That was the topic of this paper in the Southern Medical Journal. Diabetic ketoalkalosis (DKALK) refers to a complex acid base disorder in which diabetic ketoacidosis (DKA) coexists with a separate process causing metabolic alkalosis. This results in a rise in the delta ratio (DR, or delta gap/delta bicarb) to greater than 1.2 when, in simple DKA it should be around 1.0. Put another way, the coexisting metabolic alkalosis prevents the bicarb from falling as much as would be expected from the rise in the anion gap. It's a misnomer, of course, because the ketosis does not cause the alkalosis; the alkalosis is a separate process. The alkalosis is believed due to vomiting and counter regulatory responses to volume loss. The DR could be incalculable if the metabolic alkalosis is severe enough that the bicarb (and pH) are normal.
Don't forget that the opposite can occur. A DR less than 0.8 suggests a second process causing metabolic acidosis such as lactic acidosis.