Use the principles described in Fluids basics to approach this problem logically. Go back to those pages to look things up when necessary.
A complicated case. But exactly the same principles apply.
5 days after a liver transplant, a 48 year old man has a pyrexia of 40.8 degrees C. His charts for the last 24 hours reveal:
urine output:
drain output:
nasogastric output:
blood transfusion:
IV crystalloid:
oral fluids: |
2.7 litres
525 ml
1.475 litres
2 units (350 ml each)
2.5 litres
500 ml |
On examination he has a tachycardia. His supine BP is OK, but you can’t sit him up to check his erect BP. His serum [Na+] is 140 mmol/l. Questions:
- How much IV fluid is he likely to need over the next 24h, assuming these outputs remain the same? (it is of course unlikely that they will be quite the same)
- What fluids would you use?
Hints
1. Add up the fluid balance over the last 24h
- There are multiple losses and gains to consider here
- Remember insensible losses - are these likely to be normal?
2. Predicting the next 24h
- Remember that requirements today include making up yesterday's deficit
3. Now go back to the question and decide how much fluid he will need.
1. Consider the nature of his deficit
2. Consider his clinical state and the size of the deficit
- He has fallen behind on fluid replacement and has ongoing substantial losses.
3. Now go back to the question and decide what type of fluids to use.
Answer
This would be a tough Q for an undergraduate medicine exam.
1. Fluid balance
- As is often the case with complex surgical patients, he has multiple sources of luid loss. In each case, urine, drain or tube, the fluid lost will be a mixture of fluid and solutes. Drain fluid will have an electrolyte content very similar to plasma. Nasogastric fluid is chloride-rich.
- His obvious losses ( urine + drain + NG tube ) total 4.7 litres.
- His insensible losses are higher than normal because of his fever, say 800-1000 ml, giving a total loss of 5.5-5.7 litres.
- His total intake was 3.7 litres
- He is therefore deficient by 1.8-2.0 litres.
- Assuming that his total losses for this day are similar to those of the day before, he will need about 7.5 litres (a further day's losses plus yesterday's deficit; 5.5 + 2.0)in order to become euvolaemic.
Indicative marking scheme: 6 marks for 7-8.0 litres. 3 marks for 6.0-8.5 litres.
2. What type of fluids?
- He will need a mixture of fluids.
- Colloid or further blood in order to fill the intravascular compartment and maintain organ perfusion.
- Saline to replace water and solute losses
- Dextrose to make up the rest. He would become very sodium overloaded and hypernatraemic if all replacement was colloid and saline.
- He is likely to need potassium supplements but you would be guided by biochemistry results here.
Indicative marking scheme: 4 marks for an answer that covers these principles, and 'front-loads' fluid replacement to catch up on yesterday's deficit.
3. In real life
A case of this complexity will require repeated re-evaluation, and adjustment of his fluids throughout the day with serial blood tests in order to guide your infusion rate, choice of fluid, and potassium supplementation.
Provision of nutrition would be an important consideration in this patient. Nasogastric feeding is clearly not viable yet so some of your IV input could be an IV feeding solution.
If you can follow this one, you've cracked it!
Maximum marks for this question 10; pass mark 5
