During a dengue outbreak in a district hospital in Kerala, a 28-year-old woman on day 5 of illness presents with platelet count 35,000/µL, haemoglobin 16.5 g/dL, haematocrit 48%, and mild abdominal pain. Liver span is 1.5 cm below costal margin. She has no bleeding manifestations and blood pressure is 110/70 mmHg. Dengue IgM is positive. What is the most appropriate immediate next step?