Emergency treatment of neonatal hyperammonaemic coma with mild systemic hypothermia

A glance at transient hyperammonemia of the newborn: Pathophysiology, diagnosis, and treatment: A review

Hyperammonemia is the excessive accumulation of ammonia in the blood, and is usually defined as a plasma level above 100 µmol/L in neonates or above 50 µmol/L in term infants, children, and adolescents. Patients with hyperammonemia usually experience life-threatening neuropsychiatric symptoms, especially newborns. It is routinely caused by inherited metabolic diseases and also by acquired disorders, such as liver failure, portosystemic shunting, gastrointestinal hemorrhage, ureterosigmoidostomy, renal tubular acidosis, hypoxic ischemic encephalopathy, infections with urea-metabolizing organisms, and some drugs. Transient hyperammonemia of the newborn (THAN) is a special type of hyperammonemia acknowledged in the field of metabolic disease as an inwell-defined or well-understood entity, which can be diagnosed only after the exclusion of genetic and acquired causes of hyperammonemia. Although the prognosis for THAN is good, timely identification and treatment are essential. Currently, THAN is underdiagnosed and much less is mentioned for early diagnosis and vigorous treatment. Herein, we present common themes that emerge from the pathogenesis, diagnosis, and management of THAN, based on current evidence. When a newborn presents with sepsis, intracranial hemorrhage, or asphyxia that cannot explain coma and seizures, doctors should always keep this disease in mind.

CPS1: Looking at an ancient enzyme in a modern light

The mammalian urea cycle (UC) is responsible for siphoning catabolic waste nitrogen into urea for excretion. Disruptions of the functions of any of the enzymes or transporters lead to elevated ammonia and neurological injury. Carbamoyl phosphate synthetase 1 (CPS1) is the first and rate-limiting UC enzyme responsible for the direct incorporation of ammonia into UC intermediates. Symptoms in CPS1 deficiency are typically the most severe of all UC disorders, and current clinical management is insufficient to prevent the associated morbidities and high mortality. With recent advances in basic and translational studies of CPS1, appreciation for this enzyme's essential role in the UC has been broadened to include systemic metabolic regulation during homeostasis and disease. Here, we review recent advances in CPS1 biology and contextualize them around the role of CPS1 in health and disease.

Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision

In 2012, we published guidelines summarizing and evaluating late 2011 evidence for diagnosis and therapy of urea cycle disorders (UCDs). With 1:35 000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist. In the 7 years that have elapsed since the first guideline was published, abundant novel information has accumulated, experience on newborn screening for some UCDs has widened, a novel hyperammonemia-causing genetic disorder has been reported, glycerol phenylbutyrate has been introduced as a treatment, and novel promising therapeutic avenues (including gene therapy) have been opened. Several factors including the impact of the first edition of these guidelines (frequently read and quoted) may have increased awareness among health professionals and patient families. However, under-recognition and delayed diagnosis of UCDs still appear widespread. It was therefore necessary to revise the original guidelines to ensure an up-to-date frame of reference for professionals and patients as well as for awareness campaigns. This was accomplished by keeping the original spirit of providing a trans-European consensus based on robust evidence (scored with GRADE methodology), involving professionals on UCDs from nine countries in preparing this consensus. We believe this revised guideline, which has been reviewed by several societies that are involved in the management of UCDs, will have a positive impact on the outcomes of patients by establishing common standards, and spreading and harmonizing good practices. It may also promote the identification of knowledge voids to be filled by future research.

Effects of a high protein diet and liver disease in an in silico model of human ammonia metabolism

Background

After proteolysis, the majority of released amino acids from dietary protein are transported to the liver for gluconeogenesis or to peripheral tissues where they are used for protein synthesis and eventually catabolized, producing ammonia as a byproduct. High ammonia levels in the brain are a major contributor to the decreased neural function that occurs in several pathological conditions such as hepatic encephalopathy when liver urea cycle function is compromised. Therefore, it is important to gain a deeper understanding of human ammonia metabolism. The objective of this study was to predict changes in blood ammonia levels resulting from alterations in dietary protein intake, from liver disease, or from partial loss of urea cycle function.

Methods

A simple mathematical model was created using MATLAB SimBiology and data from published studies. Simulations were performed and results analyzed to determine steady state changes in ammonia levels resulting from varying dietary protein intake and varying liver enzyme activity levels to simulate liver disease. As a toxicity reference, viability was measured in SH-SY5Y neuroblastoma cells following differentiation and ammonium chloride treatment.

Results

Results from control simulations yielded steady state blood ammonia levels within normal physiological limits. Increasing dietary protein intake by 72% resulted in a 59% increase in blood ammonia levels. Simulations of liver cirrhosis increased blood ammonia levels by 41 to 130% depending upon the level of dietary protein intake. Simulations of heterozygous individuals carrying a loss of function allele of the urea cycle carbamoyl phosphate synthetase I (CPS1) gene resulted in more than a tripling of blood ammonia levels (from roughly 18 to 60 μM depending on dietary protein intake). The viability of differentiated SH-SY5Y cells was decreased by 14% by the addition of a slightly higher amount of ammonium chloride (90 μM).

Conclusions

Data from the model suggest decreasing protein consumption may be one simple strategy to decrease blood ammonia levels and minimize the risk of developing hepatic encephalopathy for many liver disease patients. In addition, the model suggests subjects who are known carriers of disease-causing CPS1 alleles may benefit from monitoring blood ammonia levels and limiting the level of protein intake if ammonia levels are high.

Electronic supplementary material

The online version of this article (10.1186/s12976-019-0109-1) contains supplementary material, which is available to authorized users.

Urea cycle disorders-update

The urea cycle is a metabolic pathway for the disposal of excess nitrogen, which arises primarily as ammonia. Nitrogen is essential for growth and life-maintenance, but excessive ammonia leads to life-threatening conditions. The urea cycle disorders (UCDs) comprise diseases presenting with hyperammonemia that arise in either the neonatal period (about 50% of cases) or later. Congenital defects of the enzymes or transporters of the urea cycle cause the disease. This cycle utilizes five enzymes, two of which, carbamoylphosphate synthetase 1 and ornithine transcarbamylase are present in the mitochondrial matrix, whereas the others (argininosuccinate synthetase, argininosuccinate lyase and arginase 1) are present in the cytoplasm. In addition, N-acetylglutamate synthase and at least two transporter proteins are essential to urea cycle function. Severity and age of onset depend on residual enzyme or transporter function and are related to the respective gene mutations. The strategy for therapy is to prevent the irreversible toxicity of high-ammonia exposure to the brain. The pathogenesis and natural course are poorly understood because of the rarity of the disease, so an international registry system and novel clinical trials are much needed. We review here the current concepts of the pathogenesis, diagnostics, including genetics and treatment of UCDs.

Evaluation of the efficacy of amplitude-integrated electroencephalography in the screening of newborns with metabolic disorder admitted to the NICU

Background

Neonate patients with metabolic disorder show encephalopathy and seizures that may lead to morbidity and mortality. Thus rapid detection and treatment of these patients is necessary. Although Amplitude-integrated electroencephalography (aEEG) has been used for more than a decade in the evaluation of infants with encephalopathy but has not been used in the assessment of neonates suffering from metabolic disorders. In this study, we tried to determine the efficacy of aEEG as an easily available diagnostic tool in the diagnosis of neonates with metabolic diseases.

Methods

All cases which admitted to the Neonatal Intensive Care Unit (NICU) of the Children’s Medical Center during a one-year period were enrolled. aEEG recordings were obtained by installing 4 electrodes on the infant’s head by a trained nurse and aEEG was recorded for at least 24 h with a description of the whole tracing. Clinical information, final outcome and questionnaires, including patient information: symptoms of the disease, gender, age, duration of hospitalization and the type of the metabolic disease were recorded in details. The obtained data was analyzed with the Spss24 software.

Results

Only 3 (two girl and one boy) out of 29 aEEGs recordings were abnormal; other patients showed normal aEEGs. The most common clinical and neurological manifestations were seizure (34.5%), hypotonia (31%), and mortality rate was 10.3%. There was no significant correlation between aEEG findings and gender, age, type of disease, laboratory tests findings and positive family history.

Conclusions

Although it has been shown that EEG has a diagnostic value in metabolic diseases, there has been no study on the efficacy of aEEG to evaluate neonates with metabolic diseases. But good accessibility and easy of working with aEEG, promote a tendency to use this procedure as screening tool for metabolic diseases.

The current study about aEEG monitoring in these patients, while limited, can be used as a pilot study for further research on this topic.

Therefore, a correct judgment in this field requires administration of aEEG on a larger population of neonates with metabolic diseases.

Brain and the Liver: Cerebral Edema, Hepatic Encephalopathy and Beyond

Occurrence of brain dysfunction is common in both chronic liver disease as well as acute liver failure. While brain dysfunction most commonly manifests as hepatic encephalopathy is chronic liver disease; devastating complications of cerebral edema and brain herniation syndromes may occur with acute liver failure. Ammonia seems to play a central role in the pathogenesis of brain dysfunction in both chronic liver disease and acute liver failure. In this chapter we outline the pathophysiology and clinical management of brain dysfunction in the critically ill patients with liver disease.

Rates and determinants of early initiation of breastfeeding and exclusive breast feeding at 42 days postnatal in six low and middle-income countries: A prospective cohort study

Background

Early initiation of breastfeeding after birth and exclusive breastfeeding through six months of age confers many health benefits for infants; both are crucial high impact, low-cost interventions. However, determining accurate global rates of these crucial activities has been challenging. We use population-based data to describe: (1) rates of early initiation of breastfeeding (defined as within 1 hour of birth) and of exclusive breastfeeding at 42 days post-partum; and (2) factors associated with failure to initiate early breastfeeding and exclusive breastfeeding at 42 days post-partum.

Methods

Prospectively collected data from women and their live-born infants enrolled in the Global Network’s Maternal and Newborn Health Registry between January 1, 2010-December 31, 2013 included women-infant dyads in 106 geographic areas (clusters) at 7 research sites in 6 countries (Kenya, Zambia, India [2 sites], Pakistan, Argentina and Guatemala). Rates and risk factors for failure to initiate early breastfeeding were investigated for the entire cohort and rates and risk factors for failure to maintain exclusive breastfeeding was assessed in a sub-sample studied at 42 days post-partum.

Result

A total of 255,495 live-born women-infant dyads were included in the study. Rates and determinants for the exclusive breastfeeding sub-study at 42 days post-partum were assessed from among a sub-sample of 105,563 subjects. Although there was heterogeneity by site, and early initiation of breastfeeding after delivery was high, the Pakistan site had the lowest rates of early initiation of breastfeeding. The Pakistan site also had the highest rate of lack of exclusive breastfeeding at 42 days post-partum. Across all regions, factors associated with failure to initiate early breastfeeding included nulliparity, caesarean section, low birth weight, resuscitation with bag and mask, and failure to place baby on the mother’s chest after delivery. Factors associated with failure to achieve exclusive breastfeeding at 42 days varied across the sites. The only factor significant in all sites was multiple gestation.

Conclusions

In this large, prospective, population-based, observational study, rates of both early initiation of breastfeeding and exclusive breastfeeding at 42 days post-partum were high, except in Pakistan. Factors associated with these key breastfeeding indicators should assist with more effective strategies to scale-up these crucial public health interventions.

Trial registration

Registration at the Clinicaltrials.gov website (ID# NCT01073475).

Who should we cool after perinatal asphyxia?

Three ongoing challenges have arisen after the introduction of therapeutic hypothermia (TH) as standard of care for term newborns with moderate or severe perinatal asphyxia: (i) to ensure that the correct group of infants are cooled; (ii) to optimize the delivery of TH and intensive care in relation to the severity of the encephalopathy; (iii) to systematically follow up the long-term efficacy of TH using comparable outcome data between centers and countries. This review addresses the entry criteria for TH, and discusses potential issues regarding patient selection, and management of TH: cooling mild, moderate, and very severe perinatal asphyxia, cooling longer or deeper, and/or starting with a greater delay. This includes cooling of patients outside of standard trial entry criteria, such as after postnatal collapse, premature infants, those with infection, and infants with metabolic, chromosomal or surgical diagnoses in addition to perinatal asphyxia.

Fatal hyperammonemia after repeat renal transplantation

A 35-year-old man had symptomatic hyperammonemia and normal liver function after repeat kidney transplantation. He presented with gastrointestinal symptoms, which quickly progressed to altered mental status. Therapy was instituted to clear the ammonia, but the ammonia level continued to rise. Eventually, the patient became unresponsive, and an emergent computed tomographic scan showed cerebral herniation. Urine acids and serum organic acids were not diagnostic of any urea cycle disorder. Histology did not reveal a clear etiology for the hyperammonemia.

High-volume hemofiltration in children with acute liver failure*

OBJECTIVES

High-volume hemofiltration has shown beneficial effects in severe sepsis and multiple organ failure, improving hemodynamics and fluid balance. Recent studies suggest that acute liver failure shares many pathophysiologic similarities with sepsis. Therefore, we assessed the systemic effects of high-volume hemofiltration in children with acute liver failure.

DESIGN

Retrospective observational cohort study.

PATIENTS

Twenty-two children.

SETTING

Forty-two-bed multidisciplinary pediatric and neonatal ICUs in a tertiary university hospital.

INTERVENTION

We evaluated high-volume hemofiltration therapy as part of standard management of 22 children admitted in our unit for acute liver failure. Fifteen patients had fulminant hepatic failure, three had acute-on-chronic liver disease, and four had primary nonfunction. High-volume hemofiltration was initiated in patients requiring emergency liver transplantation and when hepatic encephalopathy grade higher than 2 and/or hemodynamic instability requiring vasopressors occurred. High-volume hemofiltration was defined by a flow of ultrafiltrate of more than 80 mL/kg/hr. Clinical and biological variables were assessed before and 24 and 48 hours after initiation of high-volume hemofiltration therapy.

MEASUREMENTS AND MAIN RESULTS

High-volume hemofiltration was initiated with a median grade III of hepatic encephalopathy. The median flow of ultrafiltrate was 119 mL/kg/hr (range, 80-384). After 24 hours of high-volume hemofiltration treatment, we observed an increase in mean arterial pressure (p = 0.0002) and a decrease in serum creatinine (p = 0.0002). In half of the patients, the encephalopathy grade decreased. After 48 hours of treatment, mean arterial pressure (p = 0.0005), grade of hepatic encephalopathy (p = 0.04), and serum creatinine (p = 0.0002) improved. Overall mortality was 45.4% (n = 10). Emergency liver transplantation was performed in eight children. Five patients spontaneously recovered liver function.

CONCLUSIONS

High-volume hemofiltration therapy significantly improves hemodynamic stability and neurological status in children with acute liver failure awaiting for emergency liver transplantation.

Late-onset ornithine transcarbamylase deficiency: treatment and outcome of hyperammonemic crisis

Hyperammonemic crises in ornithine transcarbamylase deficiency (OTC) can be associated with devastating cerebral edema resulting in severe long-term neurologic impairment and death. We present an 8-year-old boy who had late-onset OTC deficiency in which early and aggressive management of hyperammonemia and associated cerebral edema, including therapeutic hypothermia and barbiturate-induced coma, resulted in favorable neurologic outcome. Our patient presented with vomiting and altered mental status, and was found to have a significantly elevated serum ammonia level of 1561 μmol/L. Hyperammonemia was managed with hemodialysis, 10% sodium phenylacetate, 10% sodium benzoate, L-arginine, intravenous 10% dextrose, intralipids, and protein restriction. He developed significant cerebral edema with intracranial pressures >20 mm Hg, requiring treatment with 3% saline and mannitol. Despite this treatment our patient continued to have elevated intracranial pressures, which were treated aggressively with non-conventional modalities including therapeutic hypothermia, barbiturate-induced coma, and external ventricular drainage. This therapy resulted in stabilization of hyperammonemia and resolution of cerebral edema. Molecular testing later revealed a hemizygous mutation within the OTC gene. Neuropsychological testing 1 year after discharge showed normal intelligence with no visual-motor deficits, minor deficits in working memory and processing speed, and slightly below average processing speed and executive functioning.

Feasibility of adjunct therapeutic hypothermia treatment for hyperammonemia and encephalopathy due to urea cycle disorders and organic acidemias

BACKGROUND

Children with urea cycle disorders (UCDs) or organic acidemias (OAs) and acute hyperammonemia and encephalopathy are at great risk for neurological injury, developmental delay, intellectual disability, and death. Nutritional support, intravenous alternative pathway therapy, and dialysis are used to treat severe hyperammonemia associated with UCDs and nutritional support and dialysis are used to treat severe hyperammonemia in OAs. Brain protective treatment while therapy is initiated may improve neurological and cognitive function for the lifetime of the child. Animal experiments and small clinical trials in hepatic encephalopathy caused by acute liver failure suggest that therapeutic hypothermia provides neuroprotection in hyperammonemia associated encephalopathy. We report results of an ongoing pilot study that assesses if whole body cooling during rescue treatment of neonates with acute hyperammonemia and encephalopathy is feasible and can be conducted safely.

METHODS

Adjunct whole body therapeutic hypothermia was conducted in addition to standard treatment in acutely encephalopathic, hyperammonemic neonates with UCDs and OAs requiring dialysis. Therapeutic hypothermia was initiated using cooling blankets as preparations for dialysis were underway. Similar to standard therapeutic hypothermia treatment for neonatal hypoxic ischemic encephalopathy, patients were maintained at 33.5°C±1°C for 72h, they were then slowly rewarmed by 0.5°C every 3h over 18h. In addition data of age-matched historic controls were collected for comparison.

RESULTS

Seven patients were cooled using the pilot study protocol and data of seven historic controls were reviewed. All seven patients survived the initial rescue and cooling treatment, 6 patients were discharged home 2-4weeks after hospitalization, five of them feeding orally. The main complication observed in a majority of patients was hypotension.

CONCLUSION

Adjunct therapeutic hypothermia for neonates with UCDs and OAs receiving standard treatment was feasible and could be conducted safely in pediatric and neonatal intensive care units experienced in the application of therapeutic hypothermia in critically ill neonates. However, including adjunct therapeutic hypothermia in the already involved treatment regimen of critically ill patients with hyperammonemia and encephalopathy adds to the complexity of care and should not be done unless it is proven efficacious in a randomized clinical trial.

Suggested guidelines for the diagnosis and management of urea cycle disorders

Urea cycle disorders (UCDs) are inborn errors of ammonia detoxification/arginine synthesis due to defects affecting the catalysts of the Krebs-Henseleit cycle (five core enzymes, one activating enzyme and one mitochondrial ornithine/citrulline antiporter) with an estimated incidence of 1:8.000. Patients present with hyperammonemia either shortly after birth (~50%) or, later at any age, leading to death or to severe neurological handicap in many survivors. Despite the existence of effective therapy with alternative pathway therapy and liver transplantation, outcomes remain poor. This may be related to underrecognition and delayed diagnosis due to the nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity. These guidelines aim at providing a trans-European consensus to: guide practitioners, set standards of care and help awareness campaigns. To achieve these goals, the guidelines were developed using a Delphi methodology, by having professionals on UCDs across seven European countries to gather all the existing evidence, score it according to the SIGN evidence level system and draw a series of statements supported by an associated level of evidence. The guidelines were revised by external specialist consultants, unrelated authorities in the field of UCDs and practicing pediatricians in training. Although the evidence degree did hardly ever exceed level C (evidence from non-analytical studies like case reports and series), it was sufficient to guide practice on both acute and chronic presentations, address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Also, it identified knowledge voids that must be filled by future research. We believe these guidelines will help to: harmonise practice, set common standards and spread good practices with a positive impact on the outcomes of UCD patients.

Amplitude-integrated electroencephalography in newborns with inborn errors of metabolism

BACKGROUND

The utility of amplitude-integrated electroencephalography (aEEG) monitoring has been established for patients with neonatal hypoxic-ischemic encephalopathy.

OBJECTIVE

To evaluate the role of aEEG in the diagnostic process and treatment of patients with encephalopathy due to inborn errors of metabolism.

METHODS

Cases collected through an international registry were divided into 5 groups of metabolic disorders. Common aEEG features were sought for each group.

RESULTS

In total, 21/30 (70%) cases had abnormal aEEG background patterns, 18/30 (60%) showed seizure activity. Patients with disorders of energy metabolism, hyperammonemia, and organic/amino acidopathies often showed marked aEEG depression with seizure activity. In contrast, aEEGs of patients with peroxisomal disorders did not show major background abnormalities but seizures were present in 5/6 subjects. We report two features of interest: firstly, two tracings displayed an unusual upward shift of the lower aEEG amplitude margin. Secondly, aEEGs of infants with non-ketotic hyperglycinemia showed a pattern we refer to as 'high-frequency burst-suppression pattern'.

CONCLUSIONS

aEEG in patients with inborn errors of metabolism frequently reveals abnormalities and assists clinicians in the clinical assessment, management and monitoring of these patients.

Favorable long-term outcome following severe neonatal hyperammonemic coma in a patient with argininosuccinate synthetase deficiency

This chapter reports on the sequelae-free 8-year follow-up with normal growth, intellectual development, and schooling of a boy with argininosuccinate synthetase deficiency (citrullinemia type I) who was rescued from severe neonatal hyperammonemic coma at 8 days of life (peak ammonia level of 1,058 μmol/L). Important clinical management aspects were: rapidity of response to emergency therapeutic measures that included specific drug regimen, protein restriction, optimal caloric intake and hemodialysis, short coma duration (14 h), possible neuroprotective effect of mild systemic hypothermia during the acute episode, long-term metabolic control with strict compliance to standard of care therapeutic and dietary regimens, active prevention of subsequent hyperammonemic episodes, and early neurodevelopmental evaluations and interventions. We conclude that good long-term neurological outcome following rescue from neonatal hyperammonemic coma is rarely reported but attainable. Prospective registries and interventional studies regrouping clinical data from urea cycle disorders patients will assist clinicians in instituting the appropriate therapeutic measures to provide the best prospect of positive long-term outcome for these children.

Clinical practice: the management of hyperammonemia

Hyperammonemia is a life-threatening condition which can affect patients at any age. Elevations of ammonia in plasma indicate its increased production and/or decreased detoxification. The hepatic urea cycle is the main pathway to detoxify ammonia; it can be defective due to an inherited enzyme deficiency or secondary to accumulated toxic metabolites or substrate depletion. Clinical signs and symptoms in hyperammonemia are unspecific but they are mostly neurological. Thus, in any unexplained change in consciousness or in any unexplained encephalopathy, hyperammonemia must be excluded as fast as possible. Any delay in recognition and start of treatment of hyperammonemia may have deleterious consequences for the patient. Treatment largely depends on the underlying cause but is, at least in pediatric patients, mainly aimed at establishing anabolism to avoid endogenous protein breakdown and amino acid imbalances. In addition, pharmacological treatment options exist to improve urea cycle function or to remove nitrogen, but their use depend on the underlying disorder. To improve the prognosis of acute hyperammonemia, an increased awareness of this condition is probably more needed than anything else. Likewise, the immediate start of appropriate therapy is of utmost importance. This review focuses on a better understanding of factors leading to ammonia elevations and on practical aspects related to diagnosis and treatment in order to improve clinical management of hyperammonemia.

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.

Use of amplitude integrated electroencephalography (aEEG) in patients with inborn errors of metabolism - a new tool for the metabolic geneticist

Patients with metabolic disorders often, especially as newborns, present with encephalopathy and seizures, frequently requiring intensive care during metabolic crises. Cerebral function monitoring using amplitude integrated electroencephalography (aEEG) can be utilized to supplement clinical assessment and other monitoring already in use in the intensive care setting. In this technique, a one or two-channel EEG tracing is obtained, processed, compressed and displayed. Use of aEEG is well established in evaluation and treatment of newborns with hypoxic ischemic encephalopathy. The basis of aEEG interpretation is the recognition of patterns which have been defined for different degrees of encephalopathy. Seizures are identified on the compressed tracing in combination with analysis of the corresponding raw EEG tracing. This review discusses the experience, although limited at this time, with use of aEEG in infants with inborn errors of metabolism. Through an international collaborative, the International Registry for Cerebral Function Monitoring in Patients with Genetics Disorders and Brain Malformations, aEEG tracings of patients with inborn errors of metabolism were collected. The features of 25 traces are included in this review. This collection includes patients with hyperammonemia (HA, n=4), disorders of energy metabolism (DEM, n=9), disorders of amino and organic acid metabolism (DAOAM, n=7), and peroxisomal disorders (PD, n=5). Fifteen of 25 patients demonstrated encephalopathic changes, including patients with HA, DEM and DAOAM, but not PD. In 15 of 25 patients seizure potentials were identified. In HA, DEM, and DAOAM both encephalopathy and seizures may coincide, while in peroxisomal disorders seizures were seen without background patterns indicating encephalopathy, likely due to neuronal migration defects as the underlying cause. The current experience with the use of aEEG in these patients, while limited, indicates that cerebral function monitoring techniques have a role in treatment of patients with metabolic disorders, especially during metabolic crises. Use of aEEG in this patient group is encouraged if locally available, and collaborative efforts to collect data on aEEG use in patients with metabolic disorders are encouraged to further define the scope and utility of this procedure.

Ammonia toxicity and its prevention in inherited defects of the urea cycle

The urea cycle is the final pathway for removal of surplus nitrogen from the body, and the major route in humans for detoxification of ammonia. The full complement of enzymes is expressed only in liver. Inherited deficiencies of urea cycle enzymes lead to hyperammonaemia, which causes brain damage. Severe defects present with hyperammonaemic crises in neonates. Equally devastating episodes may occur in previously asymptomatic adults with mild defects, most often X-linked ornithine transcarbamylase (OTC) deficiency. Several mechanisms probably contribute to pathogenesis. Treatment aims to reduce plasma ammonia quickly, reduce production of waste nitrogen, dispose of waste nitrogen using alternative pathways to the urea cycle and replace arginine. These therapies have increased survival and probably improve the neurological outcome. Arginine, sodium benzoate, sodium phenylbutyrate and, less often, sodium phenylacetate are used. Long-term correction is achieved by liver transplantation. Gene therapy for OTC deficiency is effective in animals, and work is ongoing to improve persistence and safety.

Therapeutic hypothermia for acute liver failure

Cerebral edema is a potentially life-threatening complication of acute liver failure, the syndrome of abrupt loss of liver function in a patient with a previously healthy liver. Although the prevalence of cerebral edema appears to be decreasing, patients with rapidly progressive (hyperacute) liver failure, such as after acetaminophen overdose, remain at highest risk. In severe cases of cerebral edema, intracranial hypertension develops and leads to brain death after brainstem herniation or to anoxic brain injury and permanent neurologic impairment. Intracranial hypertension in patients with acute liver failure often can be temporarily controlled by manipulating body position, increasing the degree of sedation, and increasing blood osmolarity through pharmacologic means. However, these maneuvers often postpone, but do not eliminate, the risk of brainstem herniation unless orthotopic liver transplantation or spontaneous liver regeneration follows in short order. To buy time, the induction of therapeutic hypothermia (core temperature 32 degrees C-35 degrees C) has been shown to effectively bridge patients to transplant. Similar to the experience in patients with cerebral edema after other neurologic insults, hypothermia reduces cerebral edema and intracranial hypertension in patients with acute liver failure by decreasing splanchnic ammonia production, restoring normal regulation of cerebral hemodynamics, and lowering oxidative metabolism within the brain. Hypothermia may also ameliorate the degree of liver injury. Hypothermia has not been adequately studied for its safety and theoretically may increase the risk of infection, cardiac dysrhythmias, and bleeding, all complications independently associated with acute liver failure. Therefore, although an ample body of experimental and human data provides a rationale for the use of therapeutic hypothermia in patients with acute liver failure, multicenter, randomized, controlled clinical trials are needed to confirm that hypothermia secures brain viability and improves survival without causing harm.

Induced hypothermia for infants with hypoxic- ischemic encephalopathy using a servo-controlled fan: an exploratory pilot study

OBJECTIVE

Several trials suggest that hypothermia is beneficial in selected infants with hypoxic-ischemic encephalopathy. However, the cooling methods used required repeated interventions and were either expensive or reported significant temperature variation. The objective of this pilot study was to describe the use, efficacy, and physiologic impact of an inexpensive servo-controlled cooling fan blowing room-temperature air.

PATIENTS AND METHODS

A servo-controlled fan was manufactured and used to cool 10 infants with hypoxic-ischemic encephalopathy to a rectal temperature of 33 degrees C to 34 degrees C. The infants were sedated with phenobarbital, but clonidine was administered to some infants if shivering or discomfort occurred. A servo-controlled radiant warmer was used simultaneously with the fan to prevent overcooling. The settings used on the fan and radiant warmer differed slightly between some infants as the technique evolved.

RESULTS

A rectal temperature of 34 degrees C was achieved in a median time of 58 minutes. Overcooling did not occur, and the mean temperature during cooling was 33.6 degrees C +/- 0.2 degrees C. Inspired oxygen requirements increased in 6 infants, and 5 infants required inotropic support during cooling, but this was progressively reduced after 1 to 2 days. Dehydration did not occur. Five infants shivered when faster fan speeds were used, but 4 of the 5 infants had hypomagnesemia. Shivering was controlled with clonidine in 4 infants, but 1 infant required morphine.

CONCLUSIONS

Servo-controlled fan cooling with room-temperature air, combined with servo-controlled radiant warming, was an effective, simple, and safe method of inducing and maintaining rectal temperatures of 33 degrees C to 34 degrees C in sedated infants with hypoxic-ischemic encephalopathy. After induction of hypothermia, a low fan speed facilitated accurate temperature control, and warmer-controlled rewarming at 0.2 degrees C increments every 30 minutes resulted in more appropriate rewarming than when 0.5 degrees C increments every hour were used.

Neurologic damage and neurocognitive dysfunction in urea cycle disorders

Although the survival of patients who have urea cycle disorders has improved with the use of modalities such as alternative pathway therapy and hemodialysis, neurologic outcome is suboptimal. Patients often manifest with a variety of neurologic abnormalities, including cerebral edema, seizures, cognitive impairment, and psychiatric illness. Current hypotheses of the pathogenesis underlying brain dysfunction in these patients have focused on several lines of investigation, including the role of glutamine in causing cerebral edema, mitochondrial dysfunction leading to energy failure and the production of free radicals, and altered neurotransmitter metabolism. Advances in understanding the pathogenetic mechanisms underlying brain impairment in urea cycle disorders may lead to the development of therapies designed to interfere with the molecular cascade that ultimately leads to cerebral edema and other brain pathological findings.

Hypothesis: proposals for the management of a neonate at risk of hyperammonaemia due to a urea cycle disorder

It is difficult to prevent hyperammonaemia in patients with urea cycle disorders that present in the newborn period. This is true, even if treatment is started prospectively because of an affected relative. We propose several additional measures that could be used in conjunction with conventional therapy to improve the metabolic control. Catabolism could be reduced by delivering the babies by elective caesarean section, by starting intravenous glucose immediately after delivery and, possibly, by using beta-blockers or octreotide and insulin. The effectiveness of sodium benzoate and sodium phenylbutyrate might be increased by giving phenobarbital to the mother before delivery and subsequently to the baby to induce the enzymes for conjugation. We would expect the proposed measures to reduce the risk of hyperammonaemia and to improve the outcome for these patients. They have not, however, previously been used in this context, so families would need to be counselled carefully and controlled studies should be undertaken.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

The use Prometheus FPSA system in the treatment of acute liver failure: preliminary results

The preliminary outcomes of patients with acute liver failure treated with the Prometheus Fractionated Plasma Separation and Absorption (FPSA) system are presented herein.

PATIENTS AND METHODS

The procedures were performed in 13 patients (4, intoxication by Amanita phalloides; 4, unknown reason; 3, acetaminophen intoxication; 1, Wilson disease, and 1, liver insufficiency after hemihepatectomy owing to metastases of colon adenocarcinoma). The patients were qualified for the procedure according to the King's College Hospital criteria. The patients' general status was assessed on basic of GCS, UNOS, and the 4-grade encephalopathy classifications. The procedures were performed with the Prometheus 4008H Fresenius Medical Care unit.

RESULTS

The 29 procedures were of mean duration 6.5 hours. There were statistically significant reductions in total bilirubin, ammonia, and aminotransferase levels. In addition, the procedures corrected water, mineral, and carbohydrate disorders. One patient did not require liver transplantation. Seven patients received liver transplants: three patients with positive outcomes; two died due to septicemia within 30 days perioperatively, one died at 6 months after OLT owing to respiratory failure; and one, owing to hemorrhagic diathesis. Four patients did not receive a liver transplant because of lack of a organ, no consent for the surgery, or neoplastic disease with metastases.

CONCLUSIONS

The Prometheus FPSA-System was an effective detoxication method for patients with acute liver failure. The system was useful as a symptomatic treatment before liver transplantation allowing a longer wait for a graft.

Keeping cool in acute liver failure: rationale for the use of mild hypothermia

Encephalopathy, brain edema and intracranial hypertension are neurological complications responsible for substantial morbidity/mortality in patients with acute liver failure (ALF), where, aside from liver transplantation, there is currently a paucity of effective therapies. Mirroring its cerebro-protective effects in other clinical conditions, the induction of mild hypothermia may provide a potential therapeutic approach to the management of ALF. A solid mechanistic rationale for the use of mild hypothermia is provided by clinical and experimental studies showing its beneficial effects in relation to many of the key factors that determine the development of brain edema and intracranial hypertension in ALF, namely the delivery of ammonia to the brain, the disturbances of brain organic osmolytes and brain extracellular amino acids, cerebro-vascular haemodynamics, brain glucose metabolism, inflammation, subclinical seizure activity and alterations of gene expression. Initial uncontrolled clinical studies of mild hypothermia in patients with ALF suggest that it is an effective, feasible and safe approach. Randomized controlled clinical trials are now needed to adequately assess its efficacy, safety, clinical impact on global outcomes and to provide the guidelines for its use in ALF.

Fulminant hepatic failure

The rare but potentially devastating clinical syndrome of fulminant hepatic failure has as its components severe encephalopathy and finally cerebral edema, hemodynamic instability, renal failure, coagulopathy, profound metabolic disturbances and a particular susceptibility to bacterial and fungal infection. Despite advances in medical management, fulminant hepatic failure in its most severe form carries a high mortality rate unless urgent orthotopic liver transplantation is carried out. However, availability of cadaveric donor organs is limited and, due to the rapidly progressive clinical course in many cases, a substantial proportion of patients will die or develop contraindications to transplantation before the procedure can be performed. Consequently, recent interest has centred on living donor transplantation and the possibility of providing temporary liver support, either through auxiliary partial organ transplantation, extracorporeal perfusion or transplantation of hepatocytes, to allow time for either a liver graft to become available or native liver regeneration, on which spontaneous survival ultimately depends, to occur.

Mild hypothermia for acute liver failure: a review of mechanisms of action

Brain edema with intracranial hypertension is a major complication in patients with acute liver failure. Current therapies for this complication include a variety of pharmacologic and interventional measures, some of which are frequently associated with adverse effects or contraindications. Even though these measures usually allow the control of intracranial hypertension for a certain period of time, recurrence is common. New therapies are therefore needed. Increasing clinical and experimental evidence suggests that induction of mild hypothermia (32 degrees C-35 degrees C) may be a therapeutic alternative. Similar to traumatic brain injury or brain stroke, induction of mild hypothermia seems highly effective to reduce intracranial pressure in patients with acute liver failure. Several mechanisms by which mild hypothermia may prevent brain edema and intracranial hypertension in this condition have been disclosed and may include beneficial effects on ammonia metabolism, as well as on the disturbances of brain osmolarity, cerebrovascular hemodynamics, brain glucose metabolism, inflammation, and others. Improvement of systemic hemodynamics and amelioration of liver injury may be other benefits of the systemic induction of mild hypothermia, but the impact of potential adverse events, such as infection, should also be taken into account. At a time when mild hypothermia is increasingly used in several specialized centers, performance of a randomized controlled trial seems critical to confirm the benefits of mild hypothermia in acute liver failure and to provide adequate guidelines for its use.

Acute liver failure

Acute liver failure is a rare and life-threatening clinical syndrome following severe hepatic injury. Depending on the rapidity of its development, two distinct complications contribute to a high mortality: in hyperacute liver failure, rapid development of massive hepatic necrosis and apoptosis gives rise to severe hyperammonemia, hepatic encephalopathy and life-threatening cerebral edema. The high risk of cerebral herniation requires early listing for emergency liver transplantation. Patients with hyperacute liver failure surviving the initial episode of cerebral edema have a substantial potential for hepatic recovery. If progressive hepatic failure develops more slowly, astrocytic osmoregulation prevents cerebral herniation in most instances. Unfortunately, these patients have a small potential of hepatic regeneration and transplantation should be performed before renal failure, sepsis or multiorgan failure emerge. Experimental treatment methods including detoxification by artificial or bioartificial liver support or by stimulating hepatic regeneration are currently evaluated. Recognition of ammonia toxicity has stimulated the search for early ammonia-lowering strategies and strongly renewed the interest in dialytic therapies. Anti-apoptotic interventions are among the most promising pharmacological options for the near future.

Blood-brain barrier permeability to ammonia in liver failure: a critical reappraisal

In patients with acute liver failure (ALF), hyperammonemia is related to development of cerebral edema and herniation. The present review discusses the mechanisms for the cerebral uptake of ammonia. A mathematical framework is provided to allow a quantitative examination of whether published studies can be explained by the conventional view that cerebral uptake of ammonia is restricted to diffusion of the unprotonated form (NH(3)) (the diffusion hypothesis). An increase in cerebral blood flow (CBF) enhanced ammonia uptake more than expected, possibly due to recruitment or heterogeneity of brain capillaries. Reported effects of pH on ammonia uptake were in the direction predicted by the diffusion hypothesis, but often less pronounced than expected. The published effects of mannitol, cooling, and indomethacin in experimental animals and patients were difficult to explain by the diffusion hypothesis alone, unless dramatic changes of capillary surface area or permeability for ammonia were induced. Therefore we considered the possible role of membrane protein mediated transport of NH(4)(+) across the blood-brain barrier (BBB). Early tracer studies in Rhesus monkeys suggested that NH(4)(+) is responsible for 20% or even more of the transport of ammonia from plasma to brain. In other locations, such as in the thick ascending limb of Hendle's loop and in isolated astrocytes, transport protein mediated translocation of NH(4)(+) is predominant. Many of the ion-transporters involved in renal NH(4)(+) reabsorbtion are also present in brain capillary membranes and could mediate uptake of NH(4)(+). Astrocytic uptake of NH(4)(+) is associated with increased extracellular K(+), which is a potent cerebral vasodilator. Such interference between transport of NH(4)(+) and other cations could be clinically important because increased cerebral blood flow often precedes cerebral herniation in acute liver failure. We suggest that protein mediated transport of NH(4)(+) through the brain capillary wall is a realistic possibility that should be more intensely studied.

Successful treatment of refractory cerebral oedema in ecstasy/cocaine-induced fulminant hepatic failure using a new high-efficacy liver detoxification device (FPSA-Prometheus)

Ecstasy-induced fulminant hepatic failure is associated with high mortality. If complicated by cerebral oedema, orthotopic liver transplantation is the only established treatment. We report a case of combined ecstasy/cocaine-induced fulminant hepatic failure presenting with severe rhabdomyolysis, myocardial infarction and multiorgan failure. Transplantation was declined by the transplant surgeons because of a history of intravenous drug abuse. As excessive hyperammonaemia (318 mumol/l) and refractory transtentorial herniation developed, treatment with a new liver detoxification device combining high-flux haemodialysis and adsorption (FPSA-Prometheus) was initiated. Within a few hours of treatment, ammonia levels normalised. Cerebral oedema was greatly reduced by day 4 and hepatic function gradually recovered. Following neurologic rehabilitation for ischaemic sequelae of herniation, the patient was discharged from hospital with only minimal deficits. In conclusion, efficient extracorporeal detoxification may be an option for reversal of hyperammonaemia and refractory cerebral oedema in ecstasy/cocaine-induced acute liver failure.

Extracorporeal treatment in fulminant hepatic failure: pathophysiologic considerations

Fulminant hepatic failure is a life-threatening clinical syndrome following severe hepatic injury leading to cerebral edema and brainstem herniation. Excessive mortality can be currently reduced only by timely orthotopic liver transplantation. Due to the shortage of donor organs, a considerable proportion of patients develop irreversible neurological damage, multiorgan failure or death while waiting for transplantation. Consequently, alternatives to orthotopic liver transplantation and methods of stabilizing patients on the waiting list including extracorporeal detoxification treatment are currently investigated. Recent advances in the pathophysiology of cerebral edema have challenged some of the traditional assumptions on which many blood detoxification systems are based. This article aims to integrate pathophysiology of hepatic encephalopathy and cerebral edema into a proposed future concept of liver support.

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.