This postoperative patient requires replacement of nasogastric tube losses in addition to maintenance fluids. In an otherwise healthy individual, maintenance fluids are calculated based on body weight as 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the second 10 kg, and 1 mL/kg/h for every additional kg body weight. A 60-kg man requires 100 mL of fluid per hour or 2400 mL of fluid per day. Five percent dextrose in 0.45% normal saline with or without potassium chloride (depending on renal function) would be an appropriate maintenance fluid. Both lactated Ringer and normal saline, which are isotonic, can be used to replace gastrointestinal losses.