A 23-year-old woman with type 1 diabetes presents with 24 hours of polyuria, vomiting and abdominal pain. She has missed several insulin doses. On examination she is tachycardic, mildly hypotensive and Kussmaul breathing is noted. Capillary glucose is 26 mmol/L. Blood tests show capillary ketones 5.5 mmol/L, venous pH 7.18 and bicarbonate 10 mmol/L. What is the most appropriate diagnosis?