A 24-year-old man with type 1 diabetes is brought to the emergency department with abdominal pain, vomiting and drowsiness. He has missed multiple insulin doses. On examination he is tachypnoeic with Kussmaul respirations, dehydrated, and his capillary blood glucose is 28 mmol/L. Venous blood gas shows pH 7.12 and bicarbonate 10 mmol/L. What is the most appropriate initial fluid resuscitation strategy?