Determinants of ammonia clearance by hemodialysis

Quantitative systems pharmacology Model to characterize valproic acid-induced hyperammonemia and the effect of L-carnitine supplementation

Valproic acid (VPA) is a short-chain fatty acid widely prescribed in the treatment of seizure disorders and epilepsy syndromes, although its therapeutic value may be undermined by its toxicity. VPA serious adverse effects are reported to have a significant and dose-dependent incidence, many associated with VPA-induced hyperammonemia. This effect has been linked with reduced levels of carnitine; an endogenous compound involved in fatty acid's mitochondrial β-oxidation by facilitation of its entrance via the carnitine shuttle. High exposure to VPA can lead to carnitine depletion causing a misbalance between the intra-mitochondrial β-oxidation and the microsomal ω-oxidation, a pathway that produces toxic metabolites such as 4-en-VPA which inhibits ammonia elimination. Moreover, a reduction in carnitine levels might be also related to VPA-induced obesity and lipids disorder. In turn, L-carnitine supplementation (CS) has been recommended and empirically used to reduce VPA's hepatotoxicity. The aim of this work was to develop a Quantitative Systems Pharmacology (QSP) model to characterize VPA-induced hyperammonemia and evaluate the benefits of CS in preventing hyperammonemia under both chronic treatment and after VPA overdosing. The QSP model included a VPA population pharmacokinetics model that allowed the prediction of total and unbound concentrations after single and multiple oral doses considering its saturable binding to plasma proteins. Predictions of time courses for 2-en-VPA, 4-en-DPA, VPA-glucuronide, carnitine, ammonia and urea levels, and for the relative change in fatty acids, Acetyl-CoA, and glutamate reflected the VPA induced changes and the efficacy of the treatment with L-carnitine. The QSP model was implemented to give a rational basis for the L-carnitine dose selection to optimize CS depending on VPA dosage regime and to assess the currently recommended L-carnitine rescue therapy after VPA overdosing. Results show that a L-carnitine dose equal to the double of the VPA dose using the same interdose interval would maintain the ammonia levels at baseline. The QSP model may be expanded in the future to describe other adverse events linked to VPA-induced changes in endogenous compounds.

Management of Acute Liver Failure: Update 2022

Abbreviated pathogenesis and clinical course of the acute liver failure syndrome. The pathogenesis and clinical course of the syndrome of acute liver failure (ALF) differs depending upon the etiology of the primary liver injury. In turn, the severity of the liver injury and resulting synthetic failure is often the primary determinant of whether a patient is referred for emergency liver transplantation. Injuries by viral etiologies trigger the innate immune system via pathogen-associated molecular patterns (PAMPs), while toxin-induced (and presumably ischemia-induced) injuries do so via damage-associated molecular patterns (DAMPs). The course of the clinical syndrome further depends upon the relative intensity and composition of cytokine release, resulting in an early proinflammatory phenotype (SIRS) and later compensatory anti-inflammatory response phenotype (CARS). The outcomes of overwhelming immune activation are the systemic (extrahepatic) features of ALF (cardiovascular collapse, cerebral edema, acute kidney injury, respiratory failure, sepsis) which ultimately determine the likelihood of death.Acute liver failure (ALF) continues to carry a high risk of mortality or the need for transplantation despite recent improvements in overall outcomes over the past two decades. Optimal management begins with identifying that liver failure is indeed present and its etiology, since outcomes and the need for transplantation vary widely across the different etiologies. Most causes of ALF can be divided into hyperacute (ischemia and acetaminophen) and subacute types (other etiologies), based on time of evolution of signs and symptoms of liver failure; the former evolve in 3 to 4 days and the latter typically in 2 to 4 weeks. Both involve intense release of cytokines and hepatocellular contents into the circulation with multiorgan effects/consequences.Management involves optimizing fluid balance and cardiovascular support, including the use of continuous renal replacement therapy, vasopressors, and pulmonary ventilation. Early evaluation for liver transplantation is advised particularly for acetaminophen toxicity, which evolves so rapidly that delay is likely to lead to death.Vasopressor support, high-grade hepatic encephalopathy, and unfavorable (subacute) etiologies heighten the need for urgent listing for liver transplantation. Prognostic scores such as Kings Criteria, Model for End-Stage Liver Disease, and the Acute Liver Failure Group prognostic index take these features into account and provide reasonable but imperfect predictive accuracy. Future treatments may include liver support devices and/or agents that improve hepatocyte regeneration.

Management of late onset urea cycle disorders-a remaining challenge for the intensivist?

Background

Hyperammonemia caused by a disorder of the urea cycle is a rare cause of metabolic encephalopathy that may be underdiagnosed by the adult intensivists because of its rarity. Urea cycle disorders are autosomal recessive diseases except for ornithine transcarbamylase deficiency (OTCD) that is X-linked. Optimal treatment is crucial to improve prognosis.

Main body

We systematically reviewed cases reported in the literature on hyperammonemia in adulthood. We used the US National Library of Medicine Pubmed search engine since 2009. The two main causes are ornithine transcarbamylase deficiency followed by type II citrullinemia. Diagnosis by the intensivist remains very challenging therefore delaying treatment and putting patients at risk of fatal cerebral edema. Treatment consists in adapted nutrition, scavenging agents and dialysis. As adults are more susceptible to hyperammonemia, emergent hemodialysis is mandatory before referral to a reference center if ammonia levels are above 200 µmol/l as the risk of cerebral edema is then above 55%. Definitive therapy in urea cycle abnormalities is liver transplantation.

Conclusion

Awareness of urea cycle disorders in adults intensive care units can optimize early management and accordingly dramatically improve prognosis. By preventing hyperammonemia to induce brain edema and herniation leading to death.

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.

Is renal replacement therapy necessary in deceased donor liver transplantation candidates with hepatorenal syndrome?: a 2-year experience at a high-volume center

Purpose

Hepatorenal syndrome (HRS) is a fatal complication in patients with end-stage liver disease awaiting liver transplantation (LT). HRS often develops in patients with high model for end-stage liver disease (MELD) score. This study investigated the outcomes of peritransplant management of HRS in a high-volume LT center in Korea for 2 years.

Methods

A total of 157 recipients that deceased donor liver transplantation (DDLT) from January 2017 to December 2018 were included. In-hospital mortality (IHM) was analyzed in relation to pre- and posttransplant application of renal replacement therapy (RRT).

Results

Primary diagnoses for DDLT were alcoholic liver disease (n = 61), HBV-associated liver cirrhosis (n = 48), retransplantation for chronic graft failure (n = 24), and others (n = 24). Mean MELD score was 34.6 ± 6.2 with 72 patients at Korean Network for Organ Sharing MELD status 2 (45.9%), 43 at status 3 (27.4%), 36 at status 4 (22.9%), and 6 at status 5 (3.8%). Pretransplant RRT was performed in 16 patients (10.2%) that did not show IHM. Posttransplant RRT was performed in 69 patients (44.0%), for whom IHM incidence was 15.9%. In 53 patients that had undergone de novo posttransplant RRT, IHM incidence increased to 20.8%. IHM in the 88 patients not requiring RRT was 2.3%.

Conclusion

The majority of adult DDLT recipients in Korean MELD score-based allocation system have very high MELD scores, which is often associated with HRS. Pretransplant RRT appears to improve posttransplant survival outcomes. We thereby recommend that, if indicated, pretransplant RRT be performed while awaiting DDLT.

Correction and Control of Hyperammonemia in Acute Liver Failure: The Impact of Continuous Renal Replacement Timing, Intensity, and Duration

OBJECTIVES

Hyperammonemia is a key contributing factor for cerebral edema in acute liver failure. Continuous renal replacement therapy may help reduce ammonia levels. However, the optimal timing, mode, intensity, and duration of continuous renal replacement therapy in this setting are unknown. We aimed to study continuous renal replacement therapy use in acute liver failure patients and to assess its impact on hyperammonemia.

DESIGN

Retrospective observational study.

SETTING

ICU within a specialized liver transplant hospital.

PATIENTS

Fifty-four patients with acute liver failure.

INTERVENTIONS

Data were obtained from medical records and analyzed for patient characteristics, continuous renal replacement therapy use, ammonia dynamics, and outcomes.

MAIN RESULTS

Forty-five patients (83%) had high grade encephalopathy. Median time to continuous renal replacement therapy commencement was 4 hours (interquartile range, 2-4.5) with 35 (78%) treated with continuous venovenous hemodiafiltration and 10 (22%) with continuous venovenous hemofiltration. Median hourly effluent flow rate was 43 mL/kg (interquartile range, 37-62). The median ammonia concentration decreased every day during treatment from 151 µmol/L (interquartile range, 110-204) to 107 µmol/L (interquartile range, 84-133) on day 2, 75 µmol/L (interquartile range, 63-95) on day 3, and 52 µmol/L (interquartile range, 42-70) (p < 0.0001) on day 5. The number of patients with an ammonia level greater than 150 µmol/L decreased on the same days from 26, to nine, then two, and finally none. Reductions in ammonia levels correlated best with the cumulative duration of therapy hours (p = 0.03), rather than hourly treatment intensity.

CONCLUSIONS

Continuous renal replacement therapy is associated with reduced ammonia concentrations in acute liver failure patients. This effect is related to greater cumulative dose. These findings suggest that continuous renal replacement therapy initiated early and continued or longer may represent a useful approach to hyperammonemia control in acute liver failure patients.

Pathophysiology and Management of Hyperammonemia in Organ Transplant Patients

Neurologic complications are common after solid-organ transplantation, occurring in one-third of patients. Immunosuppression-related neurotoxicity (involving calcineurin inhibitors and corticosteroids), opportunistic central nervous system infections, seizures, and delirium are some of the causes of neurologic symptoms following solid-organ transplantation. An uncommon often missed complication posttransplantation involves buildup of ammonia levels that can lead to rapid clinical deterioration even when treated. Ammonia levels are not routinely checked due to the myriad of other explanations for encephalopathy in a transplant recipient. A treatment of choice for severe hyperammonemia involves renal replacement therapy (RRT), but there are no guidelines on the mode or parameters of RRT for reducing ammonia levels. Hyperammonemia in a transplant recipient poses specific challenges beyond the actual condition because the treatment (RRT) involves significant hemodynamic fluctuations that may affect the graft. In this review, we describe a patient with posttransplantation hyperammonemia and discuss the pathways of ammonia metabolism, potential factors underlying the development of hyperammonemia posttransplantation, and choice of appropriate therapeutic options in these patients.

Extracorporeal Devices

Extracorporeal liver support (ECLS) emerged from the need stabilize high-acuity liver failure patients with the highest risk of death. The goal is to optimize the hemodynamic, neurologic, and biochemical parameters in preparation for transplantation or to facilitate spontaneous recovery. Patients with acute liver failure and acute-on-chronic liver failure stand to benefit from these devices, especially because they have lost many of the primary functions of the liver, including detoxifying the blood of various endogenous and exogenous substances, manufacturing circulating proteins, secreting bile, and storing energy. Existing ECLS devices are designed to mimic some of these functions.

A Controlled Study of Sorbent Suspension Dialysis in Chronic Liver Disease and Hepatic Encephalopathy

To investigate the role of extracorporeal detoxification in cirrhotic patients with advanced hepatic encephalopathy not responding to medical treatment, 20 patients were randomized to receive six hours of additional sorbent dialysis or ongoing standardized medical treatment. Following treatment, the clinical stage of encephalopathy remained unchanged in both groups. Abnormal sensory evoked potentials improved following sorbent dialysis (N70 latency, 128 ms before versus 110 ms after treatment, P<0,05; cervico-cranial transmission, 7.7 ms versus 6.8 ms, P<0.01) indicating improvement in important aspects of cerebral function. In contrast, brain function remained unchanged following medical treatment (N70 latency, 114 ms versus 113 ms; cervico-cranial transmission, 7.7 ms versus 7.2 ms, P=NS, respectively). Serum benzodiazepine levels decreased significantly after sorbent dialysis but not after medical treatment. Biocompatibility of sorbent dialysis was limited and clinical complications occurred in a proportion of patients. In conclusion, a six-hour treatment with sorbent suspension dialysis did not ameliorate the clinical stage of HE but improved neurophysiologic function in cirrhotic patients who had not responded to conventional medical treatment.

Continuous renal replacement therapy is associated with reduced serum ammonia levels and mortality in acute liver failure

Hyperammonemia has been associated with intracranial hypertension and mortality in patients with acute liver failure (ALF). We evaluated the effect of renal replacement therapy (RRT) on serum ammonia level and outcomes in ALF. This was a multicenter cohort study of consecutive ALF patients from the United States ALF Study Group registry between January 1998 and December 2016. First, we studied the association of ammonia with hepatic encephalopathy (HE) and 21-day transplant-free survival (TFS; n = 1,186). Second, we studied the effect of RRT on ammonia for the first 3 days post study admission (n = 340) and on 21-day TFS (n = 1,186). Higher admission (n = 1,186) median ammonia level was associated with grade 3-4 HE (116 vs. 83 μmol/L) and mortality at day 21 attributed to neurological (181 vs. 90 μmol/L) and all causes (114 vs. 83 μmol/L; P < 0.001 for all). Among 340 patients with serial ammonia levels, 61 (18%) were on continuous RRT (CRRT), 59 (17%) were on intermittent RRT (IRRT), and 220 (65%) received no RRT for the first 2 days. From days 1 to 3, median ammonia decreased by 38%, 23%, and 19% with CRRT, IRRT, and no RRT, respectively. Comparing to no RRT use, whereas ammonia reduction with CRRT was significant (P = 0.007), with IRRT it was not (P = 0.75). After adjusting for year of enrollment, age, etiology, and disease severity, whereas CRRT (odds ratio [OR], 0.47 [95% confidence interval {CI}, 0.26-0.82]) was associated with reduction in 21-day transplant-free all-cause mortality, IRRT (OR, 1.68 [95% CI, 1.04-2.72]) was associated with an increase. Conclusion: In a large cohort of ALF patients, hyperammonemia was associated with high-grade HE and worse 21-day TFS. CRRT was associated with a reduction in serum ammonia level and improvement of 21-day TFS. (Hepatology 2018;67:711-720).

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.

Hepatic Encephalopathy-the Old and the New

Hepatic encephalopathy occurs ubiquitously in all causes of advanced liver failure, however, its implications on mortality diverge and vary depending upon acuity and severity of liver failure. This associated mortality has decreased in subsets of liver failure over the last 20 years. Aside from liver transplantation, this improvement is not attributable to a single intervention but likely to a combination of practical advances in critical care management. Misconceptions surrounding many facets of hepatic encephalopathy exists due to heterogeneity in presentation, pathophysiology and outcome. This review is intended to highlight the important concepts, rationales and strategies for managing hepatic encephalopathy.

Emerging strategies for the treatment of patients with acute hepatic failure

PURPOSE OF REVIEW

The objective of this article is to review the latest developments related to the treatment of patients with acute liver failure (ALF).

RECENT FINDINGS

As the treatment of ALF has evolved, there is an increasing recognition regarding the risk of intracranial hypertension related to advanced hepatic encephalopathy. Therefore, there is an enhanced emphasis on neuromonitoring and therapies targeting intracranial hypertension. Also, new evidence implicates systemic proinflammatory cytokines as an etiology for the development of multiorgan system dysfunction in ALF; the recent finding of a survival benefit in ALF with high-volume plasmapheresis further supports this theory.

SUMMARY

Advances in the critical care management of ALF have translated to a substantial decrease in mortality related to this disease process. The extrapolation of therapies from general neurocritical care to the treatment of ALF-induced intracranial hypertension has resulted in improved neurologic outcomes. In addition, recognition of the systemic inflammatory response and multiorgan dysfunction in ALF has guided current treatment recommendations, and will provide avenues for future research endeavors. With respect to extracorporeal liver support systems, further randomized studies are required to assess their efficacy in ALF, with attention to nonsurvival end points such as bridging to liver transplantation.

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 Measurement of Ammonia in Human Breath and its Potential in Clinical Diagnostics

Ammonia is an important component of metabolism and is involved in many physiological processes. During normal physiology, levels of blood ammonia are between 11 and 50 µM. Elevated blood ammonia levels are associated with a variety of pathological conditions such as liver and kidney dysfunction, Reye's syndrome and a variety of inborn errors of metabolism including urea cycle disorders (UCD), organic acidaemias and hyperinsulinism/hyperammonaemia syndrome in which ammonia may reach levels in excess of 1 mM. It is highly neurotoxic and so effective measurement is critical for assessing and monitoring disease severity and treatment. Ammonia is also a potential biomarker in exercise physiology and studies of drug metabolism. Current ammonia testing is based on blood sampling, which is inconvenient and can be subject to significant analytical errors due to the quality of the sample draw, its handling and preparation for analysis. Blood ammonia is in gaseous equilibrium with the lungs. Recent research has demonstrated the potential use of breath ammonia as a non-invasive means of measuring systemic ammonia. This requires measurement of ammonia in real breath samples with associated temperature, humidity and gas characteristics at concentrations between 50 and several thousand parts per billion. This review explores the diagnostic applications of ammonia measurement and the impact that the move from blood to breath analysis could have on how these processes and diseases are studied and managed.

Extracorporeal treatment for valproic acid poisoning: systematic review and recommendations from the EXTRIP workgroup

BACKGROUND

The EXtracorporeal TReatments In Poisoning (EXTRIP) workgroup presents its systematic review and clinical recommendations on the use of extracorporeal treatment (ECTR) in valproic acid (VPA) poisoning.

METHODS

The lead authors reviewed all of the articles from a systematic literature search, extracted the data, summarized the key findings, and proposed structured voting statements following a predetermined format. A two-round modified Delphi method was chosen to reach a consensus on voting statements and the RAND/UCLA Appropriateness Method was used to quantify disagreement. Anonymous votes were compiled, returned, and discussed in person. A second vote was conducted to determine the final workgroup recommendations.

RESULTS

The latest literature search conducted in November 2014 retrieved a total of 79 articles for final qualitative analysis, including one observational study, one uncontrolled cohort study with aggregate analysis, 70 case reports and case series, and 7 pharmacokinetic studies, yielding a very low quality of evidence for all recommendations. Clinical data were reported for 82 overdose patients while pharmaco/toxicokinetic grading was performed in 55 patients. The workgroup concluded that VPA is moderately dialyzable (level of evidence = B) and made the following recommendations: ECTR is recommended in severe VPA poisoning (1D); recommendations for ECTR include a VPA concentration > 1300 mg/L (9000 μmol/L)(1D), the presence of cerebral edema (1D) or shock (1D); suggestions for ECTR include a VPA concentration > 900 mg/L (6250 μmol/L)(2D), coma or respiratory depression requiring mechanical ventilation (2D), acute hyperammonemia (2D), or pH ≤ 7.10 (2D). Cessation of ECTR is indicated when clinical improvement is apparent (1D) or the serum VPA concentration is between 50 and 100 mg/L (350-700 μmol/L)(2D). Intermittent hemodialysis is the preferred ECTR in VPA poisoning (1D). If hemodialysis is not available, then intermittent hemoperfusion (1D) or continuous renal replacement therapy (2D) is an acceptable alternative.

CONCLUSIONS

VPA is moderately dialyzable in the setting of overdose. ECTR is indicated for VPA poisoning if at least one of the above criteria is present. Intermittent hemodialysis is the preferred ECTR modality in VPA poisoning.

Pharmacotherapy for hyperammonemia

INTRODUCTION

Hepatic encephalopathy (HE) is a serious neuropsychiatric complication that is seen in patients with liver failure. The pathogenesis of HE is not entirely understood, but several hypotheses have emerged and persisted during the years. Despite the many prevalent hypotheses, most of the existing evidence point to ammonia as the main culprit behind primary and secondary symptoms making it the center of potential therapeutic options for the treatment of HE. Most treatments of hyperammonemia target the organs and metabolic processes involved in ammonia detoxification.

AREAS COVERED

This article provides a review of the current targets of therapy as well as the drugs used for hyperammonemia treatment.

EXPERT OPINION

Lactulose and rifaximin have a proven role as measures to use for secondary prophylaxis and are the mainstay of current therapy. The use of molecular adsorbent recirculating system in patients with severe HE has been proven to be efficacious, but through mechanisms that appear to be independent of ammonia. The main challenge that faces the further development of treatments for HE is finding appropriate end points, and the next step would be to provide evidence of the effectiveness of established treatments and define the role of emerging new treatments.

Preventing cerebral oedema in acute liver failure: the case for quadruple-H therapy

Severe cerebral oedema is a life-threatening complication of acute liver failure. Hyperammonaemia and cerebral hyperaemia are major contributing factors. A multimodal approach, which incorporates hyperventilation, haemodiafiltration, hypernatraemia and hypothermia (quadruple-H therapy), may prevent or attenuate severe cerebral oedema. This approach is readily administered by critical care clinicians and is likely to be more effective than the use of single therapies. Targeting of PaCO2 in the mild hyperventilation range, as seen in acute liver failure patients before intubation, aims to minimise hyperaemic cerebral oedema. Haemodiafiltration aims to achieve the rapid control of elevated blood ammonia concentrations by its removal and to reduce production via the lowering of core temperature. The administration of concentrated saline increases serum tonicity and further reduces cerebral swelling. In addition, the pathologically increased cerebral blood-flow is further attenuated by therapeutic hypothermia. The combination of all four treatments in a multimodal approach may be a safe and effective means of attenuating or treating the cerebral oedema of acute liver failure and preventing death from neurological complications.

Ammonia clearance with haemofiltration in adults with liver disease

BACKGROUND & AIMS

Ammonia is recognized as a toxin central to complications of liver failure. Hyperammonaemia has important clinical consequences, but optimal means to reduce circulating levels are uncertain. In patients with liver disease, continuous renal replacement therapy (CRRT) with haemofiltration (HF) is often required to treat concurrent kidney injury, but its effects upon ammonia levels are poorly characterized. To evaluate the effect of HF at different treatment intensities on ammonia clearance (AC) and arterial ammonia concentration.

METHODS

Prospective study of adult patients with liver failure and arterial ammonia >100 μmol/L requiring CRRT using veno-venous HF. Arterial ammonia concentration and AC measured at 1 and 24 h after initiation of low (35 ml/kg/h) or high (90 ml/kg/h) filtration volume.

RESULTS

Twenty-four patients (10 acute liver failure, 10 chronic liver disease and 4 following liver resection) were studied. Clearance of urea and ammonia solutes correlated closely (r = 0.819, P = 0.007). Ammonia clearance correlated closely with ultrafiltration rate (r = 0.86, P < 0.001). At 1 h, AC was 39 (34-54) ml/min (low volume) vs 85 (62-105) ml/min (high volume) CRRT, (P < 0.001) and at 24 h 44 (34-63) vs 105 (82-109) ml/min, (P = 0.01). Overall, a 22% reduction in median arterial ammonia concentration was observed over 24 h of HF from 156 (137-176) to 122 (85-133) μmol/L, (P ≤ 0.0001).

CONCLUSION

Clinically significant ammonia clearance can be achieved in adult patients with hyperammonaemia utilizing continuous VVHF. Ammonia clearance is closely correlated with ultrafiltration rate. HF was associated with a fall in arterial ammonia concentration.

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.

Simultaneous double hemodialysis for the control of refractory hyperammonemia

INTRODUCTION

In adults, hyperammonemia is generally associated with hepatic dysfunction or as a complication of urinary diversions when infected or obstructed. Hyperammonemia has also rarely been reported in association with multiple myeloma. With modest elevations, hyperammonemia often leads to encephalopathy. However, when ammonia reaches extreme levels cerebral edema and herniation may occur leading to coma, seizures, or death.

CASE

We describe a 72-year-old Caucasian male with a history of end-stage renal disease (ESRD) and multiple myeloma who developed profound encephalopathy and eventual obtundation. He was found to have severe hyperammonemia that was not due to any identified hepatic impairment. His hyperammonemia proved to be refractory to medical therapy with cathartics and antibiotics, prolonged high-flux hemodialysis, and even continuous venovenous hemodialysis (CVVHD). This metabolic derangement as well as encephalopathy was eventually reversed with simultaneous CVVHD and extended daily hemodialysis (EDD). A more durable response was achieved after vincristine and dexamethasone were administered, which allowed the patient to resume his previous intermittent hemodialysis (IHD) schedule. The patient regained his full sensorium and was eventually discharged to home.

CONCLUSIONS

Simultaneous double hemodialysis may be used as an important adjunct in treating refractory hyperammonemia.

Clearing of toxic substances: are there differences between the available liver support devices?

Toxins accumulating in liver failure split into water solved (e.g. ammonia) and albumin bound substances (e.g. bilirubin). Because the latter cannot be removed by conventional haemodialysis, special liver support systems have been developed. The majority of data concerning elimination efficiency exist for the cell-free devices Molecular Adsorbent Recirculating System (MARS) and Prometheus, as they have been commercially available in Europe since many years. Overall, Prometheus provides higher clearances for most liver toxins, especially if they are tightly albumin bound. However, for bile acids and cytokines no such differences could be found. Single pass albumin dialysis (SPAD) can be assumed to be equally effective as MARS. None of the bioartificial liver support systems being developed is on the market today and published clearance data are scarce. In general, clearance efficiency for albumin bound substances is relatively low in all systems currently available. Besides optimizing biocompatibility and selectivity, future technologies should also focus on improved detoxification efficiency of liver support devices.

Meta-analysis of performance of Kings's College Hospital Criteria in prediction of outcome in non-paracetamol-induced acute liver failure

BACKGROUND & AIMS

Current techniques for predicting outcome and requirement for emergency liver transplantation (ELT) in acute liver failure (ALF) are imperfect, though The Kings College Criteria (KCC) are the most commonly applied tools for this purpose. Their performance in identification of patients with non-paracetamol-induced ALF (non-POD ALF), who would not survive without ELT, has recently been questioned. Using quantitative techniques, we therefore performed a meta-analysis of outcome data of the KCC for prediction of survival in non-POD ALF.

METHODS

A systematic database search was performed and retrieved articles graded according to a pre-agreed pro-forma of methodological quality. Collated data was meta-analysed for summary sensitivity, specificity, diagnostic odds ratio (DOR) and ROC curve analysis. Pre-specified sub-group analysis was performed on the basis of methodological quality, the severity of hepatic encephalopathy (HE) of reported patients, timing of KCC application and exclusion of those who underwent ELT.

RESULTS

Eighteen studies with data on 1105 patients were available for production of 2x2 tables. Summary sensitivity was 68 (95% CI 59-77)%, specificity 82 (75-88)% and DOR 12.6 (6.5-26.1). Heterogeneity was detected in the DOR and related to methodological quality (I(2)=64% for all studies versus 47% for 'good' quality studies) and was lower in studies considering high grade HE or dynamic application of KCC (I(2)=0%). For data where ELT were excluded (13 studies) summary sensitivity was 68 (57-79)%, specificity 81 (72-90)% and DOR 12.2 (4.9-30.1) and a symmetric summary ROC curve was produced. Specificity was highest in studies of patients with high grade HE (93 (80-100)%) and where KCC were applied dynamically through the clinical course (88 (78-97)%). Sensitivity was reduced in studies published post 2005 compared with studies pre 1995 (58 (46-71)% versus 85 (76-82)%).

CONCLUSIONS

KCC for outcome in non-POD ALF have good specificity and more limited sensitivity. There is significant heterogeneity in the published data partially related to methodological quality. KCC perform best in groups with high grade encephalopathy and in historically earlier studies suggesting modern medical management of ALF may modify performance of KCC.

Treatment of hepatic encephalopathy by on-line hemodiafiltration: a case series study

Background

It is thought that a good survival rate of patients with acute liver failure can be achieved by establishing an artificial liver support system that reliably compensates liver function until the liver regenerates or a patient undergoes transplantation. We introduced a new artificial liver support system, on-line hemodiafiltration, in patients with acute liver failure.

Methods

This case series study was conducted from May 2001 to October 2008 at the medical intensive care unit of a tertiary care academic medical center. Seventeen consecutive patients who admitted to our hospital presenting with acute liver failure were treated with artificial liver support including daily on-line hemodiafiltration and plasma exchange.

Results

After 4.9 ± 0.7 (mean ± SD) on-line hemodiafiltration sessions, 16 of 17 (94.1%) patients completely recovered from hepatic encephalopathy and maintained consciousness for 16.4 ± 3.4 (7-55) days until discontinuation of artificial liver support (a total of 14.4 ± 2.6 [6-47] on-line hemodiafiltration sessions). Significant correlation was observed between the degree of encephalopathy and number of sessions of on-line HDF required for recovery of consciousness. Of the 16 patients who recovered consciousness, 7 fully recovered and returned to society with no cognitive sequelae, 3 died of complications of acute liver failure except brain edema, and the remaining 6 were candidates for liver transplantation; 2 of them received living-related liver transplantation but 4 died without transplantation after discontinuation of therapy.

Conclusions

On-line hemodiafiltration was effective in patients with acute liver failure, and consciousness was maintained for the duration of artificial liver support, even in those in whom it was considered that hepatic function was completely abolished.

Role of artificial liver support in hepatic encephalopathy

Hepatic encephalopathy (HE) refers to the reversible neuropsychiatric disorders observed in acute liver failure and as a complication of cirrhosis and/or portal hypertension. This review aims to describe the pathophysiology of HE, the rationale for the use of artificial liver support in the treatment of HE, the different concepts of artificial liver support and the results obtained. Ammonia has been considered central to its pathogenesis but recently an important role for its interaction with inflammatory responses and auto-regulation of cerebral hemodynamics has been suggested. Artificial liver support might be able to decrease ammonia and modulate inflammatory mediators and cerebral hemodynamics. Bioartificial liver support systems use hepatocytes in an extracorporeal device connected to the patient's circulation. Artificial liver support is intended to remove protein-bound toxins and water-soluble toxins without providing synthetic function. Both systems improve clinical and biochemical parameters and can be applied safely to patients. Clinical studies have shown that artificial liver support, especially albumin dialysis, is able to improve HE in acute and acute-on-chronic liver failure. Further studies are required to better understand the mechanism, however, artificial liver support can be added to the therapeutic bundle in treating HE.

Hot topics in liver intensive care

Liver dysfunction is an independent predictor of mortality among intensive care patients. Avoidance or early restoration of normal liver function should therefore be targeted in all critically ill patients. The present work seeks to provide an overview of the "hottest topics" among liver-related problems in intensive care. The management of increased intracranial pressure in severe hepatic encephalopathy is still not sufficiently documented. The promising results with regard to intracranial pressure control by the molecular adsorbent recycling system (MARS) in animal studies are only partially reproducible in patients. Intracranial pressure monitoring is inconsistently applied in various centers, mainly because of the lack of information about the risk benefit ratio. Further, we still do not know which coagulation management protocol reduces the risk of intracranial bleeding. Type I hepatorenal syndrome is a complication of liver failure that is strongly associated with bad outcomes. Only about the half of the patients will recover from dialysis-dependent hepatorenal syndrome after liver transplantation. The usefulness of combined liver and kidney transplantation has not been sufficiently clarified. Terlipressin together with fluid and albumin substitution appear to be the most promising therapeutic interventions. Extracorporeal liver support systems, such as single-pass albumin dialysis, MARS, and the dialysis- and plasmapheresis-based Prometheus, are still under investigation with regard to effectiveness of toxin elimination, appropriate indications, and number duration of treatments.

Bridging to transplantation in acute liver failure in a 7-month-old infant

BACKGROUND

Acute liver failure (ALF) in children is a rare but often fatal event. At present, liver transplantation is the only successful therapy in most cases. In the face of deteriorating hepatic encephalopathy in these children, some bridging therapy using artificial detoxification can be necessary to enable successful transplantation. In adults, albumin dialysis using the molecular absorbent recycling system (MARS) has been described as effective for bridging to liver transplantation.

CASE REPORT

A previously healthy 7-month-old infant was admitted with ALF due to autoimmune hepatitis. King's College criteria for children with ALF indicated the need for transplantation (bilirubin 13.7 mg/dl, leukocytes 18,980/mm3, INR 5.83, age<2 years). Despite moderate hyperammonemia (75 microm/l) along with the development of pneumonia, the child deteriorated hemodynamically and neurologically, showing grade III encephalopathy proven by EEG. Albumin dialysis using MARS was used to bridge 36 hours to successful living-donor split-liver transplantation, and resulted in improvements in EEG, plasma levels of amino acids and hemodynamics. Twenty-four months after transplantation the child shows normal liver function and normal neuropsychological development. The explanted liver showed 80 % tissue destruction from autoimmune hepatitis.

CONCLUSION

Albumin dialysis as described can be used successfully in infants < 1 year old for bridging to liver transplantation in cases of acute hepatic failure with deteriorating encephalopathy.

Renal replacement therapy in patients with chronic liver disease

As the prevalence of chronic liver disease and chronic kidney disease (CKD) increase, clinicians are likely to be increasingly faced with difficult diagnostic, treatment, and ethical challenges when facing both of these diseases in a single patient. Alterations in creatinine formation and elimination in cirrhotic patients render creatinine-based estimates of glomerular filtration rate and dialysis adequacy less accurate in this population. Furthermore, differentiating signs and symptoms of uremia from hepatic disease may be difficult and clear indications for renal replacement therapy (RRT) in these patients have not been defined. Hemodialysis is associated with a high rate of complications and has not been shown to prolong life in cirrhotic patients with acute renal failure (ARF), but has not been carefully examined in those with CKD. Peritoneal dialysis is, similarly, unhelpful in chronic liver disease complicated by ARF, but has been found to be a viable option in some cirrhotic patients with CKD. Continuous RRT is generally tolerated by patients with decompensated cirrhosis and either acute or chronic renal failure and may act to bridge patients to liver transplantation. Given the poor underlying survival of cirrhotic patients with renal failure, clinicians should carefully consider the utility of RRT in each patient.

Management of patients with fulminant hepatic failure and brain edema

Cerebral edema in acute liver failure is associated with a poor prognosis. Optimization of cerebral perfusion pressure and blood flow plays a key role in contemporary management of these patients. However, understanding of the pathophysiology of brain edema is required for optimal patient management. This review explains the relationships between cerebral perfusion and edema and summarizes therapies that are currently used in patients with acute liver failure to prevent and reduce intracranial pressure.

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.

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.

Improvement in central nervous system functions during treatment of liver failure with albumin dialysis MARS--a review of clinical, biochemical, and electrophysiological data

The Molecular Adsorbent Recirculating System (MARS) is a nonbiological liver support method based on the principles of dialysis, filtration, and adsorption. It allows the safe and efficient removal of both albumin-bound and water-soluble toxic metabolites, including ammonia, aromatic amino acids, tryptophan, and related phenolic and indolic products, as well as benzodiazepines. A well-documented effect of the treatment is the improvement of the hemodynamic situation of decompensated chronic patients. Systemic vascular resistance, mean arterial pressure, cerebral blood flow, and cerebral oxygen consumption increased significantly. The degree of hepatic encephalopathy decreased significantly. Increased intracranial pressure could be normalized in both chronic and fulminant liver failure. In three randomized clinical trials significant improvement of survival could be demonstrated. In a model of murine neuronal networks cultured on multi-microelectrode array plates and incubated with plasma from liver failure patients, a normalization of the spike and burst pattern could be observed, if plasma samples from MARS-treated patients before and after treatment were compared. In conclusion, MARS significantly improves central nervous system functions. It can serve as a model for the further investigation of the role of protein-bound substances in hepatic encephalopathy and cerebral hemodynamics.

Brain edema in liver failure: basic physiologic principles and management

In patients with severe liver failure, brain edema is a frequent and serious complication that may result in high intracranial pressure and brain damage. This short article focuses on basic physiologic principles that determine water flux across the blood-brain barrier. Using the Starling equation, it is evident that both the osmotic and hydrostatic pressure gradients are imbalanced across the blood-brain barrier in patients with acute liver failure. This combination will tend to favor cerebral capillary water influx to the brain. In contrast, the disequilibration of the Starling forces seems to be less pronounced in patients with cirrhosis because the regulation of cerebral blood flow is preserved and the arterial ammonia concentration is lower compared with that of patients with acute liver failure. Treatments that are known to reverse high intracranial pressure tend to decrease the osmotic pressure gradients across the blood-brain barrier. Recent studies indicate that interventions that restrict cerebral blood flow, such as hyperventilation, hypothermia, and indomethacin, are also efficient in preventing edema and high intracranial pressure, probably by decreasing the transcapillary hydrostatic pressure gradient. In our opinion, it is important to recall that rational fluid therapy, adequate ventilation, and temperature control are of direct importance to controlling cerebral capillary water flux in patients with acute liver failure. These simple interventions should be secured before more advanced experimental technologies are instituted to treat these patients.

Effects of sorbent suspension dialysis on plasma amino acid levels in cirrhotic patients with refractory hepatic encephalopathy

In cirrhotic patients, plasma amino acid levels are severely deranged. A decreased ratio of branched-chain to aromatic amino acids (Fischer ratio) has been implicated in the pathogenesis of hepatic encephalopathy. In this prospective study, we investigated the effects of extracorporeal detoxification on amino acid levels using a sorbent suspension dialysis system. Twenty patients with documented cirrhosis and hepatic encephalopathy grade II-III not responding to standard treatment were randomized to receive either six hours of sorbent dialysis and standardized conventional medical treatment or ongoing medical treatment alone. In contrast to previous uncontrolled studies, no significant effect on amino acid levels, Fischer ratio or clinical grade of hepatic encephalopathy was detected in either treatment group. In conclusion, a 6-hour treatment with sorbent dialysis did not significantly influence plasma levels of amino acids and did not ameliorate the clinical grade of hepatic encephalopathy.

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.