Fluid case 1

Use the principles described in Fluids basics to approach this problem logically. Go back to those pages to look things up when necessary.

A 62 year old man is 2 days post-colectomy. He is euvolaemic, and is allowed to drink 500ml. His urine output is 63 ml/hour.


1. How much IV fluid does he need today?

2. What type of IV fluid does he need? (How much of each)

10 marks available. Certainly read the hints, but write down your answer before clicking to read ours.


How to approach the first part of the question (click to expand/collapse)
1. Add up the losses

  • Are they beyond the normal daily assumption of 30 mls/kg/day?
  • (When you need/want to do a more detailed calculation, Have you included insensible losses? And a reasonable urine output – 1-2 L/day?)
  • Are there any additional losses? (e.g. drains, etc)

2. Add up the gains (inputs)

  • Oral
  • Other? (nasogastric feed …..)

3. If there is a difference, you need to prescribe that amount of supplementary fluids Рorally if possible; otherwise IV. Under the three headings of maintenance, replacement, resuscitation, which is relevant here?

4. If the patient has an existing fluid deficit or excess, you need to include that in your prescription.

  • You were told that this patient is euvolaemic – i.e. ‘just right’ for fluids
  • He also has a reasonable urine output of ….. per day

5. Now go back to the question and decide how much fluid to give.

How to approach the second part of the question (click to expand/collapse)
1. How much sodium does the patient require?

2. How much potassium does the patient require?

3. Give the rest of the fluid as isotonic glucose.

  • Ready-mixed bags of isotonic 4% glucose plus 0.18% NaCl (sodium chloride)¬†are available in many hospitals, and appropriate if used only as maintenance fluid (indicative 30 ml/kg/d; never more than 100ml/h, further info).
  • You can also deliver the fluid as separate bags of 5% glucose and sodium-containing bags.

4. Now go back to the question and decide how much of each fluid to give, and how much potassium.