Volatile Acids
- Defined as acids that can be converted in to gaseous form and thus eliminated via the lungs
- The primary volatile acid created in the body is carbonic acid which is created by the reaction of carbon dioxide and water. Carbon dioxide is produced in significant quantities during aerobic respiration. It is transported to the lungs where it is can be excreted
- During ketoacidosis, volatile acetone may be cleared by the lungs. Whilst this is used to recognize the condition the quantities involved are too low to be physiologically important.
Non-Volatile (Fixed) Acids
- Defined as acids that cannot be converted in to gaseous form and thus cannot be eliminated via the lung
- They can be considered as two distinct classes
Organic Acids
- Principally lactic acid and ketones
- Formed as byproducts of metabolic processes
- Elimination primarily occurs through hepatic metabolism
Inorganic Acids
- Principally sulphuric and phosphoric acids
- Formed following the metabolism of sulphur or phosphate containing amino acids
- Elimination primarily occurs through urinary excretion
- The three classes are relatively independent of each other:
- An excess of one acid cannot be corrected through excretion of another acid
- Highlights the importance of supporting individual organ systems in critical illness