When a patient is demonstrating metabolic acidosis, his or her body is pulling the HCO3 into the cells as a buffer and therefore depletes the plasma level. The body begins compensating by increasing the ventilation, and thus, renal retention of the HCO3 takes place.
When patients present with the following conditions, one must consider the patient could be a candidate for metabolic acidosis: HCO3 loss from diarrhea, shock, renal tubular acidosis, drug intoxication, salicylate poisoning, renal failure, diabetic ketoacidosis, and circulatory failure producing lactic acid.
ABG values one would see with metabolic acidosis would be: pH < 7.35; HCO3 < 22 mEq/L; and PaCO2 < 35 mm Hg if compensating.
Respiratory compensation for metabolic acidosis causes a reduction in the arterial PaCO2 by about 1.2 mmHg for every 1 mEq/L reduction in the serum HCO3. If compensation does not occur, there is likely underlying neurologic or respiratory disease.8
Calculation of the serum anion gap should be determined in metabolic acidosis. In metabolic acidosis, the anion gap may be high, normal or combined. Determining the anion gap will help determine the cause of the metabolic acidosis.
Table 6: Metabolic Acidosis
Normal (decreased if compensating)
One generally considers the ABG to be a test for respiratory conditions; however, a study of ABGs in Brazil to test patients for metabolic acidosis in relation to sepsis and shock was conducted. The study revealed a group who were not able to clear their inorganic ions had a higher morbidity rate, whereas those who were able to correct their acidosis survived.9
The severely septic patient who developed acute renal failure upon arrival to the intensive care unit (ICU) had a battery of tests, including ABG. Results of the ABG revealed: a pH of 7.32, PaCO2 of 45 mmHg, and an HCO3 of 21mEq/L. Without treatment metabolic acidosis will become progressively worse; steps need to be taken to bring the patient into a compensatory mode to recovery.
Treatment of metabolic acidosis is variable depending on the cause and whether it is acute or chronic. In severe metabolic acidosis, sodium bicarbonate is sometimes used.