High anion gap metabolic acidosis

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Cat mudpiles - causes of high anion-gap metabolic acidosis

High anion gap metabolic acidosis (HAGMA) is a type of metabolic acidosis, a condition in which the body accumulates too much acid, or does not have enough bicarbonate to neutralize the effects of the acid. The "anion gap" refers to the difference between the measured cations (positively charged ions) and anions (negatively charged ions) in the serum, which in cases of HAGMA is higher than normal. This condition is an important diagnostic tool, as it helps in identifying the cause of the acidosis.

Causes

HAGMA is often caused by the accumulation of certain acids in the body. The most common causes can be remembered by the mnemonic MUDPILES:

• M - Methanol poisoning
• U - Uremia (chronic kidney failure)
• D - Diabetic ketoacidosis
• P - Propylene glycol (found in some intravenous medications)
• I - Isoniazid and Iron poisoning
• L - Lactic acidosis
• E - Ethylene glycol (antifreeze poisoning)
• S - Salicylate poisoning (aspirin overdose)

Pathophysiology

In HAGMA, the body produces or ingests substances that are either acids themselves or are metabolized to acids, exceeding the body's capacity to neutralize or excrete them. This leads to an accumulation of non-volatile acids in the blood, increasing the anion gap. The normal anion gap is typically between 8 and 12 mEq/L, but in HAGMA, it exceeds 12 mEq/L, indicating the presence of unmeasured anions in the serum.

Symptoms

Symptoms of HAGMA depend on the underlying cause but generally include:

• Nausea and vomiting
• Fatigue
• Rapid breathing or dyspnea (as the body tries to compensate by expelling more carbon dioxide)
• Confusion or decreased alertness, which can progress to coma in severe cases

Diagnosis

Diagnosis of HAGMA involves a series of blood tests to measure the anion gap, blood pH, bicarbonate levels, and other electrolytes. A high anion gap indicates the presence of excess acids in the blood. Further tests may be required to identify the specific cause of the acidosis.

Treatment

Treatment of HAGMA focuses on addressing the underlying cause of the acidosis. This may involve:

• Administration of insulin for diabetic ketoacidosis
• Dialysis for uremia or poisoning by substances like methanol or ethylene glycol
• Administration of bicarbonate to help neutralize the acid in certain cases, although this is controversial and depends on the underlying cause

Prognosis

The prognosis for patients with HAGMA depends on the cause and the promptness of treatment. Early identification and treatment of the underlying cause are crucial for recovery.