Terminology
Adolph Kussmaul, who introduced the term, referred to breathing when metabolic acidosis was sufficiently severe for the respiratory rate to be normal or reduced. This definition is also followed by several other sources, including for instance Merriam-Webster, which defines Kussmaul breathing as "abnormally slow deep respiration characteristic of air hunger and occurring especially in acidotic states". Other sources, however, use the term Kussmaul respiration also when acidosis is less severe, in which case breathing is rapid.
Note that Kussmaul breathing occurs only in advanced stages of acidosis, and is fairly rarely reached. In less severe cases of acidosis, rapid, shallow breathing is seen. Kussmaul breathing is a kind of very deep, gasping, desperate breathing. Occasionally, medical literature refers to any abnormal breathing pattern in acidosis as Kussmaul breathing; however, this is inaccurate.
Read more about this topic: Kussmaul Breathing