Effects of cooler temperature dialysate on hemodynamic stability in "problem" dialysis patients

An update review on hemodynamic instability in renal replacement therapy patients

BACKGROUND

Hemodynamic instability in patients undergoing kidney replacement therapy (KRT) is one of the most common and essential factors influencing mortality, morbidity, and the quality of life in this patient population.

METHOD

Decreased cardiac preload, reduced systemic vascular resistance, redistribution of fluids, fluid overload, inflammatory factors, and changes in plasma osmolality have all been implicated in the pathophysiology of hemodynamic instability associated with KRT.

RESULT

A cascade of these detrimental mechanisms may ultimately cause intra-dialytic hypotension, reduced tissue perfusion, and impaired kidney rehabilitation. Multiple parameters, including dialysate composition, temperature, posture during dialysis sessions, physical activity, fluid administrations, dialysis timing, and specific pharmacologic agents, have been studied as possible management modalities. Nevertheless, a clear consensus is not reached.

CONCLUSION

This review includes a thorough investigation of the literature on hemodynamic instability in KRT patients, providing insight on interventions that may potentially minimize factors leading to hemodynamic instability.

Executive summary of the Korean Society of Nephrology 2021 clinical practice guideline for optimal hemodialysis treatment

The Korean Society of Nephrology (KSN) has published a clinical practice guideline (CPG) document for maintenance hemodialysis (HD). The document, 2021 Clinical Practice Guideline on Optimal HD Treatment, is based on an extensive evidence-oriented review of the benefits of preparation, initiation, and maintenance therapy for HD, with the participation of representative experts from the KSN under the methodologists' support for guideline development. It was intended to help clinicians participating in HD treatment make safer and more effective clinical decisions by providing user-friendly guidelines. We hope that this CPG will be meaningful as a recommendation in practice, but not on a regulatory rule basis, as different approaches and treatments may be used by health care providers depending on the individual patient's condition. This CPG consists of eight sections and 15 key questions. Each begins with statements that are graded by the strength of recommendations and quality of the evidence. Each statement is followed by a summary of the evidence supporting the recommendations. There are also a link to full-text documents and lists of the most important reports so that the readers can read further (most of this is available online).

Executive Summary of the Korean Society of Nephrology 2021 Clinical Practice Guideline for Optimal Hemodialysis Treatment

The Korean Society of Nephrology (KSN) has published a clinical practice guideline (CPG) document for maintenance hemodialysis (HD). The document, 2021 Clinical Practice Guideline on Optimal HD Treatment, is based on an extensive evidence-oriented review of the benefits of preparation, initiation, and maintenance therapy for HD, with the participation of representative experts from the KSN under the methodologists’ support for guideline development. It was intended to help clinicians participating in HD treatment make safer and more effective clinical decisions by providing user-friendly guidelines. We hope that this CPG will be meaningful as a recommendation in practice, but not on a regulatory rule basis, as different approaches and treatments may be used by health care providers depending on the individual patient’s condition. This CPG consists of eight sections and 15 key questions. Each begins with statements that are graded by the strength of recommendations and quality of the evidence. Each statement is followed by a summary of the evidence supporting the recommendations. There is also a link to full-text documents and lists of the most important reports so that the readers can read further (most of this is available online).

Absolute blood volume variations during hemodialysis: Does dialysate temperature play a role?

BACKGROUND

Vascular refilling occurs to preserve hemodynamic stability during hemodialysis (HD). Recent studies report a feasible and noninvasive method to determine absolute blood volume (ABV), and estimate vascular refilling during HD. The objective of this study is to analyze if lowering dialysate temperature modifies variations in ABV during HD.

METHODS

The study was performed in 50 patients under HD. During two different sessions, relative blood volume was assessed using dialysate temperatures of 35.5°C (cool dialysate) and 36.5°C (neutral dialysate). ABV and vascular refilling were calculated using Kron et al methodology.

RESULTS

Thirty-nine intradialytic morbid events (IMEs) were observed in 30 patients, 14 under cool dialysate and 25 during neutral dialysate. We did not found statistically differences in ABV or in refilling volume between cool and neutral temperature. When analyzing apart only those patients who presented IME, we observed lower drop in ABV in the 35.5°C dialysate treatments (0.57 L) versus 36.5°C dialysate treatments (0.71 L). When cool dialysate was used, the vascular refilling fraction tended to be higher, but data did not turn statistically significant.

CONCLUSIONS

In selected groups of patients the use of cool dialysate induces lower ABV variations that could improve hemodynamic stability during HD treatments.

Management of acute intradialytic cardiovascular complications: Updated overview (Review)

An increasing number of patients require renal replacement therapy through dialysis and renal transplantation. Chronic kidney disease (CKD) affects a large percentage of the world's population and has evolved into a major public health concern. Diabetes mellitus, high blood pressure and a family history of kidney failure are all major risk factors for CKD. Patients in advanced stages of CKD have varying degrees of cardiovascular damage. Comorbidities of these patients, include, on the one hand, hypertension, hyperlipidemia, hyperglycemia, hyperuricemia and, on the other hand, the presence of mineral-bone disorders associated with CKD and chronic inflammation, which contribute to cardiovascular involvement. Acute complications occur quite frequently during dialysis. Among these, the most important are cardiovascular complications, which influence the morbidity and mortality rates of this group of patients. Chronic hemodialysis patients manifest acute cardiovascular complications such as intradialytic hypotension, intradialytic hypertension, arrhythmias, acute coronary syndromes and sudden death. Thus, proper management is extremely important.

Dialysate temperature reduction for intradialytic hypotension for people with chronic kidney disease requiring haemodialysis

BACKGROUND

Intradialytic hypotension (IDH) is a common complication of haemodialysis (HD), and a risk factor of cardiovascular morbidity and death. Several clinical studies suggested that reduction of dialysate temperature, such as fixed reduction of dialysate temperature or isothermal dialysate using a biofeedback system, might improve the IDH rate.

OBJECTIVES

This review aimed to evaluate the benefits and harms of dialysate temperature reduction for IDH among patients with chronic kidney disease requiring HD, compared with standard dialysate temperature.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register up to 14 May 2019 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal, and ClinicalTrials.gov.

SELECTION CRITERIA

All randomised controlled trials (RCTs), cross-over RCTs, cluster RCTs and quasi-RCTs were included in the review.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted information including participants, interventions, outcomes, methods of the study, and risks of bias. We used a random-effects model to perform quantitative synthesis of the evidence. We assessed the risks of bias for each study using the Cochrane 'Risk of bias' tool. We assessed the certainty of evidence using Grades of Recommendation, Assessment, Development and Evaluation (GRADE).

MAIN RESULTS

We included 25 studies (712 participants). Three studies were parallel RCTs and the others were cross-over RCTs. Nineteen studies compared fixed reduction of dialysate temperature (below 36°C) and standard dialysate temperature (37°C to 37.5°C). Most studies were of unclear or high risk of bias. Compared with standard dialysate, it is uncertain whether fixed reduction of dialysate temperature improves IDH rate (8 studies, 153 participants: rate ratio 0.52, 95% CI 0.34 to 0.80; very low certainty evidence); however, it might increase the discomfort rate compared with standard dialysate (4 studies, 161 participants: rate ratio 8.31, 95% CI 1.86 to 37.12; very low certainty evidence). There were no reported dropouts due to adverse events. No study reported death, acute coronary syndrome or stroke.Three studies compared isothermal dialysate and thermoneutral dialysate. Isothermal dialysate might improve the IDH rate compared with thermoneutral dialysate (2 studies, 133 participants: rate ratio 0.68, 95% CI 0.60 to 0.76; I² = 0%; very low certainty evidence). There were no reports of discomfort rate (1 study) or dropouts due to adverse events (2 studies). No study reported death, acute coronary syndrome or stroke.

AUTHORS' CONCLUSIONS

Reduction of dialysate temperature may prevent IDH, but the conclusion is uncertain. Larger studies that measure important outcomes for HD patients are required to assess the effect of reduction of dialysate temperature. Six ongoing studies may provide much-needed high quality evidence in the future.

Intradialytic hypotension, blood pressure changes and mortality risk in incident hemodialysis patients

Background

Intradialytic hypotension (IDH) occurs frequently in maintenance hemodialysis (HD) patients and may be associated with higher mortality. We hypothesize that nadir intradialytic systolic blood pressure (niSBP) is inversely related to death risk while iSBP change (Δ) and IDH frequency are incrementally associated with all-cause mortality.

Methods

In a US-based cohort of 112 013 incident HD patients over a 5-year period (2007-11), using niSBP, ΔiSBP (pre-HD SBP minus niSBP) and IDH frequency (proportion of HD treatments with niSBP <90 mmHg) within the first 91 days of HD, we examined mortality-predictability at 1, 2 and 5 years using Cox models and restricted cubic splines adjusted for case-mix, comorbidities and laboratory covariates.

Results

We observed that niSBP of <90 and ≥140 mmHg had a 5-year mortality hazard ratio (HR) (95% confidence interval) of 1.57 (1.47-1.67) and 1.25 (1.18-1.33), respectively, compared with niSBP 110 to <120 mmHg. ΔiSBP of <15 and ≥50 compared with 21-30 mmHg had mortality HR of 1.31 (1.26-1.37) and 1.32 (1.24-1.39), respectively. Among patients with >40% IDH frequency, we observed a mortality HR of 1.49 (1.42-1.57) compared with 0% IDH frequency in fully adjusted models. These associations were robust at 1 and 2 years of follow-up.

Conclusion

In conclusion, we observed a U-shaped association between niSBP and ΔiSBP and mortality and a direct linear relationship between IDH frequency and mortality. Our findings lend some prognostic insight of HD blood pressure and hemodynamics, and have the potential to guide blood pressure management strategies among the HD population.

Cooling dialysate during in-center hemodialysis: Beneficial and deleterious effects

The use of cooled dialysate temperatures first came about in the early 1980s as a way to curb the incidence of intradialytic hypotension (IDH). IDH was then, and it remains today, the most common complication affecting chronic hemodialysis patients. It decreases quality of life on dialysis and is an independent risk factor for mortality. Cooling dialysate was first employed as a technique to incite peripheral vasoconstriction on dialysis and in turn reduce the incidence of intradialytic hypotension. Although it has become a common practice amongst in-center hemodialysis units, cooled dialysate results in up to 70% of patients feeling cold while on dialysis and some even experience shivering. Over the years, various studies have been performed to evaluate the safety and efficacy of cooled dialysate in comparison to a standard, more thermoneutral dialysate temperature of 37 °C. Although these studies are limited by small sample size, they are promising in many aspects. They demonstrated that cooled dialysis is safe and equally efficacious as thermoneutral dialysis. Although patients report feeling cold on dialysis, they also report increased energy and an improvement in their overall health following cooled dialysis. They established that cooling dialysate temperatures improves hemodynamic tolerability during and after hemodialysis, even in patients prone to IDH, and does so without adversely affecting dialysis adequacy. Cooled dialysis also reduces the incidence of IDH and has a protective effect over major organs including the heart and brain. Finally, it is an inexpensive measure that decreases economic burden by reducing necessary nursing intervention for issues that arise on hemodialysis such as IDH. Before cooled dialysate becomes standard of care for patients on chronic hemodialysis, larger studies with longer follow-up periods will need to take place to confirm the encouraging outcomes mentioned here.

Effect of Lowering the Dialysate Temperature in Chronic Hemodialysis: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Lowering the dialysate temperature may improve outcomes for patients undergoing chronic hemodialysis. We reviewed the reported benefits and harms of lower temperature dialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We searched the Cochrane Central Register, OVID MEDLINE, EMBASE, and Pubmed until April 15, 2015. We reviewed the reference lists of relevant reviews, registered trials, and relevant conference proceedings. We included all randomized, controlled trials that evaluated the effect of reduced temperature dialysis versus standard temperature dialysis in adult patients receiving chronic hemodialysis. We followed the Grading of Recommendations Assessment, Development and Evaluation approach to assess confidence in the estimates of effect (i.e., the quality of evidence). We conducted meta-analyses using random effects models.

RESULTS

Twenty-six trials were included, consisting of a total of 484 patients. Compared with standard temperature dialysis, reduced temperature dialysis significantly reduced the rate of intradialytic hypotension by 70% (95% confidence interval, 49% to 89%) and significantly increased intradialytic mean arterial pressure by 12 mmHg (95% confidence interval, 8 to 16 mmHg). Symptoms of discomfort occurred 2.95 (95% confidence interval, 0.88 to 9.82) times more often with reduced temperature compared with standard temperature dialysis. The effect on dialysis adequacy was not significantly different, with a Kt/V mean difference of -0.05 (95% confidence interval, -0.09 to 0.01). Small sample sizes, loss to follow-up, and a lack of appropriate blinding in some trials reduced confidence in the estimates of effect. None of the trials reported long-term outcomes.

CONCLUSIONS

In patients receiving chronic hemodialysis, reduced temperature dialysis may reduce the rate of intradialytic hypotension and increase intradialytic mean arterial pressure. High-quality, large, multicenter, randomized trials are needed to determine whether reduced temperature dialysis affects patient mortality and major adverse cardiovascular events.

Nitric oxide production and blood pressure reduction during haemodialysis

AIM

A decrease of systolic blood pressure in excess of 20 mmHg during haemodialysis treatment (IDD) is common for haemodialysis patients. Intradialytic hypotension (IDH) is symptomatic IDD by definition. Overproduction of nitric oxide (NO) is a possible cause of IDD. Dialysate nitrate and nitrite amount can be used as an indicator of intradialysis NO production. Our aim was to find the predictor of NO production in IDD patients.

METHODS

Partial dialysate samples were collected during the whole haemodialysis session and total dialysate nitrate and nitrite amount was measured to assess the association of intradialysis NO production with blood pressure change.

RESULTS

There were 31 IDD patients and 71 patients who did not develop IDD (NIDD) included in the study. Among the IDD patients, 13 were IDH patients with a mean systolic blood pressure lower than that of the other 18 symptomless IDD patients (96.6 ± 3.4 mmHg vs 125.0 ± 3.8 mmHg, P<0.001). The median value of NO production was higher in the IDD than in the NIDD patients (447.7 μg vs 238.8 μg, P<0.001). The NO production correlated linearly with blood pressure reduction (R=0.487, P<0.001). The multivariate analysis showed that NO production was positively associated with predialysis systolic blood pressure.

CONCLUSION

Nitric oxide production during haemodialysis was higher in IDD than in NIDD patients. IDH often occurred when systolic blood pressure was reduced to below 100 mmHg. The amount of NO produced during haemodialysis, which may be associated with predialysis systolic blood pressure, can be used to predict intradialysis blood pressure decrease.

Effect of cool vs. warm dialysate on toxin removal: rationale and study design

BACKGROUND

Cool dialysate is often recommended for prevention of intra-dialytic hypotensive episodes in maintenance hemodialysis (HD) patients. However, its effect on toxin removal is not studied. It is known that inter-compartmental resistance is the main barrier for toxin removal. Cool dialysate can potentially increase this resistance by vasoconstriction and thus impair the toxin removal. The aim of this trial is to compare the toxin removal outcome associated with cool vs. warm dialysate.

METHOD/DESIGN

This study is based on the hypothesis that dialysate temperature, a potential maneuver to maintain hemodynamic stability during HD, may influence inter-compartmental resistance and hence, toxin removal. Only stable HD patients will be recruited for this study. The quantum of removed toxins will be assessed by the total spent dialysate, which is a gold standard to quantify the efficacy of a single dialysis session. Collected samples will be analyzed for urea, creatinine, phosphate, β2-microglobulin, and uric acid. The study is a single center, self-controlled, randomized prospective clinical research where 20 study subjects will undergo 2 dialysis sessions: (a) cool dialysis with dialysate at 35.5°C, and (b) warm dialysis with dialysate at 37°C. Pre- and post-dialysis blood samples will be collected to quantify the dialysis adequacy and toxin reduction ratio.

DISCUSSION

This is the first clinical research to investigate the effect of dialysate temperature on removal of both small and large-sized toxins. Successful completion of this research will provide important knowledge pertaining to dialysate temperature prescription. Results can also lead to the hypothesis that cool dialysate may help in by preventing intra-dialytic hypotensive episodes, but prolonged prescription of cool dialysate may lead to comorbidities associated with excess toxin accumulation. The new knowledge will encourage for personalized dialysate temperature profiling.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier--NCT02064153.

Biofeedback dialysis for hypotension and hypervolemia: a systematic review and meta-analysis

BACKGROUND

Intradialytic hypotension (IDH) is associated with morbidity and mortality. We conducted a systematic review to determine whether biofeedback hemodialysis (HD) can improve IDH and other outcomes, compared with HD without biofeedback.

METHODS

Data sources included the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE and ISI Web of Science. We included randomized trials that enrolled adult patients (>18 years) with IDH or extracellular fluid expansion and that used biofeedback to guide ultrafiltration and/or dialysate conductivity. Two authors assessed trial quality and independently extracted data in duplicate. We assessed heterogeneity using I(2). We applied the GRADE framework for rating the quality of evidence.

RESULTS

We found two parallel-arm randomized controlled clinical trials and six randomized crossover trials meeting inclusion criteria. All trials were open-label and at least four were industry-sponsored. Studies were small (median n = 27). No study evaluated hospitalization and the evidence for effect on mortality was of very low quality. Three studies assessed quality of life (QoL); none demonstrated benefit or harm, and quality of evidence was very low. Biofeedback significantly reduced IDH (risk ratio 0.61, 95% confidence interval 0.44-0.86; I(2)= 0%). Quality of evidence for this outcome was low due to risk of bias and potential publication bias.

CONCLUSIONS

Biofeedback dialysis significantly reduces the frequency of IDH. Large and well-designed randomized trials are needed to assess the effects on survival, hospitalization and QoL.

Use of online blood volume and blood temperature monitoring during haemodialysis in critically ill patients with acute kidney injury: a single-centre randomized controlled trial

BACKGROUND

Little is known about the clinical impact on cardiovascular stability during intermittent haemodialysis (IHD) for acute kidney injury (AKI) of online monitoring devices that control blood volume (BV) and blood temperature in the intensive care unit (ICU) setting. We compared different dialysis treatment modalities with or without these new systems among critically ill patients requiring IHD.

METHODS

In a prospective single-centre three-arm randomized controlled trial, 600 dialysis sessions in 74 consecutive AKI critically ill patients were involved to assess intradialytic hypotension. Standard dialysis therapy with constant ultrafiltration (UF) rate, cool dialysate and high sodium conductivity (Treatment A) was compared to regimens with adjunctive interventions including BV control (Treatment B) and the combination of BV and active blood temperature control (Treatment C). Each dialysis session was randomly assigned to one of the three treatment arms and served as statistical unit.

RESULTS

Five hundred and seventy-two dialysis sessions were analysed (188, 190 and 194 in Treatments A, B and C, respectively). Hypotension occurred in 16.6% treatments, with similar rates among the arms. Haemodynamic parameters and dialysis-related complications did not differ between therapies. Based on generalized estimating equation adjusted to dialysate sodium conductivity, higher Sequential Organ Failure Assessment the day of dialysis session, the need for vasopressors and lower systolic blood pressure at the onset of the session were identified as independent predictors of hypotensive episodes, whereas regimens containing the new online monitors were not.

CONCLUSIONS

These results suggest that both actively controlled body temperature and UF profiled by online monitoring systems have no significant impact on the incidence of intradialytic hypotension in the ICU setting. Further research is needed before the use of these new sophisticated automatic methods can be applied routinely to the ICU setting.

Intra-dialytic hypotension and blood volume and blood temperature monitoring

Intra-dialytic hypotension (IDH) is a common problem affecting haemodialysis patients. Its aetiology is complex and influenced by multiple patient and dialysis factors. IDH occurs when the normal cardiovascular response cannot compensate for volume loss associated with ultrafiltration, and is exacerbated by a myriad of factors including intra-dialytic fluid gains, cardiovascular disease, antihypertensive medications and the physiological demands placed on patients by conventional haemodialysis. The use of blood volume monitoring and blood temperature monitoring technologies is advocated as a tool to predict and therefore prevent episodes of IDH. We review the clinical utility of these technologies and summarize the current evidence of their effect on reducing the incidence of IDH in haemodialysis population.

Dialysate and blood temperature during hemodialysis: comparing isothermic dialysis with a single-pass batch system

The Genius is a convenient single-pass batch hemodialysis system. Dialysate is heated during the preparation phase. Once the container is filled at one of the three available starting temperatures, dialysate cools spontaneously. As dialysate temperature plays an important role in hemodynamic stability, knowledge of the instantaneous dialysate temperature is important. We documented the evolution of dialysate temperature during Genius dialysis with dialysate prepared at two different temperatures (low and medium) as well as its effect on blood temperature and hemodynamic stability. Genius dialysis was compared to isothermic dialysis obtained by a module programmed to obtain a constant blood temperature. With Genius, dialysate temperature progressively decreased from 36.3 (low) and 37.6°C (medium) in the beginning to 34.4 and 35.3°C at the end of the session, both following first-order kinetics. During isothermic dialysis, dialysate cooled from 37.3 to 35.4°C, being warmer than with Genius low. Blood temperature decreased during dialysis with Genius low, from 36.4 to 36.2°C, whereas with medium temperature, blood temperature initially rose from 36.4°C at 15 min to 36.5 and 36.6°C at 30 and 60 min, respectively, followed by a decrease from 180 min onward, to 36.4°C at the end. During isothermic dialysis, blood temperature remained stable, as expected. Blood pressure decreased during all three schedules, with the highest value at 15 min during isothermic dialysis, and at the end of the session, the lowest value with isothermic dialysis.

Cool dialysate reduces asymptomatic intradialytic hypotension and increases baroreflex variability

Intradialytic hypotension (IDH) remains an important cause of morbidity and mortality in chronic hemodialysis (HD) patients and can be ameliorated by cool temperature HD. The baroreflex arc is under autonomic control and is essential in the short-term regulation of blood pressure (BP). This study aimed to investigate if the baroreflex sensitivity (BRS) response to HD differed between standard and cool-temperature dialysate. Ten patients (mean age 67+/-2 years) prone to IDH were recruited into a randomized, crossover study to compare BRS variation at dialysate temperatures of 37 degrees C (HD(37)) and 35 degrees C (HD(35)). Each patient underwent continuous beat-to-beat BP monitoring during a dialysis session of HD(37) and HD(35). During HD(37) 2 patients developed symptomatic IDH, as opposed to 1 with HD(35). However, asymptomatic IDH occurred with a frequency of 0.4 episodes per session with HD(35) and 6.2 episodes per session during HD(37) (odds ratio15.5; 95%CI 5.6-14.2). Although absolute BRS measurements did not differ between the 2 modalities, BRS variability increased during HD(35). Our study has demonstrated that in IDH-prone patients, cool HD resulted in a reduction in heart rate and a greater reduction in cardiac output and stroke volume. Mean arterial pressure was maintained through a significantly greater increase in total peripheral resistance. Furthermore, although absolute BRS values during HD were not significantly altered by a reduction in dialysate temperature, there was a greater percentage increase in BRS values during cool HD. Understanding the varied causes of, and categorizing impaired hemodynamic responses to HD will enable further individualization of HD prescriptions according to patient need.

Control of core temperature and blood pressure stability during hemodialysis

BACKGROUND AND OBJECTIVES

Cool dialysate may ameliorate intradialytic hypotension (IDH). It is not known whether it is sufficient to prevent an increase in core temperature (CT) during hemodialysis (HD) or whether a mild decline in CT would yield superior results. The aim of this study was to compare both approaches with regard to IDH.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Fourteen HD patients with a history of IDH were studied. During three mid-week HD treatments, CT was set to decrease by 0.5 degrees C ("cooling") or to remain unchanged at the baseline level ("isothermic"). "Thermoneutral" HD (no energy is added to or removed from the patient) was used as a control. Central blood volume (CBV), BP, skin temperature, heart rate variability [low and high frequency] were recorded.

RESULTS

CT increased during thermoneutral and remained respectively stable and decreased during isothermic and cooling. Skin temperature decreased significantly during isothermic and cooling, but not during thermoneutral. Nadir systolic BP (SBP) levels were lower during isothermic and thermoneutral compared with cooling. CBV tended to be higher during cooling compared with isothermic and thermoneutral. Three patients complained of shivering during cooling. Change in LF/HF was not different between cooling, isothermic, and thermoneutral.

CONCLUSIONS

IDH may be slightly improved by cooling compared with the isothermic approach, possibly because of improved maintenance of CBV. The hemodynamic effects of mild blood cooling should be balanced against a potentially higher risk of cold discomfort.

A systematic review of the clinical effects of reducing dialysate fluid temperature

BACKGROUND

Intradialytic hypotension (IDH) is a frequent complication of haemodialysis. Reducing the temperature of the dialysis fluid is a simple therapeutic strategy but is relatively underused. This may be due to concerns regarding its effects on symptoms and dialysis adequacy. We performed a systematic review of the literature to examine the effects of cool dialysis on intradialytic blood pressure, and to assess its safety in terms of thermal symptoms and small solute clearance.

METHODS

We searched the Cochrane Central Register of Controlled Trials, Medline, Embase, Cumulative Index to Nursing and Allied Health Literature, databases of ongoing trials, the contents of four major renal journals as well as hand-searching reference lists. We included all prospective randomized studies that compared any technique of reducing dialysate temperature with standard bicarbonate dialysis. These techniques included an empirical, fixed reduction of dialysate temperature or use of a biofeedback temperature-control device (BTM) to deliver isothermic dialysis or programmed patient cooling.

RESULTS

A total of 22 studies comprising 408 patients were included (16 studies examined a fixed empirical temperature reduction and six examined BTM). All studies were of crossover design and relatively short duration. IDH occurred 7.1 (95% CI, 5.3-8.9) times less frequently with cool dialysis (both fixed reduction and BTM). Post-dialysis mean arterial pressure was higher with cool-temperature dialysis by 11.3 mmHg (95% CI, 7.7-15.0). No studies reported that cool dialysis led to a reduction in dialysis adequacy as assessed by urea clearance. The frequency and severity of thermal-related symptoms were generally reported inadequately.

CONCLUSIONS

Reducing the temperature of the dialysate is an effective intervention to reduce the frequency of IDH and does not adversely affect dialysis adequacy. This applies to the fixed reduction of dialysate temperature and BTM. It remains unclear as to what extent cool-temperature dialysis causes intolerable cold symptoms during dialysis. There are no trials comparing fixed empirical temperature reduction with BTM, and no trials examining the long-term effects of cool dialysis on patient outcomes.

Reviews: The Current State of Nonuremic Applications for Extracorporeal Blood Purification

Despite the commonly accepted indications for hemodialysis and extracorporeal depuritive techniques, some clinicians have come to rely on blood purification for clinical states where the targeted substance for removal differs from uremic waste products. Over the last decade, a number of studies have emerged to help define the application of extracorporeal blood purification (ECBP) to these "nonuremic" indications. This review describes the application of extracorporeal blood purification in clinical states including sepsis, rhabdomyolysis, congestive heart failure, hepatic failure, tumor lysis syndrome, adult respiratory distress syndrome, intravenous contrast exposure, and lactic acidosis. Additional comments are provided to review existing literature on thermoregulation and osmoregulation, including acute brain injury.

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.

Predilution hemodiafiltration displays no hemodynamic advantage over low-flux hemodialysis under matched conditions

BACKGROUND

It is the prevailing view that convective dialysis techniques stabilize blood pressure. The aim of this study was to compare the intrasession hemodynamics during high-dose predilution hemodiafiltration (HDF) and low-flux hemodialsis, under strict controlled conditions.

METHODS

Twelve stable hemodialysis patients were investigated in a randomized crossover blinded controlled trial. The patients were allocated to one session of predilution HDF (substitution fluid 1.20 +/- 0.10 L/kg body weight) and one session of hemodialysis at 4(1/2) hours. To eliminate confounding factors, dialysis dose, ultrafiltration volume and arterial temperature were matched. At the start of the dialysis the patients' core temperature was "locked" by an automatic feedback system regulating the dialysate temperature; thereby, patients' temperature was kept stable throughout the whole treatment. The calcium-ion concentration in the substitution/dialysis fluid was 1.25 mmol/L. Cardiac output was measured hourly by the ultrasound velocity dilution method.

RESULTS

Mean blood pressure, cardiac output, stroke volume, cardiac work, and relative blood volume was significantly reduced in both treatments. Total peripheral resistance increased significantly in both groups. Ultrafiltration volume, cardiopulmonary recirculation, Kt/V, and total energy transfer were similar for hemodialysis and HDF. The pulse rate showed no significant change throughout both sessions. No significant differences were revealed between hemodialysis and HDF.

CONCLUSION

The hemodynamics of predilution HDF and low-flux hemodialysis displayed a similar profile during matched conditions. An acute circulatory benefit of convective solute removal over diffusive could not be demonstrated.

Haemodialysis with on-line monitoring equipment: tools or toys?

BACKGROUND

On-line monitoring of chemical/physical signals during haemodialysis (HD) and bio-feedback represents the first step towards a 'physiological' HD system incorporating adaptive and logic controls in order to achieve pre-set treatment targets.

METHODS

Discussions took place to achieve a consensus on key points relating to on-line monitoring and bio-feedback, focusing on the clinical applications.

RESULTS

The relative blood volume (BV) reduction during HD can be monitored by optic devices detecting the variations in concentration of haemoglobin/haematocrit. BV changes result from an equilibrium between ultrafiltration and the refilling capacity. However, BV reduction has little power in predicting intra-HD hypotensive episodes, while the combination of the patient-dialysate sodium gradient, the relative BV reduction between the 20th and 40th minute of HD, the irregularity of the profile of BV reduction over time and the heart rate decrease from the start to the 20th minute of HD predict intra-HD hypotension with a sensitivity of 82%, a specificity of 73% and an accuracy of 80%. A bio-feedback system drives the relative BV reduction according to desired values by instantaneously changing the ultrafiltration rate and the dialysate conductivity. This system has proved to reduce the incidence of intra-HD hypotension episodes significantly. Ionic dialysance and the patient's plasma conductivity can be calculated easily from on-line inlet and outlet dialysate conductivity measurements at two different steps of dialysate conductivity. Ionic dialysance is equivalent to urea clearance corrected for recirculation and is a tool for continuously monitoring the dialysis efficiency and detecting early problems with the delivery of the prescribed dose of dialysis. Given the strict and linear relationship between conductivity and sodium content, the conductivity values replace the sodium concentration values and this permits the development of a conductivity kinetic model, by means of which sodium balance can be achieved at each dialysis session. The conductivity kinetic model has been demonstrated to improve intra-HD cardiovascular stability in hypotension-prone patients significantly. Ionic dialysance is also a useful tool to monitor vascular access function, as it can be used to obtain serial measurements of vascular access blood flow. On-line urea monitors provide detailed information on intra-HD urea kinetics and delivered dialysis dose, but they are not in widespread use because of the costs related to the disposable materials (e.g. urease cartridge). The body temperature monitor measures the blood temperature at the arterial and venous lines of the extra-corporeal circuit and, thanks to a bio-feedback system, is able to modulate the dialysate temperature in order to influence the patient's core body temperature, which can be kept at constant values. This is associated with improved intra-HD cardiovascular stability. The module can also be used to quantify total recirculation.

CONCLUSIONS

On-line monitoring devices and bio-feedback systems have evolved from toys for research use to tools for routine clinical application, particularly in patients with clinical complications. Conductivity monitoring appears the most versatile tool, as it permits quantification of delivered dialysis dose, achievement of sodium balance and surveillance of vascular access function, potentially at each dialysis session and without extra cost.

Special Article: Improving Outcomes in CKD and ESRD Patients: Carrying the Torch from Training to Practice

Practicing nephrologists are spending more time caring for end-stage renal disease (ESRD) and chronic kidney disease (CKD) patients. Despite this focus, and considerable advances in the understanding of those aspects of care that impact on clinical outcomes, morbidity, mortality, and quality of life for these patients has not improved substantially over the past decade. One of the possible explanations for this lack of progress is the structure of current nephrology training programs, where ESRD and CKD patient care is not emphasized. To address this issue, we developed a short preceptorship for second-year nephrology fellows, including didactic lectures and workshops. Of 67 participating fellows, 50% were from programs offering 3 or fewer months of exposure to outpatient hemodialysis, and 25% reported no exposure to peritoneal dialysis. Of more concern, 25% reported no "official rounds" with an attending nephrologist on dialysis patients. If nephrologists are to take their appropriate place as leaders of the care delivery team, nephrology fellowships must be restructured with appropriate emphasis placed on the comprehensive care of ESRD and CKD patients.

Hemodialysis-Induced Hypotension: Impact of Technologic Advances

Hemodialysis-induced hypotension is one of the most serious complications in renal replacement therapy. The main cause of intradialytic hypotension is hypovolemia due to an imbalance between the amount of fluid removed and the refilling capacity of the intravascular compartment. Hypotension occurs when compensatory mechanisms for hypovolemia are overwhelmed by excessive fluid removal. As long as renal replacement therapy is limited to only a few hours per week, intradialytic hypotension will continue to be a relevant problem. Research has mainly focused on enlarging the compensatory capacity for ultrafiltration-induced hypovolemia. This article critically discusses the technical approaches that have been introduced into therapy in recent years with the promise of reducing dialysis-induced hypotensive episodes.

The effects of control of thermal balance on vascular stability in hemodialysis patients: results of the European randomized clinical trial

BACKGROUND

Many reports note that the use of cool dialysate has a protective effect on blood pressure during hemodialysis (HD) treatments. However, formal clinical trials in which dialysate temperature is tailored to the body temperature of appropriately selected hypotension-prone patients are lacking.

METHODS

We investigated the effect of thermal control of dialysate on hemodynamic stability in hypotension-prone patients selected from 27 centers in nine European countries. Patients were eligible for the study if they had symptomatic hypotensive episodes in 25% or more of their HD sessions, assessed during a prospective screening phase over 1 month. The study is designed as a randomized crossover trial with two phases and two treatment arms, each phase lasting 4 weeks. We used a device allowing the regulation of thermal balance (Blood Temperature Monitor; Fresenius Medical Care, Bad Homberg, Germany), by which we compared a procedure aimed at preventing any transfer of thermal energy between dialysate and extracorporeal blood (thermoneutral dialysis) with a procedure aimed at keeping body temperature unchanged (isothermic dialysis).

RESULTS

One hundred sixteen HD patients were enrolled, and 95 patients completed the study. During thermoneutral dialysis (energy flow rate: DeltaE = -0.22 +/- 0.29 kJ/kg x h), 6 of 12 treatments (median) were complicated by hypotension, whereas during isothermic dialysis (energy flow rate: DeltaE = -0.90 +/- 0.35 kJ/kg x h), the median decreased to 3 of 12 treatments (P < 0.001). Systolic and diastolic blood pressures and heart rate were more stable during the latter procedure. Isothermic dialysis was well tolerated by patients.

CONCLUSION

Results show that active control of body temperature can significantly improve intradialytic tolerance in hypotension-prone patients.

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.

Hemodynamics in patients with intradialytic hypotension treated with cool dialysate or midodrine

Cool dialysate and midodrine have been used successfully to treat intradialytic hypotension (IDH) in the end-stage renal disease population. However, the exact mechanisms by which these interventions improve hemodynamic stability are not well known. We undertook a study to evaluate the effect of these modalities on intradialytic hemodynamics in patients with documented dialysis-associated hypotension. We used the ultrasound dilution technique to measure cardiac output (CO), central blood volume (CBV), and peripheral vascular resistance (PVR) in these patients. The study was performed in two phases. Phase 1 consisted of control (1A) and cool dialysate (1B) studies, whereas phase 2 consisted of control (2A) and midodrine (2B) studies. CO, CBV, and PVR were measured 30 minutes after the initiation of hemodialysis (HD) and 30 minutes before the termination of HD using the HD01 monitor. Blood pressure was measured pre-HD and post-HD. Fourteen patients with documented IDH completed the study. CO and CBV were significantly more preserved in the cool dialysate and midodrine phases compared with control phases. PVR increased in all phases of the study. Declines in mean arterial pressures from pre-HD to post-HD were less with cool dialysate versus control and midodrine versus control. Ultrafiltration volumes were not significantly different between phases. Cool dialysate and midodrine appear to improve intradialytic hemodynamics in patients with dialysis-associated hypotension, mainly through the preservation of CBV and CO, rather than significantly elevating PVR.

[Relationship between dialysis solution and symptomatic arterial hypotension observed during hemodialysis sessions in patients with chronic kidney failure]

This prospective study was designed to evaluate hypotension in a group of 21 end stage renal disease patients (ESRD) on hemodialysis, with syntomatic low blood pressure. The arterial blood pressure was recorded at 4 consecutive dialysis sessions, two at 35 degrees C and two at 37 degrees C dialysate temperature. In both situations, systolic and diastolic pressures, measured during dialysis, were different from the pre-dialysis value, with progressive lowering up to the end of the procedure. Cold dialysis did not protect from lowering the blood pressure in an amount similar to that occurring at 37 degrees C.

Implications for the role of endogenous nitric oxide inhibitors in hemodialysis hypotension

Hypotensive episodes during hemodialysis in patients with end-stage renal disease in the absence of inadequate maintenance of the plasma volume, pre-existence of cardiovascular disease, or autonomic nervous system dysfunction is accompanied by increase in the plasma concentrations of the end-products of nitric oxide metabolism, above the levels expected based on the reduction of urea. Factors that can influence the synthesis of nitric oxide or the regulation of the effects of this free radical in patients with chronic renal failure are reviewed. Convergence of these factors and their interactions during the hemodialysis procedure are discussed as the basis for the generation of excessive amounts of nitric oxide that serves as an important contributing factor in the development of symptomatic hypotension.

Methylene blue, a nitric oxide inhibitor, prevents haemodialysis hypotension

BACKGROUND

Plasma nitric oxide (NO) levels have been found to be high in haemodialysis (HD) patients, especially in those prone to hypotension in dialysis. The aim of the study was to prevent dialysis hypotension episodes by i.v. administration of methylene blue (MB), an inhibitor of NO activity and/or production.

METHODS

MB was given i.v. in 18 stable HD patients with hypotensive episodes during almost every dialysis, in 18 HD patients without hypotension during dialyses, and in five healthy controls. MB was given as a bolus of 1 mg/kg bodyweight followed by a constant infusion of 0.1 mg/kg bodyweight lasting 210 min until the end of the dialysis session and only as a bolus on a non-dialysis day. Systolic and diastolic blood pressures (BP) were measured at 10-min intervals during HD sessions with or without MB and on a non-dialysis day with MB.

RESULTS

In hypotension-prone patients, MB completely prevented the hypotension during dialysis and increased both systolic and diastolic BP on non-dialysis days. In normotensive patients, MB increased BP during the first hour of dialysis and for 90 min on the non-dialysis day. The BP in the healthy controls remained unchanged. Plasma and platelet NO(2)+NO(3) (stable metabolites of NO) levels were determined. The NO(2)+NO(3) generation rate in the first post-dialysis day was calculated. The plasma and platelet NO(2)+NO(3) were higher in the hypotensive group than in the normotensive dialysis group. The generation rate of nitrates was higher (P<0.01) in the hypotensive group (1.21+/-0.13 micromol/min and 0.74+/-0.16 after MB) than in the normotensive patients (0.61+/-0.11 micromol/ min and 0.27+/-0.14 after MB). No side-effects were recorded.

CONCLUSIONS

MB is an efficient therapy in the prevention of dialysis hypotension.

Preventing dialysis hypotension: a comparison of usual protective maneuvers

BACKGROUND

Intradialytic hypotension (IH) is a common adverse event. Currently, there are several commonly utilized therapies of IH, but they have not been compared directly in the same group of patients. We performed the present study in order to learn which of these techniques is most effective so that a rational approach to treating IH could then be formulated.

METHODS

A single-blinded, crossover study design of five different protocols was undertaken in 10 hemodialysis patients with a prior history of IH. Each patient first underwent one week (three dialyses) of standard dialysis (dialysate sodium 138 mEq/L). Then each patient was subjected to one week each (three dialyses) of the four test protocols, performed in random order in a blinded fashion. The specific protocols were as follows: high sodium dialysate, in which the patient was dialyzed using a dialysate sodium of 144 mEq/L; sodium modeling, during which the dialysate sodium declined from 152 to 140 mEq/L in the last half hour of dialysis; one hour of isolated ultrafiltration followed by three hours of isovolemic dialysis; and cool temperature dialysis in which the dialysate was cooled to 35 degrees C.

RESULTS

Weight loss in each of the five protocols was essentially identical, varying between 2.9 and 3 kg. There were significantly fewer hypotensive episodes per treatment in the sodium modeling, high sodium, and cool temperature protocols as compared with the standard protocol (P < 0.05). Ultrafiltration followed by dialysis was associated with a significantly greater number of hypotensive episodes per treatment than any of the three test protocols (P < 0.05). Similarly, the number of nursing interventions required for IH per treatment was significantly greater in the standard dialysis and in the isolated ultrafiltration protocols compared with sodium modeling and cool temperature protocols (P < 0.05). The number of hypotensive signs and symptoms per treatment was also significantly reduced during the sodium modeling and cool temperature protocols compared with the standard protocol (P < 0.004 and P < 0.02, respectively). Again, the isolated ultrafiltration protocol resulted in significantly more hypotensive symptoms and signs than the three test protocols (P < 0.005). Finally, the nadir mean arterial pressures were significantly lower in the standard and isolated ultrafiltration protocols when compared with the three test protocols (P < 0.05). The upright postdialysis blood pressure was best preserved in the sodium modeling and cool temperature protocols compared with the standard and isolated ultrafiltration protocols (P < 0.05).

CONCLUSION

This study supports the use of sodium modeling as a first step in combating IH. Also effective were the use of cool-temperature dialysate and a high-sodium dialysate. All three test protocols were well tolerated. As applied in this study, isolated ultrafiltration followed by isovolemic dialysis was notably less effective in reducing IH.

Energy transfer is the single most important factor for the difference in vascular response between isolated ultrafiltration and hemodialysis

Differences in vascular reactivity between isolated ultrafiltration (i-UF) and hemodialysis (UF + HD) have been attributed to various factors, including differences in core temperature (CT) and energy transfer (ET). However, the relative importance of these thermal factors is not known. The aim of this study was to elucidate to what extent differences in ET are responsible for the divergent vascular response between i-UF and UF + HD. During four different dialysis treatments in 15 patients, four measurements were performed that consisted of 1 h of i-UF, UF + HD at a dialysate temperature (T(d)) of 37.5 degrees C (UF + HD(37.5)), UF + HD at T(d) 35.5 degrees C (UF + HD(35.5)), and UF + HD with a similar ET as during i-UF(UF + HD(ET-set)). The UF rate in all sessions was 1 L/h. CT ( degrees C) decreased significantly during i-UF and UF + HD(ET-set) (P < 0.05), increased significantly during UF + HD(37.5) (P < 0.05), and remained unchanged during UF + HD(35. 5) (NS). Forearm vascular reactivity increased significantly during i-UF, UF + HD(ET-set), and UF + HD(35.5) (P < 0.05), but not during UF + HD(37.5) (NS). Venous tone increased significantly during i-UF, UF + HD(35.5), and UF + HD(ET-set) (P < 0.05), and decreased significantly during UF + HD(37.5) (P < 0.05). When i-UF and UF + HD are matched for ET, all differences in vascular response disappear, showing that differences in ET are the single most important factor for the observed difference in vascular response between i-UF and UF + HD. In contrast to UF + HD(37.5), vascular reactivity was improved when the increase in CT was prevented during UF + HD(35.5) and appeared to increase more when CT was lowered. Preventing the increase in CT during UF + HD appears to be mandatory for optimization of hemodynamic stability during dialysis.

Hemodynamic tolerance of intermittent hemodialysis in critically ill patients: usefulness of practice guidelines

Poor hemodynamic tolerance of intermittent hemodialysis (IHD) is a common problem for patients in an intensive care unit (ICU). New dialysis strategies have been adapted to chronic hemodialysis patients with cardiovascular insufficiency. To improve hemodynamic tolerance of IHD, specific guidelines were progressively implemented into practice through the year 1996 in our 26-bed medical ICU. To evaluate the efficiency of these guidelines we retrospectively compared all IHD performed during the years before (1995) and after (1997) implementation of these recommendations. Forty-five patients underwent 248 IHD sessions in 1995 and 76 patients underwent 289 IHD sessions in 1997. The two populations were similar for age, sex, chronic hemodialysis (26% versus 17%), and secondary acute renal failure. In 1997, patients were more severely ill with a higher SAPS II (50 +/- 17 versus 59 +/- 24; p = 0.036), and more patients required epinephrine or norepinephrine infusion before dialysis sessions (16% versus 34%; p < 0.0001). The compliance to guidelines was high, inducing a significant change in IHD modalities. As a result, hemodynamic tolerance was significantly better in 1997, with less systolic blood pressure drop at onset (33% versus 21%, p = 0. 002) and during the sessions (68% versus 56%, p = 0.002). IHD with hypotensive episode or need for therapeutic interventions were less frequent in 1997 (71% versus 61%, p = 0.015). The ICU mortality was similar (53.3% in 1995 versus 47.3% in 1997; p = 0.52) but death rate in 1997, but not in 1995, was significantly less than predicted from SAPS II (47.3% versus 65.6%; p = 0.02). Length of ICU stay was also reduced for survivors in 1997 (p = 0.04). Implementation of practice guidelines for intermittent hemodialysis in ICU patients lessens hemodynamic instability and may improve outcome.

Midodrine: a selective alpha-adrenergic agonist for orthostatic hypotension and dialysis hypotension

Midodrine is an oral agent which acts as a selective peripherally-acting alpha-receptor agonist. Midodrine is a prodrug that is almost completely absorbed after oral administration and converted into its active drug de-glymidodrine in the systematic circulation, with a bioavailability of 93%. It has been used successfully in the treatment of neurogenic orthostatic hypotension and more recently, in the treatment of dialysis hypotension. It acts through vasoconstriction of the arterioles and the venous capacitance vessels, thereby increasing peripheral vascular resistance and augmenting venous return, respectively. It is a unique agent in the armamentarium against orthostatic hypotension since it has minimal cardiac and CNS effects. This article will review the literature on midodrine for conditions of autonomic dysfunction, with focus on recent studies on its use in haemodialysis patients.

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

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