A 62-year-old man presents with polyuria, polydipsia, abdominal pain and vomiting. He has type 1 diabetes and has missed several insulin doses. On examination, he is tachycardic and mildly hypotensive. Laboratory results show: glucose 28 mmol/L, venous pH 7.12, bicarbonate 10 mmol/L, positive serum ketones and anion gap metabolic acidosis. According to Diabetes Canada, what is the first priority in acute management of this diabetic ketoacidosis?