Arterial blood gas (ABG) - Metabolic acidosis: Nursing

A 55-year-old client with a history of type 1 diabetes mellitus is brought to the emergency department with a sudden onset of confusion. On assessment, her mucous membranes are dry; and she is tachycardic, hypotensive, and her respirations are deep and fast. The healthcare provider suspects metabolic acidosis secondary to diabetic ketoacidosis so, an arterial blood gas is ordered to assess for changes in acid-base balance.

So arterial blood gas, or ABG for short, is a test used to measure the acid-base components and pressure of gasses in the arterial blood. Normal ABG values for healthy adults are a pH ranging from 7.35 to 7.45, bicarbonate, or HCO3- ranging from 21 to 28 mEq/L; carbon dioxide or PaCO2 ranging from 35 to 45 mm Hg; PaO2 ranging from 80 to 100 mm Hg, and SaO2 should be more than 95%.

Okay, there are four major ways excess acid can accumulate in the body. The first way is when there’s increased acid production, like with lactic acidosis, which is caused by decreased tissue perfusion and resulting anaerobic metabolism, or with diabetic ketoacidosis, which involves extreme hyperglycemia and an excessive breakdown of fatty acids in people with diabetes. It can also be caused by increased ingestion of acids, like methanol, salicylates, or ethylene or propylene glycol.

Then there’s decreased elimination of acids, which can happen with renal failure; and finally increased elimination of base, like with excessive diarrhea, which eliminates too much HCO3- from the intestines.

You can easily remember causes of metabolic acidosis by using the mnemonic MUDPILES, where M stands for methanol; U for uremia, which happens in renal failure; D for diabetic ketoacidosis, P for propylene glycol; I for iron tablets and isoniazid, which can cause acidosis with an overdose; L for lactic acidosis; E for ethylene glycol; and finally, S for salicylates.