Hepatic Failure/GI/Endocrine Emergencies
| (b) | Because ammonia is converted to osmotically active glutamine, concentrations have |
|---|
been correlated with both encephalopathy and cerebral edema. Ammonia concentrations
greater than 200 mcg/dL are associated with cerebral herniation, whereas concentrations
less than 75 mcg/dL are rarely associated with hepatic encephalopathy. In ALF, either
because of impaired hepatocyte activity or the abnormal shunting of venous flow away
from the liver, normal mechanisms to detoxify and clear ammonia are no longer effective.
ii.
Encephalopathy is considered an indicator for the clinical presentation of cerebral edema.
Encephalopathy can be difficult to identify and may present initially as agitation and confusion;
however, it may progress rapidly to unresponsiveness. Table 3 gives useful guidelines for
measuring the severity of encephalopathy.
iii.
Occurrence of cerebral edema and elevated ICPs is generally related to the severity of hepatic
encephalopathy. Patients with grade I and grade II encephalopathy rarely have cerebral edema,
whereas cerebral edema is present in about 25%β35% of patients with grade III encephalopathy
and about 65%β75% of patients with grade IV encephalopathy.
Grade of Encephalopathy
Signs and Symptoms
Grade I
Changes in behavior with minimal change in level of consciousness
Grade II
Gross disorientation
Drowsiness
Possibly asterixis
Inappropriate behavior
Grade III
Marked confusion
Incoherent speech
Sleeping most of the time but arousable to vocal stimuli
Grade IV
Comatose
Unresponsive to pain, decorticate or decerebrate posturing
Adapted from: Conn HO, Leevy CM, Vlehcevic ZR, et al. Comparison of lactulose and neomycin in the treatment of chronic portal-systemic encephalopathy. A double
blind randomized trial. Gastroenterology 1977;72:573-83.
Cardiovascular
The primary hemodynamic concern in ALF is low systemic vascular resistance, similar to
cirrhosis. Additional hemodynamic effects in ALF include hyperdynamic circulation with
high cardiac output and decreased effective circulating volume.
ii.
Most patients are severely volume depleted on admission because of poor nutritional status and
third spacing into the extravascular space and will initially require aggressive fluid resuscitation.
iii.
In patients with an elevated ICP, maintaining adequate perfusion is essential to
preserve adequate oxygen delivery to the brain. A common goal is to maintain a
cerebral perfusion pressure (CPP) of at least 60 mm Hg. Higher mean arterial pressure
(MAP) targets may be needed in these patients in order to maintain CPP goals.
CPP = MAP β ICP.
Coagulopathy
ALF is defined by the presence of an elevated INR caused by decreased production, together
with increased consumption, of coagulation factors.
ii.
Consumption of platelets is also seen, and thrombocytopenia (150,000/mm3 or less) is common.
iii.
Despite these changes in coagulation parameters, thromboelastography studies of patients with
ALF have shown that overall hemostasis in patients with ALF is maintained by compensatory
mechanisms, even in patients with elevated INR values, potentially because of a reduction in
hepatic synthesis of natural anticoagulants.