Arterial ammonia and clinical risk factors for encephalopathy and intracranial hypertension in acute liver failure

Pathogenesis of hepatic encephalopathy and brain edema in acute liver failure: role of glutamine redefined

Acute liver failure (ALF) is characterized neuropathologically by cytotoxic brain edema and biochemically by increased brain ammonia and its detoxification product, glutamine. The osmotic actions of increased glutamine synthesis in astrocytes are considered to be causally related to brain edema and its complications (intracranial hypertension, brain herniation) in ALF. However studies using multinuclear (1)H- and (13)C-NMR spectroscopy demonstrate that neither brain glutamine concentrations per se nor brain glutamine synthesis rates correlate with encephalopathy grade or the presence of brain edema in ALF. An alternative mechanism is now proposed whereby the newly synthesized glutamine is trapped within the astrocyte as a consequence of down-regulation of its high affinity glutamine transporter SNAT5 in ALF. Restricted transfer out of the cell rather than increased synthesis within the cell could potentially explain the cell swelling/brain edema in ALF. Moreover, the restricted transfer of glutamine from the astrocyte to the adjacent glutamatergic nerve terminal (where glutamine serves as immediate precursor for the releasable/transmitter pool of glutamate) could result in decreased excitatory transmission and excessive neuroinhibition that is characteristic of encephalopathy in ALF. Paradoxically, in spite of renewed interest in arterial ammonia as a predictor of raised intracranial pressure and brain herniation in ALF, ammonia-lowering agents aimed at reduction of ammonia production in the gut have so far been shown to be of limited value in the prevention of these cerebral consequences. Mild hypothermia, shown to prevent brain edema and intracranial hypertension in both experimental and human ALF, does so independent of effects on brain glutamine synthesis; whether or not hypothermia restores expression levels of SNAT5 in ALF awaits further studies. While inhibitors of brain glutamine synthesis such as methionine sulfoximine, have been proposed for the prevention of brain edema in ALF, potential adverse effects have so far limited their applicability.

[Acute liver failure. How much diagnostic work-up and therapy does my patient need?]

Acute liver failure is a multisystem disease with predominantly sudden and severe hepatic injury and hepatic encephalopathy caused by apoptotic or necrotic hepatocyte damage. The clinical challenge in patients with acute liver failure is to promptly identify those with poor prognosis and refer them for emergency liver transplantation. This review article highlights the main aspects of decision making in the setting of acute liver failure, summarizes new aspects of its critical care management and gives an overview of sclerosing cholangitis in the critically ill patient, an under-recognized disease entity that can progress to acute liver failure.

Threshold for toxicity from hyperammonemia in critically ill children

BACKGROUND & AIMS

Hyperammonemia results from reduction of hepatocyte function or enzyme of urea cycle deficiency. Hyperammonemia contributes to cerebral edema that may lead to cerebral herniation. The threshold of toxicity of ammonemia is unknown.

METHODS

We conducted a retrospective observational study in our pediatric intensive care unit. All children who developed hyperammonemia from January 2000 to April 2009 were included. Clinical and laboratory data at admission, specific treatments implemented, and ammonemias the first 7 days after inclusion were collected. The outcome assessed was 28 day mortality. Risk of mortality was estimated by a logistic regression model.

RESULTS

Ninety patients with liver failure (63.3%) and primary or secondary urea cycle defect (23.3%) were included. Patients with urea cycle defects were more likely to receive ammonia scavengers than patients with liver failure (47.6% versus 3.5%). The 28 day mortality rate was 31.1%. Risk of mortality increased according to the ammonemia within 48 h: odds ratio 1.5, 1.9, 3.3, 2.4 for ammonemia above 100, 150, 200, and 300 μmol/L, respectively. Peak ammonemia ≥200 μmol/L within the first 48 h was an independent risk factor for mortality, with greater risk found in liver failure than in urea cycle defect.

CONCLUSIONS

Our study identifies a threshold of exposure to ammonia (≥200 μmol/L) above which mortality increases significantly, especially in liver failure. Specific treatments of hyperammonemia are rarely used in liver failure when compared with urea cycle defect even though use of ammonia scavengers may help to decrease ammonemia.

Neuropathology of acute liver failure

Cerebral edema has been identified in all forms of liver disease and is closely related to the development of hepatic encephalopathy. Cerebral edema is most readily recognized in acute liver failure (ALF), while the main cause of death in patients with ALF is multi-organ failure; brain herniation as a result of intracranial hypertension does remain a major cause of mortality. The mechanisms responsible for cerebral edema in ALF suggest both cytotoxic and vasogenic injury. This article reviews the gross and ultrastructural changes associated with cerebral edema in ALF. The primary cause of cerebral edema is associated with astrocyte swelling, mainly perivascular edema and ammonia still remains the primary neurotoxin involved in its pathogenesis. The astrocytic changes were confined to the gray matter. The other organelles involved in the pathogenesis of ALF include mitochondria, basement membrane, pericytes, microglial cells, blood-brain barrier (BBB) etc. Discrete neuronal changes have recently been reported. Recent studies in animal and humans have demonstrated the microglial changes which have the potential to cause neuronal dysfunction in ALF. The alterations in BBB still remain unclear though few studies have showed disruption of tight junction proteins indicating the involvement of BBB in cellular swelling.

Three dimensional cultures of rat liver cells using a natural self-assembling nanoscaffold in a clinically relevant bioreactor for bioartificial liver construction

Till date, no bioartificial liver (BAL) procedure has obtained FDA approval or widespread clinical acceptance, mainly because of multifactorial limitations such as the use of microscale or undefined biomaterials, indirect and lower oxygenation levels in liver cells, short-term undesirable functions, and a lack of 3D interaction of growth factor/cytokine signaling in liver cells. To overcome preclinical limitations, primary rat liver cells were cultured on a naturally self-assembling peptide nanoscaffold (SAPN) in a clinically relevant bioreactor for up to 35 days, under 3D interaction with suitable growth factors and cytokine signaling agents, alone or combination (e.g., Group I: EPO, Group II: Activin A, Group III: IL-6, Group IV: BMP-4, Group V: BMP4 + EPO, Group VI: EPO + IL-6, Group VII: BMP4 + IL-6, Group VIII: Activin A + EPO, Group IX: IL-6 + Activin A, Group X: Activin A + BMP4, Group XI: EPO + Activin A + BMP-4 + IL-6 + HGF, and Group XII: Control). Major liver specific functions such as albumin secretion, urea metabolism, ammonia detoxification, phase contrast microscopy, immunofluorescence of liver specific markers (Albumin and CYP3A1), mitochondrial status, glutamic oxaloacetic transaminase (GOT) activity, glutamic pyruvic transaminase (GPT) activity, and cell membrane stability by the lactate dehydrogenase (LDH) test were also examined and compared with the control over time. In addition, we examined the drug biotransformation potential of a diazepam drug in a two-compartment model (cell matrix phase and supernatant), which is clinically important. This present study demonstrates an optimized 3D signaling/scaffolding in a preclinical BAL model, as well as preclinical drug screening for better drug development.

Neurological complications of acute liver failure: pathophysiological basis of current management and emerging therapies

One of the major causes of mortality in patients with acute liver failure (ALF) is the development of hepatic encephalopathy (HE) which is associated with increased intracranial pressure (ICP). High ammonia levels, increased cerebral blood flow and increased inflammatory response have been identified as major contributors to the development of HE and the related brain swelling. The general principles of the management of patients with ALF are straightforward. They include identifying the insult causing hepatic injury, providing organ systems support to optimize the patient's physical condition, anticipation and prevention of development of complications. Increasing insights into the pathophysiological mechanisms of ALF are contributing to better therapies. For instance, the evident role of cerebral hyperemia in the pathogenesis of increased ICP has led to a re-evaluation of established therapies such as hyperventilation, N-acetylcysteine, thiopentone sodium and propofol. The role of systemic inflammatory response in the pathogenesis of increased ICP has also gained importance supporting the concept that antibiotics given prophylactically reduce the risk of developing sepsis during the course of illness. Moderate hypothermia has also been established as a therapy able to reduce ICP in patients with uncontrolled intracranial hypertension and to prevent increases in ICP during orthopic liver transplantation. Ornithine phenylacetate, a new drug in the treatment of liver failure, and liver replacement therapies are still being investigated both experimentally and clinically. Despite many advances in the understanding of the pathophysiological basis and the management of intracranial hypertension in ALF, more clinical trials should be conducted to determine the best therapeutic management for this difficult clinical event.

Blood-brain barrier in acute liver failure

Brain edema remains a challenging obstacle in the management of acute liver failure (ALF). Cytotoxic mechanisms associated with brain edema have been well recognized, but evidence for vasogenic mechanisms in the pathogenesis of brain edema in ALF has been lacking. Recent reports have not only shown a role of matrix metalloproteinase-9 in the pathogenesis of brain edema in experimental ALF but have also found significant alterations in the tight junction elements including occludin and claudin-5, suggesting a vasogenic injury in the blood-brain barrier (BBB) integrity. This article reviews and explores the role of the paracellular tight junction proteins in the increased selective BBB permeability that leads to brain edema in ALF.

The neurological manifestations of acute liver failure

Acute liver failure is a disorder which impacts on multiple organ systems and results from hepatocellular necrosis in a patient with no previous history of chronic liver disease. It typically culminates in the development of liver dysfunction, coagulopathy and encephalopathy, and is associated with high mortality in poor prognostic groups. In acute liver failure, some patients may develop cerebral edema and increased intracranial pressure although recent data suggest that intracranial hypertension is less frequent than previously described, complicating 29% of acute cases who have proceeded to grade 3/4 coma. Neurological manifestations are primarily underpinned by the development of brain edema. The onset of encephalopathy can be rapid and dramatic with the development of asterixis, delirium, hyperreflexia, clonus, seizures, extensor posturing and coma. Ammonia plays a definitive role in the development of cytotoxic brain edema. Patients with acute liver failure have a marked propensity to develop renal insufficiency and hence impaired ammonia excretion. The incidence of both bacterial and fungal infection occurs in approximately one third of patients. The relationship between inflammation, as opposed to infection, and progression of encephalopathy is similar to that observed in chronic liver disease. Intracranial pressure monitoring is valuable in identifying surges in intracranial hypertension requiring intervention. Insertion of an intracranial bolt should be considered only in the subgroup of patients who have progressed to grade 4 coma. Risk factors for developing intracranial hypertension are those with hyperacute and acute etiologies, progression to grade 3/4 hepatic encephalopathy, those who develop pupillary abnormalities (dilated pupils, sluggishly responsive to light) or seizures, have systemic inflammation, an arterial ammonia >150 μmol/L, hyponatremia, and those in receipt of vasopressor support. Strategies employed in patients with established encephalopathy (grade 3/4) aim to maintain freedom from infection/inflammatory milieu, provide adequate sedation, and correct hypo-osmolality.

Detoxification as a treatment goal in hepatic failure

Acute liver failure (ALF) is a dramatic clinical syndrome with high mortality because of cerebral oedema (type A hepatic encephalopathy) and multi-organ failure. With intensive care medicine and emergent liver transplantation being the mainstay of treatment, alternatives to transplantation are increasingly needed. Ammonia has been recognised as a major toxin in patients with ALF. It can be effectively removed by haemodialysis, haemofiltration and artificial liver support (a combination of extracorporeal toxin absorption and haemodialysis). Previous studies of extracorporeal detoxification, however, have either not specifically targeted ammonia or were hampered by poor biocompatibility and obsolete pathophysiological assumptions, ultimately failing to improve the prognosis. Moreover, most patients were treated only late after the emergence of advanced HE and multi-organ failure, while detoxification should prevent these complications. Acute-on-chronic liver failure (AOCLF) occurs in the setting of chronic liver disease and has an equally poor prognosis. Here, the goals of extracorporeal blood detoxification are renal support and haemodynamic stabilisation in order to support recompensation. Patients with AOCLF, unfortunately, are at a risk for treatment-related complications including bleeding, thrombocytopenia, hypotension and acute renal failure, making biocompatibility a critical issue. Peritoneal dialysis could possibly emerge as a more biocompatible way of treating refractory hepatorenal syndrome. This article will critically analyse the pathophysiological concepts and goals of extracorporeal detoxification in acute and chronic liver diseases.

Neuroinflammation in acute liver failure: mechanisms and novel therapeutic targets

It is increasingly evident that neuroinflammatory mechanisms are implicated in the pathogenesis of the central nervous system (CNS) complications (intracranial hypertension, brain herniation) of acute liver failure (ALF). Neuroinflammation in ALF is characterized by microglial activation and arterio-venous difference studies as well as studies of gene expression confirm local brain production and release of proinflammatory cytokines including TNF-α and the interleukins IL-1β and IL-6. Although the precise nature of the glial cell responsible for brain cytokine synthesis is not yet established, evidence to date supports a role for both astrocytes and microglia. The neuroinflammatory response in ALF progresses in parallel with the progression of hepatic encephalopathy (HE) and with the severity of brain edema (astrocyte swelling). Mechanisms responsible for the relaying of signals from the failing liver to the brain include transduction of systemic proinflammatory signals as well as the effects of increased brain lactate leading to increased release of cytokines from both astrocytes and microglia. There is evidence in support of a synergistic effect of proinflammatory cytokines and ammonia in the pathogenesis of HE and brain edema in ALF. Therapeutic implications of the findings of a neuroinflammatory response in ALF are multiple. Removal of both ammonia and proinflammatory cytokines is possible using antibiotics or albumen dialysis. Mild hypothermia reduces brain ammonia transfer, brain lactate production, microglial activation and proinflammatory cytokine production resulting in reduced brain edema and intracranial pressure in ALF. N-Acetylcysteine acts as both an antioxidant and anti-inflammatory agent at both peripheral and central sites of action independently resulting in slowing of HE progression and prevention of brain edema. Novel treatments that directly target the neuroinflammatory response in ALF include the use of etanercept, a TNF-α neutralizing molecule and minocycline, an agent with potent inhibitory actions on microglial activation that are independent of its antimicrobial properties; both agents have been shown to be effective in reducing neuroinflammation and in preventing the CNS complications of ALF. Translation of these findings to the clinic has the potential to provide rational targeted approaches to the prevention and treatment of these complications in the near future.

Branched-chain amino acids increase arterial blood ammonia in spite of enhanced intrinsic muscle ammonia metabolism in patients with cirrhosis and healthy subjects

Branched-chain amino acids (BCAA) are used in attempts to reduce blood ammonia in patients with cirrhosis and intermittent hepatic encephalopathy based on the hypothesis that BCAA stimulate muscle ammonia detoxification. We studied the effects of an oral dose of BCAA on the skeletal muscle metabolism of ammonia and amino acids in 14 patients with cirrhosis and in 7 healthy subjects by combining [(13)N]ammonia positron emission tomography (PET) of the thigh muscle with measurements of blood flow and arteriovenous (A-V) concentrations of ammonia and amino acids. PET was used to measure the metabolism of blood-supplied ammonia and the A-V measurements were used to measure the total ammonia metabolism across the thigh muscle. After intake of BCAA, blood ammonia increased more than 30% in both groups of subjects (both P < 0.05). Muscle clearance of blood-supplied ammonia (PET) was unaffected (P = 0.75), but the metabolic removal rate (PET) increased significantly because of increased blood ammonia in both groups (all P < 0.05). The total ammonia clearance across the leg muscle (A-V) increased by more than 50% in both groups, and the flux (A-V) of ammonia increased by more than 45% (all P < 0.05). BCAA intake led to a massive glutamine release from the muscle (cirrhotic patients, P < 0.05; healthy subjects, P = 0.12). In conclusion, BCAA enhanced the intrinsic muscle metabolism of ammonia but not the metabolism of blood-supplied ammonia in both the patients with cirrhosis and in the healthy subjects.

Hypermagnesemia does not prevent intracranial hypertension and aggravates cerebral hyperperfusion in a rat model of acute hyperammonemia

Intravenous infusion of magnesium sulfate prevents seizures in patients with eclampsia and brain edema after traumatic brain injury. Neuroprotection is achieved by controlling cerebral blood flow (CBF), intracranial pressure, neuronal glutamate release, and aquaporin-4 (Aqp4) expression. These factors are also thought to be involved in the development of brain edema in acute liver failure. We wanted to study whether hypermagnesemia prevented development of intracranial hypertension and hyperperfusion in a rat model of portacaval anastomosis (PCA) and acute hyperammonemia. We also studied whether hypermagnesemia had an influence on brain content of glutamate, glutamine, and aquaporin-4 expression. The study consisted of three experiments: The first was a dose-finding study of four different dosing regimens of magnesium sulfate (MgSO4) in healthy rats. The second involved four groups of PCA rats receiving ammonia infusion/vehicle and MgSO4) /saline. The effect of MgSO(4) on mean arterial pressure (MAP), intracranial pressure (ICP), CBF, cerebral glutamate and glutamine, and aquaporin-4 expression was studied. Finally, the effect of MgSO4 on MAP, ICP, and CBF was studied, using two supplementary dosing regimens. In the second experiment, we found that hypermagnesemia and hyperammonemia were associated with a significantly higher CBF (P < 0.05, two-way analysis of variance [ANOVA]). Hypermagnesemia did not lead to a reduction in ICP and did not affect the brain content of glutamate, glutamine, or Aqp-4 expression. In the third experiment, we achieved higher P-Mg but this did not lead to a significant reduction in ICP or CBF.

CONCLUSION

Our results demonstrate that hypermagnesemia does not prevent intracranial hypertension and aggravates cerebral hyperperfusion in rats with PCA and hyperammonemia.

Infection and systemic inflammation, not ammonia, are associated with Grade 3/4 hepatic encephalopathy, but not mortality in cirrhosis

BACKGROUND & AIMS

Patients with cirrhosis are prone to infection which is a frequent precipitant of hepatic encephalopathy (HE). Clinical studies have examined the importance of inflammation and infection in modulating the manifestation of symptoms of HE in acute liver failure and patients with cirrhosis and minimal/low grade HE. It would be logical to presume that this relationship persists in patients who develop severe HE in cirrhosis although this has not been examined to date.

METHODS

We report the findings of a prospective audit of 100 consecutive patients with cirrhosis admitted between Jan 2000 and March 2008 to a liver Intensive Care Unit (ICU) where HE was the primary indication for admission (59% Grade 3; 41% Grade 4). Haematological and microbiological data were collected at ICU admission, and organ scores and outcomes were recorded.

RESULTS

46% of patients had positive cultures taken within ± 48h from admission to ICU [25% blood] and a further 22% were culture negative but had evidence of systemic inflammation (SIRS). SIRS score (p=0.03) and SOFA score (p=0.006) were significantly higher in those patients with Grade 4 HE, who were also less likely to survive (p<0.001). HE grade/coma score did not correlate with ammonia, biochemistry or MELD score. Fifty-two percent of patients survived their ICU stay while the remainder developed progressive multiorgan failure and died; 38% survived to discharge, and 16% were transplanted.

CONCLUSIONS

These data support an association between infection/SIRS and not ammonia, in patients with cirrhosis that develop severe HE. The presence or absence of infection/SIRS did not determine survival.

Brain hypoxanthine concentration correlates to lactate/pyruvate ratio but not intracranial pressure in patients with acute liver failure

BACKGROUND & AIMS

The pathogenesis of cerebral edema in acute liver failure is suggested, in in vitro and animal studies, to involve a compromised oxidative metabolism with a decrease in cerebral ATP levels and an increase in purine concentrations. In this study we hypothesize that the cerebral concentrations of hypoxanthine, inosine, and lactate/pyruvate (LP) ratio are increased and correlated in patients with acute liver failure. Furthermore, we expect the purines and L/P ratio to correlate with intracranial pressure (ICP) (positively), and cerebral perfusion pressure (CPP) (negatively).

METHODS

In 17 patients (aged 18-60 years) with acute liver failure and severe hyperammonemia (182 ± 36 μM (mean ± SD)), cerebral microdialysis was performed, and ICP and CPP were monitored. Microdialysate concentrations of hypoxanthine, inosine, lactate, and pyruvate were measured.

RESULTS

The hypoxanthine concentration was 23.0 ± 12 μM in early samples and 11.7 ± 6.8 μM in late samples (normal level ~2.0 μM). The inosine concentration was 7.2 ± 7.1 μM and 2.8 ± 1.6 μM, and the LP ratio was 55.8 ± 21.6 and 45.6 ± 20.8, respectively (normal level ~18). Hypoxanthine correlated significantly to LP ratio (r(2)=0.40, p<0.01) while inosine did not. The purine levels and L/P ratio did not correlate to ICP or CPP, nor did they differ between patients with high ICP (>20 mmHg, n=9) and patients without (n=8).

CONCLUSIONS

This study shows that the high cerebral LP ratio correlates to the hypoxanthine level in patients with acute liver failure. However, these metabolic alterations were not related to the development of intracranial hypertension.

Extracellular brain ammonia levels in association with arterial ammonia, intracranial pressure and the use of albumin dialysis devices in pigs with acute liver failure

In acute liver failure (ALF) hyperammonemia plays a mayor role in the pathogenesis of hepatic encephalopathy (HE) but does not always correlate with the severity of mental deterioration and intracranial pressure (ICP). The aim of our study was to evaluate the association with extracellular brain ammonia, ICP and the therapeutical impact of two albumin dialysis devices. ALF was induced by complete hepatectomy in 13 pigs. All pigs were monitored and treated under intensive care conditions until death. Arterial blood and cerebral microdialysis samples were collected and ICP data recorded. Additionally in 5 pigs, standard albumin dialysis and in 3 animals an albumin dialysis prototype was initiated as a tool. Arterial ammonia increased straight after hepatectomy, while extracellular brain ammonia remained on a moderate level 10 h post ALF initiation. After 16 h the brain ammonia reached arterial ammonia levels before plateauing at 1,200 microM, though the arterial ammonia continued to rise. The ICP correlated with the brain ammonia levels. No impact of the different dialysis therapies on neither blood nor brain ammonia levels was observed. In ALF the extracellular brain ammonia revealed a delayed increase compared to arterial ammonia. It correlated strongly with the ICP and could serve as a sensitive marker for HE development. Albumin dialysis did not affect blood or brain ammonia levels.

Critical care management of patients before liver transplantation

The critical care management of patients before liver transplantation is aimed at optimizing hepatic and extrahepatic organ function before the transplant operation, with a goal to favorably influence perioperative and postoperative graft and patient outcomes. Critical illness in liver disease can present in the context of acute liver failure or acute on chronic liver failure. The differing pathophysiologic processes underlying these 2 types of liver failure necessitate specific approaches to their intensive care management. In their extreme presentations, both types of liver failure present as multiorgan system failure; and therefore, the critical care management of these entities requires a systematic multiorgan system approach to address hepatic and extrahepatic organ dysfunction. This review provides a multiorgan system-based description of critical care management of acute liver failure and acute on chronic liver failure before liver transplantation.

Neuropathological changes in the brain of pigs with acute liver failure

OBJECTIVE

Cerebral edema is a serious complication of acute liver failure (ALF), which may lead to intracranial hypertension and death. An accepted tenet has been that the blood-brain barrier is intact and that brain edema is primarily caused by a cytotoxic etiology due to hyperammonemia. However, the neuropathological changes in ALF have been poorly studied. Using a well characterized porcine model we aimed to investigate ultrastructural changes in the brain from pigs suffering from ALF.

MATERIALS AND METHODS

Sixteen female Norwegian Landrace pigs weighing 27-35 kg were randomised into two groups: ALF (n = 8) and sham operated controls (n = 8). ALF was induced with an end-to-side portacaval shunt followed by ligation of the hepatic arteries. Biopsies were harvested from three different areas of the brain (frontal lobe, cerebellum, and brain stem) following eight hours of ALF and analyzed using electron microscopy.

RESULTS

Profound perivascular and interstitial edema were found in all three areas. Disruption of pericytic and astrocytic processes were seen, reflecting breakdown/lesion of the blood-brain barrier in animals suffering from ALF. Furthermore, neurons and axons were edematous and surrounded by vesicles. Severe damage to Purkinje neuron (necrosis) and damaged myelin were seen in the cerebellum and brain stem, respectively. Biopsies from sham operated animals were normal.

CONCLUSIONS

Our data support the concept that vasogenic brain edema plays an important role in the development of intracranial hypertension in pigs with ALF.

Changing face of hepatic encephalopathy: Role of inflammation and oxidative stress

The face of hepatic encephalopathy (HE) is changing. This review explores how this neurocognitive disorder, which is associated with both acute and chronic liver injury, has grown to become a dynamic syndrome that spans a spectrum of neuropsychological impairment, from normal performance to coma. The central role of ammonia in the pathogenesis of HE remains incontrovertible. However, over the past 10 years, the HE community has begun to characterise the key roles of inflammation, infection, and oxidative/nitrosative stress in modulating the pathophysiological effects of ammonia on the astrocyte. This review explores the current thoughts and evidence base in this area and discusses the potential role of existing and novel therapies that might abrogate the oxidative and nitrosative stresses inflicted on the brain in patients with, or at risk of developing, HE.

Acute liver failure

Acute liver failure is a rare disorder with high mortality and resource cost. In the developing world, viral causes predominate, with hepatitis E infection recognised as a common cause in many countries. In the USA and much of western Europe, the incidence of virally induced disease has declined substantially in the past few years, with most cases now arising from drug-induced liver injury, often from paracetamol. However, a large proportion of cases are of unknown origin. Acute liver failure can be associated with rapidly progressive multiorgan failure and devastating complications; however, outcomes have been improved by use of emergency liver transplantation. An evidence base for practice is emerging for supportive care, and a better understanding of the pathophysiology of the disorder, especially in relation to hepatic encephalopathy, will probably soon lead to further improvements in survival rates.

Increase brain lactate in hepatic encephalopathy: cause or consequence?

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome which develops as a result of liver failure or disease. Increased concentrations of brain lactate (microdialysate, cerebrospinal fluid, tissue) are commonly measured in patients with HE induced by either acute or chronic liver failure. Whether an increase in brain lactate is a cause or a consequence of HE remains undetermined. A rise in cerebral lactate may occur due to (1) blood-borne lactate (hyperlactataemia) crossing the blood-brain barrier, (2) increased glycolysis due to energy failure or impairment and (3) increased lactate production/release or decreased lactate utilization/uptake. This review explores the different reasons for lactate accumulation in the brain during liver failure and describes the possible roles of lactate in the pathogenesis of HE.

Pathogenesis and diagnosis of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common and potentially devastating neuropsychiatric complication of acute liver failure and cirrhosis. Even in its mildest form, minimal HE (MHE), the syndrome significantly impacts daily living and heralds progression to overt HE. There is maturity in the scientific understanding of the cellular processes that lead to functional and structural abnormalities in astrocytes. Hyperammonemia and subsequent cell swelling is a key pathophysiological abnormality, but this aspect alone is insufficient to fully explain the complex neurotransmitter abnormalities that may be observable using sophisticated imaging techniques. Inflammatory cytokines, reactive oxygen species activation and the role of neurosteroids on neurotransmitter binding sites are emerging pathological lines of inquiry that have yielded important new information on the processes underlying HE and offer promise of future therapeutic targets. Overt HE remains a clinical diagnosis and the neurophysiological and imaging modalities used in research studies have not transferred successfully to the clinical situation. MHE is best characterized by psychometric evaluation, but these tests can be lengthy to perform and require specific expertise to interpret. Simpler computer-based tests are now available and perhaps offer an opportunity to screen, diagnose and monitor MHE in a clinical scenario, although large-scale studies comparing the different techniques have not been undertaken. There is a discrepancy between the depth of understanding of the pathophysiology of HE and the translation of this understanding to a simple, easily understood diagnostic and longitudinal marker of disease. This is a present area of focus for the management of HE.

Diagnosis and management of acute liver failure

PURPOSE OF REVIEW

Acute liver failure (ALF) is a devastating syndrome afflicting previously healthy individuals. Early recognition of the illness is crucial, as aggressive treatment may improve outcomes. Despite significant advances in care, however, the mortality remains high (30-100%). This brief review will focus on the causes and overall management of the complications of ALF.

RECENT FINDINGS

Our knowledge of the causes of ALF has expanded significantly in the last decade. The mechanism of hepatic encephalopathy and cerebral edema in this setting continues to be elucidated and is discussed here.

SUMMARY

Improved outcomes can be achieved with the early recognition and aggressive management of ALF.

Ammonia and the neutrophil in the pathogenesis of hepatic encephalopathy in cirrhosis

Hepatic encephalopathy (HE) constitutes a neuropsychiatric syndrome which remains a major clinical problem in patients with cirrhosis. In the severest form of HE, cirrhotic patients may develop varying degrees of confusion and coma. Ammonia has been regarded as the key precipitating factor in HE, and astrocytes have been the most commonly affected cells neuropathologically. Although the evidence base supporting a pivotal role of ammonia is robust, in everyday clinical practice a consistent correlation between the concentration of ammonia in the blood and the manifest symptoms of HE is not observed. More recently the synergistic role of inflammation and infection in modulating the cerebral effects of ammonia has been shown to be important. Furthermore, it has been recognized that infection impairs brain function both in the presence and absence of liver disease. Thus it could be postulated that in the presence of ammonia, the brain is sensitized to a systemic inflammatory stimulus and is able to elicit an inflammatory response involving both proinflammatory and neurotransmitter pathways. Ammonia is not only directly toxic to astrocytes but induces neutrophil dysfunction with the release of reactive oxygen species, which contribute to oxidative stress and systemic inflammation. This may further exacerbate the cerebral effects of ammonia and potentially reduce the capacity of the neutrophil to fight microbial attack, thus inducing a vicious circle. This evidence supports the neutrophil in addition to ammonia as being culpable in the pathogenesis of HE, making the neutrophil a target for future anti-inflammatory therapeutic strategies in addition to ammonia lowering therapies.

Treatment of brain edema in acute liver failure

OPINION STATEMENT

Cerebral edema is very common in patients with acute liver failure and encephalopathy. In severe cases, it produces brain tissue shift and potentially fatal herniation. Brain swelling in acute liver failure is produced by a combination of cytotoxic (cellular) and vasogenic edema. Accumulation of ammonia and glutamine leads to disturbances in the regulation of cerebral osmolytes, increased free radical production and calcium-mediated mitochondrial injury, and alterations in glucose metabolism (inducing high levels of brain lactate), resulting in astrocyte swelling. Activation of inflammatory cytokines can cause increased blood-brain barrier permeability leading to vasogenic edema, although the relative contribution of vasogenic edema is probably minor compared with cellular swelling. Cerebral blood flow is disturbed and generally increased in patients with acute liver failure; persistent vasodilatation and loss of autoregulation may generate hyperemia, and the consequent augmentation in cerebral blood volume may exacerbate brain edema.Adequate management of intracranial hypertension demands continuous monitoring of intracranial pressure and cerebral perfusion pressure. Coagulation status should be assessed and bleeding diathesis should be treated prior to insertion of the intracranial pressure monitor. Standard treatment measures such as hyperventilation and osmotic agents (e.g., mannitol, hypertonic saline) remain useful first-line interventions. Although hypertonic saline may be preferred in patients with coexistent hyponatremia, the rate of correction of hyponatremia must be gradual to avoid the risk of osmotic demyelination. Barbiturate coma and intravenous indomethacin are available options in refractory cases. The most promising novel therapeutic alternative is the induction of moderate hypothermia (aiming for a core temperature of 32-34°C). However, the safety and efficacy of therapeutic hypothermia for brain swelling caused by liver failure still needs to be proven in randomized, controlled clinical trials. Management of intracranial pressure in patients with acute liver failure should be guided by well-defined treatment protocols.

Review article: the current management of acute liver failure

BACKGROUND

Acute liver failure is a devastating clinical syndrome with a persistently high mortality rate despite critical care advances. Orthotopic liver transplantation (OLT) is a life-saving treatment in selected cases, but effective use of this limited resource requires accurate prognostication because of surgical risks and the requirement for subsequent life-long immunosuppression.

AIM

To review the aetiology of acute liver failure, discuss the evidence behind critical care management strategies and examine potential treatment alternatives to OLT.

METHODS

Literature review using Ovid, PubMed and recent conference abstracts.

RESULTS

Paracetamol remains the most common aetiology of acute liver failure in developed countries, whereas acute viral aetiologies predominate elsewhere. Cerebral oedema is a major cause of death, and its prevention and prompt recognition are vital components of critical care support, which strives to provide multiorgan support and 'buy time' to permit either organ regeneration or psychological and physical assessment prior to acquisition of a donor organ. Artificial liver support systems do not improve mortality in acute liver failure, whilst most other interventions have limited evidence bases to support their use.

CONCLUSION

Acute liver failure remains a truly challenging condition to manage, and requires early recognition and transfer of patients to specialist centres providing intensive, multidisciplinary input and, in some cases, OLT.

Management of acute liver failure

Acute liver failure (ALF) is a syndrome of diverse etiology, in which patients without previously recognized liver disease sustain a liver injury that results in rapid loss of hepatic function. Depending on the etiology and severity of the insult, some patients undergo rapid hepatic regeneration and spontaneously recover. However, nearly 60% of patients with ALF in the US require and undergo orthotopic liver transplantation or die. Management decisions made by clinicians who initially assess individuals with ALF can drastically affect these patients' outcomes. Even with optimal early management, however, many patients with ALF develop a cascade of complications often presaged by the systemic inflammatory response syndrome, which involves failure of nearly every organ system. We highlight advances in the intensive care management of patients with ALF that have contributed to a marked improvement in their overall survival over the past 20 years. These advances include therapies that limit the extent of liver injury and maximize the likelihood of spontaneous recovery and approaches to enable prevention, recognition and early treatment of complications that lead to multi-organ-system failure, the most common cause of death. Finally, we summarize the role of orthotopic liver transplantation in salvage of the most severely affected patients.

Severity of organ failure is an independent predictor of intracranial hypertension in acute liver failure

BACKGROUND & AIMS

Ionized ammonia (NH(3)) and partial pressure of the gaseous ammonia (pNH(3)) are associated with hepatic encephalopathy and intracranial hypertension in patients with acute liver failure; NH(3) is also believed to contribute to extrahepatic organ failure. We investigated whether the severity of organ failure was associated with intracranial hypertension and evaluated the correlation between NH(3) and pNH(3) and grade of hepatic encephalopathy.

METHODS

In 87 patients with acute liver failure admitted to the intensive care unit, we simultaneously evaluated arterial ammonia, pNH(3), clinical grade of hepatic encephalopathy, the sequential organ failure assessment score (SOFA score), and evidence of intracranial hypertension.

RESULTS

In comparing patients with intracranial hypertension (n = 37) with patients without intracranial hypertension (n = 50), the highest NH(3) and pNH(3) levels and SOFA scores before onset of intracranial hypertension were independent predictors of intracranial hypertension (P < .001). Among patients with NH(3) levels less than 146 mumol/L, those with intracranial hypertension had a higher SOFA score than those without intracranial hypertension (median, 10 vs 5.5; P = .004), despite the patients' similar levels of NH(3). NH(3) (r = 0.68, P < .0001) and pNH(3) (r = 0.78, P < .0001) both correlated with grade of hepatic encephalopathy. However, in multiple regression analysis, only pNH(3) (P < .0001) was shown to be a significant independent parameter for predicting grade of hepatic encephalopathy (P = .27).

CONCLUSIONS

SOFA score and ammonia levels are independent predictors of intracranial hypertension. In patients with acute liver failure admitted to the intensive care unit, pNH(3) level is a better predictor of clinical grade of hepatic encephalopathy than arterial NH(3) level.

Hepatic encephalopathy

Hepatic encephalopathy is characterized by a wide spectrum of neuropsychiatric abnormalities and motor disturbances in patients with advanced liver disease. It is estimated to occur in 30% to 45% of patients with liver cirrhosis and in 10% to 50% of patients with transjugular intrahepatic portosystemic shunts. It can be seen in cancer patients due to multiple factors. Early diagnosis and treatment are important but can be challenging, especially in mild forms with subtle findings. This article reviews the pathogenesis, diagnostic criteria, grading, and management of hepatic encephalopathy.

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.

An overview of animal models for investigating the pathogenesis and therapeutic strategies in acute hepatic failure

Acute hepatic failure (AHF) is a severe liver injury accompanied by hepatic encephalopathy which causes multiorgan failure with an extremely high mortality rate, even if intensive care is provided. Management of severe AHF continues to be one of the most challenging problems in clinical medicine. Liver transplantation has been shown to be the most effective therapy, but the procedure is limited by shortage of donor organs. Although a number of clinical trials testing different liver assist devices are under way, these systems alone have no significant effect on patient survival and are only regarded as a useful approach to bridge patients with AHF to liver transplantation. As a result, reproducible experimental animal models resembling the clinical conditions are still needed. The three main approaches used to create an animal model for AHF are: surgical procedures, toxic liver injury and infective procedures. Most common models are based on surgical techniques (total/partial hepatectomy, complete/transient devascularization) or the use of hepatotoxic drugs (acetaminophen, galactosamine, thioacetamide, and others), and very few satisfactory viral models are available. We have recently developed a viral model of AHF by means of the inoculation of rabbits with the virus of rabbit hemorrhagic disease. This model displays biochemical and histological characteristics, and clinical features that resemble those in human AHF. In the present article an overview is given of the most widely used animal models of AHF, and their main advantages and disadvantages are reviewed.

L-ornithine phenylacetate attenuates increased arterial and extracellular brain ammonia and prevents intracranial hypertension in pigs with acute liver failure

Hyperammonemia is a feature of acute liver failure (ALF), which is associated with increased intracranial pressure (ICP) and brain herniation. We hypothesized that a combination of L-ornithine and phenylacetate (OP) would synergistically reduce toxic levels of ammonia by (1) L-ornithine increasing glutamine production (ammonia removal) through muscle glutamine synthetase and (2) phenylacetate conjugating with the ornithine-derived glutamine to form phenylacetylglutamine, which is excreted into the urine. The aims of this study were to determine the effect of OP on arterial and extracellular brain ammonia concentrations as well as ICP in pigs with ALF (induced by liver devascularization). ALF pigs were treated with OP (L-ornithine 0.07 g/kg/hour intravenously; phenylbutyrate, prodrug for phenylacetate; 0.05 g/kg/hour intraduodenally) for 8 hours following ALF induction. ICP was monitored throughout, and arterial and extracellular brain ammonia were measured along with phenylacetylglutamine in the urine. Compared with ALF + saline pigs, treatment with OP significantly attenuated concentrations of arterial ammonia (589.6 +/- 56.7 versus 365.2 +/- 60.4 mumol/L [mean +/- SEM], P= 0.002) and extracellular brain ammonia (P= 0.01). The ALF-induced increase in ICP was prevented in ALF + OP-treated pigs (18.3 +/- 1.3 mmHg in ALF + saline versus 10.3 +/- 1.1 mmHg in ALF + OP-treated pigs;P= 0.001). The value of ICP significantly correlated with the concentration of extracellular brain ammonia (r(2) = 0.36,P< 0.001). Urine phenylacetylglutamine levels increased to 4.9 +/- 0.6 micromol/L in ALF + OP-treated pigs versus 0.5 +/- 0.04 micromol/L in ALF + saline-treated pigs (P< 0.001).

CONCLUSION

L-Ornithine and phenylacetate act synergistically to successfully attenuate increases in arterial ammonia, which is accompanied by a significant decrease in extracellular brain ammonia and prevention of intracranial hypertension in pigs with ALF.

ESPEN Guidelines on Parenteral Nutrition: hepatology

Parenteral nutrition (PN) offers the possibility to increase or to ensure nutrient intake in patients, in whom sufficient nutrition by oral or enteral alone is insufficient or impossible. Complementary to the ESPEN guideline on enteral nutrition of liver disease (LD) patients the present guideline is intended to give evidence-based recommendations for the use of PN in LD. For this purpose three paradigm conditions of LD were chosen: alcoholic steatohepatitis (ASH), liver cirrhosis and acute liver failure. The guideline was developed by an interdisciplinary expert group in accordance with officially accepted standards and is based on all relevant publications since 1985. The guideline was presented on the ESPEN website and visitors' criticism and suggestions were welcome and included in the final revision. PN improves nutritional state and liver function in malnourished patients with ASH. PN is safe and improves mental state in patients with cirrhosis and severe HE. Perioperative (including liver transplantation) PN is safe and reduces the rate of complications. In acute liver failure PN is a safe second-line option to adequately feed patients in whom enteral nutrition is insufficient or impossible.

Advance in roles of ammonia and cytokines in hepatic encephalopathy

Hyperammonia theory has been thought as a most feasible mechanism of hepatic encephalopathy following liver injury. Astroglial swelling was reckoned as pathological basis of hepatic encephalopathy. Many assumed mechanisms include oxidative stress activation, mitochondrial permeability transition and glutamine theory, by which ammonia acts on astroglial swelling. Cytokins have influence on the development of hepatic encephalopathy. There are mutual effects of both ammonia and cytokines inducing hepatic encephalopathy.

Efficacy of L-ornithine L-aspartate in acute liver failure: a double-blind, randomized, placebo-controlled study

BACKGROUND & AIMS

In acute liver failure (ALF), high blood ammonia levels have been documented that correlate with mortality and complications. L-ornithine L-aspartate (LOLA) reduces ammonia levels by increasing hepatic ammonia disposal and its peripheral metabolism. Present study evaluated efficacy and ammonia lowering effect of LOLA in ALF.

METHODS

This study was placebo-controlled and blinded. We randomized 201 patients with ALF between January 2005 and October 2007 to either placebo or LOLA infusions (30 g daily) for 3 days. Arterial ammonia was measured at baseline and daily for 6 days. The primary end point was improvement in survival. The study followed CONSORT guidelines and was registered at the ClinicalTrials.gov (Identifier: NCT00470314).

RESULTS

There was no reduction in mortality with LOLA treatment (mortality: 33.3% in placebo and 42.4% in LOLA; relative risk of death 1.27; 95% CI: 0.88-1.85; P = .204). By multivariate analysis, ammonia levels were an independent predictor of survival. There was significant decrease in ammonia levels in both groups with time (P < .001), but the levels of ammonia between the randomized groups at any time point, either during the 72 hours of LOLA infusion or during the follow-up were similar (P = .492). There was no difference between the 2 groups in the improvement in encephalopathy grade (P = .418), consciousness recovery time (P = .347), survival time (P = .612), or complications like seizures (P = .058) and renal failure (P = .615). The fetal outcome was also similar (P = .172). No adverse drug effect was noted.

CONCLUSIONS

LOLA infusion did not lower the ammonia or improved survival in ALF.

Identifying the direct effects of ammonia on the brain

Elevated concentrations of ammonia in the brain as a result of hyperammonemia leads to cerebral dysfunction involving a spectrum of neuropsychiatric and neurological symptoms (impaired memory, shortened attention span, sleep-wake inversions, brain edema, intracranial hypertension, seizures, ataxia and coma). Many studies have demonstrated ammonia as a major player involved in the neuropathophysiology associated with liver failure and inherited urea cycle enzyme disorders. Ammonia in solution is composed of a gas (NH(3)) and an ionic (NH(4) (+)) component which are both capable of crossing plasma membranes through diffusion, channels and transport mechanisms and as a result have a direct effect on pH. Furthermore, NH(4) (+) has similar properties as K(+) and, therefore, competes with K(+) on K(+) transporters and channels resulting in a direct effect on membrane potential. Ammonia is also a product as well as a substrate for many different biochemical reactions and consequently, an increase in brain ammonia accompanies disturbances in cerebral metabolism. These direct effects of elevated ammonia concentrations on the brain will lead to a cascade of secondary effects and encephalopathy.

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.

Outcome after wait-listing for emergency liver transplantation in acute liver failure: a single centre experience

BACKGROUND/AIMS

Though emergency liver transplantation (ELT) is an established treatment for severe acute liver failure (ALF), outcomes are inferior to elective surgery. Despite prioritization, many patients deteriorate, becoming unsuitable for ELT.

METHODS

We examined a single-centre experience of 310 adult patients with ALF registered for ELT over a 10-year period to determine factors associated with failure to transplant, and in those patients undergoing ELT, those associated with 90-day mortality.

RESULTS

One hundred and thirty-two (43%) patients had ALF resulting from paracetamol and 178 (57%) from non-paracetamol causes. Seventy-four patients (24%) did not undergo surgery; 92% of these died. Failure to transplant was more likely in patients requiring vasopressors at listing (hazard ratio 1.9 (95% CI 1.1-3.6)) paracetamol aetiology (2.5 (1.4-4.6)) but less likely in blood group A (0.5 (0.3-0.9)). Post-ELT survival at 90-days and one-year increased from 66% and 63% in 1994-1999 to 81% and 79% in 2000-2004 (p<0.01). Four variables were associated with post-ELT mortality; age >45 years (3 (1.7-5.3)), vasopressor requirement (2.2 (1.3-3.8), transplantation before 2000 (1.9 (1.1-3.3)) and use of high-risk grafts (2.3 (1.3-4.2).

CONCLUSIONS

The data indicate improved outcomes in the later era, despite higher level patient dependency and greater use of high-risk grafts, through improved graft/recipient matching.

Critical management decisions in patients with acute liver failure

Few admissions to the ICU present a greater clinical challenge than the patient with acute liver failure (ALF), the syndrome of abrupt loss of liver function in a previously unaffected individual. Although advances in the intensive care management of patients with ALF have improved survival, the prognosis of ALF remains poor, with a 33% mortality rate and a 25% liver transplant rate in the United States. ALF adversely affects nearly every organ system, with most deaths occurring from sepsis and subsequent multiorgan system failure, and cerebral edema, resulting in intracranial hypertension (ICH) and brainstem herniation. Unfortunately, the optimal management of ALF remains poorly defined, and practices are often based on local experience and case reports rather than on randomized, controlled clinical trials. The paramount question in any patient presenting with ALF remains defining an etiology, since specific antidotes can save lives and spare the liver. This article will consider recent advances in the assignment of an etiology, the administration of etiology-specific treatment to abate the liver injury, and the management of complications (eg, infection, cerebral edema, and the bleeding diathesis) in patients with ALF. New data on the administration of N-acetylcysteine to patients with non-acetaminophen ALF, the treatment of ICH, and assessment of the need for liver transplantation will also be presented.

Encephalopathy and cerebral edema in the setting of acute liver failure: pathogenesis and management

Cerebral edema is a potential life-threatening complication in patients with acute liver failure who progress to grade III/IV encephalopathy. The incidence is variably reported but appears to be most prevalent in those patients with hyperacute liver failure as opposed to subacute forms of liver failure. In those patients who are deemed at risk of cerebral edema and raised intracranial pressure, insertion of an intra-cranial pressure monitoring device may be considered to optimize treatment and interventions. The pathogenesis of cerebral edema in this setting remains controversial, although recent work suggests a pivotal role for arterial ammonia, whose effects appear to be potentiated by the presence of systemic inflammation. Recent work has also suggested the import of free radical formation occurring at a mitochondrial level as being the potential mediator of cellular dysfunction as opposed to ammonia per se. Treatment of such patients requires a multi-disciplinary approach incorporating both hepatology and critical care. In a significant proportion of such cases, consideration of liver transplantation may be required. Treatment should be focused at optimizing liver function and regenerative capacity and minimizing the inflammatory milieu. Controlled studies are lacking and much of the management has been extrapolated from neurocritical care. Sustained elevation of intracranial pressure may be responsive to mannitol or hypertonic saline bolus, and in those with hyperemia indomethacin has been reported as beneficial in case series. Recently, interest has developed into the use of cooling in the management of patients with acute liver failure and raised intracranial pressure. Animal studies support this treatment option as do case series, although randomized trials are still awaited.

Therapeutic hypothermia for acute liver failure: toward a randomized, controlled trial in patients with advanced hepatic encephalopathy

Acute liver failure (ALF), the abrupt loss of liver function in a patient without previous liver disease, remains a highly mortal condition. Patients with ALF often succumb to their liver injury after the development of cerebral edema, resulting in intracranial hypertension and brain herniation. While the management of cerebral edema in ALF always includes the administration of osmotically active agents, osmotherapy often reduces intracranial pressure (ICP) insufficiently, such that herniation may be delayed but not prevented. Therapeutic hypothermia, the intentional reduction of body core temperature, has been increasingly used to treat cerebral edema in patients with traumatic and hypoxic brain injury. Data in animal models of ALF also suggest that hypothermia is effective in the prevention and treatment of cerebral edema, and case reports in humans have suggested that hypothermia is an effective bridge to orthotopic liver transplantation. A randomized, controlled trial comparing the management of ALF patients under normothermic and hypothermic conditions is a logical extension of these preliminary observations. Herein, we consider the many difficulties which will be encountered in the design of such a trial in patients with ALF at high risk of developing cerebral edema.

Prevention and management of brain edema in patients with acute liver failure

1. Intracranial pressure is the pressure exerted by the cranial contents on the dural envelope and consists of the partial pressures of the brain, blood, and cerebrospinal fluid. 2. Severe cases of acute liver failure are frequently complicated by brain edema (due to cytotoxic edema) and an increase in cerebral blood flow while the cerebrospinal fluid volume remains constant. 3. The development of intracranial hypertension in patients with acute liver failure may be controlled by manipulation of the position, body temperature, plasma tonicity, arterial carbon dioxide tension, and arterial pressure. 4. If intracranial hypertension evolves despite these first-tier interventions, increased sedation, induction of hypothermia (body temperature of 33 degrees C to 34 degrees C), and the use of anti-inflammatory drugs may help secure brain viability.

Acute liver failure-induced death of rats is delayed or prevented by blocking NMDA receptors in brain

Developing procedures to delay the mechanisms of acute liver failure-induced death would increase patients' survival by allowing time for liver regeneration or to receive a liver for transplantation. Hyperammonemia is a main contributor to brain herniation and mortality in acute liver failure (ALF). Acute ammonia intoxication in rats leads to N-methyl-D-aspartate (NMDA) receptor activation in brain. Blocking these receptors prevents ammonia-induced death. Ammonia-induced activation of NMDA receptors could contribute to ALF-induced death. If this were the case, blocking NMDA receptors could prevent or delay ALF-induced death. The aim of this work was to assess 1) whether ALF leads to NMDA receptors activation in brain in vivo and 2) whether blocking NMDA receptors prevents or delays ALF-induced death of rats. It is shown, by in vivo brain microdialysis, that galactosamine-induced ALF leads to NMDA receptors activation in brain. Blocking NMDA receptors by continuous administration of MK-801 or memantine through miniosmotic pumps affords significant protection against ALF-induced death, increasing the survival time approximately twofold. Also, when liver injury is not 100% lethal (1.5 g/kg galactosamine), blocking NMDA receptors increases the survival rate from 23 to 62%. This supports that blocking NMDA receptors could have therapeutic utility to improve survival of patients with ALF.

Management of sepsis in patients with liver failure

PURPOSE OF REVIEW

Sepsis constitutes the most common cause of death in the ICU. Liver dysfunction is manifested among previously normal subjects with sepsis but even more so in populations with preexisting liver disease. Managing these patients is more challenging. We will review recent literature in sepsis and liver disease, and their bedside application.

RECENT FINDINGS

At the cellular-chemical level, studies showed that platelet aggregation and neutrophil activation occur before and are independent of microcirculatory changes which are apparent in all animal septic models. At the clinical level, early goal-directed therapy, euglycemia, low tidal volume ventilation, and early and appropriately dosed renal replacement therapy among others are all tools to improve sepsis survival. Acknowledgement of liver disease as an immunocompromised host, and identification and treatment of complications can positively change the outcome of sepsis in liver disease.

SUMMARY

Much has been advanced in the field of sepsis management. Understanding the pathophysiology of liver dysfunction and decompensation of a diseased liver incites questions for future research. Early goal-directed therapy, lactate clearance, glycemic control, low volume ventilation strategies, nutrition, adrenal insufficiency, renal dysfunction, hepatorenal syndrome prevention and treatment are some of the issues in the management of sepsis, with or without liver disease, that are relevant in this review.

Intensive care management of acute liver failure

PURPOSE OF REVIEW

The mortality of acute liver failure remains unacceptably high and liver transplantation is the only effective treatment available to date. This review focuses on new research developments in the field and aims to provide a pragmatic organ-based treatment approach for liver failure patients requiring intensive care support.

RECENT FINDINGS

The pathophysiological basis for cerebral edema formation in acute liver failure continued to be the focus of various investigations. In-vivo observations confirmed the link between ammonia, cerebral glutamine content and intracranial hypertension. The role of arterial ammonia as an important prognostic indicator formed the basis of prospective, observational studies. Reduced monocytic HLA-DR expression linked acute liver failure with poor prognosis, and the cerebral effects and side effects of vasoactive therapy with terlipressin were investigated with two studies showing contradictory results.

SUMMARY

Despite increased knowledge of the pathophysiological events leading to organ dysfunction in acute liver failure, supportive treatment options remain limited in their efficacy and largely noncurative.

Hepatic encephalopathy

Hepatic encephalopathy (HE) is a syndrome of neuropsychiatric dysfunction caused by portosystemic venous shunting, with or without intrinsic liver disease. Patients with hepatic encephalopathy often present with the onset of mental status changes ranging from subtle psychologic abnormalities to profound coma. Several hypotheses have been proposed to explain the mental impairment associated with portosystemic shunting and liver disease. Clinicians diagnosing HE frequently have the opportunity to intervene and reverse severe HE, even hepatic coma. The recent advances in understanding and management of HE are the subject of this article.