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