Psychiatryniche
A 16-year-old boy with anorexia nervosa weighing 39 kg was admitted three days ago and nasogastric feeding was commenced and increased daily. He has received thiamine each day. This morning he is confused, cannot lift his head from the pillow and is short of breath at rest. Investigations: potassium 3.2 mmol/L (3.5-5.2), magnesium 0.60 mmol/L (0.75-1.05), phosphate 0.33 mmol/L (0.8-1.5). His chest is clear and his electrocardiogram shows sinus rhythm at 58 beats per minute. Which one of the following is the most appropriate immediate management?