Continuous venovenous hemofiltration in the management of acute decompensation in inborn errors of metabolism

Intravenous branched-chain amino-acid-free solution for the treatment of metabolic decompensation episodes in Spanish pediatric patients with maple syrup urine disease

BACKGROUND

Metabolic decompensation episodes (DEs) in Maple Syrup urine disease (MSUD) result in brain accumulation of toxic branched-chain amino acids (BCAAs) and their respective branched-chain α-keto acids that could induce neuroinflammation, disturb brain bioenergetics, and alter glutamate and glutamine synthesis. These episodes require immediate intervention to prevent irreversible neurological damage. Intravenous (IV) administration of BCAA-free solution could represent a powerful alternative for emergency treatment of decompensations.

METHODS

This pediatric series discusses the management of DEs in MSUD patients with IV BCAA-free solution, as an emergency treatment for DEs or as a prophylactic in cases requiring surgery. Clinical evolution, amino acid profile and adverse effects were evaluated.

RESULTS

We evaluated the use of BCAA-free solution in 5 DEs in 5 MSUD pediatric patients, all with significantly elevated plasma leucine levels at admission (699-3296 μmol/L) and in 1 episode of risk of DE due to surgery. Leucine normalization was achieved in all cases with resolution or improvement of clinical symptoms following IV BCAA-free solution. The duration of administration ranged from 3-20 days. Administration of IV BCAA-free solution at the beginning of a DE could reverse depletion of the amino acids that compete with BCAAs for the LAT1 transporter, and the observed depletion of alanine, despite IV alanine supplementation. No related adverse events were observed.

CONCLUSIONS

Administration of standardized IV BCAA-free solution in emergency settings constitutes an important and safe alternative for the treatment of DEs in MSUD, especially in pediatric patients for whom oral or enteral treatment is not viable.

Continuous Renal Replacement Therapy for Treatment of Severe Attacks of Inborn Errors of Metabolism

Severe metabolic crises in children with inborn errors of metabolism can result in mortality or severe morbidities where continuous renal replacement therapy (CRRT) can be lifesaving . Clinical data, the pediatric risk of mortality (PRISM) scores calculated in the first 24 hours, and pediatric logistic organ dysfunction (PELOD) scores calculated in the last 24 hours before CRRT, were studied . Overall, CRRT was successful in restoring metabolic balance in 72% of patients. PELOD scores before CRRT were lower in survivors ( p  = 0.02). Despite numerous comorbid factors, CRRT can be used effectively in management of metabolic crises. Early intervention with this therapy before occurrence of complications must be targeted.

Which Organic Acids does Hemofiltrate Contain in the Presence of Acute Renal Failure?

It is not generally possible to measure most organic acids in the serum of critically ill patients, due to rapid metabolism and methodological problems. Only the regular measurement of lactic acid and the arterial ketone body ratio (acetoacetate/beta-hydroxybutyrate, AKBR) have been introduced in clinical practice, but these parameters can represent only a part of the disturbed metabolism. In pediatric patients, a chromatographical urine analysis has been established for detection of inborn errors of metabolism, which allows the determination of more than 50 organic acids simultaneously (gas chromatographic (GC) analysis in combination with mass spectrometry (MS)]. In continuous treatment of acute renal failure, hemofiltrate is always available, but it contains only low protein concentrations and after the filtration process, metabolism is rapidly stopped. The sieving coefficient of lactic acid is nearly one in hemofiltration. The aim of our study was to compare results of the regular and CG/MS methods in blood and hemofiltrate for lactic acid, and to find other organic acids of possible clinical importance. We investigated serum (lactic acid) and hemofiltrate of 40 critically ill patitens, similar to the urine analysis method for infants. All patients suffered from acute renal failure and were treated by continuous veno-venous hemofiltration (CVVH). The conditions of treatment were standardized (spontaneous ultrafiltration in the first hour), and the material (blood/hemofiltrate) was taken one hour after the beginning of extracorporeal circulation. Statistical methods included correlation analysis, nonparametric ANOVA with Wilcoxon scores (ranks of data), and stepwise discriminant analysis. Regular and GC/MS methods in hemofiltrate showed a good correlation for lactic acid. The best correlation with lactic acid was found for 4-hydroxy-phenyllactic acid (n=20, r=0.866), 2-hydroxy-valeric acid (n=22, r=0.7491) and 2-hydroxybutyric acid (n=32, r=0.5148). Age, sex, diagnosis, and APACHE II score play a subordinate role, but the presence of glyceric and citric acid possibly have prognostic importance [nonparimetric ANOVA with Wilcoxon scores (ranks of data)], as does the combination of 3-hydroxypropionic acid, glyceric acid, and threonic-acid-4-lacton (stepwise discriminant analysis). It can be concluded that in acute renal failure, the measurement of lactic acid and AKBR can reflect only a small part of disturbed metabolism. Hemofiltrate can be a useful medium in describing metabolic processes in critically ill patients with acute renal failure. Some inherited metabolic diseases in infants (phenylketonuria, maple syrup disease) and ketoacidosis show similar metabolic modifications.

Therapeutic Apheresis in Children: Experience in a Pediatric Dialysis Center

The use of apheretic procedures in pediatric patients has always been restricted by technical difficulties and the low incidence of diseases requiring this kind of treatment. The aim of the present study was to describe the solutions adopted to solve technical difficulties related to priming, vascular access and monitoring and then to evaluate clinical results.

Between 1982 and 2000, 51 consecutive children (28 male, 23 female) with a mean age of 4.9 ± 4.8 years (3 months – 14.8 years) and a mean weight of 19.7 ± 12.8 kg (5 – 52 kg), with renal and/or extra-renal diseases requiring apheretic procedures were selected for the study. The overall number of procedures performed were: 226 plasma-exchange (PE), 6 LDL-apheresis (LDL-A) and 8 protein A immunoadsorption (IAPA) sessions.

Our therapeutic protocol involves hematic flux of 20 – 100 ml/min and ultrafiltration of 5–20 ml/min. In each 70–95 minute session we exchanged plasmatic volume with fresh frozen plasma or with a solution of 6% albumin in lactated Ringer's, using heparin (10–20 UI/kg/h). We used Paired Filtration Dialysis Monitor in PE and LDL-A; Citem 10 in IAPA. As plasma separator, we used a filter made of polypropylene, 0.2 m2 surface, 30 ml priming (Hemaplex BT 900).

Hemolytic uremic syndrome was the most commonly treated disease (18/51 cases) with good results in 10/18 cases. We recorded, good results in vasculitis as well, in one girl with focal glomerulosclerosis in transplanted kidney and rapid improvement in all children with Guillaine-Barré Syndrome. PE treatment was effective in metabolic disorders such as tirosynemia and familiar hypercolesterolemia. Only 4/12 patients with acute liver failure due to viral hepatitis recovered. We had poor results in the remaining eight cases.

Complications were rare and no viral infection was found in any patient. Our data show that it is possible to use these procedures in pediatric patients even though clinical indications and real effectiveness still need to be cleared up.

Which Amino-Acids do Serum and Hemofiltrate of Critically Ill Patients with Acute Renal Failure Contain?

The removal of amino acids during continuous renal replacement therapies induces clinical problems. Previous studies on animals have shown nephroprotective (glycine, alanine) or negative effects (lysine) on renal function in occurrence of acute renal failure. Disturbed metabolism in acute renal failure needs adequate parenteral nutrition. On the other hand, experience with continuous renal replacement therapies of metabolic crises in inborn errors of metabolism indicate a good control of disturbed amino acid metabolism. The aim of our study was to find amino acids, that might play an important role in the pathogenesis, prognosis and detection of acute renal failure and severe illness, so far only estimated by lactic acid. Thirty-three probes (serum and hemofiltrate) were taken from patients, suffering with acute renal failure caused by septic shock, severe pancreatitis and hepatorenal syndrome, one hour after the beginning of extracorporal circulation, the conditions of treatment were standardized. The material was deproteinized and studied by the amino acid analyzer LBK 4251 Apha Plus (Pharmacia, Stockholm, Sweden), while the lactic acid concentration was determined in a standard laboratory. Proline, glycine, alanine, methionine and histidine showed a close relationship to the lactic acid levels, but these amino acids were an essential part of parenteral nutrition. A statistical relationship was also established in (amino acids with amide groups) asparagine, glutamine, citrulline, cystathionine and phosphoethanolamine. The mean values of most of the amino acids were higher than normal, but standard deviations were increased. The presence of these amino acids in hemofiltrate and the good sieving coefficients could mean that the better prognosis of critically ill patients in continuous renal replacement therapies may also be due to continuous control of amino acid levels (especially with amide groups).

Short-term survival of hyperammonemic neonates treated with dialysis

BACKGROUND

In severe neonatal hyperammonemia, extracorporeal dialysis (ECD) provides higher ammonium clearance than peritoneal dialysis (PD). However, there are limited outcome data in relation to dialysis modality.

METHODS

Data from infants with hyperammonemia secondary to inborn errors of metabolism (IEM) treated with dialysis were collected in six Italian centers and retrospectively analyzed.

RESULTS

Forty-five neonates born between 1990 and 2011 were enrolled in the study. Of these, 23 were treated with PD and 22 with ECD (14 with continuous venovenous hemodialysis [CVVHD], 5 with continuous arteriovenous hemodialysis [CAVHD], 3 with hemodialysis [HD]). Patients treated with PD experienced a shorter duration of predialysis coma, while those treated with HD had a shorter ammonium decay time compared with all the other patients (p < 0.05). No difference in ammonium reduction rate was observed between patients treated with PD, CAVHD or CVVHD. Carbamoyl phosphate synthetase deficiency (CPS) was significantly associated with increased risk of death (OR: 9.37 [1.52-57.6], p = 0.016). Predialysis ammonium levels were significantly associated with a composite end-point of death or neurological sequelae (adjusted OR: 1.13 [1.02-1.27] per 100 μmol/l, p = 0.026). No association was found between outcome and dialysis modality.

CONCLUSIONS

In this study, a delayed ECD treatment was not superior to PD in improving the short-term outcome of neonates with hyperammonemia secondary to IEM.

Nutrition management guideline for maple syrup urine disease: an evidence- and consensus-based approach

In an effort to increase harmonization of care and enable outcome studies, the Genetic Metabolic Dietitians International (GMDI) and the Southeast Regional Newborn Screening and Genetics Collaborative (SERC) are partnering to develop nutrition management guidelines for inherited metabolic disorders (IMD) using a model combining both evidence- and consensus-based methodology. The first guideline to be completed is for maple syrup urine disease (MSUD). This report describes the methodology used in its development: formulation of five research questions; review, critical appraisal and abstraction of peer-reviewed studies and unpublished practice literature; and expert input through Delphi surveys and a nominal group process. This report includes the summary statements for each research question and the nutrition management recommendations they generated. Each recommendation is followed by a standardized rating based on the strength of the evidence and consensus used. The application of technology to build the infrastructure for this project allowed transparency during development of this guideline and will be a foundation for future guidelines. Online open access of the full, published guideline allows utilization by health care providers, researchers, and collaborators who advise, advocate and care for individuals with MSUD and their families. There will be future updates as warranted by developments in research and clinical practice.

Utility of peritoneal dialysis in neonates affected by inborn errors of metabolism

AIM

Some inborn errors of metabolism induce metabolic encephalopathy through accumulation of neurotoxic metabolites. Rapid elimination of these metabolites by peritoneal or extracorporeal dialysis is crucial to prevent neuronal damage or death. In this retrospective study, we evaluated the outcomes of nine neonates with metabolic crisis treated with peritoneal dialysis.

METHOD

Six neonates with hyperammonemic coma (four with organic acidemias, two with urea cycle disorders) and three with leucine accumulation due to maple syrup urine disease (MSUD) were managed with peritoneal dialysis in conjunction with dietary and pharmacological therapy.

RESULTS

Three patients with organic acidemia survived. One of the patients was normal; others had moderate and severe neurological impairments. One neonate with organic acidemia and both neonates with urea cycle disorders died. Two of the three patients with MSUD survived without neurological impairment; the other had severe neurological damage and died at 9 months of age due to sepsis.

CONCLUSION

Theoretically, extracorporeal dialysis should be the first dialysis treatment of choice; however, this report demonstrates that peritoneal dialysis has a chance to prevent neurological damage in some patients. Therefore, in developing countries without extracorporeal dialysis opportunities, it can be still a life-saving procedure, if it is applied with skilled staff and standard procedures.

Symptomatic hyperammonemia after lung transplantation: lessons learnt

Hyperammonemia, post-orthotopic lung transplantation, is a rare but mostly fatal complication. Various therapies, including those to decrease ammonia generation, increase nitrogen excretion, and several dialytic methods for removing ammonia have been tried. We describe three lung transplant recipients who developed acute hyperammonemia early after transplantation. Two of the three patients survived after a multidisciplinary approach including discontinuation of drugs, which impair urea cycle, aggressive ammonia reduction with prolonged daily intermittent hemodialysis (HD), and overnight slow low-efficiency dialysis in conjunction with early weaning of steroids and other therapeutic measures. Our experience suggests that early initiation of dialysis, high dialysis dose, increased frequency, and HD preferably to less efficient modalities increases survival in these patients.

Continuous renal replacement therapy in neonates weighing less than 3 kg

PURPOSE

Continuous renal replacement therapy (CRRT) is becoming the treatment of choice for supporting critically ill pediatric patients. However, a few studies present have reported CRRT use and outcome in neonates weighing less than 3 kg. The aim of this study is to describe the clinical application, outcome, and complications of CRRT in small neonates.

METHODS

A retrospective review was performed in 8 neonatal patients who underwent at least 24 hours of pumped venovenous CRRT at the Samsung Medical Center in Seoul, Korea, between March 2007 and July 2010. Data, including demographic characteristics, diagnosis, vital signs, medications, laboratory, and CRRT parameters were recorded.

RESULTS

The data of 8 patients were analyzed. At the initiation of CRRT, the median age was 5 days (corrected age, 38(+2) weeks to 23 days), and the median body weight was 2.73 kg (range, 2.60 to 2.98 kg). Sixty-two patient-days of therapy were reviewed; the median time for CRRT in each patient was 7.8 days (range, 1 to 37 days). Adverse events included electrolyte disturbances, catheter-related complications, and CRRT-related hypotension. The mean circuit functional survival was 13.9±8.6 hours. Overall, 4 patients (50%) survived; the other 4 patients, who developed multiorgan dysfunction syndrome, died.

CONCLUSION

The complications of CRRT in newborns are relatively high. However, the results of this study suggest that venovenous CRRT is feasible and effective in neonates weighing less than 3 kg under elaborate supportive care. Furthermore, for using potential benefit of CRRT in neonates, efforts are required for prolonging filter survival.

Continuous Hemodiafiltration in the Treatment of Hyperammonemia Due to Methylmalonic Acidemia

Methylmalonic academia (MMA) is a rare inborn error of branched-chain amino acid metabolism. Therapy consists of a special formulated protein diet, carnitine supplementation, and emergent detoxification during acute decompensation. Continuous hemodiafiltration is a modality choice to treat acute metabolic decompensation in inborn error of metabolism. We report the successful use of continuous hemodiafiltration in the management of acute decompensation in patients with methylmalonic academia. Three male patients were diagnosed with methylmalonic academia with the initial presentation of hyperammonemia. Continuous hemodiafiltration was utilized to treat acute decompensation of metabolic crisis. This approach results in a rapid reduction of systemic toxin levels. Continuous hemodiafiltration should be considered as a treatment modality for symptomatic neonates with MMA where hemodialysis is not feasible.

Peritoneal dialysis in neonates with inborn errors of metabolism: is it really out of date?

Peritoneal and extracorporeal dialysis are used to treat newborns affected by inborn errors of metabolism to minimize the effects of the acute accumulation of neurotoxic metabolites that can produce irreversible and severe neurological damage and even death. In recent papers, extracorporeal dialysis has been described as more effective than peritoneal dialysis in improving the prognosis in newborns with inborn errors of metabolism and hyperammonemia. However, it appears that the outcome is primarily related to the duration of neonatal hyperammonemic coma. Here we report seven newborns with hyperammonemia caused by inborn errors of metabolism (five with organic acidemias, two with urea-cycle disorders). They received dietetic and pharmacological treatment as well as peritoneal dialysis. Four of the five patients with organic acidemia survived with and without mild neurological impairment (follow-up 3.5-10 years). One died from bacterial sepsis after peritoneal dialysis was discontinued and the peritoneal catheter was removed. One of the two patients affected by urea-cycle disorders, a boy, died during the neonatal period, and the other, a girl, died at the age of 13 months due to severe neurological damage. Our results demonstrate that peritoneal dialysis may still be an effective treatment for neonatal hyperammonemia caused by inborn errors of metabolism. Furthermore, peritoneal dialysis can be administered quickly and easily in all settings, clearly an advantage when fast intervention is so crucial.

High-Volume Continuous Venovenous Hemofiltration as an Effective Therapy for Acute Management of Inborn Errors of Metabolism in Young Children

BACKGROUND/AIM

Renal replacement therapies (RRTs) have been used for the acute management of inborn errors of metabolism. Hemodialysis is the most effective modality. The aim of this article is to demonstrate that high-volume hemofiltration can offer an alternative way to effectively remove small molecules.

METHODS

Eight patients presented with acute neurological deterioration due to ammonia or organic acid accumulation. Different RRTs were applied, including continuous venovenous hemofiltration (CVVH, n = 7), continuous arteriovenous hemofiltration (CAVH, n = 2), continuous venovenous hemodialysis (CVVHD, n = 1), intermittent hemodialysis (HD, n = 1), and peritoneal dialysis (PD, n = 2).

RESULTS

Ammonia 50% reduction time in HD was 1.7 h while in CVVH it was 2-14.5 h. The greater the ultrafiltration flow was, the sooner patients regained consciousness. CAVH, CVVHD or PD was not sufficient enough.

CONCLUSION

CVVH also has a good clearance for organic acid and ammonia if applying high-volume hemofiltration (>35 ml/kg/h). It can be therefore be considered as an alternative therapy if infant HD is not available.

Renal replacement therapy in the treatment of confirmed or suspected inborn errors of metabolism

OBJECTIVE

Analysis of mortality and risk factors for mortality in the use of renal replacement therapy to correct metabolic disturbances associated with confirmed or suspected inborn errors of metabolism.

STUDY DESIGN

A retrospective review of an institutional review board-approved pediatric acute renal failure data base at the University of Michigan. Eighteen patients underwent 21 renal replacement therapy treatments for metabolic disturbances caused by urea cycle defects (n = 14), organic acidemias (n = 5), idiopathic hyperammonemia (n = 1), and Reye syndrome (n = 1).

RESULTS

There were 14 boys (74%) and 4 girls (26%), with a mean age and weight of 56.2 +/- 71.0 months and 18.5 +/- 19.2 kg, respectively, at the initiation of renal replacement therapy. Overall treatment mortality rate was 57.2% (12 of 21 treatments), with 11 of the 18 patients (61.1%) dying before hospital discharge. Two-year follow-up on those patients demonstrated that 5 patients (71.4%) remained alive. Initial therapy with hemodialysis was associated with improved survival. Ten treatments (47.6%) required transition to another form of renal replacement therapy to maintain ongoing metabolic control, with a mean duration of 6.1 +/- 9.8 days. Time to renal replacement therapy >24 hours was associated with an increased risk of mortality, whereas a blood pressure >5th percentile for age at the initiation of therapy and the use of anticoagulation were associated with a decreased risk of mortality.

CONCLUSIONS

Renal replacement therapy can correct the metabolic disturbances that accompany suspected or confirmed inborn errors of metabolism. Our experience demonstrates an approximately 60% mortality rate associated with renal replacement treatment, with more than 70% of survivors living longer than 2 years.

Kinetic modeling of plasma leucine levels during continuous venovenous extracorporeal removal therapy in neonates with maple syrup urine disease

A kinetic modeling of leucine plasma concentration changes is proposed to describe the plasma leucine reduction rate during continuous extracorporeal removal therapy (CECRT) in neonates with maple syrup urine disease. Data were obtained from seven neonates using a bicompartmental model for the best fitted curve of plasma leucine decrease during CECRT. During the first 3 h, leucine plasma levels decreased according to an exponential curve: [Leu](t) = [Leu](i) x 0.95 x 10(-0.09t) where [Leu](t) is the leucine plasma level (mumol/L) at time t (h) during CECRT and [Leu](I) is the initial plasma level. From h 4 to the end of CECRT, a second exponential curve was observed: [Leu](t) = [Leu](i) x 0.74 x 10(-0.05t). Plasma leucine levels obtained from three other neonates were similar to those predicted by the model. The apparent distribution volumes for leucine that correspond to the two exponential equations obtained were calculated from the leucine mass removal collected in the spent dialysate and ultrafiltrate. The distribution volume was 34 +/- 3% of body weight during the first 3 h of CECRT and 72 +/- 7% from h 4 to the end of CECRT. These figures are similar to known values for the extracellular water compartment and for total body water in the newborn. The findings suggest that leucine handling during CECRT is similar to that of nonprotein-bound small-molecular-weight solutes such as urea.

Comparison of solute clearance in three modes of continuous renal replacement therapy

OBJECTIVES

To compare the clearances of low molecular weight molecules using three modalities of continuous renal replacement therapy (CRRT) at the low blood flow rates typically used in pediatric patients.

DESIGN

A controlled, in vitro laboratory study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

AN69 dialysis hemofilter.

INTERVENTIONS

CRRT was performed using a 0.6 m(2) AN69 hemofilter. Human whole blood and plasma were combined to achieve a hematocrit of approximately 30%. Urea and creatinine were added to obtain concentrations of approximately 54 mmol/L of blood urea nitrogen and 1770 micromol/L of creatinine. Clearance data for urea and creatinine at a blood flow rate of 60 mL/min were generated using predilution continuous venovenous hemofiltration (CVVH), postdilution CVVH, and continuous venovenous hemodialysis (CVVHD).

MEASUREMENTS AND MAIN RESULTS

Clearance of all three modalities was compared at a replacement solution (CVVH) or dialysate (CVVHD) flow rate of 16.7% of the blood flow rate. Both postdilution CVVH and CVVHD had a urea clearance of 11.3 mL/min, which was 15% greater than the 9.8 mL/min urea clearance of predilution CVVH (p <.005). Creatinine clearance with postdilution CVVH (10.7 mL/min) was 15% greater than the 9.0 mL/min clearance produced by predilution CVVH (p < 0.01). Predilution CVVH and CVVHD were compared at a flow rate of either replacement solution (CVVH) or dialysate (CVVHD) of 33% and 50% of the blood flow rate. Postdilution CVVH was not performed at high ultrafiltration rates due to the potential problem of hemoconcentration. CVVHD clearances of urea and creatinine were statistically superior to predilution CVVH at both flow rates.

CONCLUSIONS

CVVHD was superior to predilution CVVH for clearance of urea and creatinine. Postdilution CVVH and CVVHD gave nearly equivalent clearances. At the low blood flow rates used in pediatric patients, which raise concerns about high ultrafiltration during postdilution CVVH causing excessive hemoconcentration and filter clotting, CVVHD appears to be the optimal modality for maximizing clearance of small solutes during CRRT.

Emergency management of inherited metabolic diseases

Inherited metabolic diseases with acute severe manifestations can be divided into five categories: (1) disorders of the intoxication type, (2) disorders with reduced fasting tolerance, (3) disorders with disturbed energy metabolism, (4) disorders of neurotransmission and (5) disorders in which no specific emergency treatment is available. Diagnostic emergency laboratory evaluation should cover all differential diagnoses that are therapeutically relevant and should always include ammonia, glucose, lactate and acid-base status as well as testing the urine for ketones. These are indispensable for planning and conducting the first steps of metabolic emergency treatment and should be available within 30 min. According to the clinical situation and biochemical derangement, special metabolic investigations must be initiated in parallel. These include acylcarnitine profiling with tandem mass spectrometry (in plasma or dried blood spots) and analysis of amino acids in plasma and of organic acids in urine. The results of all laboratory investigations relevant to the diagnosis of metabolic disorders for which specific emergency therapy exists should be available within 24 h. There is general agreement with regard to some therapeutic strategies that are clearly explained by pathophysiology: in disorders with endogenous intoxication, anabolism must be promoted and specific detoxification measures initiated. In disorders with reduced fasting tolerance, administration of glucose at the rate of hepatic glucose production forms the basis of treatment. Correction of acidosis is a major goal in disorders with disturbed mitochondrial energy metabolism, while glucose supply may have to be limited. Many current therapeutic strategies are based on case reports and personal experiences at different metabolic centres. The aim of devising the 'best' management is often hampered by the lack of objective evidence of efficacy.

Emergency dialysis in neonatal metabolic crises

Metabolic crises in children with inborn errors of metabolism are caused by the accumulation of neurotoxic metabolites. Rapid elimination of these metabolites is apparently crucial to prevent irreversible neuronal damage; long-term outcome is correlated with the rate of toxin removal during the crisis. The usefulness of different blood purification techniques for removing accumulated neurotoxins is reviewed in this manuscript.

Hyperammonemia in urea cycle disorders: role of the nephrologist

Hyperammonemia associated with inherited disorders of amino acid and organic acid metabolism is usually manifested by irritability, somnolence, vomiting, seizures, and coma. Although the majority of these patients present in the newborn period, they may also present in childhood, adolescence, and adulthood with failure to thrive, persistent vomiting, developmental delay, or behavioral changes. Persistent hyperammonemia, if not treated rapidly, may cause irreversible neuronal damage. After the diagnosis of hyperammonemia is established in an acutely ill patient, certain diagnostic tests should be performed to differentiate between urea cycle defects and other causes of hyperammonemic encephalopathy. In a patient with a presumed inherited metabolic disorder, the aim of therapy should be to normalize blood ammonia levels. Recent experience has provided treatment guidelines that include minimizing endogenous ammonia production and protein catabolism, restricting nitrogen intake, administering substrates of the urea cycle, administering compounds that facilitate the removal of ammonia through alternative pathways, and, in severe cases, dialysis therapy. Initiation of dialysis in the encephalopathic patient with hyperammonemia is indicated if the ammonia blood level is greater than three to four times the upper limit of normal. Hemodialysis is the most effective treatment for rapidly reducing blood ammonia levels. Continuous hemofiltration and peritoneal dialysis are also effective modalities for reducing blood ammonia levels. An improved understanding of the metabolism of ammonia and neurological consequences of hyperammonemia will assist the nephrologist in providing optimal care for this high-risk patient population.

Continuous arteriovenous hemodiafiltration in the acute treatment of hyperammonaemia due to ornithine transcarbamylase deficiency

BACKGROUND

Acute hyperammonemia caused by urea cycle disorder is a medical emergency for which immediate managements should be taken to minimize permanent brain damage. Among different enzyme defects, ornithine transcarbamylase deficiency (OTC) is one of the most common enzyme defect in urea cycle disorders. We utilized continuous renal replacement therapy techniques in the acute treatment of hyperammonemia due to ornithine transcarbamylase deficiency.

PATIENTS AND METHODS

Three male neonates with elevated serum ammonia levels were shown, based on urine organic acid analysis and serum amino acid studies, to have OTC deficiency. Administration of sodium benzoate and sodium phenylacetate for activating alternative nitrogen waste pathway were used associated with protein restriction. Other modalities, including blood exchange transfusion, peritoneal dialysis, continuous renal replacement therapy were utilized in an attempt to lower serum ammonia concentration.

RESULTS

We report the successful use of continuous arteriovenous hemofiltration (CAVH), continuous arteriovenous hemodialysis (CAVHD), continuous arteriovenous hemodiafiltration (CAVHDF) in the acute management of hyperammonemia due to OTC deficiency. We also compared the ammonia clearance between peritoneal dialysis, exchange transfusion, CAVH, CAVHD and CAVHDF. It demonstrated the evidence that CAVHDF provides the best ammonia clearance.

CONCLUSION

Continuous renal replacement therapy including CAVH, CAVHD, and CAVHDF may be the alternative techniques for acute management of hyperammonemia in inborn error of metabolism when dialysis machine is not available. Our data suggests CAVHDF provides the best ammonia clearance.

Non-renal indications for continuous renal replacement therapy

While there is clear support for the use of continuous renal replacement therapy (CRRT) in critically ill acute renal failure patients, there are other illnesses without renal involvement where CRRT might be of value. These include sepsis and other inflammatory syndromes such as acute respiratory distress syndrome (ARDS) and cardiopulmonary bypass where removal of inflammatory mediators by hemofiltration is hypothesized to improve outcome. Adsorption appears to be the predominant mechanism of mediator elimination. However, the observed hemodynamic improvement can, at least partially, be attributed to a reduction of body temperature or to fluid removal, and the evidence for a clinically important removal of proinflammatory cytokines remains limited. Continuous and therefore smooth fluid removal may improve organ function in ARDS, after surgery with cardiopulmonary bypass, and in patients with refractory congestive heart failure. Continuous removal of endogenous toxins, eventually combined with intermittent hemodialysis, is probably beneficial in inborn errors of metabolism, severe lactic acidosis, or tumor lysis syndrome.

Continuous venovenous haemodiafiltration in the acute phase of neonatal maple syrup urine disease

Maple syrup urine disease results in accumulation of leucine and its metabolites, which may lead in the long term to neurological dysfunction. In acute neonatal crises, large amounts of leucine may be removed by continuous venovenous haemofiltration. This extracorporeal technique has its risks and hazards, which increase with duration of treatment. We report three neonates in life-threatening conditions due to maple syrup urine disease, treated for not more than 12 h with various continuous venovenous techniques: continuous haemofiltration, haemodiafiltration and haemodialysis. The efficiency of and tolerance to these techniques was evaluated. For all three patients, plasma leucine levels decreased dramatically from 2186, 3818 and 2536 mumol/L to 1131, 1275 and 488 mumol/L, respectively. Leucine clearance obtained was 4.28 ml/min in haemodiafiltration. Their patients' neurological status improved rapidly and they have a normal developmental quotient at 22 months, 13 months, and 11 months of age, respectively. Tolerance was good except for hypothermia and drop in haematocrit in all cases. Haemodiafiltration management was more cumbersome and time consuming because it required continual adjustment of the substitution fluid flow rate to precisely balance inflow and outflow rates. We recommend continuous venovenous haemodialysis as the therapy of choice. It might be anticipated that improvement of this technique, by increasing dialysate flow rate and blood flow rate, will allow leucine concentration to be decreased below 1000 mumol/L within 6-8 h, whatever the initial level.

[Survey on the practice of extrarenal hemofiltration in pediatrics]

BACKGROUND

Several methods of dialysis are currently available. The choice of whether to use one of them is determined by multiple factors that are analyzed in this study.

PATIENTS AND METHODS

One hundred and twenty-six children (mean age: 48 +/- 6 months) were treated in 29 French intensive care units and/or departments of nephrology during 1991. The underlying diseases were: hemolytic-uremic syndrome (HUS) in 28% of patients, other renal diseases in 6%, metabolic diseases in 8%, septic shock in 8%, cardiogenic shock in 9%, hypovolemic shock in 10%, multiple organ failure in 7%, acute liver disease in 9% and other diseases in 15%.

RESULTS

Peritoneal dialysis (PD) was the favorite method in patients less than 10 years: intermittent hemodialysis (IHD), continuous hemofiltration and hemodiafiltration, (HF, HDF) were preferentially used above this age. PD was used in 85% of HUS, 58% of shocks and 50% of metabolic diseases. Sixty percent of acute renal diseases other than HUS were treated by IHD. HF and HDF were used in 66% of acute liver diseases and 42% of shocks. Overall mortality was 40% but no death could be directly ascribed to the different methods of dialysis.

CONCLUSION

The choice of method depends on the type of underlying disease, age of the patient but also the equipment of centers. Progress in evaluating indications and results of the different methods of dialysis are necessary.

Anaesthetic management in maple syrup urine disease

Two children with maple syrup urine disease undergoing emergency and elective surgery are reported. The administration of ketamine to a 12-month-old boy without neurological problems and propofol infusion to a 5-year-old girl with a history of convulsions, was uneventful. We believe that a full knowledge of the pathophysiology of maple syrup urine disease and potential peri-operative problems associated with the disease are essential, so that patients are not subjected to unnecessary risks.

Removal of branched-chain amino acids and alpha-ketoisocaproate by haemofiltration and haemodiafiltration

Venovenous haemofiltration (VVHF) and haemodiafiltration (VVHDF) were performed with a neonatal haemo(dia)filter (Miniflow 10, Hospal) on 8 anaesthetized rabbits infused with branched-chain amino acids (leucine, isoleucine and valine) and alpha-ketoisocaproate. The branched-chain amino acids (BCAA) and alpha-ketoisocaproate blood levels were close to those previously observed in neonates with maple syrup urine disease when extracorporeal blood purification was required. VVHF and VVHDF performances were assessed with two different blood flows (Qb = 8.3 and 16.6 ml/min). VVHDF was performed with four dialysate flow rates (Qd = 0.5, 1.0, 2.0 and 3.0 L/h). Within each period, clearances of the three BCAA were strictly similar. BCAA clearances obtained by VVHF were similar to ultrafiltration rates (respectively, 0.78 +/- 0.14 and 1.79 +/- 0.28 ml/min at high and low Qb; p < 0.05). The alpha-ketoisocaproate clearances obtained by VVHF were 0.39 +/- 0.17 and 0.92 +/- 0.43 ml/min at low and high Qb (not significantly different). Whatever the Qd value, the VVHDF procedures always allowed higher BCAA and alpha-ketoisocaproate clearances as compared with the corresponding VVHF period with similar Qb. BCAA clearances obtained by VVHDF with a 0.5 L/h dialysate flow were 4.1 +/- 0.5 and 5.4 +/- 0.5 mL/min at low and high Qb, respectively. The concurrent alpha-ketoisocaproate clearances were 2.5 +/- 0.8 and 2.9 +/- 1.0 ml/min.

Principles of renal replacement therapy in children

Much has changed in pediatric renal replacement therapy during the past decade. Even the smallest critically ill patients can be temporarily supported, and chronic peritoneal and hemodialysis in young children has become routine. Although improved technical capabilities often may raise difficult ethical dilemmas, the health care team must know that such therapeutic modalities are available for the pediatric patient.

Renal replacement therapy after repair of congenital heart disease in children. A comparison of hemofiltration and peritoneal dialysis

The development of renal failure necessitating peritoneal dialysis after cardiac operations is associated with a reported mortality greater than 50%. Improved fluid removal and nutritional support have been reported with the use of continuous arteriovenous hemofiltration and continuous venovenous hemofiltration techniques. We have compared our experience with all three techniques in managing children who required renal replacement therapy after cardiac operations in terms of efficacy (fluid removal, calorie intake, and clearance of urea and creatinine), complications, and outcome. Over a 5-year period renal replacement therapy was initiated in 42 children, and in 34 of them it was successfully established for more than a 24-hour period: 17 were managed with peritoneal dialysis, 8 with continuous arteriovenous hemofiltration, and 9 with continuous venovenous hemofiltration. A net negative fluid balance was achieved in only 6 (35%) patients treated with peritoneal dialysis compared with 50% of those treated with continuous venovenous hemofiltration and 89% of those treated with continuous venovenous hemofiltration. In terms of nutritional support, calorie intake increased by 43% after peritoneal dialysis was started compared with 515% and 409% in the arteriovenous and venovenous hemofiltration groups, respectively, (p < 0.005). The serum urea levels fell by 36% (p = 0.02) and 39% (p = 0.005) compared with pre-therapy levels with arteriovenous and venovenous hemofiltration, respectively, and the creatinine content was reduced by 19% and 33% (p = 0.003). Neither parameter was reduced in the peritoneal dialysis group. We conclude that the use of hemofiltration as a renal replacement therapy after surgical correction of congenital heart disease offers significant advantages over the more traditional approach of peritoneal dialysis. In addition, we suggest that a more aggressive approach to the management of fluid overload and nutritional depletion with hemofiltration may result in a decrease in the very high mortality seen in renal failure after cardiac operations.

Continuous venovenous haemofiltration in the acute treatment of inborn errors of metabolism

The accumulation of toxic metabolites in children with inborn errors of metabolism may cause acute metabolic crises and result in long-term neurological dysfunction or death. Peritoneal dialysis often provides insufficient clearance to protect against these complications, while intermittent haemodialysis cannot prevent reaccumulation of metabolites between dialysis sessions. We describe the use of continuous venovenous haemofiltration (CVVH) or haemodiafiltration (CVVHD) in three infants with maple syrup urine disease (MSUD) and one child with carbamyl phosphate synthetase (CPS) deficiency. All children with MSUD had a satisfactory reduction in branched-chain amino acids within 24 h of onset of haemofiltration, and are now neurologically normal. The child with CPS deficiency had an ammonia level of < 100 mumol/l within 24 h of onset of therapy, but died 3 days later from unrelated cardiovascular complications. Complications of the therapy included the clotting of one haemofilter and the replacement of two vascular access catheters per patient on average per therapy. Two patients required blood transfusion. We report the successful use of CVVH and CVVHD in the acute management of metabolic crises associated with inborn errors of metabolism, and believe that these may be the optimal techniques for the acute clearance of toxic metabolites.

Continuous arterial-venous diahemofiltration and continuous veno-venous diahemofiltration in infants and children

Continuous arterial-venous diahemofiltration and continuous veno-venous diahemofiltration [CAVH(D)/CVVH(D)] in the infant and pediatric population is increasingly being utilized in the child needing renal replacement therapy (RRT). Difficulties with infant- and pediatric-specific equipment remains a limitation. The availability of techniques and equipment in this unique population is addressed. Use of this form of RRT as opposed to hemodialysis or peritoneal dialysis is discussed. The decision for CAVH(D) or CVVH(D) remains an individual choice.

A review of venovenous haemofiltration in seriously ill infants

Between April 1989 and October 1991, 13 severely ill infants, median age 13 days (range 1-180 days), median weight 3.5 kg (range 2.5-4.8 kg), received continuous venovenous haemofiltration (CVVH) for a median duration of 39 h (range 5-234 h). Filtration was performed through a double lumen catheter inserted into a central vein. The indications for filtration included acute renal failure (8), fluid overload (5), inborn errors of metabolism (3) and sepsis (1). Some infants had more than one indication. The median Paediatric Risk of Mortality (PRISM) score on the day of admission to the intensive care unit was 27 (range 8-42). No change in the level of respiratory support was required following the commencement of CVVH. Serum electrolyte concentrations and plasma osmolality remained normal throughout. Serum creatinine fell from a mean of 0.11 mmol/L (95% CI 0.058-0.168) to 0.07 mmol/L (CI 0.034-0.112). Urea fell from a mean of 9.5 mmol/L (CI 4.4-14.6) to 6.5 mmol/L (CI 2.7-10.3). Platelet counts fell by 40-50% from a mean of 126 x 10(6)/mm3 (CI 72-180) to 69 x 10(6)/mm3 (CI 36-103) 18 h following commencement of filtration but no bleeding was encountered. The main complication was a thrombosis of the superior and inferior vena cava in one infant. Four infants survived to be discharged from intensive care. Continuous venovenous haemofiltration, with its inherent advantages over arteriovenous haemofiltration, is feasible in small infants using standard paediatric equipment.

Pump-assisted hemofiltration in infants with acute renal failure

Hemofiltration is accepted management for acute renal failure in critically ill patients. However, in infants, obtaining arterial access or adequate flow through the access is often difficult. We report our technique and experience with pump-assisted hemofiltration (PAHF) in ten infants with acute renal failure. In five patients, double-lumen venous catheters provided access, while two catheters at separate sites were used in the remaining patients. In all patients, hemofilters were used with standard intravenous tubing added to pre-filter tubing and placed through a standard volumetric infusion pump for regulation of blood flow. The infants, aged 5-575 days, weighed from 2.8 to 11.4 kg and had primary diagnoses of post-operative congenital heart disease in five, sepsis in four, and renal dysplasia in one. The duration of PAHF averaged 158 +/- 115 h (range 20-332 h). Complications included bleeding at a catheter or surgical site in one patient each and asymptomatic hyponatremia in five patients. Thus, with adequate nurse training, PAHF using a volumetric infusion pump for blood regulation can be acceptable therapy in acute renal failure in infants.