Phenylacetate and benzoate clearance in a hyperammonemic infant on sequential hemodialysis and hemofiltration

Extracorporeal pediatric renal replacement therapy: diversifying application beyond kidney failure

The utilization of extracorporeal renal replacement therapy (RRT), including continuous renal replacement therapy (CRRT) and hemodialysis (HD), beyond the treatment of volume overload and acute kidney injury (AKI) has witnessed a significant shift, demonstrating the potential to improve patient outcomes for a range of diseases. This comprehensive review explores the non-kidney applications for RRT platforms in critically ill children, focusing on diverse clinical scenarios such as sepsis, inborn errors of metabolism, liver failure, drug overdose, tumor lysis syndrome, and rhabdomyolysis. In the context of sepsis and septic shock, RRT not only facilitates fluid, electrolyte, and acid/base homeostasis, but may offer benefits in cytokine regulation, endotoxin clearance, and immunomodulation which may improve multi-organ dysfunction as well as hemodynamic challenges posed by this life-threatening condition. RRT modalities also have an important role in caring for children with inborn errors of metabolism, liver failure, and tumor lysis syndrome as they can control metabolic derangements with the efficient clearance of endogenous toxins in affected children. In cases of drug overdose, RRT is a crucial tool for rapid extracorporeal clearance of exogenous toxins, mitigating potential organ damage. The intricate interplay between liver failure and kidney function is examined, elucidating the role of RRT and plasma exchange in maintaining fluid and electrolyte balance when hepatic dysfunction complicates the clinical picture. Furthermore, RRT and HD are explored in the context of rhabdomyolysis, highlighting their utility in addressing AKI secondary to traumatic events and crush syndrome.

Expanding the Spectrum of Extracorporeal Strategies in Small Infants with Hyperammonemia

Hyperammonemia is a life-threatening condition mainly due to the neurotoxicity of ammonia. Ammonia scavengers may be insufficient, and extracorporeal treatment may be required. Continuous treatments are preferred, and a high-dose continuous renal replacement therapy (CRRT) must be prescribed to ensure a fast ammonia depletion. Many of the children with hyperammonemia are newborns, with lower blood volume than older children. The majority of the CRRT systems are adult-based, with large extracorporeal priming volumes and inadequate UF control. Recent strides have been made in the development of CRRT systems more suitable for young children with smaller sets to use in adult machines and dedicated monitors for neonates and infants. The main advantage of the machines for adults is the higher dialysis fluid flows, however with greater hemodynamic risks. Pediatric monitors have been designed to reduce the extracorporeal volume and to increase the precision of the treatment. However, they have substantial limitation in clearance performances. In this review, we discuss on current strategies to provide CRRT in newborns and small infants with hyperammonemia. We also presented our experience with the use of CARPEDIEM™ implemented in a CVVHDF modality, boosting the diffusive clearance with a post-replacement convective mechanism.

Extracorporeal Ammonia Clearance for Hyperammonemia in Critically Ill Patients: A Scoping Review

INTRODUCTION

Hyperammonemia is a life-threatening condition. However, clearance of ammonia via extracorporeal treatment has not been systematically evaluated.

METHODS

We searched EMBASE and MEDLINE databases. We included all publications reporting ammonia clearance by extracorporeal treatment in adult and pediatric patients with clearance estimated by direct dialysate ammonia measurement or calculated by formula. Two reviewers screened and extracted data independently.

RESULTS

We found 1,770 articles with 312 appropriate for assessment and 28 studies meeting eligibility criteria. Most of the studies were case reports. Hyperammonemia was typically secondary to inborn errors of metabolisms in children and to liver failure in adult patients. Ammonia clearance was most commonly reported during continuous renal replacement therapy (CRRT) and appeared to vary markedly from <5 mL/min/m2 to >250 mL/min/m2. When measured during intermittent hemodialysis (IHD), clearance was highest and correlated with blood flow rate (R2 = 0.853; p < 0.001). When measured during CRRT, ammonia clearance could be substantial and correlated with effluent flow rate (EFR; R2 = 0.584; p < 0.001). Neither correlated with ammonia reduction. Peritoneal dialysis (PD) achieved minimal clearance, and other extracorporeal techniques were rarely studied.

CONCLUSIONS

Extracorporeal ammonia clearance varies widely with sometimes implausible values. Treatment modality, blood flow, and EFR, however, appear to affect such clearance with IHD achieving the highest values, PD achieving minimal values, and CRRT achieving substantial values especially at high EFRs. The role of other techniques remains unclear. These findings can help inform practice and future studies.

Consensus guidelines for management of hyperammonaemia in paediatric patients receiving continuous kidney replacement therapy

Hyperammonaemia in children can lead to grave consequences in the form of cerebral oedema, severe neurological impairment and even death. In infants and children, common causes of hyperammonaemia include urea cycle disorders or organic acidaemias. Few studies have assessed the role of extracorporeal therapies in the management of hyperammonaemia in neonates and children. Moreover, consensus guidelines are lacking for the use of non-kidney replacement therapy (NKRT) and kidney replacement therapies (KRTs, including peritoneal dialysis, continuous KRT, haemodialysis and hybrid therapy) to manage hyperammonaemia in neonates and children. Prompt treatment with KRT and/or NKRT, the choice of which depends on the ammonia concentrations and presenting symptoms of the patient, is crucial. This expert Consensus Statement presents recommendations for the management of hyperammonaemia requiring KRT in paediatric populations. Additional studies are required to strengthen these recommendations.

This expert Consensus Statement from the Pediatric Continuous Renal Replacement Therapy (PCRRT) workgroup presents recommendations for the management of hyperammonaemia requiring kidney replacement therapy in paediatric populations. Additional studies are needed to strengthen these recommendations, which will be reviewed every 2 years.

Basics of continuous renal replacement therapy in pediatrics

In the last three decades, significant advances have been made in the care of children requiring renal replacement therapy (RRT). The move from the use of only hemodialysis and peritoneal dialysis to continuous venovenous hemofiltration with or without dialysis (continuous renal replacement therapy, CRRT) has become a mainstay in many intensive care units. The move to CRRT is the result of greater clinical experience as well as advances in equipment, solutions, vascular access, and anticoagulation. CRRT is the mainstay of dialysis in pediatric intensive care unit (PICU) for critically ill children who often have hemodynamic compromise. The advantages of this modality include the ability to promote both solute and fluid clearance in a slow continuous manner. Though data exist suggesting that approximately 25% of children in any PICU may have some degree of renal insufficiency, the true need for RRT is approximately 4% of PICU admissions. This article will review the history as well as the progress being made in the provision of this care in children.

The impact of continuous renal replacement therapy for metabolic disorders in infants

BACKGROUND

While Continuous Renal Replacement Therapy (CRRT) is a well established treatment modality for patients with acute kidney insufficiency (AKI), it is now also being used for the management of various illnesses such as acute metabolic disorders presenting with hyperammonemia and elevated leucine levels. Herein, we aimed to describe our experience with CRRT in treatment of acute decompensation of 14 patients with a diagnosis of metabolic disorder who has been admitted to our pediatric intensive care unit (PICU) in the last year.

METHODS

Patients who have had life threatening acute metabolic crisis due to various metabolic disorders and were treated with continuous renal replacement therapy (CRRT) were evaluated retrospectively.

RESULTS

Between November 2014 and December 2015, 14 patients were found to have received CRRT for various metabolic disorders in the PICU. Ten patients had hyperammonemia and four patients had elevated leucine levels. Nine patients were male and five were female. The age interval was between 2 days and 18 months, with a mean of 5.5 ± 7.4 months. The weight distribution was between 2.5 and 18 kg, with a mean of 7.3 ± 5.6 kg. Eleven patients received continuous veno-venous hemodiafiltration (CVVHDF), and 3 patients with MSUD received continuous veno-venous hemodialysis (CVVHD). All patients have received high throughput hemodialysis and hemofiltration. The dialyzate rate was set to be minimum 4042 ml/h/1.73 m², and maximum 12,900 ml/h/1.73 m². Hemofiltration was performed with a replacement rate of 40-76 ml/kg/h. The average CRRT duration was 16.6 ± 15.6 h.

CONCLUSIONS

We suggest that CRRT is an efficient method that can be used in hyperammonemia and elevated leucine levels which are metabolic emergencies.

The Role of RRT in Hyperammonemic Patients

Hyperammonemia is an important cause of cerebral edema in both adults with liver failure and children with inborn errors of metabolism. There are few studies that have analyzed the role of extracorporeal dialysis in reducing blood ammonia levels in the adult population. Furthermore, there are no firm guidelines about when to implement RRT, because many of the conditions that are characterized by hyperammonemia are extremely rare. In this review of existing literature on RRT, we present the body's own mechanisms for clearing ammonia as well as the dialytic properties of ammonia. We review the available literature on the use of continuous venovenous hemofiltration, peritoneal dialysis, and hemodialysis in neonates and adults with conditions characterized by hyperammonemia and discuss some of the controversies that exist over selecting one modality over another.

The complexity of dialytic therapy in hyperammonemic neonates

The utilization of renal replacement therapy (RRT) in the setting of hyperammonia is a rare and complicated occurrence. Data demonstrate that the quicker the ammonia level is normalized, the better the neurological outcome. The optimal form of RRT is often decided by local practice. The recent work by Picca and colleagues details a larger series of children who underwent RRT for hyperammonia and adds some credence to the use of peritoneal dialysis (PD) in this population. While these authors conclude that PD is not optimal, they do note that the use of PD may be an option when other forms of RRT are not available. The results reinforce the general maxim that you should continue to do that which you do well and often, which in this context refers to continuing to use your form of RRT until alternative modalities are available.

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.

Renal replacement therapy in neonates

The incidence of acute kidney injury (AKI) has steadily increased in the last decade in neonates and infants. Despite the extensive proposed pharmacologic approaches to treat or prevent AKI, renal replacement therapy is the only available therapeutic approach to manage the consequences of significant AKI and maintain electrolyte homeostasis and fluid balance in infants with AKI. The objective of this article is to summarize the different approaches and modalities of renal replacement therapy in neonatal intensive care units.

A biphasic dialytic strategy for the treatment of neonatal hyperammonemia

BACKGROUND

Neonates with inborn errors of metabolism (IEM) often develop hyperammonemia which, if not corrected quickly, may result in poor neurologic outcomes. As pharmacologic therapy cannot rapidly lower ammonia levels, dialysis is frequently required. Both hemodialysis (HD) and standard-dose continuous renal replacement therapy (CRRT) are effective; however, HD may be followed by post-dialytic ammonia rebound, and standard-dose CRRT may not effect a rapid enough decrease in ammonia levels.

CASE-DIAGNOSIS/TREATMENT

We present two cases of IEM-associated neonatal hyperammonemia in which we employed a biphasic, high-dose CRRT treatment strategy, initially using dialysate flow rates of 5,000 mL/h (approximately 40,000 mL/h/1.73 m(2)) in order to rapidly decrease ammonia levels, then decreasing the dialysate flow rates to 500 mL/h (approximately 4,000 mL/h/1.73 m(2)) in order to prevent ammonia rebound.

CONCLUSIONS

This biphasic dialytic treatment strategy for neonatal hyperammonemia effected rapid ammonia reduction without rebound and accomplished during a single dialysis run without equipment changes.

Renal complications and therapy in the PICU: hypertension, CKD, AKI, and RRT

This article provides the bedside clinician an overview of the unique renal complications that are seen commonly in the pediatric intensive care unit. These sections are purposely succinct to give a quick guide to the clinician for the care of these children. We have identified four major areas that should result in discussion and cooperative care between intensive care physicians and nephrologists for the care of these children: (1) hypertension, (2) chronic kidney failure, (3) acute kidney injury, and (4) renal replacement therapy.

High-dose continuous renal replacement therapy for neonatal hyperammonemia

BACKGROUND

Infants with hyperammonemia can present with nonspecific findings so ordering an ammonia level requires a high index of suspicion. Renal replacement therapy (RRT) should be considered for ammonia concentrations of >400 μmol/L since medical therapy will not rapidly clear ammonia. However, the optimal RRT prescription for neonatal hyperammonemia remains unknown. Hemodialysis and continuous renal replacement therapy (CRRT) are both effective, with differing risks and benefits.

CASE-DIAGNOSIS/TREATMENT

We present the cases of two neonates with hyperammonemia who were later diagnosed with ornithine transcarbamylase deficiency and received high-dose CRRT. Using dialysis/replacement flow rates of 8,000 mL/h/1.73 m(2) (1,000 mL/h or fourfold higher than the typical rate used for acute kidney injury) the ammonia decreased to <400 μmol/L within 3 h of initiating CRRT and to <100 μmol/L within 10 h.

CONCLUSIONS

We propose a CRRT treatment algorithm to rapidly decrease the ammonia level using collaboration between the emergency department and departments of genetics, critical care, surgery/interventional radiology, and nephrology.

Hyperammonemia in review: pathophysiology, diagnosis, and treatment

Ammonia is an important source of nitrogen and is required for amino acid synthesis. It is also necessary for normal acid-base balance. When present in high concentrations, ammonia is toxic. Endogenous ammonia intoxication can occur when there is impaired capacity of the body to excrete nitrogenous waste, as seen with congenital enzymatic deficiencies. A variety of environmental causes and medications may also lead to ammonia toxicity. Hyperammonemia refers to a clinical condition associated with elevated ammonia levels manifested by a variety of symptoms and signs, including significant central nervous system (CNS) abnormalities. Appropriate and timely management requires a solid understanding of the fundamental pathophysiology, differential diagnosis, and treatment approaches available. The following review discusses the etiology, pathogenesis, differential diagnosis, and treatment of hyperammonemia.

Management of toxic ingestions with the use of renal replacement therapy

Although rare, renal replacement therapy (RRT) for the treatment of the metabolic, respiratory and hemodynamic complications of intoxications may be required. Understanding the natural clearance of the medications along with their volume of distribution, protein binding and molecular weight will help in understanding the benefit of commencing RRT. This information will aid in choosing the optimal forms of RRT in an urgent setting. Overdose of common pediatric medications are discussed with suggestions on the type of RRT within this educational review.

Continuous hemofiltration in the control of neonatal hyperammonemia: a 10-year experience

In a 10-year review of the utilization of continuous veno-venous hemofiltration (CVVH) for the treatment of neonatal hyperammonemia, 14 patients were identified with hyperammonemia due to either a urea cycle defect or an organic acidemia. Intensive care survival was 64%. The pretreatment level of serum ammonia and the rapidity of ammonia clearance did not differ between survivors and non-survivors (p = 0.16 and p = 0.93, respectively). Likewise, the duration of CVVH therapy did not differ between survivors and non-survivors (p = 0.1). Indicators of pretreatment physiological stress showed either a correlation with non-survival [Pediatric Risk of Mortality (PRISM) score, p = 0.006, cardioactive drug requirement, p = 0.003], or demonstrated a trend to such a correlation (serum lactate, p = 0.06). Complications associated with the CVVH technique were infrequent. Hypotension was seen in seven patients, but in only one patient did it arise de novo following the initiation of CVVH. In conclusion, neither the severity of the hyperammonemic state nor the efficacy of ammonia removal correlated with patient outcome. The pre-CVVH PRISM score and requirement for cardio-active medication were significantly greater in those patients who did not survive their acute illness. The pre-CVVH physiological condition of the neonates in this cohort was the main determinant of outcome.

Nitrogen sparing therapy revisited 2009

Although the protocol that most experienced metabolic centers in the United States follow for treating acute hyperammonemia in urea cycle disorders (UCDs) is similar to that proposed by Brusilow and Batshaw in the early 1980s, over the years a steady evolution has taken place. Continued developments in intensive care, surgical and hemodialysis techniques, fluid and electrolyte management, cardiovascular support, and emergency transport have contributed to improved management of acute hyperammonemia. Compared to historical data, survival of urea cycle patients has also improved following treatment with alternative pathway therapy, in addition to appropriate supportive care, including the provision of adequate calories to prevent catabolism and promote anabolism and hemodialysis if needed. However, overall neurological outcomes have been suboptimal. There are currently a number of exciting prospective new therapies on the horizon, including novel medications or cell-based treatments. Nevertheless, the therapeutic expertise that is currently in place at centers specializing in management of metabolic emergencies already has the potential to improve survival and outcome in these children significantly. The early identification of UCD patients so that transport to a metabolic treatment center may be carried out without delay continues to be a major area of focus and challenge.

Continuous venovenous haemodialysis (CVVHD) and continuous peritoneal dialysis (CPD) in the acute management of 21 children with inborn errors of metabolism

BACKGROUND

Newborns with inborn errors of metabolism often present with hyperammonaemic coma, requiring prompt diagnosis and specific medical therapy, nutritional support and efficient toxin removal. Little information regarding the efficacy and safety of continuous venovenous haemodialysis (CVVHD) as an option for extracorporal ammonia detoxification in children is available.

METHODS

Twenty-one patients with hyperammonaemia [19 neonates (mean age 4.1 +/- 2.4 days) and two children 1 and 7 years of age, respectively] were admitted to our hospital for dialysis between 1996 and 2008. Seventeen children (15 neonates), received CVVHD. Four neonates received continuous peritoneal dialysis (CPD). All started medical treatment with sodium benzoate, l-arginine hydrochloride and carnitine as well as protein-restricted parenteral diets with high caloric intake before dialysis.

RESULTS

Plasma ammonia levels (range 464-7267 microg/dl before dialysis and 27-3317 microg/dl after dialysis) were significantly reduced by 50% within 4.7 +/- 2.5 h with CVVHD compared with 13.5 +/- 6.2 h with CPD (P < 0.0001). Plasma ammonia levels <200 microg/dl critical range were achieved within 22.4 +/- 18.1 h in CVVHD patients compared with 35.0 +/- 24.1 h with CPD. Depending on the weight and blood pressure stability of the patients, mean blood flow velocities of 9.8 +/- 3.4 ml/kg/min and mean dialysate flow rates of 3925 +/- 2398 ml/min/1.73 m(2) were employed. Blood and dialysate flows significantly correlated with ammonia clearance and decay of ammonia in vivo. Because of the severe underlying disease, 18% of CVVHD patients died compared with 50% undergoing CPD. In total, 82% of CVVHD patients survived the first 6 months after dialysis. Among these, 43% were without sequelae, 43% developed moderate mental retardation, and two (14%) developed severe mental retardation.

CONCLUSION

CVVHD effectively and quickly eliminates plasma ammonia. To optimize long-term mental outcome, rapid identification and appropriate treatment of the underlying disease as well as starting dialysis early are of enormous therapeutic value.

Medical management and dialysis therapy for the infant with an inborn error of metabolism

Optimal care of the neonate with hyperammonemia requires expertise in the evaluation, medical management, and decision to initiate dialytic therapy, and therefore compels expeditious collaboration between neonatal intensive care physicians, medical geneticists, and pediatric nephrologists. Neonatal and dialysis nursing expertise also is paramount for the successful provision of dialysis therapy in this setting. The current article addresses the underlying causes, medical management strategies, and dialytic therapy considerations in caring for the neonate with hyperammonemia.

Renal replacement therapy in acute renal failure in children

Acute renal failure in children differs from adult patients in incidence, pathogenesis and size of the patient, but outcome is significantly better. Specific problems are access and haemodynamic stability. Where increasing reporting on the use of CRRT in children seems to convince that CRRT is the treatment of choice, we have to stress that there is no evidence for this statement. Part of this misunderstanding is that both peritoneal and haemodialysis techniques from chronic renal replacement therapy (RRT) are simply extrapolated to intensive care setting. In this paper we want to elaborate on several adaptations in the dialysis-prescription of both peritoneal dialysis and haemodialysis in the ARF setting, which may improve efficacy and outcome. Introduction of new peritoneal dialysis catheter techniques, the cyclers, bicarbonate solutions, combined glucose/amino acid solutions, and low sodium-solutions have overcome many of the inconveniences of the old CAPD-technique. Slow SLED haemodialysis, with an ambulant Genius haemodialyser, with the use of ultra pure water adds to the benefits of conventional haemodialysis (monitoring, safetyness) to better haemodynamic stability of CRRT techniques.