A eighty (80) year old man needs volume replacement to treat hypotension secondary to biliary sepsis. Compare and contrast one colloid and one crystalloid solution that maybe used in this context.

In marking this question it was realised that the candidates come from all parts of the world, especially Australia, Hong Kong and New Zealand. The choice of fluids reflected that diversity.

In  “comparing  and  contrasting”  it  was  expected  that  the  candidate  would  cover  content, manufacture, fate in the circulation, effects on organ function and idiosyncratic effects, not merely listing the properties but contrasting the properties within that list.

Eg. Normal Saline versus 4% Human Albumin (CSL).

Normal Saline is a sterile solution of 150mmol each of Na and Cl in I litre water whereas 4% albumin is prepared from human-donor, pooled blood by complex fractionation.   The albumin cannot be regarded as sterile, but is heated to 60o C for 10 hours and prepared at low pH. Prion transfer is feasible. It contains 140 mmol/L Na, 128 mmol/L Cl.

Saline would be expected to distribute 25% intravascularly and 75% interstitially whereas albumin, theoretically, is iso-oncotic and expands the vascular compartment by the administered volume. This may not be true in the critically ill with high albumin turnover and capillary leak.

Saline will have effects via expansion of the appropriate compartments and will lead to increased cardiac output proportionately. In large volumes it may lead to oedema formation, hypernatraemia and hyperchloraemic acidosis. On the other hand, colloid,eg albumin, in one meta-analysis has been associated with higher mortality. It also contains pre kalikrein activator (PKA) which, although present in low amounts, may produce hypotension and bradycardia in conjunction with ACEI use.

The half-life of albumin is said to be 20 days. The distribution half-life of saline is short (30mins) and elimination half-life will depend on the hormonal milieu (ADH, ANP, aldosterone levels) due to hypovolaemia and stress.

Cost : Saline- $1-2 per litre Albumin – free to users in Australia, theoretical cost ~$80 for 500mls.

## Discussion

Though this question is unique, it is difficult to come up with an answer which does not duplicate a series of other answers.

Instead, I will present here a copy of the table of colloid solutions (from Question 29, second paper of 2007) and a table of intravenous fluid content from the chapter on the applied physiology on fluid and electrolyte replacement.

 Property Albumin (20%) Gelofusine 4% Dextran (10%) Hydroxyethyl starch 6% Drug class Endogenous protein Succynylated bovine gelatin Branched polysaccharide Amylopectin derivative Molecular weight 69 000 Da 5 000 - 15 000 Da 14 000-18 000 Da 70 000 Da Plasma halflife 24 hours 2.5 hours 12 hours 5 days Elimination Degradation by reticuloendothelial system Renally excreted Renally excreted Some renally excreted, some metabolised by the reticuloendothelial system Plasma expansion as a percentage of infused volume 200-400% 70-80% 100-150% ~100% Advantages Antioxidant effects Free radical scavenging effects Protection of glycocalyx Cheap Relatively safe in renal failure No limits on infused volume Decreases the viscosity of blood, improving microcirculation No risk of CJ disease Cheap Large maximum allowable volume No risk of CJ disease Lowest risk of anaphylactoid recations among non-albumin colloids Disadvantages Volume overload Transfusion reaction Expensive Risk of CJ disease Volume overload Anaphylactoid reactions Coagulopathy Volume overload Anaphylaxis Coagulopathy Interference with ABO crossmatch Renal failure (ATN) Volume overload Anaphylactoid reactions Coagulopathy Accumulation Renal failure Increase in amylase
 Fluid osmolality pH dextrose Cl- HCO3 Na+ K+ Mg++ Ca++ lactate citrate acetate gluconate 5% dextrose 278 3.5-6.5 278 - - - - - - - - - - 10% dextrose 556 3.5-6.5 556 - - - - - - - - - - 50% dextrose 2780 3.5-6.5 2780 - - - - - - - - - - Normal saline 300 4.0-7.5 - 150 - 150 - - - - - - - 20% saline 6840 4.0-7.5 - 3422 - 3422 - - - - - - - Hartmanns 276 5.0-7.0 - 112 - 131 5 - 2 28 - - - Plasma-Lyte 148 294 5.0-7.0 - 98 - 140 5 1.5 2 - - 27 23 Albumin 20% 210-262 7.0 - - - 48-100 - - - - - - - Packed cells ? 340 6.79 49 150 11 150 20 - - 9 - - -

### References

References

For a definitive treatment of all of this, you ought to pay homage to the gigantic and all-encompassing "Critical Care Nephrology" by Ronco Bellomo and Kellum (2009).

There is also extra stuff is from the Ronco et al article "The haemodialysis system: basic mechanisms of water and solute transport in extracorporeal renal replacement therapies" in Nephrol Dial Transplant ( 1998) 13 [Suppl 6 ]: 3–9.

Finally, the Gambro and Fresenius websites have been an excellent source of information.