Nephrol Dial Transplant (2001) 16: 328-334
© 2001 European Renal Association-European Dialysis and Transplant Association
Efficacy and safety of haemodialysis treatment with the HemocontrolTM biofeedback system: a prospective medium-term study
Nephrology and Dialysis Unit, Hospital of Martina Franca, Taranto, Italy
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Abstract |
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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 (HemocontrolTM, Hospal Italy) to prevent destabilizing hypovolaemia. It is based on an adaptive controller incorporated in a HD machine (IntegraTM, Hospal Italy). The HemocontrolTM 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%/ 
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.
Keywords: arterial hypotension; biofeedback; bio-impedance analysis; blood volume; haemodialysis; hypovolaemia
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Introduction |
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TopAbstractIntroductionSubjects and methodsResultsDiscussionReferences |
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Hypovolaemia has been implicated as a major causal factor of morbidity during haemodialysis (HD). Despite the use of bicarbonate HD, ultrafiltration controllers, sodium modelling, and automated blood-pressure monitoring, the incidence of haemodialysis-induced hypotension (HH) has been reported to be approximately 20% [1,2]. Unfortunately, the morbidity associated with hypovolaemia is not limited to hypotension. Steuer et al. have recently demonstrated that cramping and lightheadedness occurred in 28% of all treatment sessions, and in all cases those symptoms were preceded by a pronounced reduction in blood volume (BV) [3].
A model biofeedback control system for intra-HD BV changes modeling has been developed (HemocontrolTM, Hospal Italy) to prevent destabilizing hypovolaemia. It is based on an adaptive controller incorporated in a HD machine (IntegraTM, Hospal Italy) [4]. A multicentre, prospective, randomized, cross-over study was performed in 35 hypotension-prone patients from 10 Italian dialysis units (including ours) to assess whether bicarbonate treatment equipped with the HemocontrolTM biofeedback system (HBS), as a whole, was able to reduce cardiovascular instability and patient morbidity compared with the gold standard bicarbonate treatment (BD), equipped with a constant ultrafiltration rate (UFR) and dialysate conductivity (DC). This study showed a significantly improved cardiovascular stability by BV tracking. However, this was a short-term study [5]. The main objective of the present prospective study was to compare the efficacy and safety of HBS with that of BD treatment in the medium term.
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Subjects and methods |
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TopAbstractIntroductionSubjects and methodsResultsDiscussionReferences |
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Description of HBS
A 2-week run-in period was mandatory to optimize the ideal post-dialysis body weight and to monitor the spontaneous BV trends of each patient. Subsequently, optimal individual BV targets related to optimal individual body weight loss were defined (the so-called ideal volaemia trajectories). An ideal volaemia trajectory is defined as the trajectory that shows a reduction at the start of the treatment and a trend toward isovolaemia by the end [4]. These individualized profiles may be adjusted from time to time.
The model is a closed-loop system with an input variable, the BV, and two independent or control variables, i.e. UFR and DC. The relative BV changes are measured continuously during HD by an optical absorbance system. At the same time the following are continuously calculated: (i) the mathematical coefficients that link the controlled variable to the control variables; (ii) the instantaneous errors in the actual BV trajectory compared to the ideal trajectory (iii) the differences in the body weight loss as first prescribed and then obtained. In the presence of substantial errors, the model is able to update both the UFR and DC automatically with a view to minimizing any discrepancies between the ideal volaemia trajectories and the experimentally obtained ones, as well as any relevant errors in the patient's body weight reductions. The heart of the system is a multi-input, multi-output (MIMO) adaptive controller that manages three kinds of error: errors of volaemia, of total weight loss and of sodium mass balance by means of a kinetic sodium model, which continuously calculates the equivalent DC and which, by the end of the session, tends to make the sodium mass balance the same as the one obtained in HD treatments with constant DC (Figure 1
) [4].
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Study design
Inclusion criteria
Inclusion criteria were maintenance BD for at least 6 months previously and haemodynamic instability (20% or more of HD sessions characterized by symptomatic HH). Symptomatic HH was prospectively defined as the sudden decrease of blood pressure during HD, associated with dizziness, chest pain, or blacking out responding to volume replacement.
Nineteen uraemic patients (seven males, 12 females; mean age 64.5±3.0 SEM years; on maintenance HD for 80.5±13.2 months) affected by different nephropathies including two with diabetes mellitus volunteered after informed consent for the present study. The study comprised three phases.
Medium-term studies
Enrollment started in September 1996 and ended in December 1997. The medium-term studies ended in August 1999. The study included one period of 6 months of BD followed by a period of HBS treatment ranging from 14 months (five patients) to 30 months (two patients) (mean 24.0±1.6). For each patient 80 HD runs were studied in the BD period and 312.0±20.7 HD runs during the HBS treatment period.
Measurements
Blood biochemistry
A blood sample was collected each month at the beginning of the week for blood gas analysis (Ciba-Corning 288 Blood Gas System, Italy) and determination of serum urea nitrogen, creatinine, calcium, sodium, potassium, phosphate, uric acid (routine automated methods), haemoglobin, and haematocrit (Coulter counter). Kt/V was estimated according to the algorithm suggested by Casino et al. [6].
Run sheets
Supine blood pressure and heart rate were recorded by the nursing staff, both before and after HD. The body weight at the start and at the end of the run and the weight change between dialyses were also recorded. The nursing staff also recorded the occurrence of symptomatic HH and muscle cramps.
Symptom sheets
These were completed by each patient, partly before (inter-HD symptoms, post-HD asthenia and thirst) and partly after (intra-HD symptoms, headache, and nausea) each HD run. The score was given by the patients themselves, by indicating a point on a 10-cm-long straight line. Each straight line represented a symptom: the worst score was 0 and the best score was 10.
Short-term studies
Starting in September 1999, all patients went back to BD treatment. First, a wash-out period from HBS treatment of 4 weeks was completed and then a short-term study period of a further 3 weeks (phase A) was accomplished. Afterwards, the patients once again started HBS treatment with a wash-out period from BD treatment of 4 weeks and then a short-term study period of a further 3 weeks (phase B). Thus there were nine HD runs under study for each patient, and 171 for the entire cohort of patients, both when under BD and when under HBS treatment. Supine blood pressure and heart rate were recorded by the nursing staff, both before and after HD. Body weight at the start and finish of the run and weight changes between dialyses were also recorded. The nursing staff also recorded the occurrence of symptomatic HH an muscle cramps.
Acute studies
Every patient underwent these studies during a single HD run, once in phase A and once in phase B on the same day of the week (first, second, or third run of the week for each patient). Blood samples were collected at the beginning and end of the run for the determination of serum urea nitrogen, sodium, potassium and haematocrit.
No eating or drinking was allowed during the sessions. All measurements were performed in a rigorously enforced supine position. Five time points were set for each HD run: pre-dialysis (after 20 min of rest, t0), 20 min post-dialysis (tf), and three during dialysis (t1/3, t2/3, t3/3). These were defined as every 1/3 of the programmed time of the BD run because UFR was kept constant in this modality and every 1/3 of the achieved body weight loss (as determined by a bed scale) in the HBS run. The last intra-dialysis time point was just before the end of the run in both treatment modalities. In this way, the three intra-run measurements were made at body weight losses comparable between the two modalities. At each time point the following were measured:
- (i) BV changes, as measured by the optical absorbance system (only at the three intra-run time points).
- (ii) Blood pressure, heart rate, and body weight. The nursing staff also recorded the occurrence of symptomatic HH and muscle cramps.
- (iii) Resistance (R) and reactance (Xc) utilizing a single-frequency (50-kHz) tetrapolar bioimpedance analysis (BIA) (BIA 101/S, Akern RJL Systems, Italy) [7–12]. Total body water (TBW) and extracellular fluid volume (ECV) were calculated from R, Xc, height and body weight measurements using the conventional BIA regression equations. Electrodes were placed on the body side free from the vascular access, and these remained in place during the run [13].
- (ii) Blood pressure, heart rate, and body weight. The nursing staff also recorded the occurrence of symptomatic HH and muscle cramps.
Treatment characteristics
Seven points need to be stressed: (i) all HD runs in both treatment modalities were performed with the same type of monitor (IntegraTM); (ii) DC was about 14.2 mS/cm and UFR was kept constant in each BD run; (iii) patients maintained their usual HD schedule (three times per week) throughout the study; (iv) the blood flow rate was about 300 ml/mim; the dialysate flow rate was about 500 ml/min in both treatments; (v) treatment time was conditioned by Kt/V=1.2; (vi) the same type of HD membrane (cellulose acetate) was used for each patient throughout the study; (vii) the patients were on various outpatient medications, and these were not changed during the study period.
Statistical analysis
For the medium-term studies a factorial analysis was employed for the purposes of comparing multiple measurements during each treatment modality and of comparing the treatment modalities. Where the results of the factorial analysis were significant, the difference between means was detected by a least-significant difference test [14]. The 6 months of data from the BD treatment period regarding blood biochemistries, run, and symptom sheets were averaged (pooling the data collected during the sessions of 3 consecutive months) for each of the 19 patients. The data were compared with the corresponding averaged data of HBS treatment (pooling the data collected during the sessions of 3 consecutive months).
The duration of HD runs was averaged for each patient, pooling all the data collected in each of the treatment periods. The averages were compared using the paired Student's t-test.
For the short-term and acute studies a paired Student's t-test or 
2 test was used when appropriate. In all instances a P<0.05 was accepted as statistically significant. Data are expressed as means±SEM.
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Results |
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Medium-term studies
Blood biochemistry
No change in the monthly blood biochemistry was observed in any of the parameters under study, when comparing BD with HBS treatment (only serum sodium concentrations are shown in Table 1
).
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Run sheets
No differences between the two treatments were observed when comparing pre- and post-HD supine systolic blood pressure (BP), diastolic BP, mean BP, and heart rate, pre-run body weight, inter-HD body weight gain, and intra-HD body weight loss (Table 1
, Figure 2). The overall occurrence of symptomatic HH and muscle cramps was significantly less in HBS treatment. It was respectively 31.8±0.4 and 8.0±0.2% in BD vs 21.0±0.3 and 4.8±0.1% in HBS treatment with a decrease of about 34 and 40% respectively (P<0.0001, Figure 3a).
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Symptom sheets
Self-evaluation of intra- and inter-HD symptoms revealed a statistically significant difference, as far post-HD asthenia is concerned. The overall score was significantly higher during the HBS compared with the BD treatment (6.2±0.2 vs 4.3±0.1 P<0.0001, Figure 3b). Self-evaluation of the other intra- and inter-HD symptoms (notably thirst) was not significantly different between the two treatments (data not shown).
Treatment time
Treatment time according to Kt/V=1.2 was not different between the two treatments (252.0±2.1 min in BD and 253.9±1.2 in HBS).
Short-term studies
No difference between the two treatments was observed when comparing pre- and post-HD supine systolic BP, diastolic BP, mean BP, and heart rate, pre-run body weight, inter-HD body weight gain, and intra-HD body weight loss. The absolute number of symptomatic HH and muscle cramps was significantly less in HBS treatment. They were respectively 45 and 17 in BD vs 26 and 10 in HBS treatment (P<0.002 and P<0.02 respectively, data not shown).
Acute studies
No difference between the two treatments was observed when comparing percent residual BV, R, Xc, TBW, ECV, body weights, serum sodium, and urea nitrogen concentrations, and haematocrit at the five time points (Table 2).
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Five of the 19 BD runs were characterized by the occurrence of symptomatic HH; none of the HBS runs were characterized by symptomatic HH.
Table 3 illustrates the intra-HD changes of percent residual BV, percent reduction of ECV, and body weight loss.
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The percent
ECV and the residual BV%/ECV% ratio, expression of the vascular refilling, were significantly different at some time points during HBS treatment compared with BD treatment (Table 3). The same was true when comparing five HBS runs, which were characterized by symptomatic HH, with the corresponding BD runs (Figure 4).
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Discussion |
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A variety of therapeutic approaches has been employed to treat HD symptoms associated with hypovolaemia. In addition to the introduction and worldwide distribution of bicarbonate dialysis, high dialysate sodium concentrations and/or the use of ramped sodium modelling have gained widespread application. Cool dialysis has been associated with fewer episodes of hypotension and a significantly higher blood pressure, consequent on an increase in peripheral vascular resistance. Other therapies, thought to be beneficial in the treatment of HH have included alternative dialysis techniques like haemofiltration [15]. The introduction of on-line BV continuous monitoring during HD has offered the opportunity of controlling UFR and BV preservation more accurately [4].
The primary objective of the present prospective study was to compare the efficacy of bicarbonate dialysis treatment equipped with HBS, as a whole, with the gold standard, i.e., bicarbonate dialysis treatment, equipped with a constant UFR and DC. Our results demonstrate very clearly that HBS treatment is effective in reducing some intra- and inter-HD symptoms, notably symptomatic HH. This was seen in both the medium- and short-term studies. The former lacked a time-control group continuing on BD treatment; thus, the latter were specifically designed (with an on/off treatment schedule) to determine whether the reduction in symptomatology was really related to HBS treatment or was a time effect. Both studies show very clearly that HBS is an effective treatment with a lower hypovolaemia-associated morbidity than in BD treatment.
The secondary objective of the present study was to compare the medium-term safety of HBS with BD treatment. A major concern of HBS treatment is that it could induce a less negative sodium mass balance through the adjustments of DC in order to obtain the desired pre-determined BV trajectories. Thus, the crucial question is whether HBS treatment can lead to improved cardiovascular stability with the prevention of chronic extracellular volume expansion and arterial hypertension, or, in more general terms, whether HBS treatment is a safe technique in the long term. Although we did not measure sodium mass balance directly, we have sufficient evidence to believe that sodium mass balance was not different between HBS and BD treatments. Blood pressure did not change, changes in body weight were the same, and serum sodium concentrations were identical in a follow-up of 2 years. Thus, we suggest that HBS is a safe treatment in the medium term because potentially harmful changes in blood pressure, body weight, and serum sodium concentration were not reported in our study.
Acute studies did not show any significant difference in BV reduction when comparing BV changes during HBS and BD treatments. These data confirm those of Mancini et al. [16] who showed that BV changes per se are not relevant in the identification of HH in HBS treatment, whereas the ratio between BV reduction and the percent change in body weight during dialysis appeared to be more accurate in characterizing the occurrence of HH. In our study, a higher residual BV%/ECV% ratio appeared to characterize HBS treatment, above all when comparing HBS runs with BD runs of five patients who were symptomatic during the BD runs. Thus the combination of intradialytic BV monitoring with BIA measurements, which has already been reported in some studies [17,18], allowed better elucidation of the dynamic processes induced by HBS and BD treatments. ECV is composed of intravascular and interstitial fluid compartments. Thus the combination of a percent reduction of ECV during an HBS session that is significantly less than during a BD run with the same percent BV reduction means that in HBS treatment either more water is kept in the interstitial fluid compartment or less water is replenished in the intracellular space, or both. This effect could be due to the peculiar profiles of DC and UFR, which have been specifically constructed for the first part of an HBS treatment (Figure 1) [4]. Even though a large body weight loss is concentrated in this period, necessitating a high DC, the net balance could be that of a transitory sodium gain for the patient. This could lead to a higher plasma osmolality that is able to afford a greater ECV stability. The latter could persist throughout the HBS run, thus providing more cardiovascular stability.
In conclusion, HBS is an effective treatment with a lower hypovolaemia-associated morbidity than in 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 achieved without potentially harmful changes in blood pressure, body weight, and serum sodium concentration.
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Notes |
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Correspondence and offprint requests to: Dr. Carlo Basile, Via Battisti 192, I-74100 Taranto, Italy.
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References |
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Accepted in revised form: 21. 5.00
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