytic blood Temp of the patient, both during cool- and standard-Temp dialysis. The results suggest that the hemodialysis procedure itself affects core Temp regulation, which may have important consequences for the vascular response during hypovolemia. The removal of heat by the extracorporeal circuit and/or the activation of autoregulatory mechanisms attempting to preserve core Temp might be responsible for the beneficial hemodynamic effects of cool dialysis.

The effect of dialysate temperature on energy transfer during hemodialysis (HD)

It is well known that the use of low temperature (T) dialysate can have a positive impact on hemodynamic stability during HD. However, little is known on the energy transfer (ET) from the extracorporeal system to the patient in relation to variations in dialysate T (Tdial). In this study, we assessed ET, body T (Tbody), and blood pressure (BP) during dialysis with normal Tdial (37.5 degrees C) and low Tdial (35.5 degrees C). Nine patients (4 males, 5 females; mean age 68 +/- 10 years) were studied with the patient as his/her own control. Bicarbonate was used as dialysate buffer. Hemophane membranes were used. Dialysis contained <100 CFU/mL. Ultrafiltration volume was comparable between the 2 treatment sessions. ET was assessed by continuous measurement of T in the arterial (Tart) and venous side (Tven) of the extracorporeal system (Fresenius BTM(R)) according to the formula: ET = (Tven - Tart) * blood flow * treatment time * specific thermal capacity (3.64 kJ/kg* degrees C) * blood density (1052 kg/m3). RESULTS: Results: mean+/-SD Tdial 37.5 Tdial 35.5 p Delta Syst BP mmHg -43 +/-21 -22 +/-26 <0.05 Delta Dias BP mmHg -15 +/-10 0 +/-19 0.07 Tbody before HD ( degrees C) 36.7 +/-0.3 36.4 +/-0.6 NS Tbody after HD ( degrees C) 37.2 +/-0.2 36.4 +/-0.3 <0.001 Tven after HD ( degrees C) 36.7 +/-0.1 35.0 +/-0.2 <0. 001 ET (kJ) -86 +/-43 -286 +/-74 <0.001 CONCLUSION: Tbody remained stable during Tdial = 35.5 degrees C despite significant energy loss and increased during Tdial = 37.5 degrees C despite netto ET from the patient to the extracorporeal system. The latter suggests that HD itself leads to intrinsic heat generation in the patient. The removal of this excess heat in combination with the cardiovascular response to maintain Tbody may be responsible for the beneficial hemodynamic effects of low Tdial.

Salt and hypertension in end-stage renal disease

Salt and fluid overload play an important role in the pathogenesis of hypertension in patients with end-stage renal disease. However, in the individual patient, the relation between salt loading and blood pressure response is variable and appears to be influenced by various neurohumoral regulatory mechanisms. This may also have implications for the pathogenesis of structural cardiovascular abnormalities in patients with end-stage renal disease.

[Cardiovascular diseases in dialysis patients]

Cardiovascular morbidity and mortality are higher among dialysis patients than among the general population. The cardiovascular problems often exist before the start of dialysis. Their pathogenesis is multifactorial in dialysis patients also. The prevalence of left ventricular hypertrophy is strongly increased. Adequate therapy may lead to partial remission. Cardiac ischaemia is frequent among dialysis patients and may occur without severe coronary artery disease. The prognosis of myocardial infarction in dialysis patients is poorer than in the general population. There is no proven difference between the various dialysis techniques regarding cardiovascular morbidity and mortality, while kidney transplantation may have a beneficial effect. Early diagnosis and treatment aimed at risk factors for cardiovascular disease are indicated.

[Arterial perfusion disorders of the hand in 9 patients with arteriovenous fistula for hemodialysis]

OBJECTIVE

To describe the treatment of hand ischaemia as a complication of arteriovenous fistulas, which have been used for haemodialysis vascular access.

DESIGN

Retrospective.

METHODS

In 1990-1998 there were in the University Hospital Maastricht, (AZM), the Netherlands, 9 patients with hand ischaemia as a complication of arteriovenous fistulas for haemodialysis. Five of these originated from the AZM, where in the same period 341 fistulas had been created. Data were collected from archives about the treatment in the 9 patients and its results.

RESULTS

The patients were 7 women and 2 men, with a mean age of 61 years (range: 35-73). Four patients had diabetes mellitus. All patients had a high-flow AV fistula (mean flow: 1556 ml/min) at the level of the elbow. Surgical revision to diminish access flow volume was carried out in 2 patients, while fistula closure with creation of a new AV fistula was performed in 7 patients. Because of persistent ischaemia in 2 patients the access site was closed. Finger amputation was necessary in 3 patients.

CONCLUSION

Of all patients with new vascular accesses 1.5% developed symptomatic ischaemic complications. Two out of 9 AV fistulas could be preserved after surgical correction and in 3 patients finger amputations were carried out because of irreversible necrosis.

Fluid state and blood pressure control in patients treated with long and short haemodialysis

BACKGROUND

Patients treated at the haemodialysis (HD) centre in Tassin, France have been reported to have superior survival and blood pressure (BP) control. This control has been ascribed to maintenance of an adequate fluid state, antihypertensive drugs being required in < 5% of the patients, although it could not be excluded that a high dose of HD regarding removal of uraemic toxins might also have been of value.

METHODS

The aim of the study was to assess the fluid state and BP in normotensive patients on long HD (8 h) in Tassin (group TN) using bioimpedance to measure extracellular volume (ECV), ultrasound for determining the inferior vena cava diameter (IVCD), and 'on-line' monitoring of the change in blood volume (BV), and to compare them with normotensive (group SN) and hypertensive (group SH) patients on short HD (3-5 h) at centres in Sweden. ECV was normalized (ECVn) by arbitrarily setting the median ECV (in % of body weight) in SN patients at 100% for each gender, recalculating the individual values and combining the results for male and female patients in each group.

RESULTS

The dose of HD (Kt/V urea) was higher for TN patients than for Swedish patients who had a similar Kt/V, whether hypertensive or not. SH patients had significantly higher ECVn and IVCD than TN and SN patients. TN and SN patients did not differ significantly regarding ECVn and IVCD before and after HD. However, in a subgroup of eight TN patients, ECVn was below the range of that in SH and SN patients, due to obesity with a high body mass index. Another subgroup of 14 TN patients had a higher ECVn than most of the SN patients and also higher than the median ECVn in the SH group, without any difference in body mass index, but they were nevertheless normotensive. The fall in BV was greater in SN than in TN patients, presumably due to a higher ultrafiltration rate in SN patients. However, SH patients had a smaller change in BV than SN patients, presumably because their state of overhydration facilitated refilling of BV from the interstitial fluid.

CONCLUSIONS

Normotension can be achieved independently of the duration and dose (Kt/V urea) of HD, if the control of post-dialysis ECV is adequate. However, this is more difficult to achieve with short than with more prolonged HD during which the ultrafiltration rate is lower, BV changes are smaller and intradialysis symptoms less frequent. The results in the subgroup of patients with high ECVn at Tassin suggest that normotension may also be achieved in patients with fluid overload provided that the dialysis time is long enough to ensure more efficient removal of one or more vasoactive factors that cause or contribute to hypertension.

The hemodynamic effect of different ultrafiltration rates in patients with cardiac failure and patients without cardiac failure: comparison between isolated ultrafiltration and ultrafiltration with dialysis

OBJECTIVE

The increasing number of dialysis patients with cardiovascular diseases will lead to an increase in the incidence of intradialytic hypotension. Intradialytic hypotension is determined by changes in plasma volume, changes in vascular reactivity and structural cardiovascular changes. In this study the effect of two different ultrafiltration rates (UF-rate), i. e. 500 and 1000 ml/h, on plasma volume, extracellular volume and arterial blood pressure was studied during different treatments of 2 hours combined ultrafiltration + hemodialysis (UF+HD) and 2 hours isolated ultrafiltration (i-UF).

PATIENTS AND METHODS

15 Patients, 8 patients with cardiac failure, CFpts (NYHA classification III and IV) and 7 patients without cardiac failure (NCFpts) were investigated during a standardized dialysis treatment.

RESULTS

The decrease in plasma volume and decrease in extracellular volume was comparable both between i-UF and UF+HD and comparable between CFpts and NCFpts and was only dependent on the UF-rate. i-UF resulted in minor blood pressure changes in both CFpts and NCFpts. In CFpts UF+HD resulted in a significant decrease in systolic blood pressure (SBP) at both UF-rates while in NCFpts SBP decreased significantly only at the higher UF-rate during UF-HD. Although there were no significant differences in hemodynamic stability during the different treatment modalities between CFpts and NCFpts, the decrease in SBP in CFpts at the higher UF-rate during UF+HD was much more pronounced.

CONCLUSION

From this clinical study we conclude that differences in hemodynamic stability between i-UF and UF+HD and between CFpts and NCFpts are not related to differences in plasma volume preservation. Other factors like different changes in vascular reactivity and in CFpts structural cardiovascular changes might be responsible for the observed differences.

Effect of dialysate calcium concentrations on intradialytic blood pressure course in cardiac-compromised patients

To prevent hypercalcemia in the treatment of secondary hyperparathyroidism, low calcium (L-Ca) dialysate is advocated. However, changes in ionized calcium (i-Ca) levels have a pivotal role in myocardial contraction and could influence blood pressure stability during dialysis. Recently, our group found in patients with normal cardiac function a significant decrease in blood pressure (decrease in systolic blood pressure [DSBP]: -13 mm Hg and decrease in mean arterial pressure [DMAP]: -7 mm Hg) during dialysis with L-Ca dialysate compared with high calcium (H-Ca) dialysate, and this was mainly related to a decreased left ventricular contractility with use of L-Ca dialysate. On the basis of these data, it could be expected that changes in i-Ca levels during dialysis are of more clinical importance in cardiac-compromised patients (CCpts), New York Heart Association classifications III and IV. In this study, the effects of L-Ca dialysate (1.25 mmol/L) and H-Ca dialysate (1.75 mmol/L) on arterial blood pressure parameters (systolic [SBP], diastolic [DBP], and mean arterial blood pressure [MAP]), heart rate, stroke distance (SDist), and minute distance (MDist) during 3 hours of a standardized ultrafiltration/hemodialysis (UF+HD) in nine CCpts was investigated. i-Ca levels increased significantly with H-Ca dialysate UF+HD, whereas there was no change with L-Ca dialysate. SBP, DBP, and MAP decreased statistically and clinically significantly during UF+HD with L-Ca dialysate and were significantly lower with the use of L-Ca dialysate compared with H-Ca dialysate. SDist and MDist decreased significantly with L-Ca dialysate, whereas there were no changes in SDist and MDist with H-Ca dialysate. The predialysis and postdialysis index of systemic vascular resistance (SVRI) was similar between L-Ca dialysate and H-Ca dialysate use. Between the two groups, there were no significant differences in changes in SVRI. From this study, we can conclude that changes in i-Ca levels are a very important determinant of the blood pressure response during UF+HD in CCpts, and this response is mediated by changes in myocardial contractility.

Arterial compliance in patients on long-treatment-time dialysis

Arterial compliance is found to be reduced in haemodialysis patients. It is not clear whether decreased arterial compliance in uraemic patients is a consequence of long-standing increased mean arterial blood pressure or a consequence of the uraemic state. An adequate blood pressure can be achieved by long-treatment-time dialysis of 8 h three times a week. We studied femoral and carotid artery wall properties in 24 normotensive patients on long-treatment-time dialysis and 24 normal controls matched for mean arterial pressure, age, sex, and body mass index. Arterial distensibility coefficient and compliance coefficient were determined with a vessel wall movement detector system, 24 h after dialysis in the supine position. The patients were 5.9 +/- 6.6 years on long-treatment-time dialysis at a Kt/V of 1.8 +/- 0.4. We found no significant differences in mean arterial pressure or pulse pressure between patients (85 +/- 13, 55 +/- 17 mmHg) and controls (84 +/- 6, 50 +/- 13 mmHg). Femoral distensibility coefficient and compliance coefficient were lower in patients (6.0 +/- 2.4 10(-3)/kPa; P < 0.05, 0.52 +/- 0.28 mm2/kPa; n.s.) compared to the controls (8.8 +/- 4.0 10(-3)/kPa, 0.67 +/- 0.38 mm2/kPa). No differences in carotid distensibility coefficient and compliance coefficient were found between patients (12.8 +/- 4.6 10(-3)/kPa, 0.72 +/- 0.30 mm2/kPa) and controls (14.1 +/- 4.4 10(-3)/kPa, 0.70 +/- 0.23 mm2/kPa). We conclude that patients on long-treatment-time-dialysis have an increased stiffening of the muscular femoral artery but not of the more elastic carotid artery. Results suggest that the uraemic state itself has a deleterious effect on the elastic properties of the muscular femoral artery.

The influence of bicarbonate supplementation on plasma levels of branched-chain amino acids in haemodialysis patients with metabolic acidosis

BACKGROUND

It has been hypothesized that correction of metabolic acidosis might improve the nutritional state of acidotic haemodialysis (HD) patients partly because of a reduced oxidation of branched-chain amino acids (BCAA).

AIM

We investigated whether bicarbonate (Bic) supplementation in acidotic HD patients results in increased plasma levels of BCAA.

METHODS

In a longitudinal study (run-in period, 2 months; study period, 6 months), the effect of Bic supplementation on plasma levels of BCAA was studied in 12 acidotic HD patients (7 men, 5 women, mean age 54 +/- 18 years) with a predialysis bicarbonate (Bic) concentration smaller or equal to 22 mmol/l. Bic was supplemented by increasing Bic concentration of the dialysate and by oral Bic supplementation.

RESULTS

Predialysis Bic increased significantly during the study period (18.7 +/- 2.7 vs. 23.1 +/- 11.5 mmol/l). There was no change in nutritional parameters. However, plasma levels of the BCAA valine, leucine, and isoleucine increased significantly.

CONCLUSIONS

In haemodialysis patients with metabolic acidosis, Bic supplementation over a 6-months period resulted in an increase in plasma levels of BCAA. Further study is needed to elucidate the mechanisms behind, and the clinical importance of the observed changes in plasma BCAA levels.

Effects of hypervolemia on interdialytic hemodynamics and blood pressure control in hemodialysis patients

The influence of hypervolemia on hemodynamics and interdialytic blood pressure, as well as in relation to vascular compliance, was investigated in 10 hemodialysis patients who were not receiving vasoactive medication. All subjects were studied during a relative normovolemic interdialytic period (from 1 kg below dry weight postdialytic until dry weight predialytic) and a hypervolemic interdialytic period (from 1 kg above dry weight postdialytic until 3 kg above dry weight predialytic). Interdialytic blood pressure was measured with an ambulatory blood pressure monitor. Cardiac output was echographically measured and total peripheral resistance calculated postdialytic, mid-interdialytic, and predialytic. At the same time, a blood sample was drawn for analyzing vasoactive hormones, sodium, and hematocrit. In all patients, ideal dry weight was estimated by echography of the caval vein. Arterial and venous compliance were measured with an ultrasound vessel wall movement detector system and a strain-gauge plethysmograph. After fluid load, an increase in intravascular volume, an increase in caval vein diameter and cardiac output, and a decrease in peripheral resistance was observed. No significant influence of a 3-L fluid load was found on interdialytic blood pressure course (153+/-24 mm Hg/90+/-19 mm Hg in the hypervolemic period and 146+/-27 mm Hg/89+/-22 mm Hg in the normovolemic period). Sodium and osmolality were similar in the hypervolemic and normovolemic interdialytic periods. After fluid load, a decrease in arginine vasopressin and angiotensin II was observed, which probably contributed to the decreased systemic vascular resistance. Catecholamines were not influenced by fluid load, but increased during the interdialytic period, suggesting accumulation after dialysis. Three of the 10 patients had higher systolic but not diastolic blood pressures after fluid load (159+/-13 mm Hg/81+/-22 mm Hg in the hypervolemic period and 135+/-16 mm Hg/81+/-22 mm Hg in the normovolemic period). No correlation could be found between arterial or venous compliance and blood pressure changes. We concluded that a 3-L interdialytic fluid load does not result in higher blood pressure in most hemodialysis patients.

Critical role of the extracorporeal blood temperature in the hemodynamic response during hemofiltration

Impaired vascular reactivity during combined ultrafiltration-hemodialysis (UF+HD) compared with hemofiltration (HF) remains a rather enigmatic problem, the causes of which are still not well understood. Although a number of factors have been claimed to be responsible, most recent studies point to a major role of the extracorporeal blood temperature, which is usually lower during HF compared with UF + HD. However, previous studies in which hemodynamics were studied during UF + HD and HF in relation to the extracorporeal blood temperature are limited by the use of acetate in UF + HD, and measurements were often confined to BP and heart rate. Therefore, arterial BP, as well as forearm vascular resistance (FVR) and venous tone (strain-gauge plethysmography), was measured in 11 hemodialysis patients during 3 h UF + HD (37.5 degrees C) and predilution HF (39.0 degrees C = warm HF), resulting in equivalent extracorporeal blood temperatures. Patients were also studied during cold HF at an infusate temperature of 36.0 degrees C. UF + HD and HF were matched with respect to the dialysate and infusate composition (bicarbonate), bio-compatibility factors, and small molecule clearance. At equivalent temperatures, UF + HD and HF were associated with a comparable vascular and BP response. Only cold HF was associated with a significant increase in FVR. In addition, FVR and venous tone, as well as arterial BP, were all significantly higher during cold HF compared with both UF + HD and warm HF. These results indicate that the disparity in vascular reactivity between UF + HD and HF is primarily related to differences in the extracorporeal blood temperature.

Influence of changes in ionized calcium on cardiovascular reactivity during hemodialysis

In order to prevent hypercalcemia due to the treatment of secondary hyperparathyroidism the use of low calcium dialysate is advocated. However, as calcium ions play a pivotal role in both myocardial and vascular smooth muscle contraction, lowering the dialysate calcium concentration might result in a further impairment of the cardiovascular response during dialysis. Therefore, arterial blood pressure, forearm vascular resistance (FVR) and venous tone (VT) (straing-gauge plethysmography) as well as cardiac dimensions and output (echocardiography) were measured in 10 hemodynamically stable dialysis patients (ejection fraction > 30%) during two standardized sessions of three-hour combined ultrafiltration-hemodialysis (UF + HD) at two different dialysate calcium concentrations: 1.25 and 1.75 mmol/l. High calcium UF + HD resulted in a significant increase in plasma ionized calcium (+0.19 +/- 0.11 mmol/l; p < 0.01) while ionized calcium remained unchanged during low calcium UF + HD (-0.02 +/- 0.07 mmol/l). As a result, systolic, diastolic and mean arterial blood pressure were respectively 14 +/- 10, 5 +/- 7 and 9 +/- 9 mmHg higher during high calcium UF + HD as compared to low calcium UF +/- HD (p < 0.05). There were no significant differences in FVR and VT between the two treatments. During both treatments FVR increased while VT decreased. In addition, there were no differences in calculated systemic vascular resistance. However, with comparable end-diastolic dimensions, stroke volume (-18 +/- 13 ml) and cardiac output (-1.3 +/- 1.5 l/min) decreased significantly (p < 0.05) only during low calcium UF + HD. We conclude that even in hemodynamically stable patients changes in plasma ionized calcium are an important determinant of the blood pressure response during dialysis therapy. Whereas peripheral vascular reactivity is unaffected by changes in ionized calcium, myocardial contractility is improved with higher dialysate calcium concentrations.