Dialysis disequilibrium syndrome (DDS) in the rat: role of the "reverse urea effect"

Prevention of dialysis disequilibrium syndrome in children with advanced uremia with a structured hemodialysis protocol: A quality improvement initiative study

BACKGROUND

Dialysis disequilibrium syndrome (DDS) is a rare but significant concern in adult and pediatric patients undergoing dialysis initiation with advanced uremia or if done after an interval. It is imperative to gain insights into the epidemiological patterns, pathophysiological mechanisms, and preventive strategies aimed at averting the onset of this ailment.

DESIGN

Prospective observational quality improvement initiative cohort study.

SETTING AND PARTICIPANTS

A prospective single-center study involving 50 pediatric patients under 18 years recently diagnosed with chronic kidney disease stage V with blood urea ≥200 mg/dL, admitted to our tertiary care center for dialysis initiation from January 2017 to October 2023.

QUALITY IMPROVEMENT PLAN

A standardized protocol was developed and followed for hemodialysis in pediatric patients with advanced uremia. This protocol included measures such as lower urea reduction ratios (targeted at 20%-30%) with shorter dialysis sessions and linear dialysate sodium profiling. Prophylactic administration of mannitol and 25% dextrose was also done to prevent the incidence of dialysis disequilibrium syndrome.

MEASURES

Incidence of dialysis disequilibrium syndrome and severe dialysis disequilibrium syndrome, mortality, urea reduction ratios (URRs), neurological outcome at discharge, and development of complications such as infection and hypotension. Long-term outcomes were assessed at the 1-year follow-up including adherence to dialysis, renal transplantation, death, and loss to follow-up.

RESULTS

The median serum creatinine and urea levels at presentation were 7.93 and 224 mg/dL, respectively. A total of 20% of patients had neurological symptoms attributable to advanced uremia at the time of presentation. The incidence of dialysis disequilibrium syndrome was 4% (n = 2) with severe dialysis disequilibrium syndrome only 2% (n = 1). Overall mortality was 8% (n = 4) but none of the deaths were attributed to dialysis disequilibrium syndrome. The mean urea reduction ratios for the first, second, and third dialysis sessions were 23.45%, 34.56%, and 33.50%, respectively. The patients with dialysis disequilibrium syndrome were discharged with normal neurological status. Long-term outcomes showed 88% adherence to dialysis and 38% renal transplantation.

LIMITATIONS

This study is characterized by a single-center design, nonrandomized approach, and limited sample size.

CONCLUSIONS

Our structured protocol served as a framework for standardizing procedures contributing to low incidence rates of dialysis disequilibrium syndrome.

Dialysis Disequilibrium Syndrome and Intracranial Pressure Fluctuations in Neurosurgical Patients Undergoing Renal Replacement Therapy: Systematic Review and Pooled Analysis

BACKGROUND

Dialysis disequilibrium syndrome is a rare, well-known, potentially life-threatening complication of renal replacement therapy (RRT), often involving cerebral edema and increased intracranial pressure (ICP). However, the impact of RRT on ICP and rate of dialysis disequilibrium syndrome in neurosurgical patients have not been systematically assessed.

METHODS

In February 2022, a systematic review following PRISMA guidelines was conducted using various combinations of 9 keywords in the MEDLINE database. Eleven papers were selected. Individual patient data were extracted, pooled, and analyzed.

RESULTS

Fifty-eight patients, 44 men and 14 women with a mean age of 48 years (6-78 years), were analyzed. Neurosurgical conditions included the following: spontaneous intracranial hemorrhage (n = 27), traumatic brain injury (n = 16), ischemic stroke/anoxic brain injury (n = 6), intracranial tumor (n = 6), and others (n = 3). Neurosurgical interventions included the following: craniotomy/craniectomy (n = 23), external ventricular drain or ICP monitor placement (n = 16), and burr hole or twist drill craniostomy (n = 4). Intermittent dialysis was used in 33 patients, continuous RRT in 20, and a combination thereof in 4. During RRT, ICP increased in 35 patients (60.3%), remained unchanged in 20, and decreased in 3. Thirty-four patients (65.4%) died. Intermittent dialysis was associated with increased ICP (73% vs. 37.5%, P = 0.01) and mortality (75% vs. 39.1%, P = 0.01).

CONCLUSIONS

In neurosurgical patients, ICP increases during RRT are common, affecting up to 60%, and potentially life-threatening, with mortality rates as high as 65%. The use of a continuous rather than intermittent RRT technique may reduce the risk of this complication. Prospective studies are warranted.

The instant impact of a single hemodialysis session on brain morphological measurements in patients with end-stage renal disease

Objective

To investigate the instant impact of hemodialysis (HD) on the cerebral morphological measurements of patients with end-stage renal disease (ESRD).

Materials and methods

Twenty-five patients undergoing maintenance HD and twenty-eight age-, sex-, and education-matched healthy control (HC) were included. The HD group and HC group had 3D high-resolution structural magnetic resonance imaging (MRI) scans twice and once, respectively. Both groups underwent neuropsychologic tests. The morphological measurements of structural MRI were measured using CAT12 and these measures were compared among three groups. The relationship between morphological measures and clinical parameters and neuropsychological tests were investigated through multiple regression analysis.

Results

Compared to the HC group, the cortical thickness before HD significantly decreased in the bilateral temporal lobe and significantly decreased in the left superior temporal gyrus after HD. The cortical thickness significantly increased in the bilateral temporal lobe, frontal lobe and occipital lobe after HD compared to before HD. The sulcus depth in the bilateral insula, frontal lobe, and parietal lobe after HD significantly increased compared to before HD. No significant differences in sulcus depth between HD and HC were detected. After HD, the cortical thickness of the right parsopercularis was positively correlated with the number connection test-A. Cortical thickness in multiple regions were positively correlated with blood flow velocity and cortical thickness in the left parahippocampal gyrus was negatively correlated with ultrafiltration volume. Patients showed better performance in the digit symbol test and line tracing test after HD compared to before HD, but there were no significant differences in the comparison of neuropsychologic tests between patients and HC.

Conclusion

The instant morphological changes were captured during a single hemodialysis in HD patients. There was an association between these instant changes in the brain and clinical parameters and neuropsychologic tests. This work implied the instant impact of a single hemodialysis impact on the brain in HD patients.

Dialysis Disequilibrium: Is Acidosis More Important than Urea?

Dialysis disequilibrium syndrome is a severe complication associated with dialysis treatment. Manifestations may range from mild such as headache to severe such as seizures and coma. Risk factors for development include initial dialysis treatment, uraemia, metabolic acidosis, and extremes of age. We report a case of dialysis disequilibrium in a patient with a failing kidney transplant secondary to the recurrence of IgA nephropathy. Disturbance in cognition and neurologic functioning occurred six hours after the completion of initiation of intermittent haemodialysis. During two sessions of intermittent haemodialysis of 3 and 4 hours, urea was reduced by 21.9 and 17.2 mmol/L and measured serum osmolality was reduced by 25 and 14 mOsm/kg, respectively. Subsequent admission to the intensive care unit and initiation of continuous renal replacement therapy for 48 hours resulted in complete resolution of symptoms. In this case report, we discuss atypical clinical and radiologic features of dialysis disequilibrium occurring with modest reductions in urea and serum osmolality.

Dialysis disequilibrium syndrome (DDS) in pediatric patients on dialysis: systematic review and clinical practice recommendations

BACKGROUND AND OBJECTIVES

Dialysis disequilibrium syndrome (DDS) is a rare neurological complication, most commonly affecting patients undergoing new initiation of hemodialysis (HD), but can also be seen in patients receiving chronic dialysis who miss regular treatments, patients having acute kidney injury (AKI), and in those treated with continuous kidney replacement therapy (CKRT) or peritoneal dialysis (PD). Although the pathogenesis is not well understood, DDS is likely a result of multiple physiological abnormalities. In this systematic review, we provide a synopsis of the data available on DDS that allow for a clear picture of its pathogenesis, preventive measures, and focus on effective management strategies.

METHODS

We conducted a literature search on PubMed/Medline and Embase from January 1960 to January 2021. Studies were included if the patient developed DDS irrespective of age and gender. A summary table was used to summarize the data from individual studies and included study type, population group, age group, sample size, patient characteristics, blood and dialysate flow rate, and overall outcome. A descriptive analysis calculating the frequency of population size, symptoms, and various treatments was performed using R software version 3.1.0.

RESULTS

A total of 49 studies (321 samples) were identified and analyzed. Out of the included 49 studies, a total of 48 studies reported the presence of DSS among patients (1 study reported based on number of dialysis and therefore was not considered for analysis). Among these 48 studies, 74.3% (226/304) patients were reported to have DSS. The most common symptoms were nausea (25.2%), headache (24.8%), vomiting (23.9%), muscle cramps (18.1%), affected level of consciousness (8.8%), confusion (4.4%), and seizure (4.9%) among the 226 DDS patients. Furthermore, 12 studies decided to switch from HD to alternative dialysis modalities including continuous venovenous hemofiltration/hemodiafiltration (CVVH/CVVHDF) or PD which reported no DDS symptoms.

CONCLUSION

Early recognition and timely prevention are crucial for DDS patients. We have provided comprehensive clinical practice points for pediatric, adolescent, and young adult populations. However, it is essential to recognize that DDS was reported more frequently in the early dialysis era, as there was a lack of advanced dialysis technology and limited resources.

Dysnatremias in Chronic Kidney Disease: Pathophysiology, Manifestations, and Treatment

The decreased ability of the kidney to regulate water and monovalent cation excretion predisposes patients with chronic kidney disease (CKD) to dysnatremias. In this report, we describe the clinical associations and methods of management of dysnatremias in this patient population by reviewing publications on hyponatremia and hypernatremia in patients with CKD not on dialysis, and those on maintenance hemodialysis or peritoneal dialysis. The prevalence of both hyponatremia and hypernatremia has been reported to be higher in patients with CKD than in the general population. Certain features of the studies analyzed, such as variation in the cut-off values of serum sodium concentration ([Na]) that define hyponatremia or hypernatremia, create comparison difficulties. Dysnatremias in patients with CKD are associated with adverse clinical conditions and mortality. Currently, investigation and treatment of dysnatremias in patients with CKD should follow clinical judgment and the guidelines for the general population. Whether azotemia allows different rates of correction of [Na] in patients with hyponatremic CKD and the methodology and outcomes of treatment of dysnatremias by renal replacement methods require further investigation. In conclusion, dysnatremias occur frequently and are associated with various comorbidities and mortality in patients with CKD. Knowledge gaps in their treatment and prevention call for further studies.

Acute Kidney Injury at the Neurocritical Care Unit

Neurocritical care has advanced substantially in recent decades, allowing doctors to treat patients with more complicated conditions who require a multidisciplinary approach to achieve better clinical outcomes. In neurocritical patients, nonneurological complications such as acute kidney injury (AKI) are independent predictors of worse clinical outcomes. Different research groups have reported an AKI incidence of 11.6% and an incidence of stage 3 AKI, according to the Kidney Disease: Improving Global Outcomes, that requires dialysis of 3% to 12% in neurocritical patients. These patients tend to be younger, have less comorbidity, and have a different risk profile, given the diagnostic and therapeutic procedures they undergo. Trauma-induced AKI, sepsis, sympathetic overstimulation, tubular epitheliopathy, hyperchloremia, use of nephrotoxic drugs, and renal hypoperfusion are some of the causes of AKI in neurocritical patients. AKI is the result of a sum of events, although the mechanisms underlying many of them remain uncertain; however, two important causes that merit mention are direct alteration of the physiological brain-kidney connection and exposure to injury as a result of the specific medical management and well-established therapies that neurocritical patients are subjected to. This review will focus on AKI in neurocritical care patients. Specifically, it will discuss its epidemiology, causes, associated mechanisms, and relationship to the brain-kidney axis. Additionally, the use and risks of extracorporeal therapies in this group of patients will be reviewed.

Half the V by 120: A practical approach to the prevention of the dialysis disequilibrium syndrome

The dialysis disequilibrium syndrome (DDS) results from osmotic shifts between the blood and the brain compartments. Patients at risk for DDS include those with very elevated blood urea nitrogen, concomitant hypernatremia, metabolic acidosis, and low total body water volumes. By understanding the underlying pathophysiology and applying urea kinetic modeling, it is possible to avoid the occurrence of this disorder. A urea reduction ratio (URR) of no more than 40%-45% over 2 h is recommended for the initial hemodialysis treatment. The relationship between the URR and Kt/V is useful when trying to model the dialysis treatment to a specific URR target. A simplified relationship between Kt/V and URR is provided by the equation: Kt/V = -ln (1 - URR). A URR of 40% is roughly equivalent to a Kt/V of 0.5. The required dialyzer urea clearance to achieve this goal URR in a 120-min treatment can simply be calculated by dividing half the patient's volume of distribution of urea by 120. The blood flow rate and dialyzer mass transfer coefficient (K₀ A) required to achieve this clearance can then be plotted on a nomogram. Other methods to reduce the risk of DDS are reviewed, including the use of continuous renal replacement therapy.

Dialysis Disequilibrium Syndrome in a Patient With Acute Kidney Injury on Chronic Kidney Disease

Dialysis disequilibrium syndrome (DDS) is a neurological complication that has been known to occur after hemodialysis (HD). In recent years, the prevalence of DDS has been low as the symptoms are widely recognized; hence, preventive therapies, such as the slow and gentle procedure for HD, are often administered before starting dialysis. However, once DDS occurs, it may cause seizures, coma, and even death in severe cases. Since there has been no established treatment, recognizing risk factors and preventing the syndrome is important.

A 76-year-old man was admitted to our hospital due to exacerbation of chronic heart failure. He also had a history of chronic kidney disease and had consulted with his home doctor about the preparation for HD a month before admission. After treatment with diuretics, the symptoms ameliorated, but he experienced presyncope and malaise. Laboratory tests revealed acute anemia and a decrease in renal function. Upper gastrointestinal endoscopy revealed active bleeding from a gastric ulcer, which was successfully stopped. However, his consciousness deteriorated because of uremia; hence, HD was initiated. We used a cellulose triacetate membrane with a surface area of 1.3 m² and maintained a dialysate flow rate of 500 ml/min with a blood flow rate of 120 ml/min. Four hours after starting HD, he suddenly developed generalized tonic convulsions. The dialysis was immediately stopped, and the patient was transferred to an intensive care unit. A computed tomography scan of the head showed mild edematous change of the brain, and laboratory tests also revealed a rapid decrease of urea nitrogen. We rationalized that he might have developed DDS. After injection of levetiracetam for the treatment of seizures, we initiated continuous hemodiafiltration as renal replacement therapy. Fortunately, his consciousness gradually improved, and he was completely alert on day 18 after admission.

With reference to our current report, DDS can occur even following acute kidney injury, as the progression rate of the injury and accumulation of blood urea may not correlate with the risk of the syndrome.

A case report with a literature review: cerebral meningioma diagnosed by convulsion and consciousness disorder on initiating hemodialysis

Background

Neurological symptoms sometimes occur in hemodialysis patients, with causes including cerebral infarction, cerebral hemorrhaging, meningitis, and encephalitis. Dialysis disequilibrium syndrome (DDS) is widely known as a complication of hemodialysis and is typically encountered in severe uremic patients newly started on hemodialysis. The pathogenesis of DDS is thought to be brain edema that manifests as neurological symptoms, including headache, nausea, confusion, seizures, and coma. However, the relationship between brain tumors and neurological manifestations during hemodialysis is poorly understood.

Case presentation

The patient was a 55-year-old man with severe renal dysfunction and uremia symptoms. Blood chemistry showed severe azotemia and acidosis. The patient was placed on short-duration hemodialysis (2 h) with a relatively small surface area, low blood flow (100 mL/min), and intradialytic glycerol infusion to prevent DDS. However, after his first hemodialysis treatment, he complained of disturbed consciousness. We diagnosed his neurological condition as DDS and observed the progress carefully. The next morning, his symptoms had completely resolved, so the patient was started on his second hemodialysis session with the same conditions. However, 2 h after starting the second hemodialysis session, he suffered convulsions accompanied by impaired consciousness. Brain computed tomography (CT) revealed a convexity meningioma and cerebral edema with a midline shift. Before starting the hemodialysis, he had shown no history of seizures, morning headache, or other neurological symptoms. In this case, meningioma was diagnosed based on an increase in the intracranial pressure which occurred after the initiation of hemodialysis.

Conclusion

We report this suggestive case to prompt physicians to consider the potential effect of hemodialysis introduction on the brain pressure.

Cerebral blood flow regulation in end-stage kidney disease

Patients with chronic kidney disease (CKD) and end-stage kidney disease (ESKD) experience an increased risk of cerebrovascular disease and cognitive dysfunction. Hemodialysis (HD), a major modality of renal replacement therapy in ESKD, can cause rapid changes in blood pressure, osmolality, and acid-base balance that collectively present a unique stress to the cerebral vasculature. This review presents an update regarding cerebral blood flow (CBF) regulation in CKD and ESKD and how the maintenance of cerebral oxygenation may be compromised during HD. Patients with ESKD exhibit decreased cerebral oxygen delivery due to anemia, despite cerebral hyperperfusion at rest. Cerebral oxygenation further declines during HD due to reductions in CBF, and this may induce cerebral ischemia or "stunning." Intradialytic reductions in CBF are driven by decreases in cerebral perfusion pressure that may be partially opposed by bicarbonate shifts during dialysis. Intradialytic reductions in CBF have been related to several variables that are routinely measured in clinical practice including ultrafiltration rate and blood pressure. However, the role of compensatory cerebrovascular regulatory mechanisms during HD remains relatively unexplored. In particular, cerebral autoregulation can oppose reductions in CBF driven by reductions in systemic blood pressure, while cerebrovascular reactivity to CO₂ may attenuate intradialytic reductions in CBF through promoting cerebral vasodilation. However, whether these mechanisms are effective in ESKD and during HD remain relatively unexplored. Important areas for future work include investigating potential alterations in cerebrovascular regulation in CKD and ESKD and how key regulatory mechanisms are engaged and integrated during HD to modulate intradialytic declines in CBF.

Renal Replacement Therapy in Neonates

Acute kidney injury (AKI) is a highly prevalent disease entity in the NICU, affecting nearly one-quarter of critically ill neonates by some reports. Though medical management remains the mainstay in the treatment of AKI, renal replacement therapy (RRT) is indicated when conservative measures are unable to maintain electrolytes, fluid balance, toxins, or waste products within a safe margin. Several modalities of RRT exist for use in neonatal populations, including peritoneal dialysis, hemodialysis, and continuous RRT. It is the aim of this review to introduce each of these RRT modalities, as well as to discuss their technical considerations, benefits, indications, contraindications, and complications.

In vivo evaluation of drug dialyzability in a rat model of hemodialysis

It is important to calculate the drug removal by hemodialysis (HD) for drug dosing regimens in HD patients. However, there are limited and inconsistent information about the dialyzability of drugs by HD. Therefore, the aim of our study is to evaluate drug removal by utilizing a rat model of HD (HD rat) and to extrapolate this result to the drug removal rate in HD patients. HD rats received bilateral nephrectomy and HD for 2 h. The dialysis removal of 6 drugs was evaluated in HD rats. Dialysis efficiency, plasma protein binding rate (PBR) and distribution volume (Vd) of drugs were also measured. Furthermore, we examined the correlation between the dialyzability of drug in HD rats and humans and constructed the prediction formula of the drug dialyzability in HD patients. The clearance of urea and creatinine and normalized dialysis dose in HD rats were 0.83 ± 0.07 mL/min, 0.70 ± 0.08 mL/min, and 0.13 ± 0.06, respectively. The drug dialyzability in HD rats was similar to reported clinical data except for doripenem. A higher correlation was observed between drug dialyzability in reported clinical data and HD rats which were adjusted for PBR (r² = 0.936; p < 0.001) compared to unadjusted (r² = 0.812; p = 0.009). Therefore, we constructed the prediction formula of the drug dialyzability in HD patients by utilizing the HD rat model and PBR. This study is useful for evaluating the dialyzability of high-risk drugs in a clinical setting and might provide appropriate preclinical dialyzability data for new drug.

A vanishing complication of haemodialysis: Dialysis disequilibrium syndrome

Dialysis disequilibrium syndrome (DDS) is a rare syndrome characterised by neurological symptoms related to cerebral oedema. New patients who are started on haemodialysis are at the greatest risk for developing dialysis disequilibrium syndrome. Classical DDS develops during or immediately after haemodialysis. It is a generally self-limiting condition and settles with supportive management. Our case report describes DDS in a patient on chronic haemodialysis. She developed a tonic-clonic seizure shortly after completing 4 h of haemodialysis. This occurred in the context of having missed one session of dialysis, but with no new changes made to her usual dialysis regime. She was managed supportively in the intensive care unit and made a full recovery.

Real-time Noninvasive Monitoring of Intracranial Fluid Shifts During Dialysis Using Volumetric Integral Phase-Shift Spectroscopy (VIPS): A Proof-of-Concept Study

BACKGROUND

Cerebral edema, which is associated with increased intracranial fluid, is often a complication of many acute neurological conditions. There is currently no accepted method for real-time monitoring of intracranial fluid volume at the bedside. We evaluated a novel noninvasive technique called "Volumetric Integral Phase-shift Spectroscopy (VIPS)" for detecting intracranial fluid shifts during hemodialysis.

METHODS

Subjects receiving scheduled hemodialysis for end-stage renal disease and without a history of major neurological conditions were enrolled. VIPS monitoring was performed during hemodialysis. Serum osmolarity, electrolytes, and cognitive function with mini-mental state examination (MMSE) were assessed.

RESULTS

Twenty-one monitoring sessions from 14 subjects (4 women), mean group age 50 (SD 12.6), were analyzed. The serum osmolarity decreased by a mean of 6.4 mOsm/L (SD 6.6) from pre- to post-dialysis and correlated with an increase in the VIPS edema index (E-Dex) of 9.7% (SD 12.9) (Pearson's correlation r = 0.46, p = 0.037). Of the individual determinants of serum osmolarity, changes in serum sodium level correlated best with the VIPS edema index (Pearson's correlation, r = 0.46, p = 0.034). MMSE scores did not change from pre- to post-dialysis.

CONCLUSIONS

We detected an increase in the VIPS edema index during hemodialysis that correlated with decreased serum osmolarity, mainly reflected by changes in serum sodium suggesting shifts in intracranial fluids.

Osmotic Shifts, Cerebral Edema, and Neurologic Deterioration in Severe Hepatic Encephalopathy

OBJECTIVES

We sought to determine the effect of acute electrolyte and osmolar shifts on brain volume and neurologic function in patients with liver failure and severe hepatic encephalopathy.

DESIGN

Retrospective analysis of brain CT scans and clinical data.

SETTING

Tertiary care hospital ICUs.

PATIENTS

Patients with acute or acute-on-chronic liver failure and severe hepatic encephalopathy.

INTERVENTIONS

Clinically indicated CT scans and serum laboratory studies.

MEASUREMENTS AND MAIN RESULTS

Change in intracranial cerebrospinal fluid volume between sequential CT scans was measured as a biomarker of acute brain volume change. Corresponding changes in serum osmolality, chemistry measurements, and Glasgow Coma Scale were determined. Associations with cerebrospinal fluid volume change and Glasgow Coma Scale change for initial volume change assessments were identified by Spearman's correlations (rs) and regression models. Consistency of associations with repeated assessments was evaluated using generalized estimating equations. Forty patients were included. Median baseline osmolality was elevated (310 mOsm/Kg [296-321 mOsm/Kg]) whereas sodium was normal (137 mEq/L [134-142 mEq/L]). Median initial osmolality change was 9 mOsm/kg (5-17 mOsm/kg). Neuroimaging consistent with increased brain volume occurred in 27 initial assessments (68%). Cerebrospinal fluid volume change was more strongly correlated with osmolality (r = 0.70; p = 4 × 10) than sodium (r = 0.28; p = 0.08) change. Osmolality change was independently associated with Glasgow Coma Scale change (p = 1 × 10) and cerebrospinal fluid volume change (p = 2.7 × 10) in initial assessments and in generalized estimating equations using all 103 available assessments.

CONCLUSIONS

Acute decline in osmolality was associated with brain swelling and neurologic deterioration in severe hepatic encephalopathy. Minimizing osmolality decline may avoid neurologic deterioration.

Intracranial pressure during hemodialysis in patients with acute brain injury

BACKGROUND

Because osmotic fluid shifts may occur over the blood-brain barrier, patients with acute brain injury are theoretically at risk of surges in intracranial pressure (ICP) during hemodialysis. However, this remains poorly investigated. We studied changes in ICP during hemodialysis in such patients.

METHODS

We performed a retrospective study of patients with acute brain injury admitted to Rigshospitalet (Copenhagen, Denmark) from 2012 to 2016 who received intermittent hemodialysis (IHD) or continuous renal replacement therapy (CRRT) while undergoing ICP monitoring. Data from each patient's first dialysis session were collected. Area under the curve divided by time (AUC/t) for ICP was calculated separately before and during dialysis.

RESULTS

Thirteen patients were included. During dialysis, ICP increased from a baseline of 11.9 mm Hg (median; interquartile range 6.3-14.7) to a maximum of 21 mm Hg (18-27) (P = 0.0024), and AUC/t for ICP was greater during dialysis (15.2 (13.4-18.8) vs 11.7 mm Hg (6.4-15.1), P = 0.042). The maximum ICP increase was independent of dialysis modality, but peak values were reached earlier in patients treated with IHD (N = 4) compared to CRRT (N = 9) (75 [30-90] vs 375 min [180-420] after start of treatment, P = 0.0095). The maximum ICP increase correlated positively to the baseline plasma urea concentration (Spearman's r = 0.69, P = 0.017).

CONCLUSION

Hemodialysis is associated with increased ICP in neurocritically ill patients, and the magnitude of the increase may be related to initial plasma urea levels.

Pathogenesis of cerebral edema in patients with acute renal and liver failure and the role of the nephrologist in the management

PURPOSE OF REVIEW

Acute liver failure (ALF) is a severe and complex illness and one of the most daunting conditions managed in the ICU. Because the renal care is intertwined with multiple disciplines, the aim of this review is to examine the multifactorial pathogenesis of cerebral edema in ALF, covering basic established facts as well as recent advances in our understanding of this condition.

RECENT FINDINGS

Acetaminophen remains the most common cause of ALF in the United States and many European countries. The incidence of cerebral edema continues to decline owing to earlier detection and improved management. The pathogenesis of cerebral edema has shifted from a unifactorial hypothesis involving the failed liver to a multifactorial cause. Recent evidence focuses on the role of liver-induced systemic inflammation and its implication in increasing the permeability of the blood-brain barrier. The role of brain aquaporin-4 in mediating water entry into the brain is further clarified. Controversial data regarding the effect of acute kidney injury on the brain emerged. Hyponatremia has been shown to worsen the outcome in acute-on-chronic liver failure patients thus validating findings in animal models. New evidence shed the light on the changes in serum osmolality and potential tissue hypoxia during continuous renal replacement therapy and points to the risks associated with such therapy.

SUMMARY

ALF is a severe systemic illness that is potentially reversible. Understanding the interaction between the multiple failed organs will help the nephrologist provide well tolerated and efficient care.

Diagnosis, Treatment, and Prevention of Hemodialysis Emergencies

Given the high comorbidity in patients on hemodialysis and the complexity of the dialysis treatment, it is remarkable how rarely a life-threatening complication occurs during dialysis. The low rate of dialysis emergencies can be attributed to numerous safety features in modern dialysis machines; meticulous treatment and testing of the dialysate solution to prevent exposure to trace elements, toxins, and pathogens; adherence to detailed treatment protocols; and extensive training of dialysis staff to handle medical emergencies. Most hemodialysis emergencies can be attributed to human error. A smaller number are due to rare idiosyncratic reactions. In this review, we highlight major emergencies that may occur during hemodialysis treatments, describe their pathogenesis, offer measures to minimize them, and provide specific interventions to prevent catastrophic consequences on the rare occasions when such emergencies arise. These emergencies include dialysis disequilibrium syndrome, venous air embolism, hemolysis, venous needle dislodgement, vascular access hemorrhage, major allergic reactions to the dialyzer or treatment medications, and disruption or contamination of the dialysis water system. Finally, we describe root cause analysis after a dialysis emergency has occurred to prevent a future recurrence.

Plasma Changes of Calcitonin Gene-Related Peptide and Substance P in Patients with Dialysis Headache

Little is known of mechanism of dialysis headache (DH). As suggested for migraine, a role for neuropeptides has been investigated. Twenty-four patients under haemodialysis were studied. Twelve of them suffered from DH. The remaining patients were headache free. Blood samples for radioimmunoassay of calcitonin gene-related peptide (CGRP) and substance P (SP) were collected from the arteriovenous fistula before and after dialysis treatment. Basal plasma concentrations of CGRP were found to be higher in headache patients. Dialysis significantly decreased CGRP concentrations in both groups. No difference in basal plasma concentrations of SP was observed between groups. At the end of the treatment plasma SP concentrations were reduced in headache-free patients but increased in headache patients. Elevated plasma concentrations of CGRP in patients with DH could represent a biochemical factor contributing to susceptibility to headache. Because of the disputable role of SP in migraine, the significance of the increase of the peptide in plasma during DH remains to be elucidated.

Disequilibrium syndrome and prevention in nonhemodialysis patients

Disequilibrium syndrome (DS) is a central nervous system disorder described in hemodialysis (HD) patients. The authors present 4 cases of elevated blood urea nitrogen (BUN); the first patient passed away from suspected DS, whereas the other 3 patients were identified as having a high risk of developing DS on the basis of their BUN. The authors tried to lower their BUN slowly and prevent rapid correction by different methods. This is the first study in which DS has been studied in patients who are not on HD, and methods are described to identify and prevent DS in such patients. They also review the existing literature on the pathogenesis of DS and highlight the importance of recognizing this syndrome in non-HD patients, while suggesting some innovative ways to prevent it.

Development of dialysis disequilibrium-like clinical signs during postobstructive management of feline urethral obstruction

OBJECTIVE

To describe the clinical features, treatment, and outcome of a cat with acute neurologic signs subsequent to relief of urethral obstruction and rapid resolution of severe azotemia, suggesting a process similar to dialysis disequilibrium syndrome.

CASE SUMMARY

A male castrated domestic short-hair cat was presented for weakness and dull mentation. Initial physical examination was consistent with urethral obstruction and laboratory data demonstrated severe azotemia, hyperkalemia, and acidemia. Interventions for hyperkalemia and urethral catheterization were performed without complication. The patient demonstrated a marked postobstructive diuresis and 7 hours after presentation suffered a grand mal seizure and was neurologically inappropriate. These changes corresponded with marked decreases in blood urea nitrogen (from 89.25 mmol/L to 19.99 mmol/L [250 mg/dL to 56 mg/dL]) and calculated serum osmolality (429 mOsm/kg to 359 mOsm/kg) from initial presentation without other apparent cause for seizure activity. The patient was treated with hypertonic saline (bolus and continuous infusion) for presumed osmotic injury (dialysis disequilibrium-like clinical signs) along with other supportive care. All neurologic signs resolved within 48 hours, the urinary catheter was removed, and the patient was discharged after 24 hours of observation of spontaneous urination.

NEW OR UNIQUE INFORMATION PROVIDED

Dialysis disequilibrium syndrome has been documented in small animals, but similar signs have not been reported as a sequelae of treatment of feline urethral obstruction. Urethral obstruction is a common emergency and practitioners should be aware of this potential complication as a cause of delayed neurologic recovery or seizures in the postobstructive period.

Dialysis disequilibrium syndrome induced by neoplastic meningitis in a patient receiving maintenance hemodialysis

BACKGROUND

Dialysis disequilibrium syndrome is characterized by neurological symptoms resulting from cerebral edema, which occurs as a consequence of hemodialysis. Dialysis disequilibrium syndrome most often occurs in patients who have just started hemodialysis, during hemodialysis, or soon after hemodialysis; although it may also occur in patients who are under maintenance hemodialysis with pre-existing neurological disease.

CASE PRESENTATION

A 70-year-old woman, who had been receiving maintenance hemodialysis for one year, was diagnosed with ovarian cancer by ascites cytological examination. Two years later, she reported severe headache and nausea during hemodialysis and was diagnosed with dialysis disequilibrium syndrome. Although brain images revealed mild hydrocephalus without any mass lesions, poorly differentiated adenocarcinoma cells were detected in her cerebrospinal fluid. These findings indicated that DDS was induced by neoplastic meningitis due to ovarian cancer metastasis.

CONCLUSION

Neoplastic meningitis should be considered and excluded in hemodialysis patients with dialysis disequilibrium syndrome and malignancy by cytological examination of the cerebrospinal fluid even if cerebral imaging shows no obvious lesions. This is the first reported case of dialysis disequilibrium syndrome induced by neoplastic meningitis in a patient receiving maintenance hemodialysis.

Changes in osmol gap in chronic kidney disease: an exploratory study

AIM

There is no data on osmol gap (OG) in chronic kidney disease (CKD) by stage and limited data on OG in adults on maintenance hemodialysis (HD). We aimed to examine the OG between different stages of CKD and to compare the OG pre- and post-HD in those on maintenance HD.

METHODS

We conducted a cross-sectional study of 67 patients. The participants were divided into six groups: Group 1-reference group (normal renal function), Group 2-CKD stage 2; Group 3-CKD stage 3; Group 4-CKD stage 4; Group 5-CKD stage 5 and not on dialysis. Group 6 were subjects on maintenance HD.

RESULTS

The means of OG ± standard deviation of Groups 1-6 were 15.25 ± 3.0, 20.73 ± 2.68, 22.85 ± 6.99, 24.11 ± 3.64, 25.15 ± 5.06, and 28.88 ± 3.45, respectively (p < 0.001). In the HD group, the difference between the pre-HD and post-HD OG was statistically significant (p < 0.001).

CONCLUSION

There is a statistically significant upward trend for OG as CKD stage increases. The OG is elevated in patients on maintenance HD and is normalized by the HD. OG can be a valuable additional tool to suggest CKD stage and serve as a marker of dialysis adequacy.

Dialysis disequilibrium syndrome occurring during continuous renal replacement therapy

The dialysis disequilibrium syndrome (DDS) is characterized by progressive neurological symptoms and signs attributable to cerebral edema that occurs due to fluid shifts into the brain following a relatively rapid decrease in serum osmolality during hemodialysis (HD). Since continuous renal replacement therapy (CRRT) is less efficient at solute clearance than intermittent HD, it seems logical that this mode of therapy is less likely to cause DDS. This entity has not been previously reported to occur with this modality. Here, we report two cases of DDS associated with CRRT that provide insights into its pathophysiological mechanisms and suggest strategies for its prevention.

Dialysis disequilibrium syndrome

The dialysis disequilibrium syndrome is a rare but serious complication of hemodialysis. Despite the fact that maintenance hemodialysis has been a routine procedure for over 50 years, this syndrome remains poorly understood. The signs and symptoms vary widely from restlessness and headache to coma and death. While cerebral edema and increased intracranial pressure are the primary contributing factors to this syndrome and are the target of therapy, the precise mechanisms for their development remain elusive. Treatment of this syndrome once it has developed is rarely successful. Thus, measures to avoid its development are crucial. In this review, we will examine the pathophysiology of this syndrome and discuss the factors to consider in avoiding its development.

Medulloblastoma presenting as dialysis disequilibrium syndrome

Dialysis disequilibrium syndrome (DDS) is a central nervous system disorder that occurs during or after hemodialysis. This is caused by brain edema that manifests as neurological symptoms that include headache, emesis, nausea, blurring of vision, disturbed consciousness, tremors and seizures, and in severe cases, death. The incidence of DDS is very high among patients with preexisting neurological diseases. There has been much debate about the origin of DDS. We report a case of DDS, as presenting syndrome of a medulloblastoma in a child aged 5 years, and discuss the pathogenesis and the possible role of DDS for an earlier detection of occult brain lesions in dialyzed patients.

Intracranial pressure fluctuation during hemodialysis in renal failure patients with intracranial hemorrhage

Coagulopathy in renal failure patients often makes them vulnerable to intracranial hemorrhage. Emergency decompression to remove the hematoma and to stop bleeding is always indicated. After the surgery, hemodialysis (HD) should be arranged to maintain the BUN/Cr. level, and I/O balance. During HD, intracranial pressure in all of the patients in this study fluctuated. This phenomenon always resulted in neurological deterioration in acute or chronic renal failure. We present intracranial pressure (ICP) changes during HD in five acute or chronic renal failure patients with intracranial hemorrhage. They all underwent craniectomy or craniotomy with ICP monitors implantation. Different HD protocols were arranged for these patients and then we observed clinical results. ICP elevated during HD and resulted in severe brain swelling. This situation was one of the clinical presentations of dialysis disequilibrium syndrome (DDS). Four patients died because of this complication and one survived. ICP fluctuation seemed to be correlated with the fluid amount and frequency of HD. The prevalence and pathophysiology of DDS remain unclear. Renal failure patient with intracranial hemorrhage may be complicated with DDS when HD was performed. An attempt to reduce the fluid amount and to increase the frequency of HD might help these patients.

Dialysis disequilibrium syndrome: a narrative review

Dialysis Disequilibrium Syndrome (DDS) is characterized by neurological symptoms caused by rapid removal of urea during hemodialysis. It develops primarily from an osmotic gradient that develops between the brain and the plasma as a result of rapid hemodialysis. This results in brain edema that manifests as neurological symptoms such as headache, nausea, vomiting, muscle cramps, tremors, disturbed consciousness, and convulsions. In severe cases, patients can die from advanced cerebral edema. Recent advancements in cell biology implicate the role of urea disequilibrium (with a smaller contribution from organic osmolytes) as the pathophysiological mechanism responsible for this syndrome. In this review, we discuss the pathogenesis, clinical features and prevention of DDS.

Molecular basis for the dialysis disequilibrium syndrome: altered aquaporin and urea transporter expression in the brain

BACKGROUND

Cerebral disorders caused by brain oedema characterize the dialysis disequilibrium syndrome, a complication of rapid haemodialysis. Brain oedema is presumably caused by the 'reverse urea effect', i.e. the significant urea gradient between blood and brain after dialysis, with, as a result, an inflow of water into the brain. To assess the molecular basis of this effect, we examined the expression of urea transporter UT-B1 and aquaporin (AQP) 4 and AQP9 in the brain of uraemic rats.

METHODS

Brain, kidneys and one testis were collected from four sham-operated (control) and four uraemic rats, 10 weeks after 5/6 nephrectomy (Nx). Protein abundance was measured by semi-quantitave immunoblotting using affinity-purified rabbit anti-rat antibodies applied on tissue crude homogenates.

RESULTS

The results are expressed as means+/-SE of band density (arbitrary units). In Nx compared with control rats, the brain expression of UT-B1 was reduced by half (32+/-3 vs 62+/-8, P<0.01) whereas that of AQ4 was doubled (251+/-13 vs 135+/-5, P<0.001), and that of AQP9 increased by 65% (253+/-22 vs 154+/-10, P<0.01). UT-B1 expression was also lowered by Nx in kidney medulla (45+/-21 vs 141+/-4, P<0.01) but was unchanged in testis.

CONCLUSIONS

The conjunction of a reduced expression of UT-B and an increased expression of AQPs in brain cells may bring a new clue to understanding the DDS mechanism. Because of low UT-B abundance, urea exit from astrocytes is most probably delayed during rapid removal of extracellular urea through fast dialysis. This creates an osmotic driving force that promotes water entry into the cells (favoured by abundant AQPs) and subsequent brain swelling.

Brain dysfunction in uremia: a question of cortical hyperexcitability?

OBJECTIVE

To investigate whether patients with end-stage renal disease (ESRD) in different stages of the disease and undergoing different treatments display alterations in cortical excitability.

METHOD

A total of 36 patients with ESRD were evaluated at different stages of the disease and under different treatment by using standard transcranial magnetic stimulation (TMS) parameters. Moreover patients under haemodialysis underwent a double-blind crossover study (mannitol vs placebo) in order to better elucidate the pathophysiology of the acute effects of haemodialysis on cortical excitability.

RESULTS

Patients with ESRD in conservative therapy showed a significant reduction of short-interval intra-cortical inhibition (SICI). This alteration could be reversed by haemodialysis, peritoneal dialysis and by renal transplantation. After haemodialysis there was a significant increase of intra-cortical facilitation (ICF) inversely correlated with the drop in plasma osmolarity induced by the dialytic procedure. Mannitol infusion prevented the drop in plasma osmolarity and the haemodialysis-related changes in ICF.

CONCLUSIONS

ESRD patients showed alterations in cortical excitability that can be reversed by replacement therapies. We propose that the drop in plasma osmolarity is a key to the mechanism underlying post-haemodialysis cortical hyperexcitability.

SIGNIFICANCE

The results of this study give further insight to the pathophysiology of brain abnormalities in patients with chronic renal failure.

Neurological complications in renal failure: a review

Neurological complications whether due to the uremic state or its treatment, contribute largely to the morbidity and mortality in patients with renal failure. Despite continuous therapeutic advances, many neurological complications of uremia, like uremic encephalopathy, atherosclerosis, neuropathy and myopathy fail to fully respond to dialysis. Moreover, dialytic therapy or kidney transplantation may even induce neurological complications. Dialysis can directly or indirectly be associated with dialysis dementia, dysequilibrium syndrome, aggravation of atherosclerosis, cerebrovascular accidents due to ultrafiltration-related arterial hypotension, hypertensive encephalopathy, Wernicke's encephalopathy, hemorrhagic stroke, subdural hematoma, osmotic myelinolysis, opportunistic infections, intracranial hypertension and mononeuropathy. Renal transplantation itself can give rise to acute femoral neuropathy, rejection encephalopathy and neuropathy in graft versus host disease. The use of immunosuppressive drugs after renal transplantation can cause encephalopathy, movement disorders, opportunistic infections, neoplasms, myopathy and progression of atherosclerosis. We address the clinical, pathophysiological and therapeutical aspects of both central and peripheral nervous system complications in uremia.

Dialysis Disequilibrium Syndrome: brain death following hemodialysis for metabolic acidosis and acute renal failure--a case report

Background

Dialysis disequilibrium syndrome (DDS) is the clinical phenomenon of acute neurologic symptoms attributed to cerebral edema that occurs during or following intermittent hemodialysis (HD). We describe a case of DDS-induced cerebral edema that resulted in irreversible brain injury and death following acute HD and review the relevant literature of the association of DDS and HD.

Case Presentation

A 22-year-old male with obstructive uropathy presented to hospital with severe sepsis syndrome secondary to pneumonia. Laboratory investigations included a pH of 6.95, PaCO2 10 mmHg, HCO3 2 mmol/L, serum sodium 132 mmol/L, serum osmolality 330 mosmol/kg, and urea 130 mg/dL (46.7 mmol/L). Diagnostic imaging demonstrated multifocal pneumonia, bilateral hydronephrosis and bladder wall thickening. During HD the patient became progressively obtunded. Repeat laboratory investigations showed pH 7.36, HCO3 19 mmol/L, potassium 1.8 mmol/L, and urea 38.4 mg/dL (13.7 mmol/L) (urea-reduction-ratio 71%). Following HD, spontaneous movements were absent with no pupillary or brainstem reflexes. Head CT-scan showed diffuse cerebral edema with effacement of basal cisterns and generalized loss of gray-white differentiation. Brain death was declared.

Conclusions

Death is a rare consequence of DDS in adults following HD. Several features may have predisposed this patient to DDS including: central nervous system adaptations from chronic kidney disease with efficient serum urea removal and correction of serum hyperosmolality; severe cerebral intracellular acidosis; relative hypercapnea; and post-HD hemodynamic instability with compounded cerebral ischemia.

Does uremia protect against the demyelination associated with correction of hyponatremia during hemodialysis? A case report and literature review

Rapid correction of chronic hyponatremia is known to cause demyelination syndromes, which are attributed to the rapid shift of water out of the brain. In uremic patients with hyponatremia, depending on the dialysate sodium concentration and delivered Kt/V, serum sodium levels may be rapidly corrected inadvertently during the hemodialysis (HD) session. It is not known whether uremic patients are as susceptible to the development of demyelination as patients with normal renal function. Since urea diffuses slowly across the blood-brain barrier, it can act as an effective osmole between plasma and the brain if levels are changed abruptly. During HD, blood urea levels drop suddenly and significantly and cerebral edema may develop (dialysis disequilibrium syndrome). This effect may counteract the fluid shift out of the brain during correction of hyponatremia. Therefore, theoretically, uremic patients may be less prone to develop demyelination. We present a patient with renal failure whose hyponatremia was corrected rapidly during HD to illustrate the potential problem. The patient tolerated rapid correction of hyponatremia without sustaining any neurologic damage. We performed a literature search looking for similar case reports and reviewed the scientific evidence behind the above hypothesis.

Rapid (24-hour) reaccumulation of brain organic osmolytes (particularly myo-inositol) in azotemic rats after correction of chronic hyponatremia

It was recently demonstrated that renal failure and exogenous urea prevent myelinolysis induced by rapid correction of experimental hyponatremia. To determine why elevated blood urea levels favorably affect brain tolerance to osmotic stress, the changes in brain solute composition that occur when chronic hyponatremia is rapidly corrected were studied in rats with or without mercuric chloride-induced renal failure. After 48 h of hyponatremia, the brains of azotemic and nonazotemic animals became depleted of sodium, potassium, and organic osmolytes. Twenty-four hours after rapid correction of hyponatremia, the brains of animals without azotemia remained depleted of organic osmolytes, with little increase in myo-inositol or taurine contents above those observed in animals with uncorrected hyponatremia; brain electrolytes were rapidly reaccumulated, increasing the brain sodium content to a level 17% higher than values for normonatremic control animals. In contrast, within 2 h after correction of hyponatremia, brain myo-inositol contents in azotemic rats returned to control levels and brain taurine levels were significantly higher than those in azotemic animals with uncorrected hyponatremia (16.5 versus 9 micromol/g dry weight). There was no "overshooting" of brain sodium and water contents after rapid correction in the azotemic animals. Rapid reaccumulation of brain organic osmolytes after correction of hyponatremia could explain why azotemia protects against myelinolysis.

Massive reduction of urea transporters in remnant kidney and brain of uremic rats

BACKGROUND

The facilitated urea transporters (UT), UT-A1, UT-A2, and UT-B1, are involved in intrarenal recycling of urea, an essential feature of the urinary concentrating mechanism, which is impaired in chronic renal failure (CRF). In this study, the expression of these UTs was examined in experimentally induced CRF.

METHODS

The abundance of mRNA was measured by Northern analysis and that of corresponding proteins by Western blotting in rats one and five weeks after 5/6 nephrectomy (Nx).

RESULTS

At five weeks, urine output was enhanced threefold with a concomitant decrease in urine osmolality. The marked rise in plasma urea concentration and fall in urinary urea concentration resulted in a 30-fold decrease in the urine/plasma (U/P) urea concentration ratio, while the U/P osmoles ratio fell only fourfold. A dramatic decrease in mRNA abundance for the three UTs was observed, bringing their level at five weeks to 1/10th or less of control values. Immunoblotting showed complete disappearance of the 97 and 117 kD bands of UT-A1, and considerable reduction of UT-A2 and UT-B1 in the renal medulla. Similar, but less intense, changes were observed at one-week post-Nx. In addition to the kidney, UT-B1 is also normally expressed in brain and testis. In the brain, its mRNA expression remained normal one-week post-Nx, but decreased to about 30% of normal at five-weeks post-Nx, whereas no change was seen in testis.

CONCLUSIONS

(1) The decline in urinary concentrating ability seen in CRF is largely due to a major reduction of UTs involved in the process of urea concentration in the urine, while factors enabling the concentration of other solutes are less intensely affected. (2) The marked reduction of brain UT expression in CRF may be responsible for brain edema of dialysis disequilibrium syndrome observed in some patients after fast dialysis.

Azotemia (48 h) decreases the risk of brain damage in rats after correction of chronic hyponatremia

Brain myelinolysis complicates excessive correction of chronic hyponatremia in man. Myelinolysis appear in rats for correction levels deltaSNa) > 20 mEq/l/24 h. We previously showed in rats that when chronic hyponatremia was corrected with urea, the incidence and the severity of brain lesions were significantly reduced compared to hypertonic saline. In man, hyponatremia is frequently associated with azotemia and hemo-dialysis usually corrects rapidly the serum sodium (SNa) but only few patients apparently develop demyelination. We hypothesize that uremic state protects brain against myelinolysis. This hypothesis was evaluated in rats developing azotemia by administration of mercuric chloride (HgCl2, 1.5 mg/kg). Severe (SNa < 120 mEq/l) hyponatremia (3 days) was induced by S.C. AVP and i.p. 2.5% D-glucose for 3 days. HgCl2 was injected on day 2. Hyponatremia was corrected on day 4 by i.p. injections of 5% NaCl in order to obtain a correction level largely above the toxic threshold for brain (deltaSNA approximately 30 mEq/l/24 h). Surviving rats were decapitated on day 10 for brain analysis. In the group with renal failure (Group I, n = 15, urea 59 mmol/l) the outcome was remarkably favourable with only three rats (3/15) dying before day 10 and only one of them (1/3) presenting myelinolysis-related neurologic symptoms. The 12 other rats (80%) survived in Group I without symptoms and brain analysis was normal in all of them despite large correction level (deltaSNa: 32 mEq/l/24 h). On the contrary in nine rats in which HgCl, did not produce significant azotemia (control 1, n = 9, urea: 11 mmol/l), all the rats developed severe neurologic symptoms and eight of them died before day 10. Similar catastrophic outcome was observed in the non-azotemic controls (control 2, no HgCl2 administration, n = 15, urea: 5 mmol/l). All of them developed myelinolysis-related neurologic symptoms and only four of them survived with severe brain lesions (survival 12/15 in Group I vs. 5/24 in pooled controls 1 and 2, p < 0.001). In conclusion, we showed for the first time that chronic hyponatremic rats with azotemia (48 h) tolerated large increases in SNa (approximately 30 mEq/l/24 h) without significant brain damage.