Acidosis and Alkalosis

Tests
The goals of testing are to identify whether a patient has an acid-base disorder, to determine how severe the disorder is, and, to help diagnose underlying diseases or conditions (such as diabetic ketoacidosis or the ingestion of a toxin) that have caused the acid-base disorder. Testing is also done to monitor critically ill patients, as well as patients with conditions known to affect acid-base balance, such as chronic lung disease and kidney disease. The primary tests used to identify, evaluate, and monitor acid-base disorders are blood gases and electrolytes.

Blood gases are a group of tests performed together on an arterial blood sample (blood obtained from an artery instead of a vein). They are a snapshot of the blood’s pH, PO2 (the amount of oxygen dissolved in the blood), and PCO2 (the amount of carbon dioxide dissolved in the blood). From these results HCO3- (the amount of bicarbonate) can be calculated.

Results seen:

Acid-Base Disorder	H+	pH	HCO3	PCO2	Body Compensation
Metabolic acidosis	↑	↓	↓↓	↓	Increased breathing rate (hyperventilation) to increase CO2 elimination
Metabolic alkalosis	↓	↑	↑↑	↑	Slowed breathing (hypoventilation) to decrease CO2 elimination
Respiratory acidosis	↑	↓	↑	↑↑	Kidney increases production of HCO3- and excretion of H+ (acid)
Respiratory alkalosis	↓	↑	↓	↓↓	Decreased production of HCO3- and excretion of H+
↑ increased level; ↑↑ greatly increased level; ↓ decreased level; ↓↓ greatly decreased level

Electrolytes refers to a group of four tests: Na+ (sodium), K+ (potassium), Cl- (chloride) and bicarbonate (total CO2 content).

An anion gap can be calculated from the electrolytes and provides a clue to the cause of the acid/base imbalance.

Depending on the suspected cause, a number of other tests may be ordered: CMP (comprehensive metabolic panel), ketones in blood and ketones in urine, lactate, salicylates, ethylene glycol, and methanol, to name a few.