Cerebral hemodynamic and metabolic profiles in fulminant hepatic failure: relationship to outcome

Role of point-of-care ultrasound (POCUS) in clinical hepatology

Hospitalized patients with cirrhosis frequently require critical care management for sepsis, HE, respiratory failure, acute variceal bleeding, acute kidney injury (AKI), shock, and optimization for liver transplantation, while outpatients have unique care considerations. Point-of-care ultrasonography (POCUS) enhances bedside examination of the hepatobiliary system and relevant extrahepatic sites. POCUS includes cardiac US and is used to assess volume status and hemodynamic parameters like cardiac output, systemic vascular resistance, cardiac contractility, and pulmonary artery pressure, which aid in the early and accurate diagnosis of heart failure, cirrhotic cardiomyopathy, porto-pulmonary hypertension, hepatopulmonary syndrome, arrhythmia, and pulmonary embolism. This also helps in fluid management and vasopressor use in the resuscitation of patients with cirrhosis. Lung ultrasound (LUS) can help in differentiating pneumonia, effusion, and edema. Further, US guides interventions such as line placement, drainage of abdominal collections/abscesses, relief of tension pneumothorax, drainage of pleural and pericardial effusions, and biliary drainage in cholangitis. Additionally, its role is essential to assess liver masses foci of sepsis, for appropriate sites for paracentesis, and to assess for vascular disorders such as portal vein or hepatic vein thrombosis. Renal US can identify renal and postrenal causes of AKI and aid in diagnosis of prerenal AKI through volume assessment. In this review, we address the principles and methods of POCUS in hospitalized patients and in outpatients with cirrhosis and discuss the application of this diverse modality in clinical hepatology.

TCD assessment in fulminant hepatic failure: Improvements in cerebral autoregulation after liver transplantation

INTRODUCTION AND OBJECTIVES

Acute liver failure, also known as fulminant hepatic failure (FHF), includes a spectrum of clinical entities characterized by acute liver injury, severe hepatocellular dysfunction and hepatic encephalopathy. The objective of this study was to assess cerebral autoregulation (CA) in 25 patients (19 female) with FHF and to follow up with seventeen of these patients before and after liver transplantation.

PATIENTS AND METHODS

The mean age was 33.8 years (range 14-56, SD 13.1 years). Cerebral hemodynamics was assessed by transcranial Doppler (TCD) bilateral recordings of cerebral blood velocity (CBv) in the middle cerebral arteries (MCA).

RESULTS

CA was assessed based on the static CA index (SCAI), reflecting the effects of a 20-30 mmHg increase in mean arterial blood pressure on CBv induced with norepinephrine infusion. SCAI was estimated at four time points: pretransplant and on the 1st, 2nd and 3rd posttransplant days, showing a significant difference between pre- and posttransplant SCAI (p = 0.005). SCAI peaked on the third posttransplant day (p = 0.006). Categorical analysis of SCAI showed that for most patients, CA was reestablished on the second day posttransplant (SCAI > 0.6).

CONCLUSIONS

These results suggest that CA impairment pretransplant and on the 1st day posttransplant was re-established at 48-72 h after transplantation. These findings can help to improve the management of this patient group during these specific phases, thereby avoiding neurological complications, such as brain swelling and intracranial hypertension.

Defining a Taxonomy of Intracranial Hypertension: Is ICP More Than Just a Number?

Intracranial pressure (ICP) monitoring and control is a cornerstone of neuroanesthesia and neurocritical care. However, because elevated ICP can be due to multiple pathophysiological processes, its interpretation is not straightforward. We propose a formal taxonomy of intracranial hypertension, which defines ICP elevations into 3 major pathophysiological subsets: increased cerebral blood volume, masses and edema, and hydrocephalus. (1) Increased cerebral blood volume increases ICP and arises secondary to arterial or venous hypervolemia. Arterial hypervolemia is produced by autoregulated or dysregulated vasodilation, both of which are importantly and disparately affected by systemic blood pressure. Dysregulated vasodilation tends to be worsened by arterial hypertension. In contrast, autoregulated vasodilation contributes to intracranial hypertension during decreases in cerebral perfusion pressure that occur within the normal range of cerebral autoregulation. Venous hypervolemia is produced by Starling resistor outflow obstruction, venous occlusion, and very high extracranial venous pressure. Starling resistor outflow obstruction tends to arise when cerebrospinal fluid pressure causes venous compression to thus increase tissue pressure and worsen tissue edema (and ICP elevation), producing a positive feedback ICP cycle. (2) Masses and edema are conditions that increase brain tissue volume and ICP, causing both vascular compression and decrease in cerebral perfusion pressure leading to oligemia. Brain edema is either vasogenic or cytotoxic, each with disparate causes and often linked to cerebral blood flow or blood volume abnormalities. Masses may arise from hematoma or neoplasia. (3) Hydrocephalus can also increase ICP, and is either communicating or noncommunicating. Further research is warranted to ascertain whether ICP therapy should be tailored to these physiological subsets of intracranial hypertension.

Neurological Monitoring in Acute Liver Failure

Cerebral oedema and Intracranial Hypertension (ICH) are serious complications of acute liver failure affecting approximately 30% of patients, resulting in neurological injury or death. Multiple pathogenetic mechanisms contribute to the pathogenesis of HE including circulating neurotoxins such as ammonia, systemic and neuro-inflammation, infection and cerebral hyperaemia due to loss of cerebral vascular autoregulation. Early recognition and diagnosis is often difficult as clinical signs of elevated Intracranial Pressure (ICP) are not uniformly present and maybe masked by other organ support. ICP monitoring provides early diagnosis and monitoring of ICH, allowing targeted therapeutic interventions for prevention and treatment. ICP monitoring is the subject of much debate and there exists significant heterogeneity of clinical practice regarding its use. The procedure is associated with risks of haemorrhage but may be considered in highly selected patients such as those with highest risk for ICH awaiting transplant to allow for patient selection and optimisation. There is limited evidence that ICP monitoring confers a survival benefit which may explain why in the context of risk benefit analysis there is reduced utilisation in clinical practice. Less or non-invasive techniques of neurological monitoring such as measurement of jugular venous oxygen saturation to assess cerebral oxygen utilisation, and transcranial Doppler CNS to measure cerebral blood flow can provide important clinical information. They should be considered in combination as part of a multi-modal platform utilising specific roles of each system and incorporated within locally agreed algorithms. Other tools such as near-infrared spectrophotometry, optic nerve ultrasound and serum biomarkers of brain injury are being evaluated but are not used routinely in current practice.

Lawrence K, Amendolia O, Quattrone F, Balu R, Kofke WA, Yodh AG. Noninvasive continuous optical monitoring of absolute cerebral blood flow in critically ill adults

We investigate a scheme for noninvasive continuous monitoring of absolute cerebral blood flow (CBF) in adult human patients based on a combination of time-resolved dynamic contrast-enhanced near-infrared spectroscopy (DCE-NIRS) and diffuse correlation spectroscopy (DCS) with semi-infinite head model of photon propogation. Continuous CBF is obtained via calibration of the DCS blood flow index (BFI) with absolute CBF obtained by intermittent intravenous injections of the optical contrast agent indocyanine green. A calibration coefficient ( γ ) for the CBF is thus determined, permitting conversion of DCS BFI to absolute blood flow units at all other times. A study of patients with acute brain injury ( N = 7 ) is carried out to ascertain the stability of γ . The patient-averaged DCS calibration coefficient across multiple monitoring days and multiple patients was determined, and good agreement between the two calibration coefficients measured at different times during single monitoring days was found. The patient-averaged calibration coefficient of 1.24 × 10 9    ( mL / 100    g / min ) / ( cm 2 / s ) was applied to previously measured DCS BFI from similar brain-injured patients; in this case, absolute CBF was underestimated compared with XeCT, an effect we show is primarily due to use of semi-infinite homogeneous models of the head.

Analysis of cerebral blood flow and intracranial hypertension in critical patients with non-hepatic hyperammonemia

Hyperammonemia in adults is generally associated with cerebral edema, decreased cerebral metabolism, and increased cerebral blood flow. The aim of this study was to evaluate the association between non-hepatic hyperammonemia and intracranial hypertension assessed by Doppler flowmetry and measurement of the optic nerve sheath. A prospective cohort study in critically ill patients hospitalized in intensive care units of a University Hospital between March 2015 and February 2016. Clinical data and severity scores were collected and the Glasgow coma scale was recorded. Serial serum ammonia dosages were performed in all study patients. Transcranial Doppler evaluation was carried out for the first 50 consecutive results of each stratum of ammonemia: normal (<35 μmol/L), mild hyperammonemia (≥35 μmol/L and < 50 μmol/L), moderate hyperammonemia (≥50 μmol/L and < 100 μmol/L), and severe hyperammonemia (≥100 μmol/L). The measurement of the optic nerve sheath was performed at the same time as the Doppler examination if the patient scored less than 8 on the Glasgow coma scale. There was no difference in flow velocity in the cerebral arteries between patients with and without hyperammonemia. Patients with hyperammonemia presented longer ICU stay. Optic nerve sheath thickness was higher in the group with severe hyperammonemia and this group presented an association with intracranial hypertension. Higher mortality was observed in the severe hyperammonemia group. There was an association between severe hyperammonemia and signs of intracranial hypertension. No correlation was found between ammonia levels and cerebral blood flow velocity through the Doppler examination.

Impaired cerebral microcirculation induced by ammonium chloride in rats is due to cortical adenosine release

BACKGROUND & AIMS

Liver failure results in hyperammonaemia, impaired regulation of cerebral microcirculation, encephalopathy, and death. However, the key mediator that alters cerebral microcirculation remains unidentified. In this study we show that topically applied ammonium significantly increases periarteriolar adenosine tone on the brain surface of healthy rats and is associated with a disturbed microcirculation.

METHODS

Cranial windows were prepared in anaesthetized Wistar rats. The flow velocities were measured by speckle contrast imaging and compared before and after 30 min of exposure to 10 mM ammonium chloride applied on the brain surface. These flow velocities were compared with those for control groups exposed to artificial cerebrospinal fluid or ammonium plus an adenosine receptor antagonist. A flow preservation curve was obtained by analysis of flow responses to a haemorrhagic hypotensive challenge and during stepwise exsanguination. The periarteriolar adenosine concentration was measured with enzymatic biosensors inserted in the cortex.

RESULTS

After ammonium exposure the arteriolar flow velocity increased by a median (interquartile range) of 21.7% (23.4%) vs. 7.2% (10.2%) in controls (n = 10 and n = 6, respectively, p <0.05), and the arteriolar surface area increased. There was a profound rise in the periarteriolar adenosine concentration. During the hypotensive challenge the flow decreased by 27.8% (14.9%) vs. 9.2% (14.9%) in controls (p <0.05). The lower limit of flow preservation remained unaffected, 27.7 (3.9) mmHg vs. 27.6 (6.4) mmHg, whereas the autoregulatory index increased, 0.29 (0.33) flow units per millimetre of mercury vs. 0.03 (0.21) flow units per millimetre of mercury (p <0.05). When ammonium exposure was combined with topical application of an adenosine receptor antagonist, the autoregulatory index was normalized.

CONCLUSIONS

Vasodilation of the cerebral microcirculation during exposure to ammonium chloride is associated with an increase in the adenosine tone. Application of a specific adenosine receptor antagonist restores the regulation of the microcirculation. This indicates that adenosine could be a key mediator of the brain dysfunction seen during hyperammonaemia and is a potential therapeutic target.

LAY SUMMARY

In patients with liver failure, disturbances in brain function are caused in part by ammonium toxicity. In our project we studied how ammonia, through adenosine release, affects the blood flow in the brain of rats. In our experimental model we demonstrated that the detrimental effect of ammonia on blood flow regulation was counteracted by blocking the adenosine receptors in the brain. With this observation we identified a novel potential treatment target. If we can confirm our findings in a future clinical study, this might help patients with liver failure and the severe condition called hepatic encephalopathy.

Pathophysiological central nervous system changes in a porcine model of acetaminophen-induced acute liver failure

BACKGROUND

Critical care management of patients suffering from acute liver failure (ALF) continues to be challenging. Animal models studying the pathophysiological central nervous system alterations during the course of ALF provide an opportunity to improve diagnostic and therapeutic strategies. The aim of this study was to analyse the course of cerebral oxygenation in addition to conventional neuromonitoring during the course of acetaminophen-induced ALF.

METHODS

ALF was induced by intrajejunal acetaminophen administration in 20 German landrace pigs. All animals underwent invasive hemodynamic and neuromonitoring and were maintained under standardized intensive care support. Neuromonitoring consisted of continuous intraparenchymatous recording of intracranial pressure and brain partial oxygen pressure. Hemodynamic and ventilation parameters were continuously recorded; laboratory parameters were analysed every eight hours. Mean values were compared using the Wilcoxon test.

RESULTS

Acute liver failure occurred in all intoxicated animals after 23±2h, resulting in death due to ALF after further 15±2h. Continuous neuromonitoring was performed in all animals during the whole experiment without observing signs of intracranial haemorrhage. Two hours after manifestation of ALF an increase in brain tissue oxygen (PtiO2) was observed. Brain oxygenation stayed stable until nine hours before death. Intracranial pressure (ICP) remained basically at a plateau level until manifestation of ALF. In the following ten hours a linear and slow increase was observed until five hours before death, followed by a fast and continuous rise in ICP to a final level of 35±1mmHg. Cerebral perfusion pressure (CPP) began to decrease 25h prior to exitus, further decreasing to 18±2mmHg at the end of the experiment. A strong negative linear correlation was found between PtiO2 and ICP (R=0.97). Arterial partial pressure of oxygen (PaO2) below 100mmHg was associated with lower PtiO2 levels. Changes in arterial partial pressure of carbon dioxide (PaC02) did not influence PtiO2 values. Hemoglobin values below 7g/dl were associated with lower PtiO2 values.

CONCLUSIONS

The results of our experiments demonstrate that ICP and PtiO2 measurements indicate impending damage well before serious complications occur and their use should be considered in order to protect endangered brain function in the presence of acetaminophen-induced ALF.

Protocol based invasive intracranial pressure monitoring in acute liver failure: feasibility, safety and impact on management

Background

Acute liver failure (ALF) may result in elevated intracranial pressure (ICP). While invasive ICP monitoring (IICPM) may have a role in ALF management, these patients are typically coagulopathic and at risk for intracranial hemorrhage (ICH). Contemporary ICP monitoring techniques and coagulopathy reversal strategies may be associated with a lower risk of hemorrhage. Our objective was to evaluate the safety, feasibility, impact on clinical management and outcomes associated with protocol-directed use of IICPM in ALF.

Methods

Adult patients admitted between June 2011 and October 2016, with ALF and grade-4 encephalopathy with a reasonable likelihood of survival, were eligible for IICPM. The coagulopathy reversal protocol included administration of recombinant Factor VIIa (rFVIIa) and desmopressin, a goal platelet count >50,000/mm³ and fibrinogen >100 mg/dL. Monitor insertion was performed within an hour of the rFVIIa dose. Only intraparenchymal monitors were used. Computed tomography of the brain was performed prior to and within 24 hours of monitor placement. Outcomes of interest included ICH, sustained intracranial hypertension, therapeutic intensity level (TIL) for ICP management, mortality and functional outcome on the Glasgow Outcome Scale (GOS) at discharge and 6 months.

Results

A total of 24/37 patients (65%) with ALF underwent IICPM. The most common reason for exclusion was encephalopathy grade <4. Four patients underwent liver transplantation. There was one asymptomatic ICH following IICPM, in a patient who had an excellent outcome. Sustained intracranial hypertension occurred in 13/24 monitored patients (54%), 5/24 (21%) required extreme measures (TIL-4) for ICP control, which were successful in 4 patients: 12/24 patients (50%) died but only 4 deaths (17%) were attributed to intracranial hypertension. Six of the 8 survivors with 6-month follow up had good functional outcome (GOS >3).

Conclusions

Protocol-directed use of IICPM in ALF is feasible, associated with a low incidence of serious complications and has a significant impact on clinical management.

Gene expression profiling of brain cortex microvessels may support brain vasodilation in acute liver failure rat models

Development of brain edema in acute liver failure can increase intracranial pressure, which is a severe complication of the disease. However, brain edema is neither entirely cytotoxic nor vasogenic and the specific action of the brain microvasculature is still unknown. We aimed to analyze gene expression of brain cortex microvessels in two rat models of acute liver failure. In order to identify global gene expression changes we performed a broad transcriptomic approach in isolated brain cortex microvessels from portacaval shunted rats after hepatic artery ligation (HAL), hepatectomy (HEP), or sham by array hybridization and confirmed changes in selected genes by RT-PCR. We found 157 and 270 up-regulated genes and 143 and 149 down-regulated genes in HAL and HEP rats respectively. Western blot and immunohistochemical assays were performed in cortex and ELISA assays to quantify prostaglandin E metabolites were performed in blood of the sagittal superior sinus. We Identified clusters of differentially expressed genes involving inflammatory response, transporters-channels, and homeostasis. Up-regulated genes at the transcriptional level were associated with vasodilation (prostaglandin-E synthetase, prostaglandin-E receptor, adrenomedullin, bradykinin receptor, adenosine transporter), oxidative stress (hemoxygenase, superoxide dismutase), energy metabolism (lactate transporter) and inflammation (haptoglobin). The only down-regulated tight junction protein was occludin but slightly. Prostaglandins levels were increased in cerebral blood with progression of liver failure. In conclusion, in acute liver failure, up-regulation of several genes at the level of microvessels might suggest an involvement of energy metabolism accompanied by cerebral vasodilation in the cerebral edema at early stages.

Multimodal brain monitoring in fulminant hepatic failure

Acute liver failure, also known as fulminant hepatic failure (FHF), embraces a spectrum of clinical entities characterized by acute liver injury, severe hepatocellular dysfunction, and hepatic encephalopathy. Cerebral edema and intracranial hypertension are common causes of mortality in patients with FHF. The management of patients who present acute liver failure starts with determining the cause and an initial evaluation of prognosis. Regardless of whether or not patients are listed for liver transplantation, they should still be monitored for recovery, death, or transplantation. In the past, neuromonitoring was restricted to serial clinical neurologic examination and, in some cases, intracranial pressure monitoring. Over the years, this monitoring has proven insufficient, as brain abnormalities were detected at late and irreversible stages. The need for real-time monitoring of brain functions to favor prompt treatment and avert irreversible brain injuries led to the concepts of multimodal monitoring and neurophysiological decision support. New monitoring techniques, such as brain tissue oxygen tension, continuous electroencephalogram, transcranial Doppler, and cerebral microdialysis, have been developed. These techniques enable early diagnosis of brain hemodynamic, electrical, and biochemical changes, allow brain anatomical and physiological monitoring-guided therapy, and have improved patient survival rates. The purpose of this review is to discuss the multimodality methods available for monitoring patients with FHF in the neurocritical care setting.

Therapeutic hypothermia as a bridge to transplantation in patients with fulminant hepatic failure

The most important topics in fulminant hepatic failure are cerebral edema and intracranial hypertension. Among all therapeutic options, systemic induced hypothermia to 33 - 34ºC has been reported to reduce the high pressure and increase the time during which patients can tolerate a graft. This review discusses the indications and adverse effects of hypothermia.

Factors affecting intraoperative changes in regional cerebral oxygen saturation in patients undergoing liver transplantation

BACKGROUND

Regional oxygen saturation (rSO(2)) is a sensitive marker of cerebral hypoperfusion during liver transplantation. However, bilirubin absorbs near-infrared light, resulting in falsely low rSO(2) values. We sought to determine whether rSO(2) values vary in response to bilirubin concentrations during liver transplantation and to assess whether rSO(2) changes were associated with factors reflecting cerebral oxygen delivery in patients with hyperbilirubinemia.

METHODS

Measurements of rSO(2) values continuous cardiac output (CO), mean arterial pressure, central venous pressure, body temperature, arterial blood gas analysis, and laboratory parameters were simultaneously performed at 1 hour after the surgical incision (baseline) and at 3 predetermined times during the anhepatic and neohepatic phases in 95 end-stage liver disease patients including 67 males of Child A/B/C/29/29/37 categories respectively. Relationships between changes in parameters were evaluated by correlation and multivariate regression analyses.

RESULTS

The 273 measurements revealed changes in rSO(2) (range, -18% to 40%) to correlate significantly with alterations in hemoglobin (Hb), serum glucose, lactate, prothrombin time, pH, partial arterial CO(2) pressure (PaCO(2)), and CO, but not with serum total bilirubin (TB). Multivariate linear regression analysis revealed that changes in Hb, CO, PaCO(2), and pH were independent of rSO(2) changes during liver transplantation.

CONCLUSIONS

Our findings showed that rSO(2) changes were independently associated with factors reflecting cerebral oxygen delivery, such as Hb, CO, PaCO(2), and pH, whereas rSO(2) values did not correlate with changes in bilirubin concentrations, indicating that rSO(2) changes reveal cerebral oxygen balance regardless of TB levels among patients undergoing liver transplantation.

A reproducible, clinically relevant, intensively managed, pig model of acute liver failure for testing of therapies aimed to prolong survival

BACKGROUND

A clinically relevant, translational large animal model of acute liver failure (ALF) is required for testing of novel therapies to prolong survival in acute liver failure, to permit spontaneous liver recovery or to act as a bridge to transplantation.

AIMS

The aim was to establish a pig model of acetaminophen-induced ALF that mimics the human clinical syndrome, is managed as in a human intensive care unit and has a predictable survival time.

METHODS

Nine female pigs were anaesthetised and instrumented for continuous intensive care monitoring and management using: target-driven protocols for treatment of cardiovascular collapse, metabolic acidosis and electrolyte abnormalities; intermittent positive pressure ventilation; and continuous renal replacement therapy. Six animals were induced to ALF with acetaminophen (paracetamol). Three animals acted as controls.

RESULTS

Irreversible acute liver failure, defined as rise in prothrombin time >3 times normal, occurred 19.3 ± 1.8 h after the onset of acetaminophen administration. Death occurred predictably 12.6 ± 2.7 h thereafter, with acute hepatocellular necrosis in all animals. Clinical progression of liver failure mimicked the human condition including development of coagulopathy, intracranial hypertension, hyperammonaemia, cardiovascular collapse, elevation in creatinine, metabolic acidosis and hyperlactataemia. In addition, cardiovascular monitoring clearly demonstrated progressive cardiac dysfunction in ALF.

CONCLUSIONS

A reproducible, clinically relevant, intensively managed, large animal model of acute liver failure, with death as a result of multi-organ failure, has been successfully validated for translational studies of disease progression and therapies designed to prolong survival in man.

Monitoring and intraoperative management of elevated intracranial pressure and decompressive craniectomy

Elevated intracranial pressure can be caused by a variety of underlying conditions. Several physiologic and pharmacologic factors have a significant impact on intracranial hypertension, mostly caused by changes on cerebral blood volume, flow, and oxygenation. There are many therapies that can be used to decrease intracranial pressure ranging from pharmacologic to the surgical decompressive removal of the calvarium. Special consideration is made for the anesthetic management of these patients perioperatively.

Artificial liver support system reduces intracranial pressure more effectively than bioartificial system: an experimental study

OBJECTIVES

Extracorporeal liver support (ELS) may play a role in bridging therapy in patients with acute liver failure (ALF). The aim of this study was to compare the influence of nonbiological and biological methods on intracranial pressure (ICP) in an animal model of ALF.

METHODS

A surgical devascularization model of ALF in pigs (35-40 kg) was used. Elimination therapy started after the onset of hypoglycemia. Biochemical parameters (bilirubin, ammonia, lactate, etc.) as well as ICP and cerebral perfusion pressure (CPP) were monitored for 12 hours. Of the total 31 pigs with ALF, 14 animals were treated by fractionated plasma separation and absorption (FPSA), 10 were treated with a bioartificial liver (BAL), and 7 animals were used as a control group.

RESULTS

FPSA and BAL treatment started on average 3 hours 17 minutes and 2 hours 21 minutes, after devascularization and lasted for 5 hours 54 minutes and 5 hours 43 minutes, respectively. Ammonia levels were lower in the FPSA group, and bilirubin levels differed significantly in both the FPSA and BAL groups compared with controls. However, ICP values were reduced more effectively in pigs treated by FPSA: 19.1 vs. 27.0 mm Hg at 9 hours, 22.5 vs. 28.7 mm Hg at 11 hours, and 24.0 vs. 33.0 mm Hg at 12 hours (p<0.05).

CONCLUSIONS

The artificial liver support system FPSA reduced ICP values more effectively than the Performer O. Liver RanD BAL system. Compared with this BAL system, the nonbiological elimination method of FPSA is a simpler application with the advantage that it can be applied in a more continuous way.

Region-specific causal mechanism in the effects of ammonia on cerebral glucose metabolism in the rat brain

Ammonia, which is considered to be the main agent responsible for hepatic encephalopathy, inhibits oxidative glucose metabolism in the brain. However, the effects of ammonia on cerebral glucose metabolism in different brain regions remains unclear. To clarify this issue, we added ammonia directly to fresh rat brain slices and measured its effects on glucose metabolism. Dynamic positron autoradiography with [(18)F]2-fluoro-2-deoxy-D-glucose and 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) colorimetric assay revealed that ammonia significantly increased the cerebral glucose metabolic rate and depressed mitochondrial function, as compared to the unloaded control in each of the brain regions examined (cerebral cortex, striatum, and cerebellum), reflecting increased glycolysis that compensates for the decrease in aerobic metabolism. Pre-treatment with (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), a N-methyl-D-aspartate (NMDA) receptor antagonist, significantly attenuated these changes induced by ammonia in cerebellum, but not in cerebral cortex or striatum. The addition of ammonia induced an increase in cyclic guanosine monophosphate (cGMP) levels in cerebellum, but not in cerebral cortex or striatum, reflecting the activation of the NMDA receptor-nitric oxide-cGMP pathway. These results suggested that NMDA receptor activation is responsible for the impairment of glucose metabolism induced by ammonia specifically in cerebellum.

Systematic review: acute liver failure - one disease, more than 40 definitions

BACKGROUND

Acute liver failure (ALF) is a clinical syndrome with very high mortality estimates ranging between 60% and 80%.

AIM

To investigate the explicitness and extent of variability in the used ALF definitions in the ALF prognostic literature.

METHODS

All studies that pertain to the prognosis of patients with ALF were electronically searched in MEDLINE (1950-2012) and EMBASE (1950-2012). Identified titles and abstracts were independently screened by three reviewers to determine eligibility for additional review. We included English articles that reported original data from clinical trials or observational studies on ALF patients.

RESULTS

A total of 103 studies were included. Of these studies 87 used 41 different ALF definitions and the remaining 16 studies did not report any explicit ALF definition. Four components underlying ALF definitions accounted for the differences: presence and/or grading of hepatic encephalopathy (HE); the interval between onset of disease and occurrence of HE; presence of coagulopathy and pre-existing liver disease.

CONCLUSIONS

The diversity in acute liver failure definitions hinders comparability and quantitative analysis among studies. There is room for improvement in the reporting of acute liver failure definitions in prognostic studies. The result of this review may be useful as a starting point to create a uniform acute liver failure definition.

Neuroimaging in acute liver failure

Acute liver failure (ALF) is frequently complicated by the development of brain edema that can lead to intracranial hypertension and severe brain injury. Neuroimaging techniques allow a none-invasive assessment of brain tissue and cerebral hemodynamics by means of transcranial Doppler ultrasonography, magnetic resonance and nuclear imaging with radioligands. These methods have been very helpful to unravel the pathogenesis of this process and have been applied to patients and experimental models. They allow monitoring the outcome of patients with ALF and neurological manifestations. The increase in brain water can be detected by observing changes in brain volume and disturbances in diffusion weighted imaging. Neurometabolic changes are detected by magnetic resonance spectroscopy, which provides a pattern of abnormalities characterized by an increase in glutamine and a decrease in myo-inositol. Disturbances in cerebral blood flow are depicted by SPECT or PET and can be monitored and the bedside by assessing the characteristics of the waveform provided by transcranial Doppler ultrasonography. Neuroimaging methods, which are rapidly evolving, will undoubtedly lead to future diagnostic and therapeutic progress that could be very helpful for patients with ALF.

Hyperemic hydrocephalus: a new form of childhood hydrocephalus analogous to hyperemic intracranial hypertension in adults

OBJECT

In the majority of adults with idiopathic intracranial hypertension (IIH), there is an elevation in venous pressure associated with a venous outflow stenosis. In about 15% of IIH patients the elevated venous pressure is associated with an elevation in blood flow but little or no evidence of a stenosis. Venostenotic IIH and idiopathic hydrocephalus in children with a normal blood inflow have been shown to be equivalent. The aim of this study was to test whether children with hydrocephalus and an elevated arterial inflow have a vascular pathophysiology that is analogous to the hyperemic form of IIH in adults.

METHODS

Nine children with idiopathic hydrocephalus underwent MR imaging with flow quantification and were found to have arterial inflows 2 SDs above the mean for normal controls. Measurements of the head circumference, ventricular enlargement, total blood inflow, superior sagittal sinus (SSS)/straight sinus (SS) outflow, and the degree of collateral venous flow were performed. The results were compared with findings in 14 age-matched controls.

RESULTS

In hyperemic hydrocephalus the cerebral blood inflow was elevated but the SSS and SS outflows were in the normal range. The sinus outflow as a percentage of the inflow was reduced by 8 percentage points in the SSS territory and 5 percentage points in the SS territory compared with findings in the controls (p = 0.04, p = 0.003, respectively), suggesting blood was returning via collateral channels.

CONCLUSIONS

Similar to patients with hyperemic IIH, children with hyperemic hydrocephalus show a significant elevation in collateral venous flow, indicating that the same venous pathophysiology may be operating in both conditions.

Continuous peritransplant assessment of consciousness using bispectral index monitoring for patients with fulminant hepatic failure undergoing urgent liver transplantation

BACKGROUND

Rapid deterioration of consciousness is a critical situation for patients with fulminant hepatic failure (FHF). Bispectral (BIS) index was derived from electroencephalography parameters, primarily to monitor the depth of unconsciousness.

AIM

To assess the usability of peritransplant BIS monitoring in patients with FHF.

METHODS

A prospective study using peritransplant BIS monitoring was performed in 26 patients with FHF undergoing urgent liver transplantation (LT).

RESULTS

Pre-transplant Child-Pugh score was 12.2 +/- 1.0; model for end-stage liver disease score was 32.4 +/- 4.4; Glasgow coma score (GCS) was 9.9 +/- 1.3; and BIS index was 44.0 +/- 6.7. Pre-transplant sedation significantly decreased BIS index. After LT, all patients having endotracheal intubation recovered consciousness within one to three d and showed progressive increase in BIS index, which appeared slightly earlier and was more evident than the increase in derived GCS score. There was a significant correlation between BIS index and derived GCS scores (r(2) = 0.648). Timing of eye opening to voice was matched with BIS index of 66.3 +/- 10.4 and occurred 12.7 +/- 8.3 h after passing BIS index of 50.

CONCLUSION

These results suggest that BIS monitoring is a non-invasive, simple, easy-to-interpret method, which is useful in assessing peritransplant state of consciousness. BIS monitoring may therefore be a useful tool during peritransplant intensive care for patients with FHF showing hepatic encephalopathy.

Near fatal posterior reversible encephalopathy syndrome complicating chronic liver failure and treated by induced hypothermia and dialysis: a case report

Introduction

Posterior reversible encephalopathy syndrome is a clinico-neuroradiological entity characterized by headache, vomiting, altered mental status, blurred vision and seizures with neuroimaging studies demonstrating white-gray matter edema involving predominantly the posterior region of the brain.

Case presentation

We report a 47-year-old Caucasian man with liver cirrhosis who developed posterior reversible encephalopathy syndrome following an upper gastrointestinal hemorrhage and who was managed with induced hypothermia for control of intracranial hypertension and continuous veno-venous hemodiafiltration for severe hyperammonemia.

Conclusion

We believe this is the first documented case report of posterior reversible encephalopathy syndrome associated with cirrhosis as well as the first report of the use of induced hypothermia and continuous veno-venous hemodiafiltration in this setting.

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.

Transcranial doppler sonography is useful for the decision-making at the point of care in patients with acute hepatic failure: a single centre's experience

Acute hepatic failure (ALF) is an uncommon disease characterized by a rapid deterioration of the hepatic function with severe derangements of the mental status in previously healthy subjects due to massive hepatocytes necrosis. Neurological impairment, due to intracranial hypertension and cerebral ischemia, is a key factor because it is a main criterion to decide when to proceed to liver transplantation, which is only treatment for these patients. Therefore, neurological monitoring holds an essential role in the clinical management of ALF patients but it needs to be performed at the point-of-care in the majority of the cases as such critically ill patients cannot be moved away from the ICU because they frequently need continuous hemodynamic, ventilatory and renal support. We herein report and discuss our experience relating to the use of transcranial sonography as a neuro-monitoring tool in ALF patients. In our series this technique allowed a repeatable and reliable non-invasive assessment of cerebral blood flow changes at the bedside thus avoiding the complications associated with the use of an intracranial probe to measure intra-cranial pressure and making it possible to correctly evaluate the timing and feasibility of liver transplantation.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Application of intensive care medicine principles in the management of the acute liver failure patient

1. Acute liver failure is a paradigm for multiple system organ failure that develops as a consequence of sepsis. 2. In the United States, systemic inflammatory response, sepsis, and septic shock are common reasons for intensive care unit admission. Intensive care management of these patients serves as a template for the management of patients with acute liver failure. 3. Acute liver failure is attended by high mortality. Although intensive care results in improved survival, the key treatment is liver transplantation. Intensive care unit intervention may open a "window of opportunity" and enable successful liver transplantation in patients who are too ill at presentation. 4. Intracranial hypertension complicates the course for many patients with acute liver failure. Initially, intracranial hypertension results from hyperemia, which is cerebral edema that reduces cerebral blood flow and eventuates in herniation. The precepts of neurocritical care-monitoring cerebral perfusion pressure, cerebral blood flow, and cortical activity-with rapid response to hemodynamic abnormalities, maintenance of normoxia, euglycemia, control of seizures, therapeutic hypothermia, osmotic therapy, and judicious hyperventilation are key to reducing mortality attributable to neurologic failure.

[Sedation and analgesia for the brain-injured patient]

Sedation-analgesia occupies an essential place in the specific therapeutic arsenal of the brain-injured patients. The maintenance of the perfusion of the brain, its relaxation and its protection are the fundamental objectives whose finality is to avoid the extension of the lesions and to preserve the neuronal capital. Sedation is instituted when patients are severely agitated or present a deterioration of their state of consciousness (GCS< or =8). Under cover of mechanical ventilation, sedation is the first line treatment of intracranial hypertension, a common pathway of various acute brain diseases of traumatic, vascular or other origin. The use of the combination of hypnotic and opioids is the rule. The combined action of these two classes reinforces and improves their sedative effects. Midazolam is the 2 benzodiazepine of reference. Propofol is more and more frequently added to the combination of hypnotic and opioids. The "propofol infusion syndrome" is a severe limitation to its long term administration in particular among patients presenting a severe septic or inflammatory state. Propofol will be imperatively stopped in the event of metabolic acidosis, rhabdomyolysis, acute renal insufficiency, hyperkaliemia or increase in the blood triglyceride levels. The use of thiopental is restricted to the most severe cases. Its use as a monotherapy at high doses is abandoned to the profit of a co-administration with midazolam or even with the combination of midazolam and propofol. Thiopental overdose is very frequent in the event of associated hypothermia. Etomidate does not have its place apart from induction in fast sequence. The neuro-protective effects of ketamine require to be demonstrated in man before being recommended routinely. Withdrawal of sedation can be responsible for a state of agitation which can be controlled by neuroleptics.

Management of hepatic encephalopathy in patients with cirrhosis

The term hepatic encephalopathy encompasses a spectrum of neuropsychiatric abnormalities seen in patients with liver dysfunction. Distinct syndromes are identified in acute liver failure and cirrhosis. Rapid deterioration in consciousness level and increased intracranial pressure that may result in brain herniation and death are a feature of acute liver failure whereas manifestations of hepatic encephalopathy in cirrhosis include psychomotor dysfunction, impaired memory, increased reaction time, sensory abnormalities, poor concentration and in severe forms, coma. In patients with acute-on-chronic liver failure the pathophysiology remains undefined. Ammonia has been considered central to its pathogenesis. In the brain, the astrocyte is the main site for ammonia detoxification, during the conversion of glutamate to glutamine. An increased ammonia level raises the amount of glutamine within astrocytes, causing an osmotic imbalance resulting in cell swelling and ultimately brain oedema. Recent studies suggest that inflammation and it modulators may play a synergistic role with ammonia in the pathogenesis of hepatic encephalopathy. Therapy of hepatic encephalopathy is directed primarily at reducing ammonia generation and increasing its detoxification. The currently accepted regimens to treat hepatic encephalopathy such as lactulose and protein restricted diets need further clinical trials and therefore placebo controlled clinical trials in hepatic encephalopathy are justified. In liver failure, ammonia metabolism involves multiple organs and therefore ammonia reduction will require simultaneous targeting of these organs. The present review describes the pathophysiological basis of hepatic encephalopathy and evaluates the available therapies.