A 23-year-old man with type 1 diabetes presents with abdominal pain, vomiting and Kussmaul respirations after a viral illness. Bedside capillary glucose is 24 mmol/L, venous pH 7.12, bicarbonate 10 mmol/L and serum ketones 6.0 mmol/L. After initial fluid resuscitation, an insulin infusion is commenced. According to an Australian adult DKA protocol, what is the most appropriate strategy once his blood glucose falls to 14 mmol/L while ketonaemia persists?