15B01: Exam Report
Compare and contrast 0.9% saline and 4% albumin.
21% of candidates passed this question.
It was expected answers would include a comparison of the composition, physicochemical features and relevant physiology. Many candidates failed to adequately describe the differences in distribution across the body compartments or differences in physical properties of both fluids. In particular, how albumin is manufactured did not appear to be well understood by candidates.
I2i / 15B01: Compare and contrast 0.9%NaCl and 4% Albumin
Definition
0.9% NaCl
Isotonic replacement fluid
4% Albumin
Colloid
Manufacturing
0.9% NaCl
From sterile water and Sodium Chloride
4% Albumin
From human plasma donated by voluntary human donors
Virus inactivation/removal procedures are included in the manufacturing process
Components
0.9% NaCl
- 9g NaCl
- 154mmol Cl
- 154mmol Na
- Osmolarity 308 mOsm/L
- pH 5
- Water
4% Albumin
140mmol Na
128mmol Cl
Albumin 4g/ml
Osmolarity 260mmol/L
Presentation
0.9% NaCl
250ml, 500ml, 1000ml
4% Albumin
500ml glass bottle
Immediate distribution
0.9% NaCl
ECF
Isotonic – no osmotic shift
In ECF:
ISF 75% = +750ml
Plasma 25% = +250ml
4% Albumin
Na remains in ECF
Albumin diffuses slowly from intravascular compartment to entire ECF compartment at rate 4% per hour
Volume receptors
0.9% NaCl
blood volume increases 250ml
= 5%
Not enough to activate volume receptors
4% Albumin
Blood volume increases 500ml
= 10%
Activates volume receptors
Promotes water loss
Osmoreceptors
0.9% NaCl
no change in plasma osmolarity
∴ no activation by osmoreceptors
4% Albumin
no change in plasma osmolarity
∴ no activation by osmoreceptors
Oncotic pressure
0.9% NaCl
No colloid particles but the plasma volume (250ml) sufficient to dilute ↑plasma proteins
∴↓oncotic P
↑GFR &↓Na+ reabsorption in PCT
↑urinary flow and excretion of XS salt and fluid
KA Glomerulotubular Balance
4% Albumin
↑oncotic pressure
Promotes retention of fluid in intravascular space (in the short term)
Albumin is eventually metabolised