METABOLIC ACID-BASE IMBALANCES
The body has the remarkable ability to maintain plasma pH within the narrow range of 7.35–7.45. It does so by means
of chemical buffering mechanisms by the kidneys and the lungs. Although single acid-base (e.g., metabolic acidosis)
imbalances do occur, mixed acid-base imbalances are more common (e.g., metabolic acidosis/respiratory acidosis as
occurs with cardiac arrest).
METABOLIC ACIDOSIS (PRIMARY BASE BICARBONATE [HCO
(primary base bicarbonate [HCO
] deficiency) reflects an excess of acid (hydrogen) and a deficit of
base (bicarbonate) resulting from acid overproduction, loss of intestinal bicarbonate, inadequate conservation of
bicarbonate, and excretion of acid, or anaerobic metabolism. Metabolic acidosis is characterized by normal or high
anion gap situations. If the primary problem is direct loss of bicarbonate, gain of chloride, or decreased ammonia
production, the anion gap is within normal limits. If the primary problem is the accumulation of organic anions (such as
ketones or lactic acid), the condition is known as high anion gap acidosis. Compensatory mechanisms to correct this
imbalance include an increase in respirations to blow off excess CO
, an increase in ammonia formation, and acid
) by the kidneys, with retention of bicarbonate and sodium.
High anion gap acidosis occurs in diabetic ketoacidosis; severe malnutrition or starvation, alcoholic lactic acidosis;
renal failure; high-fat, low-carbohydrate diets/lipid administration; poisoning, e.g., salicylate intoxication (after initial
stage); paraldehyde intoxication; and drug therapy, e.g., acetazolamide (Diamox), NH
Normal anion gap acidosis is associated with loss of bicarbonate form the body, as may occur in renal tubular
acidosis, hyperalimentation, vomiting/diarrhea, small-bowel/pancreatic fistulas, and ileostomy and use of IV sodium
chloride in presence of preexisting kidney dysfunction, acidifying drugs (e.g., ammonium chloride).
This condition does not occur in isolation but rather is a complication of a broader problem that may require inpatient
care in a medical-surgical or subacute unit.