A 70 kg, 58-year-old woman is nil by mouth after an uncomplicated laparotomy, with no abnormal losses, normal electrolytes and normal renal function. The FY1 asks how to prescribe her routine maintenance intravenous fluids for the next 24 hours according to NICE guidance. Which prescription is most appropriate?
- AAbout 25 to 30 mL/kg/day of water with roughly 1 mmol/kg/day each of sodium, potassium and chloride and 50 to 100 g/day of glucose, reviewed daily
- BFour litres of 0.9% saline with no potassium
- CThree litres of Hartmann's solution daily with added potassium chloride in every single bag, regardless of the measured serum electrolyte levels each day
- DOne litre of 5% dextrose per week
- EMaintenance fluids need no potassium because the kidneys conserve it
Show answer and explanation
Correct answer: A
NICE guidance frames routine maintenance for the patient who simply cannot drink: 25 to 30 mL/kg/day of water (1,750 to 2,100 mL for 70 kg), about 1 mmol/kg/day each of sodium, potassium and chloride, and 50 to 100 g/day of glucose — not for nutrition, but to limit starvation ketosis. In practice this is often delivered as a glucose-saline combination with potassium, and the prescription is exactly that: a prescription, reviewed daily against clinical examination, fluid balance, weight and electrolytes, adjusted down in the elderly, frail, cardiac or renally impaired (20 to 25 mL/kg/day). The commonest prescribing errors are the distractors: routine multi-litre saline regimens deliver several times the daily sodium and chloride requirement, causing salt and water overload and hyperchloraemic acidosis; omitting potassium in a fasting patient with obligatory renal potassium losses (the kidney cannot conserve potassium the way it conserves sodium) produces iatrogenic hypokalaemia within days; and maintenance must be separated conceptually from resuscitation (boluses for shock) and replacement (matching measured abnormal losses such as nasogastric aspirate, which are replaced volume-for-volume with an appropriate composition on top of maintenance).
Why the others are wrong: B — four litres of saline is double the water and many times the sodium requirement, with no potassium. C — blanket potassium 'in every bag regardless' ignores levels and renal function. D — a litre a week is a drop, not maintenance. E — renal potassium wasting continues in fasting; omission causes hypokalaemia.
Key point: Maintenance is 25–30 mL/kg/day water, ~1 mmol/kg/day sodium, potassium and chloride, plus 50–100 g glucose, reviewed daily — and it is distinct from resuscitation and from replacement of measured losses; routine saline overload and forgotten potassium are the classic errors.
Guidelines: NICE intravenous fluid therapy guidance (CG174): routine maintenance is 25-30 mL/kg/day water with about 1 mmol/kg/day each of sodium, potassium and chloride and 50-100 g/day glucose, reassessed daily with a fluid-balance and weight chart.