Practice question

A 75-year-old woman is admitted to hospital with a fractured neck of femur. She is normally mobile and independent. Her AMTS is 8/10. Pre-operative bloods show sodium 137 mmol/L, potassium 3.8 mmol/L, urea 7.2 mmol/L, creatinine 98 µmol/L. She is prescribed 1 litre of 0.9% sodium chloride over 8 hours pre-operatively. What is the primary reason for this fluid prescription in this patient?