Use the principles described in Fluids basics to approach this problem logically. Go back to those pages to look things up when necessary.
Three days after her admission, a 43 year old woman with diabetic ketoacidosis has a blood pressure of 88/46 mmHg & pulse of 110 bpm. Her charts show that her urine output over the last 3 days was 26.5 litres, whilst her total intake was 18 litres.
|1. How much fluid does she need to regain a normal blood pressure and make up her losses?
2. What fluids would you use?
10 marks available. Read the hints, but write down your answer before clicking to read ours.
|This is a more complex question but the principles are exactly the same.
Assume that the blood glucose is OK after 3 days in hospital, though this may be an unsafe assumption, as the fluid balance has been screwed up so comprehensively.
1. Add up the deficit
2. In considering inputs
3. Now go back to the question and decide how much fluid to give.
|1. In choosing fluids to give and in what order, consider
2. How much potassium does the patient require?
3. Now go back to the question and decide how much of each fluid to give.
The hyperglycaemia of diabetic ketoacidosis causes glycosuria which results in an osmotic diuresis. This causes high losses of water and dehydration occurs if fluid balance is not attended to. How to control glucose is not considered here. Potassium disturbances are usual.
1. Total volume of fluid
- She has lost 26.5 litres of urine plus at least 1.5 litres insensible losses over the last 3 days; her input has been 18 litres. This equals a deficit of 10 litres, and it is not suprising that she appears to be hypovolaemic with hypotension and tachycardia.
|Indicative marking scheme: 4 marks for 9.5-10.5 litres; 2 marks for 8-11 litres|
2. What should the fluids be? and how should they be given?
- As she has a low BP, we can assume that her blood volume is low, and that organ perfusion is at risk. She therefore needs to be resuscitated with solutions that will expand the intravascular compartment. More on fluid compartments; or fluid therapy guide on resuscitation fluids.
- As she has lost mainly water, a large part of this should be isotonic glucose, and serum [ Na+ ] should be monitored in order to assess the need for IV saline.
- Rate of infusion – the first couple of litres of fluid could be given very quickly, e.g. in 1-1.5h, next couple over 2-3h, rest more slowly. In a patient with heart disease you may need to be more cautious to prevent pulmonary oedema from overfilling of the intravascular space before fluid diffuses into other compartments.
|Indicative marking scheme: 3 marks for appropriate 1000-2000mls resuscitation fluids given quite quickly initially, or up to 5 litres of sodium-containing fluids if heavily ‘front-loaded’; PLUS 2 marks if 4-7 litres of 5% glucose or equivalent given.|
3. Today’s requirements?
- If you were tackling this problem in real life, you would have to plan today’s fluids too. However in a situation of this complexity it would be essential to review the patient repeatedly to assess cardiovascular status, urine output, and possibly to check electrolytes before writing up fluids for the next few hours.
- You should never attempt to predict a whole day’s output ahead when such large volumes are required.
- In a high-dependency setting where things may be changing, the instruction to give fluids at a rate depending on hourly urine flow can be very helpful, e.g.
|0.9% sodium chloride 500mls||Input per hour = Last hour’s output + 40 mls|
|5% glucose 500mls + 20mmol KCL|
|0.9% sodium chloride 500mls|
|5% glucose 500mls + 20mmol KCL|
This prevents inadvertently accruing very large deficits or gains (assuming urine is the major source of fluid loss) – but it is essential to review this type of prescription frequently.
|Maximum marks for this question 10; pass mark 6|