A 26-year-old man presents to the emergency department with vomiting, abdominal pain and deep rapid breathing. He has type 1 diabetes and missed several insulin doses. On examination he is drowsy, tachycardic and dehydrated. Venous blood gas shows pH 7.10, bicarbonate 9 mmol/L and ketones 5.5 mmol/L. Blood glucose is 26 mmol/L. What is the MOST appropriate immediate management priority?