The literature from the pediatric world showed for years that insulin bolus prior to a drip is not only helpful, but it can also be harmful, resulting in cerebral edema. The data from the adult world has been lacking, and most people have been using anecdotal evidence on whether or not the insulin bolus of 0.1 U/kg should be given prior to the 0.1 to 0.14 units/kg/h drip.
The best study looking at this issue is by Goya, et al in the Journal of Emergency Medicine in 2010. It was a prospective cohort chart review study over a one year time period. Of 157 patients treated for DKA, 78 received the initial insulin bolus and 79 did not. The results were impressive. There were no statistically significant differences in hypoglycemia, rate of change of glucose, anion gap, or length of stay in the ED or hospital. The only negative to this study is that the power could be higher to reliably interpret the results.
Dr. Abbas Kitabchi, who has published quite a bit in the world of diabetes, performed a small study in which patients with DKA either received a 0.07 units insulin bolus followed by 0.07 units/kg/h drip, no bolus with a 0.07 units/kg/h drip, or no bolus with a 0.14 units/kg/h drip. They found that the bolus is not necessary as long as the drip is 0.14 units/kg/h. This study was also very small. Interestingly, Dr. Kitabchi is the author of the Up To Date article on DKA, in which he states the insulin bolus in DKA is optional. However, he states that no bolus may be given if the drip is 0.14 units/kg/h; the 0.1 units/kg/h drip is for situations in which the drip was given.
Goyal N, Miller J, et al. Utility of initial bolus insulin in the treatment of diabetic ketoacidosis. The Journal of Emergency Medicine. 2010. 38(4): 422-427.
Kitabchi A, Murphy M, et al. Is a priming dose of insulin necessary in a low-dose insulin protocol for the treatment of diabetic ketoacidosis? Diabetes Care. Nov, 2008. 31(11):2081-5.
Kitabchi A, Rose B. Treatment of diabetic ketoacidosis and hyperosmolar hyperglycemic state in adults. Uptodate.com. Feb 16, 2011.