metabolic acidosis

Metabolic Acidosis 

Definition

Metabolic acidosis is a pH imbalance in which the body has accumulated too much acid and does not have enough bicarbonate to effectively neutralize the effects of the acid.

Description

Metabolic acidosis, as a disruption of the body's acid/base balance, can be a mild symptom brought on by a lack of insulin, a starvation diet, or a gastrointestinal disorder like vomiting and diarrhea. Metabolic acidosis can indicate a more serious problem with a major organ like the liver, heart, or kidneys. It can also be one of the first signs of drug overdose or poisoning.

Causes and symptoms

Metabolic acidosis occurs when the body has more acid than base in it. Chemists use the term "pH" to describe how acidic or basic a substance is. Based on a scale of 14, a pH of 7.0 is neutral. A pH below 7.0 is an acid; the lower the number, the stronger the acid. A pH above 7.0 is a base; the higher the number, the stronger the base. Blood pH is slightly basic (alkaline), with a normal range of 7.36-7.44.

Acid is a natural by-product of the breakdown of fats and other processes in the body; however, in some conditions, the body does not have enough bicarbonate, an acid neutralizer, to balance the acids produced. This can occur when the body uses fats for energy instead of carbohydrates. Conditions where metabolic acidosis can occur include chronic alcoholism, malnutrition, and diabetic ketoacidosis. Consuming a diet low in carbohydrates and high in fats can also produce metabolic acidosis. The disorder may also be a symptom of another condition like kidney failure, liver failure, or severe diarrhea. The build up of lactic acid in the blood due to such conditions as heart failure, shock, or cancer, induces metabolic acidosis. Some poisonings and overdoses (aspirin, methanol, or ethylene glycol) also produce symptoms of metabolic acidosis.

In mild cases of metabolic acidosis, symptoms include headache, lack of energy, and sleepiness. Breathing may become fast and shallow. Nausea, vomiting, diarrhea, dehydration, and loss of appetite are also associated with metabolic acidosis. Diabetic patients with symptoms of metabolic acidosis may also have breath that smells fruity. The patient may lose consciousness or become disoriented. Severe cases can produce coma and death.

Diagnosis

Metabolic acidosis is suspected based on symptoms, but is usually confirmed by laboratory tests on blood and urine samples. Blood pH below 7.35 confirms the condition. Levels of other blood components, including potassium, glucose, ketones, or lactic acid, may also be above normal ranges. The level of bicarbonate in the blood will be low, usually less than 22 mEq/L. Urine pH may fall below 4.5 in metabolic acidosis.

Treatment

Treatment focuses first on correcting the acid imbalance. Usually, sodium bicarbonate and fluids will be injected into the blood through a vein. An intravenous line may be started to administer fluids and allow for the quick injection of other drugs that may be needed. If the patient is diabetic, insulin may be administered. Drugs to regulate blood pressure or heart rate, to prevent seizures, or to control nausea and vomiting might be given. Vital signs like pulse, respiration, blood pressure, and body temperature will be monitored. The underlying cause of the metabolic acidosis must also be diagnosed and corrected.

Prognosis

If the metabolic acidosis is recognized and treated promptly, the patient may have no long-term complications, however, the underlying condition that caused the acidosis needs to be corrected or managed. Severe metabolic acidosis that is left untreated will lead to coma and death.

Prevention

Diabetic patients need to routinely test their urine for sugar and acetone, strictly follow their appropriate diet, and take any medications or insulin to prevent metabolic acidosis. Patients receiving tube feedings or intravenous feedings must be monitored to prevent dehydration or the accumulation of ketones or lactic acid.

Resources

Books

"Fluid, Electrolyte, and Acid-Base Disorders." In Family Medicine Principles and Practices. 5th ed. New York: Springer-Verlag, 1998.

Key terms

Diabetic ketoacidosis — A condition caused by low insulin levels where the amount of sugar and ketones in the blood is high.

pH — A measurement of the acidity or alkalinity of a solution based on the amount of hydrogen ions available. Based on a scale of 14, a pH of 7.0 is neutral. A pH below 7.0 is an acid; the lower the number, the stronger the acid. A pH above 7.0 is a base; the higher the number, the stronger the base. Blood pH is slightly alkaline (basic) with a normal range of 7.36-7.44.

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acidosis /ac·i·do·sis/ (as″ĭ-do´sis)

1. the accumulation of acid and hydrogen ions or depletion of the alkaline reserve (bicarbonate content) in the blood and body tissues, decreasing the pH.

2. a pathologic condition resulting from this process. Cf. alkalosis. acidot´ic

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compensated acidosis  a condition in which the compensatory mechanisms have returned the pH toward normal.

diabetic acidosis  metabolic acidosis produced by accumulation of ketones in uncontrolled diabetes mellitus.

hypercapnic acidosis  respiratory a.

hyperchloremic acidosis  metabolic acidosis accompanied by elevated plasma chloride.

lactic acidosis  a metabolic acidosis occurring as a result of excess lactic acid in the blood, due to conditions causing impaired cellular respiration.

metabolic acidosis , nonrespiratory acidosis a disturbance in which the acid-base status shifts toward the acid because of loss of base or retention of noncarbonic, or fixed (nonvolatile), acids.

renal hyperchloremia acidosis , renal tubular acidosis (RTA) metabolic acidosis resulting from impairment of renal function.

respiratory acidosis  acidosis due to excess retention of carbon dioxide in the body.

starvation acidosis  metabolic acidosis due to accumulation of ketone bodies which may accompany a caloric deficit.

uremic acidosis  metabolic acidosis seen in chronic renal disease when the ability to excrete acid is decreased.

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metabolic acidosis

n.

Decreased pH and bicarbonate concentration of the body fluids caused either by the accumulation of excess acids stronger than carbonic acid or by abnormal losses of bicarbonate from the body.

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metabolic acidosis,

acidosis in which excess acid is added to the body fluids or bicarbonate is lost from them. Acidosis is indicated by a pH of blood below 7.4. In starvation and in uncontrolled diabetes mellitus, glucose is not present or is not available for oxidation for cellular nutrition. This glucose lack causes breakdown of fats for energy, resulting in acidic ketone bodies. The body uses plasma bicarbonate to neutralize these acids. Metabolic acidosis also occurs when oxidation takes place without adequate oxygen, as in heart failure or shock. Severe diarrhea, renal failure, ingestion of toxic substances (e.g., antifreeze and large doses of aspirin) and lactic acidosis also may result in metabolic acidosis. Hyperkalemia may accompany the condition. See also diabetic ketoacidosis.

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acidosis

a pathological condition resulting from accumulation of acid or depletion of the alkaline reserve (bicarbonate content) in the blood and body tissues, and characterized by increase in hydrogen ion concentration (decrease in pH).

The optimal acid-base balance is maintained by chemical buffers, biological activities of the cells, and effective functioning of the lungs and kidneys. The opposite of acidosis is alkalosis.

It is rare that acidosis occurs in the absence of some underlying disease process. The more obvious signs of severe acidosis are muscle twitching, involuntary movement, cardiac arrhythmias, disorientation and coma.

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compensated acidosis

a condition in which the compensatory mechanisms have returned the pH toward normal.

diabetic acidosis

a metabolic acidosis produced by accumulation of ketones in uncontrolled diabetes mellitus.

hypercapnic acidosis

respiratory acidosis.

iatrogenic acidosis

may result from administration of drugs, such as urinary acidifiers, or anesthetic agents which depress respiration.

lactic acidosis

the accumulation of lactate in the rumen in ruminants and the stomach of horses, and hence in the blood, as a result of overfeeding with readily fermentable carbohydrate. See also carbohydrate engorgement.

metabolic acidosis

acidosis resulting from accumulation in the blood of keto acids (derived from fat metabolism) at the expense of bicarbonate, thus diminishing the body's ability to neutralize acids. This type of acidosis can occur when there is an acid gain, as in diabetic ketoacidosis, lactic acidosis, poisoning and failure of the renal tubules to reabsorb bicarbonate. It can also result from bicarbonate loss due to diarrhea or a gastrointestinal fistula.

mixed alkalosis and acidosis

characterized by low serum chloride, normal or slightly elevated plasma bicarbonate and a very high anion gap.

organic acidosis

accumulation of organic anions occurs in uremia, diabetic acidosis and lactic acidosis, and ingestion of salicylates, ethylene glycol or methanol.

renal tubular acidosis

renal tubular malfunction leads to faulty resorption of bicarbonate or excretion of acid and the production of alkaline urine; types I (distal tubular acidosis) and II (proximal tubular acidosis) are identified.

respiratory acidosis

acidosis resulting from ventilatory impairment and subsequent retention of carbon dioxide.

ruminal acidosis

acidosis caused by an altered metabolic state, usually lactic acidosis, in the rumen.

starvation acidosis

a metabolic acidosis due to accumulation of ketones following a severe caloric deficit.

uncompensated acidosis

a condition in which the compensatory mechanisms have not been applied sufficiently to return the pH of the blood to normal.

uremic acidosis

see metabolic acidosis (above).

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metabolic acidosis

Physiology A condition in which there is a ↓ pH due to either an ↑ in acids or loss of bicarbonate Lab pH < 7.35, HCO₃^– < 22 mEq/L, and in 'compensating' cases PaCO₂ < 35 mm Hg Etiology Bicarbonate–HCO₃– depletion due to renal disease, diarrhea, fistulas of GI tract; ↑ production of organic acids due to liver disease, endocrinopathies–eg, DM, hypoxia, shock, drug overdose; ↓ excretion of acids due to renal disease Clinical Rapid, deep breathing, fruity breath, headache, lethargy, N&V, coma. See Metabolic alkalosis, Respiratory acidosis, Respiratory alkalosis.