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Fluids, electrolytes and fluid balance: RCSI aptitude test practice questions
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Fluids, electrolytes and fluid balance on the RCSI theory paper
The 5 Rs, signs of hypovolaemia, the 500 ml bolus, 25 to 30 ml/kg maintenance, potassium rules, sodium and chloride limits, reading a fluid balance chart, dehydration.
28 multiple-choice questions, each with an explanation and the document it was checked against. Three questions are free; the pass opens the other 25 and every other topic. Wrong answers come back first the next time you practise, and a question counts as mastered after two correct answers in a row.
Sample questions from this topic
Question 1
What does a urinary sodium below 30 mmol/L suggest in a patient with high-volume gut losses?
- ANormal kidney function with nothing that needs correcting
- BTotal body sodium depletion, even with a normal plasma sodium
- CExcess sodium chloride infusion spilling into the urine
- DRenal failure with the kidney retaining sodium inappropriately
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Answer: B. NICE CG174 1.2.4: in high-volume gastrointestinal losses, reduced urinary sodium excretion (under 30 mmol/L) may indicate total body sodium depletion even when plasma sodium reads normal; the kidney is hanging on to every ion it can. The value misleads in renal impairment or with diuretics.
Source: NICE CG174: Intravenous fluid therapy in adults in hospital, 1.2.4
Question 2
How often should a stable inpatient on ongoing intravenous fluids be weighed?
- AOnce a week
- BOnly on admission and discharge
- CEvery day
- DTwice a week
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Answer: D. NICE CG174 1.2.4: patients continuing on IV fluids need at least daily clinical review, daily urea, creatinine and electrolytes and a fluid balance chart, with weight measured twice weekly. Weight is the most honest fluid balance chart there is, because it does not depend on anyone remembering to write down a cup of tea.
Source: NICE CG174: Intravenous fluid therapy in adults in hospital, 1.2.4
Question 3
A fluid balance chart shows 24-hour intake 1 850 ml and output 2 600 ml. What is the balance and what does it mean?
- AZero: intake and output are within normal limits
- BMinus 4 450 ml: severe dehydration needing urgent fluid replacement
- CMinus 750 ml: the patient lost more than they took in
- DPlus 750 ml: the patient is retaining fluid and may be overloaded
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Answer: C. Balance is intake minus output: 1 850 minus 2 600 is minus 750 ml, a negative balance. Read with the trend, weight and bloods (NICE 1.2.2), it may be the intended result of a diuretic or a warning of dehydration. Every source counts: oral drinks, IV fluids and drugs, feeds, blood on one side; urine, vomit, stool, drains and stoma output on the other.
Source: NICE CG174: Intravenous fluid therapy in adults in hospital, 1.1.7 and 1.2.2
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Documents behind these questions
Every fact was checked against the public document named on the answer. This topic draws on: