Fluids prescribing

Question 1

What are the two pressures going in and out of a capillary?

Answer 1

Hydrostatic pressure pushes water out of capillary and osmotic pressure draws water into capillary - net effect of these pressures determines water loss/gain to capillary

In illness these pressures can change - higher hydrostatic pressure meaning fluid will leave vessel. Albumin conc drop/RI gives smaller osmotic pressure and oedema forms

Question 2

What is ECF and ICF balance of potassium, chloride and sodium?

Answer 2

K - 140 ICF, 5 ECF
Na - 15 ICF, 140 ECF
Cl - 5 ICF, 110 ECF

Question 3

What is insensible water loss?

Answer 3

Transepidermal diffusion - water passes through the skin and is lost by evaporation
Evaporative loss from respiratory tract

Question 4

What are the risks associated with IV fluids?

Answer 4

Peripheral vascular catheter required - S. aureus risk
Easy to give too much fluid (esp in sick people)
Prescribing errors

Question 5

What sort of things do you need to identify in patient’s history before prescribing fluids?

Answer 5

Limited intake?
Abnormal losses? (how much, what kind of fluid, ongoing)
Co-morbidities?
Current illness?
Symptomatic?
Fluid balance charts?

Question 6

Examination for before prescribing fluids

Answer 6

Vital signs - systolic BP (< 100mmHg), HR (>90), cap refill (>2s), RR (20), urine output/colour (<0.5mls/kg/min)

All these show hypovolaemia - also dry mucous membranes, decreased skin turgor, responsiveness to passive leg raising

Question 7

What are factors which should make you think of fluid overload?

Answer 7

History of cardiac/renal problems
Raised JVP
Peripheral oedema
Inspiratory crackles at lung bases
HTN

Question 8

What investigations can be helpful in assessment of volume status?

Answer 8

FBC, U&E, CXR, lactate, urine biochem

Question 9

What are electrolyte requirements?

Answer 9

1mmol/kg/24h for sodium and potassium

Question 10

What are different fluid regimes?

Answer 10

Maintenance - no excess losses, if no other intake approx 30ml/kg/24h. May only need part of this Iv if some oral intake.

Replacement - previous and/or current abnormal losses - addition to maintenance fluid

Resuscitation fluid - hypovolaemic patient and requires urgent correction of intravascular depletion

Question 11

Give examples of IV fluids that are crystalloids

Answer 11

• 5% dextrose (glucose) - initially distributes through ISF and plasma, glucose metabolised so effectively adding just water, further distributes into cells as well as ISF and plasma
• 0.18% NaCl 4% dextrose
• 0.9% NaCl (isotonic saline)
• Plasmalyte - distributes through ISF and plasma, does not enter cells

Question 12

Give example of IV fluid that is a colloid

Answer 12

Gelofusine - high Na and Cl amounts

4.5% albumin - supplied in 0.9% NaCl, tends to stay in plasma, does not enter cells, blood product
Hydrolysed gelatin - supplied in 0.9% NaCl, initially tends to stay in plasma, does not enter cells, protein metabolised over time so then equivalent to 0.9% NaCl

Question 13

When should a fluid challenge be considered?

Answer 13

Lots of urine or hypotension and no signs of overload
Used therapeutically and diagnostically
500mls balanced salt solution quickly (< 15 mins) then re-assess, can repeat up to 2000mls

Question 14

When should fluids be cautioned?

Answer 14

Obese patients (use IBW)
Elderly or frail
RI
Cardiac failure
Malnourished or at risk of re-feeding syndrome