Effect of hemodialysis on blood volume distribution and cardiac output

Vancomycin loading dose individualization in a population of obese patients undergoing haemodialysis based on population pharmacokinetic model

This study aimed to develop a vancomycin population pharmacokinetic model in obese adult patients treated with intermittent haemodialysis and propose a model-based loading dose strategy ensuring attainment of newly recommended AUC-based PK/PD target. Retrospective cross-sectional analysis was performed among obese haemodialysis dependent adult patients treated with intravenous vancomycin. A pharmacokinetic population model was developed using a nonlinear mixed-effects modelling approach and Monte Carlo simulations were used to identify the optimal loading dose for PK/PD target attainment during the first 48 h of treatment. Therapeutic drug monitoring data from 27 patients with a BMI of 30.2-52.9 kg/m2 were analysed. Among all tested variables, only LBM as a covariate of vancomycin Vd significantly improved the model, while vancomycin CL did not correlate with any of the tested variables. The median (IQR) value from the conditional mean of individual estimates of Vd and CL was 68.4 (56.6-84.2) L and 0.86 (0.79-0.90) L/h, respectively. To ensure optimal vancomycin exposure during the first 48 h of therapy, the vancomycin loading dose of 1500, 1750, 2000, 2250, 2500 and 2750 mg should be administered to obese patients with a lean body mass of ˂50, 50-60, 60-70, 70-80, 80-85 and >85 kg, respectively.

Peripheral arterial response during haemodialysis - is two-dimensional speckle-tracking a useful arterial reactivity assessment tool?

Aim: 2D speckle tracking is a method used in myocardial strain assessment. However, several studies have confirmed the suitability of its application in the assessment of arterial strain (a marker of arterial stiffness). The aims of our study were to evaluate whether 2D speckle tracking can assess the changes in carotid and femoral strain caused by fluid loss during haemodialysis, and to determine the direction and amount of these changes. Material and methods: We examined the distal common carotid and proximal femoral arteries in 74 haemodialysed patients (28 women and 46 men) before and after their haemodialysis sessions. EchoPac software was used to analyse the recorded ultrasound examinations. Circumferential strain values were acquired for further analysis. Results: We found a decrease in carotid circumferential strain values after haemodialysis sessions (5.916 ± 2.632% before haemodialysis and 4.909 ± 2.409% after haemodialysis, p = 0.000022). The amount of fluid lost during haemodialysis sessions correlated (correlation coefficient of 0.434, p = 0.000222) with the decrease of carotid circumferential strain. The correlation coefficients were slightly higher (0.445, p = 0.000146) when a ratio of fluid loss volume to the BMI was used. No statistically significant changes were found in femoral circumferential strain. Conclusions: Our findings suggest that arterial response to body fluid loss may be assessed by 2D speckle tracking. This method enabled us to measure carotid circumferential strain changes caused by fluid volume contraction during haemodialysis sessions. We found an important decrease in the carotid circumferential strain values after the procedure. The amount of this decrease correlated significantly with the decrease in the volume of fluid lost during the haemodialysis session.

Effect of Blood Pump Flow and Arteriovenous Fistula Blood Flow on the Blood Pressure and Cardiac Function in Patients Undergoing Maintenance Hemodialysis

The effect of blood pump flow rate on the cardiac functions of hemodialysis patients with arteriovenous fistula (AVF) is largely unknown. This study aimed to investigate if blood pump flow rate (Qb) and AVF access flow rate (Qa) can affect the cardiac function of Chinese hemodialysis patients. A total of 72 patients undergoing AVF hemodialysis were included from March 2010 to June 2014 and dichotomized into the high- and low-flow groups using the medians of Qb (220 mL/min) and Qa (1000 mL/min) as the cutoffs. The cardiac function parameters were measured by ultrasound dilution technique within the first (t + 30) and the last (t - 30) 30 min of dialysis. At t + 30, Qb-high group had significantly higher systolic blood pressure (SBP) and mean arterial pressure (MAP) than Qb-low group. At t - 30, Qb-high group had higher SBP, diastolic blood pressure (DBP), and MAP than Qb-low group. Qa-high group had higher SBP, MAP, cardiac output (CO), cardiac index (CI), central blood volume (CBV), and lower peripheral resistance than Qa-low group. Multiple linear regression showed that at t - 30, Qb was positively correlated with SBP and MAP. Qa was positively correlated with CO, CI, CBV, and PR but negatively correlated with heart rate. Although Qb > 220 mL/min and Qa >1000 mL/min would elevate some parameters, the means of SBP, DBP, MAP remain within the normal range, indicating that appropriate increase in blood pump flow rate has little effect on the cardiac function of hemodialysis patients.

Intradialytic hypotension and splanchnic shifting: Integrating an overlooked mechanism with the detection of ischemia-related signals during hemodialysis

In the most simple analysis, a patient's hematocrit during hemodialysis will rise when the rate of ultrafiltration exceeds the rate at which the fluid is mobilized from extravascular spaces; the greater the rise in hematocrit, the lower blood volume is and the more likely intradialytic hypotension (IDH) is to occur. A secondary mechanism of IDH may be due to sudden shift of blood volume away from the heart under conditions of borderline cardiac filling. A substantial portion of blood volume resides in the splanchnic venous system. During the early part of dialysis, a centripetal shift of red cells from this anatomical region to the central circulation has been documented to occur. The magnitude of this shift is unpredictable, and it may depend on the level of splanchnic vasoconstriction predialysis. The amount of splanchnic shift may also be reduced in patients with autonomic dysfunction. Once this central shift in blood volume has occurred, it can be reversed during further ultrafiltration due to ischemia-induced release of vasodilatory molecules that cause dilation of upstream splanchnic arterioles; this causes increased transmission of arterial pressure to the splanchnic veins, acutely increasing their capacity. The increased splanchnic venous capacity may cause a sudden shift of blood away from the central circulation to fill these veins under conditions where cardiac filling has already been reduced. The result can be severe IDH due to insufficient cardiac filling and cardiac output. One fruitful preventive approach might be to continuously monitor the blood or dialysate for the sudden appearance of such ischemia-related molecules or other signals which may herald not only dialysis hypotension but tissue stunning, warning that the fluid removal rate should be immediately reduced.

Distinct in vitro Complement Activation by Various Intravenous Iron Preparations

BACKGROUND

Intravenous (IV) iron preparations are widely used in the treatment of anemia in patients undergoing hemodialysis (HD). All IV iron preparations carry a risk of causing hypersensitivity reactions. However, the pathophysiological mechanism is poorly understood. We hypothesize that a relevant number of these reactions are mediated by complement activation, resulting in a pseudo-anaphylactic clinical picture known as complement activation-related pseudo allergy (CARPA).

METHODS

First, the in-vitro complement-activating capacity was determined for 5 commonly used IV iron preparations using functional complement assays for the 3 pathways. Additionally, the preparations were tested in an ex-vivo model using the whole blood of healthy volunteers and HD patients. Lastly, in-vivo complement activation was tested for one preparation in HD patients.

RESULTS

In the in-vitro assays, iron dextran, and ferric carboxymaltose caused complement activation, which was only possible under alternative pathway conditions. Iron sucrose may interact with complement proteins, but did not activate complement in-vitro. In the ex-vivo assay, iron dextran significantly induced complement activation in the blood of healthy volunteers and HD patients. Furthermore, in the ex-vivo assay, ferric carboxymaltose and iron sucrose only caused significant complement activation in the blood of HD patients. No in-vitro or ex-vivo complement activation was found for ferumoxytol and iron isomaltoside. IV iron therapy with ferric carboxymaltose in HD patients did not lead to significant in-vivo complement activation.

CONCLUSION

This study provides evidence that iron dextran and ferric carboxymaltose have complement-activating capacities in-vitro, and hypersensitivity reactions to these drugs could be CARPA-mediated.

Personal viewpoint: Limiting maximum ultrafiltration rate as a potential new measure of dialysis adequacy

While the solute clearance marker (Kt/Vurea ) is widely used, no effective marker for volume management exists. Two principles apply to acute volume change in hemodialysis: (1) the plasma refill rate, the maximum rate the extracellular fluid can replace a contracting intravascular volume (±5 mL/kg/hour) and (2) the rate of intravascular volume contraction where coronary hypoperfusion, myocardial stun, and vascular risk escalates (observed at ≥10 mL/kg/hour). In extended hour and higher frequency hemodialysis, intravascular contraction rates are usually equilibrated by the plasma refill rate, but in "conventional" in-center hemodialysis, volume contraction rates commonly exceed the capabilities of the plasma refill rate, resulting in inevitable hypovolemia. To minimize cardiovascular risk, fluid removal rates should ideally be ≤10 mL/kg/hour, acknowledging that this may be challenging in the in-center setting. Two options exist to limit volume removal to >10 mL/kg/hour: restricting interdialytic weight gain (always conflict-fraught, often unachievable) or extending sessional duration to allow additional removal time. Just as Kt/Vurea quantifies solute removal, a simple-to-apply rate variable should also apply for volume removal. As predialysis and target postdialysis weights are both known, a simple measure--a maximum rate for ultrafiltration (UFRmax )--would advise the sessional duration (T) required to minimize organ stun by removing the required fluid load (V) from any patient of predialysis weight (W). This would ensure a removal rate no greater than 10 mL/kg/hour-T (hours) = V (mL)/10 × W (kg). Used together, Kt/Vurea and UFRmax would form a solute and volume composite, each dialysis treatment continuing until both solute and volume requirements are fulfilled.

Effects of frequent hemodialysis on ventricular volumes and left ventricular remodeling

BACKGROUND AND OBJECTIVES

Higher left ventricular volume is associated with death in patients with ESRD. This work investigated the effects of frequent hemodialysis on ventricular volumes and left ventricular remodeling.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Frequent Hemodialysis Network daily trial randomized 245 patients to 12 months of six times per week versus three times per week in-center hemodialysis; the Frequent Hemodialysis Network nocturnal trial randomized 87 patients to 12 months of six times per week nocturnal hemodialysis versus three times per week predominantly home-based hemodialysis. Left and right ventricular end systolic and diastolic volumes, left ventricular mass, and ejection fraction at baseline and end of the study were ascertained by cardiac magnetic resonance imaging. The ratio of left ventricular mass/left ventricular end diastolic volume was used as a surrogate marker of left ventricular remodeling. In each trial, the effect of frequent dialysis on left or right ventricular end diastolic volume was tested between predefined subgroups.

RESULTS

In the daily trial, frequent hemodialysis resulted in significant reductions in left ventricular end diastolic volume (-11.0% [95% confidence interval, -16.1% to -5.5%]), left ventricular end systolic volume (-14.8% [-22.7% to -6.2%]), right ventricular end diastolic volume (-11.6% [-19.0% to -3.6%]), and a trend for right ventricular end systolic volume (-11.3% [-21.4% to 0.1%]) compared with conventional therapy. The magnitude of reduction in left and right ventricular end diastolic volumes with frequent hemodialysis was accentuated among patients with residual urine output<100 ml/d (P value [interaction]=0.02). In the nocturnal trial, there were no significant changes in left or right ventricular volumes. The frequent dialysis interventions had no substantial effect on the ratio of left ventricular mass/left ventricular end diastolic volume in either trial.

CONCLUSIONS

Frequent in-center hemodialysis reduces left and right ventricular end systolic and diastolic ventricular volumes as well as left ventricular mass, but it does not affect left ventricular remodeling.

Determinants of left ventricular mass in patients on hemodialysis: Frequent Hemodialysis Network (FHN) Trials

BACKGROUND

An increase in left ventricular mass (LVM) is associated with mortality and cardiovascular morbidity in patients with end-stage renal disease.

METHODS AND RESULTS

The Frequent Hemodialysis Network (FHN) Daily Trial randomized 245 patients to 12 months of 6 times per week daily in-center hemodialysis or conventional hemodialysis; the FHN Nocturnal Trial randomized 87 patients to 12 months of 6 times per week nocturnal hemodialysis or conventional hemodialysis. The main cardiac secondary outcome was change in LVM. In each trial, we examined whether several predefined baseline demographic or clinical factors as well as change in volume removal, blood pressure, or solute clearance influenced the effect of frequent hemodialysis on LVM. In the Daily Trial, frequent hemodialysis resulted in a significant reduction in LVM (13.1 g; 95% CI, 5.0-21.3 g; P=0.002), LVM index (6.9 g/m(2); 95% CI, 2.4-11.3 g/m(2); P=0.003), and percent change in geometric mean of LVM (7.0%; 95% CI, 1.0%-12.6; P=0.02). Similar trends were noted in the Nocturnal Trial but did not reach statistical significance. In the Daily Trial, a more pronounced effect of frequent hemodialysis on LVM was evident among patients with left ventricular hypertrophy at baseline. Changes in LVM were associated with changes in blood pressure (conventional hemodialysis: R=0.28, P=0.01, daily hemodialysis: R=0.54, P<0.001) and were not significantly associated with changes in other parameters.

CONCLUSIONS

Frequent in-center hemodialysis reduces LVM. The benefit of frequent hemodialysis on LVM may be mediated by salutary effects on blood pressure. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00264758.

Hypertrophy and fibrosis in the cardiomyopathy of uremia--beyond coronary heart disease

Cardiac disease is the leading cause of death in uremic patients. In contrast to previous opinion, coronary events account for a relatively small proportion of cardiac deaths, the most common causes being sudden death and heart failure. Against this background the current text will discuss noncoronary cardiac pathology, specifically the pathogenesis and the morphological findings caused by (pathological) cardiac hypertrophy, cardiac interstitial fibrosis and microvascular disease.

Impact of Augmenting Dialysis Frequency and Duration on Cardiovascular Function

Conventional hemodialysis (CHD) only delivers 10% to 15% of renal function in a nonphysiological intermittent mode. Because it occurs nightly and is sustained over a longer dialysis time, the uremic clearance provided by nocturnal hemodialysis (NHD) far exceeds that of CHD. Increasing the dose and frequency of dialysis by NHD has been demonstrated, in both short- and long-term studies, to reverse several important risk factors for adverse cardiovascular events in patients with end-stage renal disease such as hypertension, left ventricular hypertrophy, systolic dysfunction, conduit artery stiffness, attenuated baroreflex regulation of heart rate, disturbed heart rate variability, sleep apnea, and endothelium-dependent vasodilation. In addition, the Toronto NHD experience has reported an emerging body of evidence demonstrating the benefits of NHD on anemia management, inflammation, and endothelial progenitor cell biology. The mechanism(s) by which nocturnal hemodialysis improves cardiovascular outcomes are under active investigation by our group. It is tempting to speculate that NHD has the potential to decrease endothelial/myocardial injury and restore simultaneously endothelial repair, thereby improving cardiovascular function in patients with end-stage renal disease. The objectives of the present document are (1) to review the mechanisms underlying dialysis-associated cardiovascular morbidity and (2) to describe the restorative potential of NHD on the cardiovascular system.

Dialysis-Induced Regional Left Ventricular Dysfunction Is Ameliorated by Cooling the Dialysate

Dialysis patients who develop cardiac failure have a poor prognosis. Recurrent subclinical myocardial ischemia is important in the genesis of heart failure in nondialysis patients. It has previously been demonstrated that subclinical ischemia occurs during hemodialysis; therefore, this study examined whether the improved stability of cool-temperature dialysis lessens this phenomenon. Ten patients who were prone to intradialytic hypotension entered a randomized, crossover study to compare the development of dialysis-induced left ventricular (LV) regional wall motion abnormalities (RWMA) at dialysate temperatures of 37 and 35 degrees C. Serial echocardiography with quantitative analysis was used to assess ejection fraction and regional systolic LV function. BP and hemodynamic variables were measured using continuous pulse wave analysis. The severity of thermal symptoms was scored using a simple questionnaire. Forty-nine new RWMA developed in nine patients during hemodialysis with dialysate at 37 degrees C (HD(37)), compared with thirteen RWMA that developed in four patients during HD(35) (odds ratio 3.8; 95% confidence interval 2.1 to 6.9). The majority of RWMA displayed improved function by 30 min after dialysis. Overall, regional systolic LV function was significantly more impaired during HD(37) (P < 0.001). BP was higher during HD(35), with fewer episodes of hypotension as a result of a higher peripheral resistance and no difference in stroke volume. The development of thermal symptoms was heterogeneous, with most patients tolerating HD(35) well. This study confirms previous findings of reversible LV RWMA that develop during hemodialysis. It also shows that this phenomenon can be ameliorated by reducing dialysate temperature, a simple intervention with no cost implications.

Newer Paradigms in Renal Replacement Therapy: Will They Alter Cardiovascular Outcomes?

Cardiovascular disease remains the leading cause of morbidity and mortality for patients with end-stage renal disease. Conventional hemodialysis has had limited impact on cardiovascular risk factors and mortality. Increasing evidence suggests that nocturnal home hemodialysis has beneficial effects on cardiovascular parameter outcomes. This article reviews the documented effects of nocturnal home hemodialysis on blood pressure control, cardiac geometry and left ventricular systolic function, lipid profiles, calcium-phosphate metabolism, parathyroid hormone levels, homocysteine levels, sleep apnea, and autonomic modulation of heart rate. It discusses possible mechanisms to explain these observed changes.

DAILY HEMODIALYSIS-SELECTED TOPICS: Cardiovascular Effects of Frequent Intensive Hemodialysis

Cardiovascular disease remains the leading cause of morbidity and mortality for patients with end-stage renal disease (ESRD). Frequent intensive hemodialysis (short daily hemodialysis [2 hours per session, six sessions per week] and nocturnal home hemodialysis [6 hours per session, five to six sessions per week]) has recently gained increasing popularity as an alternative to conventional hemodialysis (4 hours per session, three sessions per week). There is an emerging body of evidence that frequent intensive hemodialysis offers superior uremic toxin clearance, blood pressure control, and other cardiovascular outcomes. The goals of the present review are to systematically evaluate the available evidence in blood pressure control and cardiovascular outcomes in ESRD and the achievable changes after converting from conventional dialysis to frequent intensive hemodialysis, and to provide possible physiological explanations to account for these important changes of potent markers of adverse events in this patient population.

Cardiovascular disease in chronic renal failure: pathophysiologic aspects

Cardiovascular complications are the leading cause of mortality in patients with end-stage renal disease (ESRD). The excess cardiovascular risk and mortality is already demonstrable in early renal disease and in patients with chronic renal failure (CRF), with the highest relative risk of mortality in the youngest patients. The high risk for cardiovascular disease (CVD) results from the additive effect of multiple factors, including hemodynamic overload and several metabolic and endocrine abnormalities more or less specific to uremia. CVD includes disorders of the heart (left ventricular hypertrophy [LVH], cardiomyopathy) and disorders of the vascular system (atherosclerosis, arteriosclerosis), these two disorders being usually associated and interrelated. LVH is the most frequent cardiac alteration in ESRD, resulting from a combined pressure and volume overload. LVH in general is an ominous prognostic sign and an independent risk factor for arrhythmias, sudden death, heart failure, and myocardial ischemia. Regression of LVH needs a combined intervention to reduce hemodynamic overload and is associated with improved prognosis and survival. Clinical studies have shown that damage of large conduit arteries is a major contributing factor for the high incidence of congestive heart failure (CHF), LVH, ischemic heart disease (IHD), sudden death, cerebrovascular accidents, and peripheral artery diseases. Damage to large conduit arteries is principally related to highly calcified occlusive atherosclerotic lesions and to stiffening of large capacitive arteries. These two complications are independent risk factors for survival, and improvement of arterial stiffness is associated with better prognosis and survival. The present review summarizes the most recent works dealing with the pathophysiology of CVD and some aspects of the therapeutic approach.

The changes in cardiac dimensions and function in patients with end stage renal disease undergoing hemodialysis

BACKGROUND

It is absolutely necessary to evaluate cardiac function on starting and during hemodialysis in patients with end stage renal disease. In this study, we tried to determinate the changes of cardiac function associated with hemodialysis.

METHODS

Twenty patients with end stage renal disease, who had been in a hemodialysis program from February, 1997 to August, 1999 in Pusan National University Hospital, were enrolled. They were examined with echocardiography and gated blood pool scintigraphy on starting hemodialysis and after follow-up. The data were analyzed by paired t-test.

RESULTS

The patients were 46.2 +/- 16.8 years old and male to female ratio was 8:12. The underlying diseases were diabetes mellitus (n = 10), hypertension, glomerulonephritis and others. The duration of symptoms associated with end stage renal disease and underlying diseases was 3.4 +/- 2.6 years and the duration of hemodialysis was 13.8 +/- 7.0 months. The LVEDID, LVESID and RVC decreased significantly (-6.10, -7.80 and -20.00%, respectively, p < 0.05) with no significant changes for LAD, IVS, PWT and EF (p > 0.05). In ten cases associated with diabetes, LVEDID decreased (-7.90%, p < 0.05). In twelve cases associated with cardiac diseases, LVEDID and LVESID decreased (-8.60 and -10.50%, respectively, p < 0.05). In four cases associated with diabetes without cardiac diseases, LAD decreased (-5.10%, p < 0.05) and in four cases associated with cardiac diseases without diabetes there were no significant changes in cardiac dimensions and EF. In seven cases associated with diabetes and cardiac diseases, LVEDID decreased (-10.50%, p < 0.05). The EF on gated blood pool scintigraphy decreased (-0.9%, p < 0.05) as a whole while it increased (5.90%, p < 0.05) in the cases associated with diabetes and cardiac diseases.

CONCLUSION

During the early hemodialysis stage of end stage renal disease, we found a change of concentric left ventricular hypertrophy and relatively preserved left ventricular function. Furthermore, we can expect that adequate hemodialysis--with dry weight as low as possible--may prevent progression to eccentric left ventricular hypertrophy and dilated cardiomyopathy.

Isothermic dialysis for hypotension-prone patients

Standard hemodialysis (dialysate temperature >or=37 degrees C) induces an increase in body temperature capable of eliciting circulatory adjustments dictated by the maintenance of thermal homeostasis. These adjustments oppose, and can overcome, those elicited by the hypovolemia caused by the ultrafiltration process, and thus predispose patients to develop hypotensive crises during the treatment. Hemodynamic studies in hypotension-prone patients treated with standard hemodialysis showed that during the hypotensive crisis the peripheral vascular resistances decrease, while the stroke volume decreases proportionally more than the blood volume, suggesting cardiac underfilling due to blood volume redistribution. On the other hand, removal of the body heat surplus by cool dialysis helped the same patients to sustain their peripheral vasoconstriction and cardiac filling. To prevent the increase in body temperature, dialysate temperature should be regulated in such a way as to remove through the dialyzer the heat surplus accumulated in the body as a result of the ultrafiltration process. The amount of heat removal should be tailored to each patient because there are wide interindividual and intraindividual variations in baseline body temperature and ultrafiltration requirements. This can be accomplished by the use of a device that can adjust the dialysate temperature automatically in order to keep the body temperature of the patient unchanged (isothermic hemodialysis). Isothermic hemodialysis reduced from 50% to 25% the incidence of treatments complicated by episodes of symptomatic hypotension in a large randomized clinical trial involving 95 high-risk patients. The thermoregulated treatment results in better patient tolerance because the cold stress inherent in this procedure is lower than that inflicted by the use of a fixed low temperature as was done in the past. Overall, the available evidence supports the Gotch hypothesis that the increase in body temperature during hemodialysis is due to the ultrafiltration process eliciting peripheral vasoconstriction and heat accumulation in the body. Heat accumulation brings into play the thermal homeostatic mechanisms endangering cardiovascular tolerance to ultrafiltration.

Hemodynamic monitoring during hemodialysis

Intradialytic monitoring of hemodynamic parameters is an active area of research; future developments in this field will decrease intradialytic morbidity and the mortality of end-stage renal disease patients treated by hemodialysis. Recent investigations have been assisted by the development of devices that can continuously and noninvasively measure hematocrit and plasma protein concentration during the treatment. Intradialytic morbidity, fluid overload, and hypertension in chronic hemodialysis patients have been shown to be associated with either large or small intradialytic decreases in blood or plasma volume that can be routinely measured by these devices. The use of intradialytic changes in blood volume as a feedback control parameter to vary the ultrafiltration rate and dialysate sodium concentration, so called profiling, is now possible, but further research in this area is necessary to show how to optimize the control algorithms. Other, more preliminary studies suggest that monitoring of central blood volume, extracellular volume, and cardiac output during hemodialysis may permit improved hemodynamic stability during treatment and better control of blood pressure. Although optimal application of these techniques and devices remains to be shown, their routine use during maintenance hemodialysis therapy will likely be the standard of care in the near future.

Proportional changes in body fluid with hemodialysis evaluated by dual-energy X-ray absorptiometry and transthoracic bioimpedance with particular emphasis on the thoracic region

Alterations in body composition during extracorporeal hemodialysis (HD) were investigated in 12 hemodialysis patients (9 males and 3 females, mean age 50 +/- 15 years) with a mean ultrafiltration of 2.6 +/- 1.0 L. Analysis was performed using a dual-energy x-ray absorptiometry technique (DXA), which measures 3 principal components of the body: fat mass (FM): lean body mass (LBM), i.e., all soft tissues excluding fat; and bone mineral content (BMC). These 3 components were calculated for the whole body and for different body regions (namely, the thorax, trunk, lower limbs, and upper limbs). The thoracic cage region could be defined manually, separately from the trunk, and its tissue composition was calculated. DXA analysis was performed concomitant with a measurement of the basal thoracic impedance (TFI) by bioimpedance cardiography prior to and 1 h after dialysis. We found a significant decrease in the total LBM, from 55.8 +/- 8.8 to 53.3 +/- 9.3 kg (p < 0.05), but no change in either the FM or BMC. Moreover, there was a disproportional reduction in the LBM in different regions, being significantly greater in the thorax (7.47 +/- 3.7%) than in the other body regions (trunk 4.3 +/- 2.0%, lower limbs 5.4 +/- 2.1%, and upper limbs 4.7 +/- 1.5%). Regarding bioimpedance, a stronger significant correlation was detected between the percentage changes in the TFI and the changes in thoracic fluid (r = 0.80, p < 0.01) than between the changes in the TFI and the changes in the total body fluid (r = 0.63, p < 0.01). The absolute values of the TFI were also significantly and negatively correlated to the thoracic lean mass to fat mass ratio, both before and after HD (r = 0.82, p < 0.001 and r = 0.86, p < 0.001, respectively). In conclusion, DXA is a very sensitive technique to detect fluid changes during HD in the thorax when the thoracic cavity is defined as a region of interest as well as for the whole body. The data also indicate an extracellular compartmental imbalance between different regions with a significantly greater change in the thoracic region. Transthoracic bioimpedance is a useful technique for evaluating the HD induced changes in the thoracic fluid, rather than total body fluid.

Cardiac disease in chronic uremia: pathogenesis

Cardiomyopathy in chronic uremia results from pressure and volume overload. The former causes concentric left ventricular [LV] hypertrophy, results from hypertension and aortic stenosis, and is also associated with diabetes mellitus and anemia. Volume overload causes LV dilatation, results from arteriovenous shunting, salt and water overload, and anemia, and is also associated with ischemic heart disease, hypertension, and hypoalbuminemia. Decreased major arterial compliance and an early return of arterial wave reflections are also associated with the extent of LV hypertrophy. Cardiomyopathy predisposes to diastolic and systolic dysfunction. The latter results from myocyte death, and predisposing factors include ischemic heart disease and the uremic environment. Ischemic heart disease may be atherosclerotic or nonatherosclerotic in origin. Multiple factors contribute to the vascular pathology of chronic uremia, including injury to the vessel wall, dyslipidemia, prothrombotic factors, increased oxidant stress, and hyperhomocysteinemia. Ischemic risk factors include hypertension, LV hypertrophy, hypoalbuminemia, and perhaps hyperparathyroidism. The clinical consequences of cardiomyopathy include heart failure, ischemic heart disease, dialysis hypotension, and arrhythmias. The adverse impact of ischemic heart disease is probably mediated through the development of cardiac failure.

Splanchnic erythrocyte content decreases during hemodialysis: a new compensatory mechanism for hypovolemia

Splanchnic and splenic erythrocyte volumes decrease during postural changes and exercise to help maintain central blood volume and cardiac output. The contribution of this compensatory mechanism to hemodynamic stability during dialysis has not been studied, however. In 8 ESRD patients, age 51.0 +/- 4.5 years old, we measured changes in the splanchnic/splenic erythrocyte volume during dialysis by tagging the patients' erythrocytes with technetium and following abdominal radioactivity over time. Splanchnic radioactivity decreased to 90.2 +/- 3.8% (mean +/- SEM) of the baseline value after 2 hr of accelerated fluid removal (3.7 +/- 0.4 liters) during dialysis (DUF), while it remained relatively unchanged after two hours of dialysis without fluid removal (DD) [106.5 +/- 2.3%, P (DUF vs. DD) = 0.03]. Splenic radioactivity decreased to 89.2 +/- 5.0% of the initial value during DUF versus 103 +/- 3.8% during DD, but the decrease was noted only during the last 30 minutes of DUF and did not attain statistical significance. Autonomic nervous system integrity was measured by the spontaneous variation of the R-R interval during deep respiration (E/I ratio) and by the Valsalva ratio. The mean E/I and Valsalva ratios in the eight patients were 1.13 +/- 0.03 (+/-SEM) and 1.42 +/- 0.1 respectively, suggesting reasonably adequate autonomic nervous system functioning. The results suggest that contraction of the splanchnic, and possibly the splenic, vascular beds occurs during fluid removal associated with hemodialysis. The resultant addition of erythrocytes to the circulation may help maintain central blood volume and cardiac output.

Influence of hydration state on plasma volume changes during ultrafiltration

To assess the influence of hydration state on plasma volume (PV) changes during ultrafiltration, 11 clinically normhydrated patients on maintenance hemodialysis were studied intraindividually during 2 hydration states differing by 2-15% of lean body mass (LBM). Plasma volume was measured continually during a 15-min ultrafiltration test including an ultrafiltration of 1% of target weight and during a 45-min follow-up period of blood recirculation through the dialyzer without ultrafiltration. In all patients a maximal decrease in relative PV was more pronounced when there was less hydration and when the grade of hydration correlated inversely with the maximal response of PV decrease (r = -0.68, p < 0.001). The same was observed between the hydration state and the slope of the PV decrease (r = -0.69, p < 0.001). Plasma refilling was estimated in the period following ultrafiltration. The slope of the plasma volume increase correlated with the grade of hydration (r = 0.31, p < 0.05) as did the asymtote of PV (r = 0.4, p < 0.01). It is concluded that the less hydrated a dialysis patient is, the more pronounced will be the fall of the ultrafiltration-induced plasma volume and the less distinct will be the recovery of the plasma volume after the discontinuation of ultrafiltration.

Impact of hemodialysis on left and right ventricular Doppler diastolic filling indices

Hemodialysis is associated with acute reduction in intravascular volume. To assess the impact of volume reduction on left and right ventricular diastolic filling indexes obtained by Doppler echocardiography, 24 patients on chronic hemodialysis were consecutively studied before, during, and immediately after one hemodialysis session. Twenty four normal sex and age-matched volunteers served as a control group. Study patients had abnormal diastolic indexes when compared to controls. At 2 hours of dialysis (mid dialysis) there was a significant decrease in peak early mitral flow velocity (E), no change in peak atrial filling velocity (A), and a reduction in the E/A ratio. The deceleration time of the mitral E wave also was prolonged compared to baseline. Similar findings were observed with respect to right ventricular filling indices. These changes occurred during the first 2 hours of dialysis and remained unaltered at end dialysis. When patients were subdivided according to weight loss, only the group that lost 1 or more kilograms had significant changes in the Doppler parameters of the left and right ventricle, as well as reduction of the left ventricular dimensions. These findings suggest that preload reduction is the main mechanism that accounts for acute changes in Doppler diastolic indices observed during hemodialysis.

The role of peripheral capacitance and resistance vessels in hypotension following hemodialysis

The arterial pressure (AP) response to hemodialysis was studied with echocardiography and strain gauge plethysmography in 17 patients with end-stage renal disease; mean AP was unchanged in seven (group A) and was reduced by more than 10 mm Hg in 10 patients (group B). Following dialysis, body weight decreased and heart rate increased equally in both groups. Ejection fraction did not change in the two groups. Left ventricular end-diastolic volume fell by 13 +/- 10% in group A and by 24 +/- 16% in group B. Cardiac index (CI) fell in group B, but remained unchanged in group A. Systemic vascular resistance (SVR) did not change in both groups. The change in mean AP before and after dialysis was significantly correlated with that in Cl (r = 0.49, p less than 0.05), but not with that in SVR. Calf venous pressure-volume curves were not different between the two groups before dialysis. Hemodialysis shifted the curve toward the volume axis for group B but not for group A. These results suggest that hypotension following dialysis is mainly due to the fall in cardiac output, in which increases in venous distensibility play an important role.

Salt and water retention and calcium blockade in uremia

Blood pressure, echocardiography, and aortic and peripheral arterial pulse-wave velocity were studied in 40 hypertensive patients on long-term hemodialysis during a 24-week administration of nitrendipine (1,4-dihydro-2,6-dimethyl-4-[m-nitrophenyl]-3,5-pyridine-dicarboxylic acid ethyl methylester) monotherapy. In a double-blind placebo-randomized study, nitredipine effectively lowered the blood pressure (p less than 0.001) before hemodialysis without causing postdialysis hypotension. The antihypertensive effect of nitrendipine was greater in patients with significant salt and water retention, as indicated by interdialytic body weight gain (delta BW), that is, a significant correlation was observed between delta BW and the decrease in blood pressure (r = 0.72; p less than 0.001). The antihypertensive effect was not related to age, pretreatment plasma renin activity, or serum-ionized calcium concentration. After nitrendipine, a time-related decrease in aortic (p less than 0.005) and femoral (p less than 0.05) pulse-wave velocity was observed with a significant time-treatment interaction (p less than 0.01). Nitrendipine treatment did not influence left ventricular mass (which was positively correlated with delta BW; p less than 0.01) but was associated with an increase in the left ventricular ejection fraction. The increase in ejection fraction was correlated with changes in aortic pulse-wave velocity (r = 0.548; p less than 0.02) but not with changes in blood pressure (r = 0.352; p = 0.19) or delta BW.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracorporeal treatment of acute renal failure in the intensive care unit: a critical view

Acute renal failure in critically ill patients is seldom an isolated problem but is more usually associated with multiple organ failure. When choosing an extracorporeal kidney replacement therapy, these other failing organs must be taken into account. Therefore the choice of an artificial kidney in patients requiring intensive care depends on both the efficacy of the technique and its possible adverse effects on cerebral, pulmonary and cardiovascular function. The most important pathogenic factors in the development of dysequilibrium syndromes, arterial hypoxemia and hypotension are treatment timing, diffusive solute transfer, bio-incompatible membranes and some specific dialysate components (buffer, electrolyte concentrations). It is important to understand the mechanisms by which these factors exert their adverse effects. Application of these pathophysiological mechanisms to the cardiopulmonary and neurologic status of the individual patient permits the prediction of their clinical outcome. This approach will lead to individualised treatment selection, thereby avoiding deleterious side-effects without loss of efficacy.

Hemodynamic consequences of continuous arteriovenous hemofiltration

Continuous arteriovenous hemofiltration (CAVH) is an extracorporeal treatment in which fluid, electrolytes, and low and middle molecular weight solutes are removed from the blood by ultrafiltration. It is efficacious in the management of acute or chronic renal failure complicated by fluid overload, and following surgery. In this study, cardiac filling pressures, cardiac indices, and BP were monitored in nine patients. A mean of 7 kg of fluid was removed in ten treatments without the induction of hypotension. In nine of ten treatments, cardiac index increased following fluid removal. An increment in myocardial pump function was noted even in patients with low output heart failure. This treatment differs from dialysis in its ability to remove large fluid volumes without compromising cardiac hemodynamics. In addition, CAVH may have a role in treating volume overload patients with renal insufficiency and heart failure resistant to pharmacologic intervention.

Heterogeneity of the cardiovascular response to hemofiltration

Twenty-one stable maintenance hemodialysis patients were studied in a crossover format with hemofiltration to determine whether the lower incidence of symptomatic hypotension noted with hemofiltration could be correlated with changes in baroreflex function as tested using the cold pressor test and amyl nitrite inhalation study. Baroreflex function remained abnormal and unchanged in all patients in the face of a reduced incidence of symptomatic hypotension. Subdivision of the patients into frequent (greater than 1 episode/treatment) and infrequent (less than 1 episode/treatment) reactors during the hemodialysis control period resulted in the infrequent reactors, showing a significant increase in episodes of symptomatic hypotension/hemofiltration treatment where a significant reduction was noted with the frequent reactors. No clear correlation could be made between the incidence of symptomatic hypotension and the pre- to post-treatment change in body temperature. The presence of pretreatment hypertension, another previously identified correlate of symptomatic hypotension with hemodialysis, also could not be corroborated. Further, changes from baseline predialysis values in mean arterial pressure noted with hemofiltration could not be correlated with a changed incidence of symptomatic hypotension. We conclude that previously identified correlates of symptomatic hypotension noted in the hemodialysis setting may be dissociated during treatment with hemofiltration and that there is a heterogeneous patient response to this treatment. These data suggest that there are additional, as yet undetermined, pathophysiologic events that underly the symptomatic hypotension of artificial kidney treatment.

Transcapillary colloid osmotic gradient and body fluid volumes in renal failure

The aim was to study the transcapillary fluid balance in dialysis patients during and after ultrafiltration. Plasma and subcutaneous interstitial fluid (wick technique) colloid osmotic pressure, plasma volume (I125-albumin space) and extracellular fluid volume (radiosulfate space) were measured in nine patients on maintenance hemodialysis before (pre-dialysis state) and after (dry-weight state) ultrafiltration. In the pre-dialysis state, interstitial colloid osmotic pressure was reduced compared to normal controls (12.7 +/- 3.5 versus 15.8 +/- 2.7 mmHg, mean values +/- SD) and transcapillary colloid osmotic gradient increased (15.3 +/- 3.0 versus 12.8 +/- 2.7 mmHg). Ultrafiltration resulted in a parallel decrease of plasma volume and interstitial fluid volume of 19 to 20%, and an increase in mean interstitial colloid osmotic pressure of 3.4 mmHg and in mean transcapillary colloid osmotic gradient of 1.9 mmHg. The mean ultrafiltration rate was 21.9 +/- 1.9 ml/min and the plasma refilling rate was 16.5 +/- 2.7 ml/min. It is concluded that the changes in plasma and interstitial fluid colloid osmotic pressure tend to preserve plasma volume and limit the interdialytic increase in interstitial fluid volume.

Blood pressure responses to dietary sodium manipulation during normotensive human pregnancy

Short-term salt loading and salt restriction in a group of normal pregnant women produced no changes in lying, sitting or standing blood pressures or heart rates. Home blood pressures showed no trend to change over the periods of altered salt intake. Although plasma volume and plasma renin activity changed with altered salt intake, there were no relationships between changes in these parameters and changes in mean arterial pressures (MAP) between the low and high salt diets. Capillary permeability and echocardiographic dimensions were unchanged by salt intake once sodium balance had been established.

Plasma volume recovery after ultrafiltration in patients with chronic renal failure

We studied the effect of standardized ultrafiltration (UF, 2 liters in 60 min) on plasma volume (PV, 131I-albumin space) and its recovery, with special reference to the tissue hydration before UF. Twenty-one UF sessions were performed in 15 patients with endstage renal failure. The PV reduction, which varied considerably, was maximal at the end of UF (range, -0.7 to -21.9%); after that PV recovered reaching a plateau in the second hour after UF. A highly significant negative correlation was found between the interstitial fluid volume (IVF, calculated from 82Br space-PV) and the PV reduction at this stage (r = -0.89, P less than 0.0001). Despite avoidance of major changes in total extracellular fluid in the next 24 hr, a further restoration of PV took place which was partial in subjects with normal tissue hydration, but complete or even excessive in grossly overfilled subjects. This PV repletion was accompanied by an increase in the intravascular mass of albumin (P less than 0.02). The negative correlation between initial IFV and PV change persisted after 24 hr (r = -0.83, P less than 0.0005). In most occasions the blood pressure fell, but only in eight occasions frank hypotension followed. Heart rate remained remarkably unaltered, even during hypotensive episodes. Changes in plasma renin activity followed no uniform pattern. Our findings indicate that the tissue hydration state has a strong influence on changes in PV during fluid removal and the subsequent repletion of PV.

Hemodynamic changes during acetate and bicarbonate hemodialysis

In a crossover, double-blind comparison, circulatory changes induced by hemodialysis with bicarbonate versus acetate dialysate were evaluated at the first exposure as well as after 2 weeks of acclimatization to each dialysate. Hemodialysis with bicarbonate dialysate resulted in only minor changes in blood pressure and left ventricular (LV) function as assessed by M-mode echocardiography. In contrast, the first exposure to acetate resulted in significant decreases in systolic (30 mm Hg) and diastolic (17 mm Hg) blood pressure as well as in LV end-diastolic and end-systolic dimensions (5-6 mm) and a rise in ejection fraction. After acclimatization, tolerance developed for the arterial vasodilatory effects of acetate, but not for the venous vasodilatory effect (persistent decrease in LV end-diastolic dimension). These results indicate that some of the circulatory changes induced by hemodialysis may be related more to the acetate infused than to fluid losses or relative autonomic insufficiency.

Acute effects of hemodialysis on echographic-determined cardiac performance: improved contractility resulting from serum increased calcium with reduced potassium despite hypovolemic-reduced cardiac output

The hemodialysis session leads to reduction in circulating blood volume (TBV) and arterial pressure (BP) plus correction of electrolyte imbalance. The effect of these alterations on cardiac performance was evaluated in 18 patients with end-stage renal disease. Hemodialysis for 5 hours led to significant reduction (p less than 0.001) in weight TBV, and BP. Neither ejection fraction nor percentage fiber shortening was altered, whereas mean velocity of circumferential fiber shortening (mean VCF) and mean systolic ejection rate (MSER) were both significantly increased (1.17 +/- 0.20 to 1.38 +/- 0.28 circ/sec and 2.38 +/- 0.27 to 2.80 +/- 0.40 EDV/sec, respectively; p less than 0.001 for each). Since both venous return and systolic BP were decreased, increase in velocity of ventricular contraction implies enhancement of cardiac performance beyond what would be expected from alterations in ventricular filling and resistance to ejection. This enhancement is possibly related to concomitant reduction in serum potassium (p less than 0.001) and increase in serum calcium (p less than 0.005) achieved by hemodialysis.

Massive intoxication with acetaminophen and propoxyphene: unexpected survival and unusual pharmacokinetics of acetaminophen

A 28-year-old woman ingested an estimated 58 g acetaminophen and 9 g propoxyphene 20 h before hospitalization. Her serum acetaminophen concentration at 22 h was 485 micrograms/mL and declined with an unusually long half-life of 14 h. Hemodialysis for 4 h (started at 36 h) reduced the acetaminophen concentration from 250 to 32 micrograms/mL. The patient's complete recovery was remarkable because of the large amounts of drugs ingested, the delayed treatment, and prior exposure to enzyme inducers (known to increase acetaminophen hepatotoxicity). Administration of N-acetylcysteine prevented inorganic sulfate depletion usually caused by acetaminophen and may have increased the formation of acetaminophen sulfate. Some patients eliminate large overdoses of acetaminophen very slowly. Measures to enhance the elimination of this drug and its toxic metabolite by these individuals may be useful even when diagnosis or hospitalization is delayed.

Hemodynamic effects of hemodialysis and hemofiltration

The hemodynamic effects (n = 8) of hemodialysis (HD) and hemofiltration (HF) were compared in the same group of dialyzed patients. The two procedures induced the same decrease in body weight, total blood volume, and blood pressure; however, hemodynamic alterations were different. Cardiac index and stroke index decreased markedly with HD and did not change significantly with HF, and peripheral resistance remained stable after HD and decreased significantly after HF. These results suggest that the maintenance of a high cardiac output may account for the lack of acute hypotensive episodes reported during HF. The reduction of blood pressure after HF is related to the decrease in total peripheral resistance. Thus, the arterial vasodilator effect induced by HF might explain the improvement of severe hypertension on long-term treatment with HF, as reported previously.