Judith J. Dasselaar

Haemodialysis is associated with a pronounced fall in myocardial perfusion

BACKGROUND Whereas haemodialysis (HD) is lifesaving by replacement of renal function, there are data to suggest that the HD procedure itself may contribute to the high cardiac risk in dialysis patients. The HD procedure is associated with an increased risk of sudden death, and there is accumulating evidence that HD can elicit myocardial ischaemia. In this study, we evaluated the effect of HD on global and regional myocardial blood flow (MBF) and left ventricular (LV) function in non-diabetic, non-cardiac compromised patients. METHODS (13)N-NH(3) positron emission tomography (PET) was used to quantify changes in MBF, LV wall motion, cardiac output (CO), LV end-diastolic volume (LVEDV) and end-systolic volume (LVESV) in seven non-diabetic patients with uneventful cardiac histories. PET scans were performed before and at 30 and 220 min of HD. RESULTS In all patients global MBF fell during HD. At 30 min of HD without ultrafiltration (UF), global MBF had fallen 13.5 +/- 11.5% (P < 0.05) while CO, LVEDV and LVESV were 4.6 +/- 5.3% (NS), 5.6 +/- 4.2% (P < 0.05) and 6.9 +/- 7.2% (P < 0.05) lower, respectively. At 220 min of HD, after UF of 2.5 +/- 0.9 l, global MBF had fallen 26.6 +/- 13.9% (P < 0.05) from baseline while CO, LVEDV and LVESV were 21.0 +/- 19.7%, 31.1 +/- 12.7% and 36.4 +/- 17.5% (all P < 0.05) lower, respectively. In two patients, new LV regional wall motion abnormalities (RWMA) developed at 220 min of HD. MBF was reduced to a greater extent in regions that developed LV RWMA compared to those that did not. CONCLUSIONS Haemodialysis induced a pronounced fall in MBF. Since MBF fell already early during HD not only hypovolaemia but also acute dialysis-associated factors seem to play a role. Haemodialysis-associated reductions in MBF may contribute to the high cardiac event rate of dialysis patients.

Automatic feedback control of relative blood volume changes during hemodialysis improves blood pressure stability during and after dialysis

Automatic feedback systems have been designed to control relative blood volume changes during hemodialysis (HD) as hypovolemia plays a major role in the development of dialysis hypotension. Of these systems, one is based on the concept of blood volume tracking (BVT). BVT has been shown to improve intra‐HD hemodynamic stability. We first questioned whether BVT also improves post‐HD blood pressure stability in hypotension‐prone patients and second, whether BVT is effective in reducing the post‐HD weight as many hypotension‐prone patients are overhydrated because of an inability to reach dry weight. After a 3‐week period on standard HD, 12 hypotension‐prone patients were treated with two consecutive BVT treatment protocols. During the first BVT period of 3 weeks, the post‐HD target weight was kept identical compared with the standard HD period (BVT‐constant weight; BVT‐cw). During the second BVT period of 6 weeks, we gradually tried to lower the post‐HD target weight (BVT‐reduced weight; BVT‐rw). In the last week of each period, we studied intra‐HD and 24 hr post‐HD blood pressure behavior by ambulatory blood pressure measurement (ABPM). Pre‐ and post‐HD weight did not differ between standard HD and either BVT‐cw or BVT‐rw. Heart size on a standing pre‐dialysis chest X‐ray did not change significantly throughout the study. There were less episodes of dialysis hypotension during BVT compared with standard HD (both BVT periods: p<0.01). ABPM data were complete in 10 patients. During the first 16 hr post‐HD, systolic blood pressure was significantly higher with BVT in comparison with standard HD (both BVT periods: p<0.05). The use of BVT in hypotension‐prone patients is associated with higher systolic blood pressures for as long as 16 hr post‐HD. BVT was not effective in reducing the post‐HD target weight in this patient group.

Relative blood volume measurements during hemodialysis: Comparisons between three noninvasive devices

The monitoring of relative blood volume changes (ΔRBV) has been advocated for the prevention of hemodialysis (HD) hypotension. Stand‐alone devices (Crit‐Line) or devices incorporated into the HD apparatus (blood volume monitor [BVM], Hemoscan) are widely used for this purpose. Comparisons between devices are scarce. The aim of this study was, first, to compare ΔRBV results from these 3 devices with ΔRBV calculated from changes in laboratory‐derived hemoglobin (ΔRBV‐lab‐Hb) and, second, to compare ΔRBV results between the different devices. Fourteen patients received 2 HD treatments in a randomized order: one with the Hemoscan and Crit‐Line combination and one with the BVM and Crit‐Line combination. ΔRBV‐lab‐Hb was measured at 2 and 4 hr into the HD session. Bland‐Altman analyses showed that ΔRBV results from the 3 devices differed systematically from ΔRBV‐lab‐Hb, i.e., the difference between the 3 devices and ΔRBV‐lab‐Hb varied significantly (p<0.05) with the magnitude of the measurement. The interdevice comparison showed considerable differences in ΔRBV results. At the end of the treatment, a significant difference (p<0.05) between ΔRBV measured by the Hemoscan and Crit‐Line device (−9.8±2.7% and −11.5±4%, respectively) was found. In most patients, a systematic difference between Crit‐Line and Hemoscan and between Crit‐Line and BVM was observed. Relative blood volume change measurements by Crit‐Line, Hemoscan, and BVM yield results that differ systematically from the results obtained from laboratory‐derived Hb changes. Furthermore, there are substantial differences in ΔRBV results between the 3 ΔRBV devices.

Critical Evaluation of Blood Volume Measurements during Hemodialysis

Devices that continuously measure relative blood volume (RBV) changes during hemodialysis (HD) are increasingly used for the prevention of dialysis hypotension and fine-tuning of dry weight. However, RBV measurements are subject to various limitations. First, RBV devices provide information on relative blood volume changes but not on absolute blood volume. Since blood volume varies with the hydration status, identical reductions of RBV may result in very different absolute blood volumes at the end of HD. Second, RBV changes underestimate the change of total blood volume due to translocation of lower-hematocrit blood from the microcirculation to the central circulation. Third, changes in posture before and during HD, food intake, exercise, and administration of intravenous fluids may influence the validity of the RBV measurement. Fourth, results obtained by various RBV devices show large interdevice differences. Finally, although a fall in blood volume is an important factor in dialysis hypotension, frank dialysis hypotension only occurs when the cardiovascular compensatory mechanisms can no longer compensate for the reduction in blood volume. Therefore, the dialysis staff should not exclusively focus on RBV, but also search for opportunities in the dialysis prescription to facilitate cardiovascular compensatory mechanisms, e.g. by lowering dialysate temperature. In the opinion of the authors, routine RBV monitoring should be used with caution until the major conceptual and methodological problems that are inherent to the indirect RBV estimation are clarified.

Influence of ultrafiltration volume on blood volume changes during hemodialysis as observed in day-of-the-week analysis of hemodialysis sessions

Monitoring of relative blood volume changes (&Dgr;RBV) has been propagated for the prevention of hemodialysis hypotension. Although the influence of ultrafiltration volume on &Dgr;RBV is well-known, there is no mention in the literature that &Dgr;RBV results should be interpreted differently for the first, second, or third hemodialysis session of the week. To elucidate whether &Dgr;RBV and its derivative, &Dgr;RBV normalized for ultrafiltration volume (&Dgr;RBV/ultrafiltration ratio), vary systematically over the week, we separately analyzed these parameters for the first, second, and third hemodialysis session of the week in 13 chronic hemodialysis patients over a 17-week period. As expected, mean (±SD) ultrafiltration volume was significantly (p < 0.001) higher during the first session than during the second and third hemodialysis sessions (3163 ± 615, 2622 ± 674 and 2607 ± 638 ml, respectively). &Dgr;RBV was significantly (p < 0.01) more negative at the first session than at the second and third hemodialysis sessions (−10.1 ± 2.7, −9.3 ± 3.0 and −9.3 ± 3.1%, respectively). The &Dgr;RBV/ultrafiltration ratio was significantly (p < 0.01) less negative at the first session than at the second and third hemodialysis sessions (−3.2 ± 0.6, −3.5 ± 0.8 and −3.6 ± 0.6%/l, respectively). In conclusion, &Dgr;RBV and the &Dgr;RBV/ultrafiltration ratio differ systematically between the first and other hemodialysis sessions in patients on a thrice-weekly hemodialysis schedule, most likely as a result of different ultrafiltration volumes.

Variability of Predialytic, Intradialytic, and Postdialytic Blood Pressures in the Course of a Week: A Study of Dutch and US Maintenance Hemodialysis Patients

BACKGROUND Patients with thrice-weekly hemodialysis have higher predialysis weights and ultrafiltration rates at the first compared with subsequent dialysis sessions of the week. We hypothesized that these variations in weight and ultrafiltration rate are associated with a systematic difference in blood pressure. STUDY DESIGN Observational study. SETTING & PARTICIPANTS During 3 months, we prospectively collected hemodynamic data for 4,007 hemodialysis sessions involving 124 Dutch patients. A similar analysis was performed with 789 US patients, comprising 6,060 hemodialysis sessions. FACTOR First versus subsequent hemodialysis sessions of the week. OUTCOMES Blood pressure. MEASUREMENTS Blood pressure, weight, and ultrafiltration rate were analyzed separately for the first, second, and third dialysis sessions of the week. Comparisons were made with linear mixed models. RESULTS In Dutch patients, predialysis weight and ultrafiltration rate were significantly greater at the first compared with subsequent hemodialysis sessions of the week (P < 0.001). Predialysis systolic and diastolic blood pressures were higher at the first than at subsequent sessions of the week (P < 0.001). Predialysis blood pressure differences persisted throughout the session: systolic and diastolic blood pressures were on average 5.0 and 2.5 mm Hg higher during the first compared to the third session of the week. Postdialysis blood pressures followed a similar pattern (P < 0.001). Blood pressure differences between the first and subsequent days of the week persisted after adjustment for possible confounders. Results in the US cohort were materially identical despite differences in patient characteristics and treatment practice between the 2 cohorts. LIMITATIONS Dry weight was not assessed by objective methods. CONCLUSIONS Blood pressure of patients on a thrice-weekly dialysis schedule varies systematically over the week. Predialysis blood pressure is highest at the first hemodialysis session of the week, most likely due to greater interdialytic weight gain. Intra- and postdialytic blood pressures also are highest at the first session of the week despite higher ultrafiltration rates.

Effect of high and low ultrafiltration volume during hemodialysis on relative blood volume

Achieving an optimal posthemodialysis hydration status may be difficult because objective criteria for dry weight are lacking. Both relative blood volume changes (&Dgr;RBV) at the end of hemodialysis and &Dgr;RBV normalized for ultrafiltration volume (&Dgr;RBV/UF ratio) have been reported to indicate posthemodialysis volume status. A parameter for volume status should not be influenced by variations in ultrafiltration volume. However, if the volume that has to be ultrafiltrated to reach dry weight varies as a result of variations in prehemodialysis weight, either &Dgr;RBV or the &Dgr;RBV/UF ratio (or both) must change. To elucidate the relation between intradialytic ultrafiltration volume versus &Dgr;RBV and its derivative, the &Dgr;RBV/UF ratio, we studied the effect of a relatively high (mean ± SD, 2.7 ± 0.5 l) and low (1.5 ± 0.3 l) intradialytic ultrafiltration volume on these parameters in eight patients. Posthemodialysis weight was comparable in low and high ultrafiltration volume sessions. The average end-hemodialysis &Dgr;RBV did not differ between high (–6.7 ± 2.5%) and low ultrafiltration volume sessions (–7.3 ± 1.0%; NS), but the intraindividual variation was considerable. The &Dgr;RBV/UF ratio differed markedly (p < 0.001) between high (–2.4 ± 0.8 %/l) and low (–4.9 ± 1.3 %/l) ultrafiltration volume sessions. In conclusion, the considerable random intraindividual variation of &Dgr;RBV and the systematic change of the &Dgr;RBV/UF ratio with variations in intradialytic ultrafiltration volume limit the use of these parameters as an aid to assess hydration status in hemodialysis patients.

Comparison of Cardiac Positron Emission Tomography Perfusion Defects During Stress Induced by Hemodialysis Versus Adenosine

The cardiac stress imposed by hemodialysis may differ from that induced by pharmacologic agents used for myocardial perfusion imaging-based stress testing. With repetitive intradialytic [(13)N]ammonia positron emission tomography, we showed that standard hemodialysis had an acute adverse effect on cardiac perfusion and left ventricular function that was not detected by standard diagnostic adenosine stress testing.

Clinical Applications of Biofeedback Systems in Hemodialysis

Despite the tremendous progress in hemodialysis technology over the past decades, hemodynamic instability during hemodialysis is still a frequent complication. This is caused by the fact that in most patients large amounts of fluid are being removed over a short period of time, in combination with an increasingly higher proportion of (elderly) patients with significant cardiovascular co-morbidity. In recent years various closed-loop techniques have been developed to prevent hemodynamic instability during hemodialysis. These techniques differ with respect to the input and output parameters but have in common that they are based on current concepts of the pathophysiology of dialysis hypotension. In this chapter we will outline the pathophysiology of dialysis hypotension and discuss the various closed-loop techniques for hemodialysis that are currently available.