Final answer:
The patient's weight increase from 97.5 kg to 99 kg indicates a fluid retention of approximately 1.5 liters.
Step-by-step explanation:
The increase in patient weight from 97.5 kg to 99 kg, in the context of fluid intake and output, corresponds to a fluid retention. Since 1 kg of body weight is roughly equivalent to 1 liter of fluid, the weight gain of 1.5 kg suggests a fluid retention of approximately 1.5 liters.