Page 540 - ACCCN's Critical Care Nursing

Gastrointestinal, Liver and Nutritional Alterations 517

which is secreted by the hepatocytes. Bile drains from the areas of surviving cells to restore the lost tissue whilst
hepatocytes into bile ducts and then into the common maintaining homeostasis during hepatic regenera-
hepatic duct, before passing into the gall bladder via the tion. 234,239,240 However, with chronic injury, fibrosis or
common bile duct. scarring occurs, resulting in the loss of the functional
architecture and cell mass and ultimately in cirrhosis.
The arrangement of the circulation to the liver with its
rich vascular architecture enables it to perform the vital Cirrhosis results in destruction of the normal liver vascu-
functions of carbohydrate, fat and protein metabolism; lature, increased resistance to blood flow, and back pres-
production of bile to aid in digestion; the production, sure into the portal circulation. Dilation of the venous
conjugation and elimination of bilirubin; immunologi- system leading into the liver results in the formation of
241
cal and inflammatory responses; glycogen storage; and varices.
detoxification of toxins and drugs. 1 Liver cell injury may occur to such a degree that a critical
amount of hepatic necrosis results in the failure of the
As the kidneys are responsible for clearance of water- liver to maintain metabolic, synthetic and clearance func-
soluble toxins from the body, the liver clears protein tions leading to death. Liver cell injury may also occur
(largely albumin)-bound toxins and excretes them into more slowly, giving rise to chronic liver injury. 236
the gastrointestinal tract for elimination, or reabsorption
in water-soluble form for subsequent renal excretion. EPIDEMIOLOGY OF VIRAL HEPATITIS

MECHANISMS OF LIVER CELL INJURY In developed countries such as Australia and New
Zealand, viral infection, primarily from hepatitis B and
Liver cell injury and death can occur either as a direct hepatitis C viruses, is the major cause of liver cell injury
result of injury to the cell, resulting in cell necrosis, or as leading to liver failure. 242,243 Although viral hepatitis can
a result of ‘cellular stress’ and the triggering of apoptotic result in acute liver failure, it more often results in chronic
pathways, leading to ‘programmed cell death’. 233 Major disease that may lead to cirrhosis and hepatocellular
factors for the triggering of the apoptotic pathway are carcinoma. 243 While the prevalence of hepatitis B in Aus-
hypoxia with resulting ischaemia and reperfusion; reac- tralia and New Zealand is generally low, infection rates
tive oxygen metabolites resulting from alcohol or drug among social subgroups, such as the socially disadvan-
ingestion; accumulation of bile acids resulting from cho- taged, migrants from Asian countries, injecting drug
lestasis; and inflammatory cytokines such as tumour users, homosexual males, and those with a history of
necrosis factor alpha (TNF-α). 233 The apoptotic pathway incarceration, are high. 244,245 Hepatitis C is blood-borne,
results in the deconstruction of the cellular structure from with intravenous drug use the cause of about 80% of
the inside out, while necrosis results in cell rupture and hepatitis C infections. Blood screening has greatly reduced
release of cellular contents. Although these processes may the incidence of hepatitis C infections. 246 In Australia in
overlap, it is thought that the apoptotic pathway is a way 2009, approximately 217,000 people were living with
of preventing the inflammatory response that is triggered chronic hepatitis C infection, with 46,000 in the moder-
with cell necrosis. The activation of the inflammatory ate to severe liver disease category. 247 However, about
response results in secondary liver cell injury and contrib- 25% of people with exposure to hepatitis C virus have
utes to the multiple organ dysfunction seen in liver cleared the virus and are not chronically infected. It is
failure. 233,234 estimated that the number of people with hepatitis C will
The degree and time course of liver cell damage from viral increase in Australia and New Zealand due to lack of
247-249
hepatitis depends on the immune response. Immune rec- access to antiviral therapy. Vertical transmission
ognition and destruction of infected cells may result in (transmission from the mother to the child during the
either clearance of the virus or ongoing inflammation, perinatal period) at birth is a major cause of such infec-
243
cell death and fibrosis if the virus is not cleared. This tions in children.
process may progress over 20–40 years to cirrhosis and
hepatocellular carcinoma. 235 Chronic excessive alcohol Practice tip
intake may also result in a slower chronic course of liver
injury that eventually results in cirrhosis, liver failure or Use appropriate infection control practices and personal pro-
hepatocellular carcinoma. 236 tective equipment for patients at high risk of hepatitis B virus
(HBV) and hepatitis C (HCV) infections.
Liver cells may also be injured by the toxic effects of drugs
or their metabolites, as in paracetamol overdose, or by
drugs at therapeutic doses (e.g. non-steroidal anti- LIVER DYSFUNCTION/FAILURE
inflammatory drugs, phenytoin, antimalarial agents). Liver dysfunction can be acute or chronic. Chronic liver
Other poisoning from the ingestion of mushrooms (e.g. disease is usually associated with cirrhosis and can
Amanita phalloides), and from recreational drug use (e.g. develop from viral (hepatitis B and C), drug (alcohol),
ecstasy and amphetamines), may result in liver cell death metabolic (Wilson’s disease), or autoimmune (primary
and liver failure. 237 Diseases of the biliary system such as biliary cirrhosis) conditions. Acute liver failure (ALF) is
primary biliary cirrhosis and primary sclerosing cholan- an uncommon condition associated with rapid liver dys-
gitis also result in liver dysfunction and failure. 238
function leading to jaundice, hepatic encephalopathy and
250
The liver has a remarkable regenerative capacity. After coagulopathy. The term ‘fulminant hepatic failure’ is
injury and necrosis, liver cells rapidly regenerate around often used synonymously; however, it has been proposed