Explain the pathophysiology, precipitating factors, and clinical features of hyperglycaemic hyperosmolar state. Recognize the diagnostic criteria for HHS and differentiate it from diabetic ketoacidosis (DKA) and mixed DKA-HHS. Outline the initial assessment and investigations required to evaluate patients with HHS, including glucose, electrolytes, renal function, ketones, acid–base status, and serum osmolality. Describe the principles of fluid resuscitation and the selection of appropriate intravenous fluids based on haemodynamic status, sodium concentration, and comorbidities. Discuss the role, timing, and appropriate administration of intravenous insulin in the management of HHS. Explain the principles of electrolyte monitoring and correction, particularly potassium and sodium, during treatment. Describe the appropriate monitoring of glucose, serum osmolality, fluid balance, renal function, and neurological status during treatment. Identify potential complications of HHS treatment, including hypoglycaemia, hypokalaemia, fluid overload, cerebral oedema, and osmotic demyelination syndrome. Recognize and manage precipitating factors, including infections, myocardial infarction, stroke, and medication-related hyperglycaemia. Outline the criteria for treatment escalation, transition to subcutaneous insulin, and prevention of recurrent HHS.