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. Questions:
- How much IV fluid does he need today?
- 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.
Hints
1. Add up the losses
- Have you included insensible losses?
- What urine volume are you accounting for? Is it a reasonable quantity? (e.g. 1-2 litres)
- 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 fluids
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.
1. How much sodium does the patient require?
- What is the normal daily requirement?
- How much 0.9% saline is required to provide that? (revise this)
- Is his requirement different? (does he have an increased sodium loss?)
2. How much potassium does the patient require?
- What is the normal daily requirement? (revise this)
- How should you prescribe that? (we haven't told you this yet, you're about to find out. Concentrate on the amount for now.)
3. Give the rest of the fluid as 5% dextrose.
- It is more physiological to alternate saline and dextrose when giving multiple bags, but that's not part of this question.
- Ready-mixed bags of isotonic dextrose-with-saline are available in some hospitals, but are less flexible.
4. Now go back to the question and decide how much of each fluid to give, and how much potassium.
Answer
The marking scheme is 'as if this was being used as a question in an OSCE'.
1. Total volume of fluid
- Urine output was 1500 mls per 24h
- Insensible losses are 500mls per 24h
- Total replacement required is therefore 2000mls
- Patient is taking 500mls of water (probably; or low sodium sugary drinks) orally
- Therefore need to give about 1500 mls IV
Indicative marking scheme: 4 marks for 1250-1750mls; 2 marks for 1000-2000 mls
2. How much should be 0.9% saline?
- 1 litre of saline provides 150mmol, which is comfortably more than the normal daily requirement. (revise this)
- To provide much more than this on a regular basis may lead to fluid retention, although you would get away with it for a single day.
Indicative marking scheme: 4 marks for 500-1000mls; 2 marks for 1000-1500 mls if some 5% dextrose also given.
3. How much potassium?
- Daily requirement is probably about 60 mmol.
- This is always given as an addition to IV fluids, as infusions must be slow to avoid dangerous hyperkalaemia.
- Bags are now supplied with KCl pre-added e.g. 20mmol in 500mls (40mmol per litre), to prevent dangerous accidental errors from use of concentrated KCl ampoules.
Indicative marking scheme: 2 marks for 40-80 mmols included in infusions in a spaced pattern. 1 mark for 20-40 mmols.
Sample prescription:
|
Fluid
|
Rate
|
| 0.9% saline 500mls + 20mmol KCL |
8hrly |
| 5% dextrose 500mls |
8hrly |
| 0.9% saline 500mls + 20mmol KCL |
8hrly |
Maximum marks for this question 10; pass mark 5
