Hypothermia for the management of intracranial hypertension in acute liver failure

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

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

Neurological management of fulminant hepatic failure

Acute liver failure (ALF) is uncommon in the United States, but presents acutely and catastrophically, often with deadly consequences. Hepatic encephalopathy, cerebral edema, elevated intracranial pressure, and intracranial hemorrhage due to coagulopathy are common occurrences in patients with ALF. Appropriate management of multi-system organ failure and neurological complications are essential in bridging patients to transplant and ensuring satisfactory outcomes.

A simple dummy liver assist device prolongs anhepatic survival in a porcine model of total hepatectomy by slight hypothermia

BACKGROUND

Advances in intensive care support such as therapeutic hypothermia or new liver assist devices have been the mainstay of treatment attempting to bridge the gap from acute liver failure to liver transplantation, but the efficacy of the available devices in reducing mortality has been questioned. To address this issue, the present animal study was aimed to analyze the pure clinical effects of a simple extracorporeal dummy device in an anhepatic porcine model of acute liver failure.

METHODS

Total hepatectomy was performed in ten female pigs followed by standardized intensive care support until death. Five animals (dummy group, n = 5) underwent additional cyclic connection to an extracorporeal dummy device which consisted of a plasma separation unit. The separated undetoxified plasma was completely returned to the pigs circulation without any plasma substitution or exchange in contrast to animals receiving intensive care support alone (control group, n = 5). All physiological parameters such as vital and ventilation parameters were monitored electronically; laboratory values and endotoxin levels were measured every 8 hours.

RESULTS

Survival of the dummy device group was 74 ± 6 hours in contrast to 53 ± 5 hours of the control group which was statistically significant (p < 0.05). Body temperature 24 hours after hepatectomy was significantly lower (36.5 ± 0.5°C vs. 38.2 ± 0.7°C) in the dummy device group. Significant lower values were measured for blood lactate (1.9 ± 0.2 vs. 2.5 ± 0.5 mM/L) from 16 hours, creatinine (1.5 ± 0.2 vs. 2.0 ± 0.3 mg/dL) from 40 hours and ammonia (273 ± 122 vs. 1345 ± 700 μg/dL) from 48 hours after hepatectomy until death. A significant rise of endotoxin levels indicated the onset of sepsis at time of death in 60% (3/5) of the dummy device group animals surviving beyond 60 hours from hepatectomy.

CONCLUSIONS

Episodes of slight hypothermia induced by cyclic connection to the extracorporeal dummy device produced a significant survival benefit of more than 20 hours through organ protection and hemodynamic stabilisation. Animal studies which focus on a survival benefit generated by liver assist devices should especially address the aspect of slight transient hypothermia by extracorporeal cooling.

New Strategies for Acute Liver Failure: Focus on Xenotransplantation Therapy

Acute liver failure (ALF) has a poor prognosis and, despite intensive care support, reported average survival is only 10-40%. The most common causes responsible for ALF are viral hepatitis (mainly hepatitis A and B) and acetaminophen poisoning. Hepatic transplantation is the only appropriate treatment for patients with unlikely survival with supportive care alone. Survival rates after transplantation can be as high as 80-90% at the end of the first year. However, there is a shortage of donors and is not uncommon that no appropriate donor matches with the patient in time to avoid death. Therefore, new technologies are in constant development, including blood purification therapies as plasmapheresis, hemodiafiltration, and bioartificial liver support. However, they are still of limited efficacy or at an experimental level, and new strategies are welcome. Accordingly, cell transplantation has been developed to serve as a possible bridge to spontaneous recovery or liver transplantation. Xenotransplant of adult hepatocytes offers an interesting alternative. Moreover, the development of transgenic pigs with less immunogenic cells associated with new immunosuppressor strategies has allowed the development of this area. This article reviews some of the newly developed techniques, with focus on xenotransplant of adult hepatocytes, which might have clinical benefits as future treatment for ALF.

Use of induced hypothermia for neuroprotection: indications and application

Therapeutic temperature regulation has become an exciting field of interest. Mild-to-moderate hypothermia is a safe and feasible management strategy for neuroprotection and control of intracranial pressure in neurological catastrophies such as traumatic brain injury, subarachnoid and intracerebral hemorrhage, and large hemispheric stroke. Fever is associated with worse neurological outcome in patients with brain injury, normothermia may be of benefit in this patient population. The efficacy of mild-to-moderate hypothermia has been proven for neuroprotection after cardiac arrest with ventricular fibrillation as initial rhythm, and after neonatal asphyxia. Application of hypothermia and fever control in neurocritical care, available cooling technologies and systemic effects and complications of hypothermia will be discussed.

Mechanisms of brain edema in acute liver failure and impact of novel therapeutic interventions

Continued elucidation of the mechanisms of brain edema in acute liver failure (ALF) has established ammonia and the astrocyte as major players in its pathogenesis. The metabolism of ammonia to glutamine appears to be a requisite, and is followed by an osmotic disturbance in the brain, mitochondrial dysfunction with oxidative/nitrosative stress, and alterations of brain glucose metabolism. Cerebral blood flow (CBF) is also altered in ALF and strongly influence the development of brain edema and intracranial hypertension. Additional factors such as systemic inflammation, alterations of the brain extracellular concentration of amino acids and neurotransmitters, and others have been identified and may contribute to the cerebral alterations of ALF. Such pathophysiologic insights are reflected in the various clinical trials of novel therapeutic interventions using ammonia-lowering agents, N-acetylcysteine, hypertonic saline, indomethacin, high-volume plasmapheresis, bio-artificial liver assist devices, albumin dialysis and mild hypothermia.

Brain cytokine flux in acute liver failure and its relationship with intracranial hypertension

BACKGROUND

In acute liver failure (ALF), it is unclear whether the systemic inflammatory response associated with intracranial hypertension is related to brain cytokine production.

AIM

To determine the relationship of brain cytokine production with severity of intracranial hypertension in ALF patients.

METHOD

We studied 16 patients with ALF. All patients were mechanically ventilated and cerebral blood flow measured using the Kety-Schmidt technique and intracranial pressure (ICP) measured with a Camino subdural catheter. We sampled blood from an artery and a reverse jugular catheter to measure proinflammatory cytokines (TNF-alpha, IL-6 and IL-1beta) and ammonia. Additionally, in 3 patients, serial samples were obtained over a 72 h period.

RESULTS

In ALF patients a good correlation between arterial pro-inflammatory cytokines and ICP (r (2) = 0.34, 0.50 and 0.52; for IL-6, IL-1beta and TNF-alpha respectively) was observed. There was a positive cerebral cytokine 'flux' (production), in ALF patients with uncontrolled ICP. Plasma ammonia between groups was not statistically significant. In the ALF patients studied longitudinally, brain proinflammatory cytokine production was associated with uncontrolled ICP.

CONCLUSION

Our results provide novel data supporting brain production of cytokines in patients with uncontrolled intracranial hypertension indicating activation of the inflammatory cascade in the brain. Also, the appearance of these cytokines in the jugular bulb catheter may indicate a compromised blood brain barrier at this late stage.

Management of patients with fulminant hepatic failure and brain edema

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