Cardiac changes in uremia and their possible relation to cardiovascular instability on dialysis

Hemodynamic response to fluid removal during hemodialysis: categorization of causes of intradialytic hypotension

Background

Intradialytic hypotension is a clinically significant problem, however, the hemodynamics that underlie ultrafiltration and consequent hypotensive episodes has not been studied comprehensively.

Methods

Intradialytic cardiac output, cardiac power and peripheral resistance changes from pretreatment measurements were evaluated using a novel regional impedance cardiographic device (NICaS, NI Medical, Peta Tikva, Israel) in 263 hemodialysis sessions in 54 patients in dialysis units in the USA and Brazil with the goal of determining the various hemodynamic trends as blood pressure decreases.

Results

Hypotensive episodes occurred in 99 (13.5%) of 736 intra- and postdialytic evaluations. The hemodynamic profiles of the episodes were categorized: (i) The cardiac power index significantly decreased in 35% of episodes by 36%, from 0.66 [95% confidence interval (CI) 0.60-0.72] to 0.43 (95% CI 0.37-0.48) [w/m2] with a small reduction in the total peripheral resistance index. (ii) The total peripheral resistance index significantly decreased in 37.4% of episodes by 33%, from 3342 (95% CI 2824-3859) to 2251 (95% CI 1900-2602) [dyn × s/cm5 × m2] with a small reduction in the cardiac power index. (iii) Both the cardiac power index and total peripheral resistance index significantly decreased in 27.3% of episodes, the cardiac power index by 25% from 0.63 (95% CI 0.57-0.70) to 0.48 (95% CI 0.42-0.53) [w/m2] and the total peripheral resistance index by 23% from 2964 (95% CI 2428-3501) to 2266 (95% CI 1891-2642).

Conclusions

The hemodynamic profiles clearly define specific hemodynamic mechanisms of cardiac power reduction and/or vasodilatation as underlying intradialytic hypotensive episodes. A reduction in cardiac power (reduction of both blood pressure and cardiac output) could be the result of preload reduction due to a high ultrafiltration rate with not enough refilling or low target weight. A reduction in peripheral resistance (reduction in blood pressure and increase in cardiac output) could be the result of relative vasodilatation as arteries do not contract to compensate for volume reduction due to autonomous dysfunction. As both phenomena are independent, they may appear at the same time. Based on these results, a reduction of ultrafiltration rate and an increase in target weight to improve preload or immediate therapeutic actions to increase peripheral resistance are rational measures that could be taken to maintain blood pressure and prevent hypotensive ischemic complications in dialysis patients.

Real-time three-dimensional echocardiography provides advanced haemodynamic information associated with intra-dialytic hypotension in patients with autonomic dysfunction

BACKGROUND

Real-time three-dimensional echocardiography (RT3DE) has emerged as a more accurate and effective tool for assessing left ventricular (LV) function, compared to traditional two-dimensional (2D) methods. In this study, we used this new tool to revise the controversial relationship between LV function and intra-dialytic hypotension.

METHODS

This study enrolled 29 intra-dialytic hypotensive patients (the IDH group) and 34 controls (the CON group) on regular maintenance haemodialysis. The RT3DE- and 2D-derived ejection fraction (EF), stroke volume index (SVI) and ratio of early transmitral inflow velocity to diastolic early tissue velocity were assessed at pre-dialysis and mid-dialysis. The intravascular volume was assessed by the inferior vena cava collapsibility index.

RESULTS

Pre-dialysis evaluation showed no difference in RT3DE- and 2D-derived parameters between the two groups. At mid-dialysis, the IDH group had a lower 2D EF (54 +/- 9.1 versus 62 +/- 6.8% in the CON group, P < 0.001), RT3DE EF (53 +/- 6 versus 60 +/- 7% in the CON group, P < 0.001) and SVI (24.3 +/- 8 versus 30.6 +/- 12.2 mL in the CON group, P = 0.02). From pre-dialysis to mid-dialysis, the IDH group had greater decrease in the change in 2D EF (-4.8% +/- 12.6% versus 5% +/- 13.7% in the CON group, P = 0.004), RT3DE EF (-11.8 +/- 10.3 versus -3.4 +/- 11.5% in the CON group, P = 0.003) and SVI (-17.3 +/- 18.5 versus -9.2 +/- 19.8% in the CON group, P = 0.004). The calculated cardiac index change also showed a greater decrease in the IDH group (-17.8 +/- 20.2 versus -5.7 +/- 18.5% in the CON group, P = 0.02). No significant difference in the ratio of early transmitral inflow velocity to diastolic early tissue velocity, heart rate, systemic vascular resistance index or inferior vena cava collapsibility index was found between the two groups at the baseline or mid-dialysis. A lack of an increase in heart rate and the systemic vascular resistance index in the IDH group during the hypotensive episodes implies that these patients have autonomic dysfunction. Multivariate analysis showed that the RT3DE EF change of < -9.5% (odds ratio = 6, P = 0.003) and the presence of diabetes (odds ratio = 4.4, P = 0.013) had significant and independent associations with intra-dialytic hypotension.

CONCLUSIONS

By adopting RT3DE to assess LV performance, our data demonstrated that an inadequate compensation in the LV systolic function is the main mechanism mediating the occurrence of intra-dialytic hypotension in patients with autonomic dysfunction.

Effect of Ultrafiltration on Thermal Variables, Skin Temperature, Skin Blood Flow, and Energy Expenditure during Ultrapure Hemodialysis

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

Relationship between volume status and blood pressure during chronic hemodialysis

BACKGROUND

The relationship between volume status and blood pressure (BP) in chronic hemodialysis (HD) patients remains incompletely understood. Specifically, the effect of interdialytic fluid accumulation (or intradialytic fluid removal) on BP is controversial.

METHODS

We determined the association of the intradialytic decrease in body weight (as an indicator of interdialytic fluid gain) and the intradialytic decrease in plasma volume (as an indicator of postdialysis volume status) with predialysis and postdialysis BP in a cross-sectional analysis of a subset of patients (N=468) from the Hemodialysis (HEMO) Study. Fifty-five percent of patients were female, 62% were black, 43% were diabetic and 72% were prescribed antihypertensive medications. Dry weight was defined as the postdialysis body weight below which the patient developed symptomatic hypotension or muscle cramps in the absence of edema. The intradialytic decrease in plasma volume was calculated from predialysis and postdialysis total plasma protein concentrations and was expressed as a percentage of the plasma volume at the beginning of HD.

RESULTS

Predialysis systolic and diastolic BP values were 153.1 +/- 24.7 (mean +/- SD) and 81.7 +/- 14.8 mm Hg, respectively; postdialysis systolic and diastolic BP values were 136.6 +/- 22.7 and 73.9 +/- 13.6 mm Hg, respectively. As a result of HD, body weight was reduced by 3.1 +/- 1.3 kg and plasma volume was contracted by 10.1 +/- 9.5%. Multiple linear regression analyses showed that each kg reduction in body weight during HD was associated with a 2.95 mm Hg (P=0.004) and a 1.65 mm Hg (P=NS) higher predialysis and postdialysis systolic BP, respectively. In contrast, each 5% greater contraction of plasma volume during HD was associated with a 1.50 mm Hg (P=0.026) and a 2.56 mm Hg (P < 0.001) lower predialysis and postdialysis systolic BP, respectively. The effects of intradialytic decreases in body weight and plasma volume were greater on systolic BP than on diastolic BP.

CONCLUSIONS

HD treatment generally reduces BP, and these reductions in BP are associated with intradialytic decreases in both body weight and plasma volume. The absolute predialysis and postdialysis BP levels are influenced differently by acute intradialytic decreases in body weight and acute intradialytic decreases in plasma volume; these parameters provide different information regarding volume status and may be dissociated from each other. Therefore, evaluation of volume status in chronic HD patients requires, at minimum, assessments of both interdialytic fluid accumulation (or the intradialytic decrease in body weight) and postdialysis volume overload.

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.

Effect of intravenous fluids on blood pressure course during hemodialysis in hypotensive-prone patients

Hypertonic and hyperoncotic solutions are generally used as acute treatment for symptomatic hypotension during dialysis. Administration of hydroxyethylstarch (HES) was recently shown to be an effective substitution fluid in preserving blood volume (BV) and systolic BP (SBP) in a group of stable dialysis patients during dialysis. In this study, in nine cardiac-compromised dialysis patients with frequent symptomatic hypotensive episodes, the efficacy of three fluids (hypertonic saline [3%], albumin [20%], and HES [10%]) was assessed during three treatment sessions with combined ultrafiltration and hemodialysis, which only differed in the type of fluid administered intravenously. Changes in SBP and relative BV were compared. Fluids were given when SBP was less than 100 mmHg or when the decrease in SBP was more than 25 mmHg versus the start of the treatment. The ultrafiltration was continued at the same rate. When comparing SBP at the end of the dialysis session (t = end) with that at the time of infusion (t = iv), SBP decreased with saline, increased with albumin, and increased significantly with HES. The change in SBP in t = end versus t = iv was significantly greater when using saline compared with HES, and tended to decrease more when using saline compared with albumin (P = 0.09). Between albumin and HES there were no significant differences. BV decreased significantly (t = end) versus baseline (t = 0) during ultrafiltration and hemodialysis in all three treatment sessions. The decrease was significantly higher when using saline compared with albumin and saline compared with HES. Between albumin and HES there were no significant differences. When the values at t = end were compared with those at t = iv, BV decreased, although not significantly, with saline and albumin, but remained unchanged with HES. It is concluded that HES is an effective fluid in maintaining SBP and preserving BV in hypotensive-prone dialysis patients, comparable to albumin but superior to hypertonic saline.

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.

Assessment of dry weight in hemodialysis: an overview

Fluid balance is an integral component of hemodialysis treatments to prevent under- or overhydration, both of which have been demonstrated to have significant effects on intradialytic morbidity and long-term cardiovascular complications. Fluid removal is usually achieved by ultrafiltration to achieve a clinically derived value for "dry weight." Unfortunately, there is no standard measure of dry weight and as a consequence it is difficult to ascertain adequacy of fluid removal for an individual patient. Additionally, there is a lack of information on the effect of ultrafiltration on fluid shifts in the extracellular and intracellular fluid spaces. It is evident that a better understanding of both interdialytic fluid status and fluid changes during hemodialysis is required to develop a precise measure of fluid balance. This article describes the current status of dry weight estimation and reviews emerging techniques for evaluation of fluid shifts. Additionally, it explores the need for a marker of adequacy for fluid removal.

Role of the venous system in hemodynamics during ultrafiltration and bicarbonate dialysis

A reduced venous compliance (VC) and inadequate venoconstriction may impair hemodynamics during hemodialysis, the first by impairing plasma volume preservation and by inducing a steep fall in central venous pressure (CVP) during minor plasma volume loss, the second by inadequate mobilization of hemodynamically inactive blood volume. For the protocol A, the relation between VC, the fall in plasma volume and the decline in central venous pressure (CVP) was assessed in 12 hemodialysis (HD) patients, aged 40 to 74 years, during isolated ultrafiltration (UF). The patients were ultrafiltrated for one hour at an UF rate of 1 to 1.5 liter/hr. VC was measured by strain gauge plethysmography with direct i.v. pressure measurements. CVP was assessed directly via a subclavian catheter. PVP was measured using the serial hematocrit method. VC correlated inversely with the fall in plasma volume (r = -0.66; P less than 0.025) and with the fall in CVP (corrected for UF volume) (r = -0.62; P less than 0.025). In the protocol B, the constriction of veins and resistance vessels was assessed sequentially during isolated UF and during UF combined with bicarbonate HD (UF + HD) by measuring the change in venous tone (VT) and vascular resistance (FVR) of the forearm. Twelve HD patients were studied (age 30 to 64 years). VT and FVR were measured using strain gauge plethysmography. The UF rate was equal during isolated UF and UF + HD (1 liter/hr). In six patients, the measurements were started with isolated UF and in six patients with UF + HD.(ABSTRACT TRUNCATED AT 250 WORDS)