• Colloid solutions are comprised of large molecules dissolved in a crystalloid solution; when administered these molecules help maintain intravascular oncotic pressure.
• They are divided into two groups
  • Natural colloids, such as albumin
  • Semisynthetic colloids, including gelatins, dextrans, and hydroxyethyl starches
• The goal of fluid administration is to improve organ perfusion through optimization of volume status (1) [A]. Colloids can be utilized perioperatively to aid volume expansion.

• Total body water (TBW)
  • Comprises 60% of body weight and is measured in kilograms.
  • Two-thirds is intracellular fluid (ICF)
  • One-third is extracellular fluid (ECF); of which 80% is interstitial, while the remainder is intravascular.
  • Varies with age, sex, pathologic conditions, and other factors.
• Starling forces define flow from intravascular to interstitial/extravascular space. Intravascular oncotic pressure opposes the filtration or hydrostatic process (see equations). Net driving force or net filtration is determined by the following factors (pressures are measured in mm Hg).
  • Capillary hydrostatic pressure (P_c) favors filtration across the capillary endothelium into the interstitium.
  • Interstitial hydrostatic pressure (P_i) drives fluid back into the capillaries and therefore opposes filtration of capillary fluid into the interstitial fluid.
  • Capillary oncotic pressure prevents movement of solvent and small ions across the capillary membrane, thereby opposing filtration.
  • Interstitial oncotic pressure prevents movement of solvent and small ions across the capillary membrane, favoring filtration.
  • Filtration coefficient is comprised of capillary surface area and capillary hydraulic conductance. Increased water permeability is demonstrated by an increased value.
  • Reflection coefficient functions to account for the small permeability of albumin and other proteins. Protein permeability results in greater than expected oncotic pressure in interstitial fluids.
• Crystalloids are composed of ionized salts and water-soluble molecules dissolved in water.
  • The salts and molecules provide electrolytes and osmolarity but not oncotic pressure.
  • Crystalloids can freely diffuse across intravascular endothelial walls into the interstitium.
  • In theory, ~20–30% of crystalloid solution infused will remain intravascular.
• Colloids are composed of large molecules that provide oncotic pressure and are suspended in a crystalloid solution. The molecules do not easily cross semipermeable membranes.
  • Molecular weight (MW) of the colloid is proportional to size; larger molecules are less easily filtered (higher reflection coefficient).
  • Those molecules that are not filtered by the kidneys are eventually taken up by the reticuloendothelial system or excreted through the gut.
  • Balanced solutions (isotonic) have less adverse effects than normal saline (hyperchloremic metabolic acidosis).
• Albumin (MW 69 kDa) is made from pooled human plasma that has been heated (60°C for 10 hours), screened for viruses, and ultrafiltered.
  • Monomer; all molecules have the same size.
  • Available in a 5% (isooncotic) for volume expansion and 25% (hyperoncotic) solutions for hypoalbuminemic states (1) [A].
  • Expanding effects may last between 16 and 24 hours.
• Gelatins are produced from bovine collagens. While they provide high osmotic pressure, their low molecular size allows them to be rapidly filtered by the glomeruli; overall they produce similar volume expansion to crystalloids.
  • Least likely of the colloids to affect hemostasis.
  • Half-life has been reported to be 3.5–4 hours.
  • New generation gelatins (e.g., Polygeline, Plasmagel) have been developed and have higher molecular size (greater oncotic pressure), but are not commonly used in the US.
• Dextrans are highly branched polysaccharide molecules produced by bacteria containing dextran sucrose that grows on sucrose medium.
  • Available in 10% dextran 40 (MW 40 kDa) and 6% dextran 70 (MW 70 kDa). Dextran 70 resembles human albumin in regard to MW.
  • Dextran 40 promotes microvascular blood flow in vascular surgery by decreasing red blood cell (RBC) aggregation, but is rapidly filtered by the kidneys and not used for volume expansion.
  • Dextran 70 is capable of up to 100–150% volume expansion with maximal expansion reached ~1 hour after infusion. Dextran 70 has expanding effects that last between 6 and 12 hours.
• Hydroxyethyl starches are made of amylopectin modified through hydrolysis and hydroxyethyl substitution.
  • Capable of up to 100% volume expansion.
  • With greater substitution, the molecule becomes more resistant to degradation in the body and the duration of its expansion effects also increase compared to other colloids.
  • Hespan is presented in normal saline, while Hextend comes in a balanced electrolyte solution (1).
  • Believed to have anti-inflammatory properties and to preserve intestinal microvascular perfusion in endotoxemia.
  • Does not appear to interfere with coagulation at doses <50 mL/kg.
  • Molecules <50,000 kDa are excreted by the urine within 24 hours; the larger molecules are slowly degraded enzymatically to molecules small enough to be excreted.

• The most commonly accepted indications of colloid administration is for the treatment of hypoalbuminemic states in the presence of salt/water overload (1) and replacing blood loss prior to blood administration (2). Hypoalbuminemia can result from reduced production (liver disease) or increased loss (renal disease). Serum albumin normally comprises ~50–60% of plasma proteins. It functions as a carrier of intermediate metabolites, trace metals, drugs, dyes, fatty acids, hormones, and enzymes, and hence affects the transport, inactivation, and/or exchange of tissue products.
• Adverse effects of colloids
  • Increased vascular permeability is often seen in the setting of surgical tissue trauma, hypoperfusion states, trauma, sepsis, and burns. This can result in oncotic molecules entering the interstitial compartment and edema formation (net driving force favors fluid movement out of the intravascular compartment).
  • The use of colloids in trauma patients may be associated with an increased mortality, especially in patients with traumatic brain injury (1).
  • Volume overload
• Gelatins
  • Greatest risk of anaphylactic reactions.
  • Theoretical risk of Creutzfeldt–Jacob disease (CJD) (2).
• Dextrans
  • Can cause coagulopathies from reduced platelet adhesiveness and dilution of factor VIII as well as fibrinolysis.
  • Can interfere with the ability to cross-match blood, by coating the RBC surface. If administered, the blood bank should be informed.
  • May result in acute renal failure due to accumulation of molecules in the renal tubule.
  • Anaphylaxis can be reduced by pretreating with dextran 1, which acts as a hapten to bind antibodies.
• Hespan
  • Coagulopathies can occur from reduced circulating factor VIII and von Willebrand factor levels and impaired platelet function; manifests as a prolonged PT and PTT.
  • Pruritus
  • Anaphylaxis
  • Renal impairment, higher creatinine levels, oliguria, and acute renal failure in patients who were critically ill with existing renal impairment.
  • Can increase amylase levels, which is typically not clinically significant.
  • May increase the erythrocyte sedimentation rate.

• Controversy exists over the use of colloids for volume resuscitation. Outcome studies have not supported its use over crystalloids.
• Arguments for the use of colloids
  • Venodilation from anesthetics can decrease preload and exacerbate hypovolemic states. If necessary, colloids can be used for rapid expansion of plasma volume, while limiting total volume load and peripheral edema (2). Traditionally, intraoperative blood loss has been replaced with 3 mL crystalloids or 1 mL colloids for every 1 mL blood loss (3).
  • Theoretically can increase oncotic pressure and provide greater volume expansion than crystalloids.
  • Do not require special preparation and are immediately available while awaiting blood products.
  • May be utilized in Jehovah's witnesses (though some object to albumin).
  • Less peripheral and pulmonary edema with associated impaired function. In particular, during intra-abdominal procedures, intestinal edema may result from excessive fluid administration, which has been associated with significant postoperative complications (3) [A].
• Arguments against colloids
  • Recent Cochrane review and Saline versus Albumin Fluid Evaluation (SAFE) Study Subgroup analysis have found a possible increase in mortality in using colloids in trauma, especially patients with traumatic brain injury (1) [A].
  • Cochrane subgroup analysis has also linked colloid use with an increased risk of death in hypoalbuminemic and burn patients (4).
  • The use of crystalloids remains the mainstay in acute resuscitation of the trauma patient, per advanced trauma life support (ATLS) guidelines (5).

J_v = k[(P_c – P_i) – (_c – _i)], where J_v = vascular flow, k = filtration coefficient, P_c = intravascular hydrostatic pressure, P_i = interstitial hydrostatic pressure, = reflection coefficient of the colloids, _c = intravascular colloid pressure, _i = interstitial colloid pressure (4).

Seth R. Cohen , DO

Raymond M. Planisic , MD