Types of fluid therapy

Question 1

What are the 4 main groups of fluids

Answer 1

• crystalloids
• synthetic colloids
• blood products
• haemoglobin based oxygen carriers

Question 2

What are crystalloids

Answer 2

Fluids containing electrolytes and other solutes which freely cross the capillary endothelium.
- They include isotonic hypertonic and hypotonic.

classified by their tonicity relative to plasma

Question 3

Why is hypertonic saline beneficial for volume expansion

Answer 3

• creates an osmotic gradient between the intracellular and extracellular space.
• water moves from cell to interstitium then vasculature.
• so the intravascular volume expansion is greater than the volume administered.

Question 4

Does hypertonic saline have any proposed benefits other than volume expansion

Answer 4

• increased cardiac contractility
• Microvascular effects improve renal blood flow.
• immunomodulatory effects
• hyperosmolar agent to reduce ICP

Question 5

What rate is hypertonic saline given at and why

Answer 5

5ml/kg dog and 3ml/kg cat over no less than 5 minutes.
- given too quickly can cause reflex bradycardia, hypotension and bhronchoconstriction.

Question 6

How is HTS redistributed

Answer 6

• Volume expanding effect short lived, reduced afer 30min and only lasts a few hours.
• • In USA sometimes given alongside colloids to prolong this.

Question 7

How does the electrolyte composition of most isotonic crystalloids differ to plasma.

Answer 7

• higher in sodium and lower in K+
• Potassium must be monitored, particularly in inappetant patients.

Question 8

What is the difference between hypotonic “maintanence” solutions and free water solutions?

Answer 8

• Maintanence relatively low sodium and higher potassium, include half strength saline.
• free water solutions contain no or few electrolytes but with added glucose for safe administration - this is metabolised after administering to give free water

Question 9

What can happen if hypotonic solutions are given too quickly?

Answer 9

• They reduce extracellular osmolality causing fluid shift into cells.
• If given rapidly they can cause red cell lysis and cerebral oedema

never Bolus

Question 10

What are synthetic colloids?

Answer 10

• Contain artificial high molecular weight molecules suspended in isotonic crystalloid.
• They effect plasma COP and theorectically retain fluid withing the intravascular space after administration.

Question 11

What is the main indication for colloids

Answer 11

intravascular volume expansion, especially when hypovolaemia has not responded to crystalloids.

Question 12

What are the the categories of synthetic colloids

Answer 12

• Starches
• Dextrans
• Gelatins

Question 13

Why is the molecular weight (low, medium, high) of HES significant

Answer 13

• The higher the weight the longer it persists in the plasma
• Lower molecular weight = more molecules = greater oncotic effects.
• usually choose a medium weight eg voluven.

Question 14

Why had synthetic colloids historically been recommended with hypoalbuminaemia

Answer 14

Aiming to keep COP at at lease 15mmHg to reduce the risk of interstitial oedema formation

Question 15

Why are colloids in hypoalbuminaemia now controversial

Answer 15

• understanding of the glycocalyx, not as useful as once thought.
• over correction of COP could surpress albumin synthesis.
• HES associated with poor outcomes in critically ill people.

also renal. coags.

Question 16

What is the suspected mechanism of HES induced coagulopathy

Answer 16

• Dilution of clotting factors and platelets
• interaction with vWF and factor 8
• seems to be dose dependant

Question 17

what are dextrans

Answer 17

colloid produced from bacterial fermentation of sucrose
40 - 70 da
not recommended (coags, renal anaphylaxis)

Question 18

What are gelatins

Answer 18

a colloid produced from hydrolysed bovine collagen
short half life
associated with renal injury

Question 19

Which blood products have colloidal effects

Answer 19

FP, FFP and whole blood (not packed cells)