Guidelines recommend checking an ABG or VBG in all patients with DKA. This practice is not evidence-based and should be abandoned.
ABG or VBG provides little information about whether or not the patient has DKA (beyond what is already known from the serum chemistries).
Rather than pH, serum bicarbonate may be used to gauge the severity of acidosis.
There is no evidence that detecting or reacting to a very low pH is helpful.
Decisions about the level of ventilatory support that a patient needs can almost always be made on a clinical basis. When in doubt, close attention to the patient with serial examination is often a sound approach. Focus on the patient, not the blood gas.
VBG might be helpful in cases where it is unclear whether the patient requires intubation, or if there is a significant underlying respiratory disease (e.g. COPD or obesity hypoventilation syndrome).