Types and causes of hepatic coma
Hepatic coma represents the final stage of liver damage. Depending on the mechanisms of development, two main types of this pathological condition are distinguished:
- Shunt coma (synonym: bypass coma).
- Cause of development: Severe intoxication of the body with exogenous substances and toxic metabolic products. Under normal conditions, these compounds should be taken up and detoxified by hepatocytes. However, in this form, blood flow bypasses the liver through newly formed vascular shunts, causing toxins to circulate freely in the systemic bloodstream.
- Parenchymal coma (synonym: hepatocellular coma).
- Cause of development: Massive intoxication caused by direct damage and physical death of a significant mass of the liver parenchyma. Triggers can include extensive trauma, massive necrosis of organ tissue, or surgical removal of a part of the liver.
- Pathogenetic features: In the parenchymal form, absolutely all liver functions are totally disrupted, making the condition extremely severe and hardly reversible.
Key links in pathogenesis
The development of hepatic coma is a complex cascade of pathophysiological reactions occurring against the background of severe hepatic failure. Pathogenesis includes several closely intertwined links:
- Hypoglycemia. Occurs as a direct consequence of critical impairment in glycogen formation (glycogenesis) and its breakdown (glycogenolysis) in damaged liver cells.
- Metabolic acidosis. The primary cause of the pH shift is the disruption of lipid and carbohydrate metabolism in the liver. As the condition worsens in the final stages of coma, excretory and respiratory forms of acidosis join the process.
- Pronounced ionic imbalance. Electrolyte redistribution is observed: intracellular concentrations of sodium ions ($Na^+$), calcium ions ($Ca^{2+}$), and hydrogen protons ($H^+$) pathologically increase. Simultaneously, the concentration of potassium ($K^+$) sharply increases in the interstitial space and blood plasma.
- Endotoxemia. Global intoxication of the body occurs due to the accumulation of unprocessed products of lipid and protein metabolism. A crucial factor of intoxication is the accumulation of unconjugated bilirubin, which is associated with the inhibition of its binding (conjugation) process with glucuronic acid in hepatocytes.
Systemic disorders and multiple organ failure
In addition to metabolic failures, hepatic coma is accompanied by fatal disruptions in the functioning of other organ systems, which closes the vicious circle of pathogenesis.
Hemodynamic disorders Disturbances progress at all levels of circulation: central hemodynamics, organ-tissue blood flow, and microhemocirculation suffer. The main causes of these hemodynamic catastrophes are concurrent heart failure (HF), critical disorders of arteriolar tone, and the development of rheological disorders — the sludge phenomenon (sludge).
Multiple organ failure (MOF) Toxic damage to the nervous system leads to the earliest and most pronounced impairment of the cardiovasomotor and respiratory centers. The outcome of such multisystem damage is severe mixed hypoxia. Without successful medical intervention, cessation of cardiac activity and complete respiratory arrest naturally ensue, leading to biological death.
Briefly: answers to topical questions
What specific toxic products of protein metabolism (other than bilirubin) accumulate in the blood during hepatic coma?
During hepatic coma, specific protein breakdown products in the large intestine, as well as toxic ammonium compounds, accumulate in the blood.
- Protein breakdown products — putrescine, cadaverine, derivatives of phenol, indole, and skatole.
- Ammonium compounds — ammonium carbonate, ammonium carbamate, and ammonium hydroxide.
- Ammonia — its excess acts as an important pathogenetic link, causing inhibition of $Na^+, K^+$-ATPase, formation of toxic metabolites, and damage to benzodiazepine receptors.
To memorize the links of pathogenesis, use the acronym HADIS-P: Hypoglycemia, Acidosis, Disbalance of ions, Intoxication (endotoxemia), Cardiovascular (hemodynamic) disorders, Multiple organ failure.
Class and exam questions
What is the principal difference between shunt coma and parenchymal coma?
In shunt coma, intoxication occurs because blood containing toxins is shunted into the systemic circulation bypassing the liver. In parenchymal coma, toxins accumulate due to direct death of the liver cells themselves (resulting from trauma or necrosis), which leads to the impairment of all organ functions.
Why does the level of unconjugated bilirubin increase during hepatic coma?
This occurs due to the inhibition of unconjugated bilirubin conjugation with glucuronic acid in damaged hepatocytes, as a result of which it does not convert into the conjugated form and accumulates in the blood.
How does ion concentration change during hepatic coma?
The levels of sodium, calcium, and hydrogen ions dangerously increase inside cells, while the concentration of potassium rises in the interstitium and systemic circulation.
Which nervous system centers are affected most rapidly in multiple organ failure?
When multiple organ failure develops against the background of a coma, the functions of the respiratory and cardiovasomotor centers are impaired earliest and most prominently, leading to mixed hypoxia.
What else to study on this topic
- Mechanisms of vascular shunt formation in portal hypertension
- Pathogenesis of impaired bilirubin conjugation with glucuronic acid
- The role of the sludge phenomenon in microhemocirculation disorders
- Mechanisms of development of respiratory and excretory acidosis in the final stages of coma
- Pathophysiology of cardiovasomotor and respiratory center depression in endotoxemia
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