Crystalloid vs colloid: Side effects

Crystalloid

Crystalloids are solutions composed of sterile water with added electrolytes to give a composition similar to plasma. In general, crystalloids are used to replace fluid losses and to expand total extracellular volume. Typically, crystalloids remain intravascular for 20-30 min before equilibrating and distributing throughout the entire extracellular fluid space, i.e., risk of causing excessive edema as fluids will not remain intravascular. In order to replace intravascular volume using crystalloid, 3-4x the volume is needed, as compared to colloid. Hypotonic solutions must be infused slowly so as to not cause hemolysis.

Crystalloid Side Effects

• Slower postoperative GI recovery due to GI wall edema. Crystalloid solutions have significant hydrostatic effects on capillaries leading to subsequent extracellular fluid accumulation and GI wall edema.

• Patients with pre-existing cardiac systolic dysfunction or renal disease are predisposed to pulmonary edema.

• Risk of hemodilution

• Risk of hyperchloremic acidosis with large volumes of normal saline. A meta-analysis by Bampoe et al. analyzed 1,096 surgical patients in randomized control trials. They demonstrated that perioperative administration of buffered electrolyte solutions had a lower incidence of minor metabolic derangements such as metabolic acidosis when compared with normal saline. There was no significant effect on mortality or renal replacement therapy.

• Plasma-lyte: has good buffer capacity with pH equivalent to plasma. However, due to high magnesium content, it is cautioned in those with renal insufficiency.

• Lactated Ringer’s (LR)—Main additional electrolyte constituents are Ca and K (risk of hyperkalemia and hypercalcemia with excessive use). Lactate relies on hepatic metabolism to form CO₂ and water. Therefore, LR is not recommended for patients with end-stage liver disease where PlasmaLyte is preferred. The literature also recommends that LR should not be used as a diluting agent for blood transfusions as calcium binds to citrate anticoagulant in blood products.

Colloids

Colloids have higher oncotic pressure and lead to volume expansion. Colloids improve plasma oncotic pressure but their use does not show evidence of mortality benefit. The use of colloids is associated with a small risk of anaphylactic/anaphylactoid reactions and may be associated with coagulopathy given in large quantities. Low doses typically preserve coagulation factors and hematocrit to maintain appropriate coagulation. Colloid solutions are prepared in normal saline and therefore can also cause a hyperchloremic metabolic acidosis. Some colloids including albumin come from human donors and certain patient populations, i.e., Jehovah’s Witness, may not be accepting of these products.

Specific Colloid Side Effects

• Hydroxyethyl starches: These are generally avoided in North America due to effects on hemostasis and renal toxicity (CHEST, VISEP and 6S trials). Hetastarch can impair platelet reactivity and decrease circulating plasma concentrations of Factor VII and von Willebrand factor. Therefore, clot formation is weakened and there is a subsequent increase in need for transfusions compared to other colloids. Recommendations are to limit the dose to 20mL/kg to minimize coagulopathy. Also, hetastarch can elevate serum amylase and is associated with anaphylactic reactions.

• Gelatin: not used in the US due to rapid excretion in urine and high incidence of anaphylaxis

• Albumin: Should be avoided in those with severe traumatic brain injury. SAFE trial demonstrated higher mortality with albumin in trauma patients compared to normal saline.

• Dextran: Side effect profile includes anaphylactic reactions, increased bleeding time, rare cases of noncardiogenic pulmonary edema and acute renal failure.