Colloids - an overview

Dr. S. Parthasarathy MD., DA., DNB, MD (Acu),

Dip. Diab. DCA, Dip. Software statistics PhD (physio)

Mahatma Gandhi medical college and research institute , puducherry – India

Colloids

• Colloids tend to be larger molecules than crystalloids

• dispersed throughout the solvent rather than forming true solutions.

• The component particles tend to arrange as groups of molecules and so do not readily pass through clinical semipermeable membranes.

• They therefore have an oncotic potential that is usually measured as colloid osmotic pressure (COP).

Image of a colloid

But crystalloids !!!

• Crystalloid solutions are solutions of sugar or salt or mixture of salt and sugar in water.

• Crystalloids remain intravascular for short period and metabolise to carbon dioxide, water, ions and yields energy.

In simple terms

• Osmotic pressure • Exerted by salts to push fluid out

• Oncotic pressure exerted by colloids to get fluid in the blood vessel

Colloids

• Colloids are solutions of high molecular weight substances that largely remain in the intravascular compartment for longer period and generate an oncotic pressure as well as slowly being metabolized.

Colloids

• number of molecules per volume of solution is usually lower than crystalloid solution.

• No effect on osmolarity

• Hence electrolytes are added.

Half life

• the intravascular half-life of a crystalloid solution is 20–30 min,

• most colloid solutions have intravascular half-lives between 3 and 6 h.

Characters

• General characteristics of the colloid are

• (i) particles have high molecular weight,

• (ii) high osmolality. and high oncotic pressure

(iii) longer plasma half life

• (iv) higher plasma volume expansion

• 25 % Vs 125%

Types of colloids

• colloids are either natural or artificial. • The natural colloids are blood, human

albumin and fresh frozen plasma.• Artificial colloids are dextrans, gelatins and

starch. Artificial colloids are polymers containing molecules with wide range of molecular weight

• Monodisperse and polydisperse

Characters

• Molecular weight : oncotic pressure • Osmolality and oncotic pressure: Almost all

colloid solutions have a normal osmolality. The oncocity of the solution will influence the vascular expansion.

• Plasma half-life: The plasma half-life of a colloid depends on its MW, the elimination route, and, the involved organ function (mainly eliminated by the renal route

Characters

• MW --- oncotic pressure – initial volume expansion ---- half life – persistence

• The degree of volume expansion is mainly determined by the MW, whereas the intravascular persistence is also determined by the elimination of the colloid.

Characters

• Acid-base composition: Albumin and gelatin solutions have physiological pH, while other solutions tend to have acidic pH.

• Electrolyte content: The sodium concentration is low in “salt-poor albumin

Others same

Human albumin solution

• principal natural colloid comprising 50 to 60% of all plasma proteins

• contributes to 80% of the normal oncotic pressure in health.

• MW = 69,000 Dalton• Synthesis – liver

Human albumin solution

• 5% solution is isooncotic and leads to 80% initial volume expansion

• 25% solution is hyperoncotic and leads to 200 - 400% increase in volume within 30 minutes.

• The effect persists for 16 - 24 h

Structure of albumin

Indications:

• a. Emergency treatment of shock specially due to the loss of plasma

• b. Acute management of burns• c. Fluid resuscitation in intensive care• d. Clinical situations of hypo-albumineamia i. Following paracentesis ii. Patients with liver cirrhosis (For

extracorporeal albumin dialysis (ECAD)) iii. After liver transplantation• e. Spontaneous bacterial peritonitis• f. Acute lung injury

Advantages:

• Natural • Volume expansion • possesses antioxidant and scavenging effects• Disadvantages:• Costly , ‘leakiness’ of the vascular

endothelium and volume overload

Dextran

• highly branched polysaccharide molecules • Artificial • synthesis using the bacterial enzyme dextran

sucrase from the bacterium Leuconostoc mesenteroides

• 6% solution with an average molecular weight of 70,000 (dextran 70)

• 10% solution with an average weight of 40,000 (dextran 40, low-molecular-weight dextran)

characters

• Kidneys primarily excrete dextran solutions.• Both dextran-40 and dextran-70 lead to a

higher volume expansion as compared to HES and 5% albumin. (100 to 150%)

• The duration lasts for 6–12 hours

Dextran – slowly decreasing uses

• used mainly to improve micro-circulatory flow

in microsurgical re-implantations.

• Extracorporeal circulation:

Disadvantages

• Anaphylactic reactions:

• Coagulation abnormalities:

• Interference with cross-match:

• Precipitation of acute renal failure:

Gelatins

• Gelatin is the name given to the proteins formed when the connective tissues of animals are boiled

• If you cool, it may gellify !!

Modified gelatins

• Succinylated or modified fluid gelatins (e.g.,

Gelofusine, Plasmagel, Plasmion)

• Urea-crosslinked gelatins (e.g., Polygeline)

• Oxypolygelatins (e.g., Gelifundol)

• Polygeline (‘Haemaccel’, Hoechst) is produced by the action of alkali and then boiling water (thermal degradation) on collagen from cattle bones.

• MW = 35000

haemaccel

• . Polygeline is supplied as a 3.5% solution with electrolytes (Na+ 145, K+ 5.1, Ca++ 6.25 & Cl − 145 mmol/l).

• calcium ions -- increase in serum calcium concentration following large volume resuscitation.

• Polygeline also contains potassium ions:

Succinated gelatin

Character and indications

• Kidneys excrete • 70 -80 % volume expansion • 2 -3 hours• Hypovolemia due to acute blood loss.• Acute normovolaemic haemodilution.• Extracorporeal circulation – cardiopulmonary by-

pass.• Volume pre-loading prior to regional anaesthesia.•

ADVANTAGES AND DISADVANTAGES

• Cost effective:• No limit of infusion:• No effect of renal impairment:

• Higher anaphylaxis than albumin • Coagulation – platelet adhesions decreased• Increased PRA and possible circulatory

problems

Hydroxyethyl starches (HES)

• Starch is polysaccharide carbohydrate and

seen to produce less morbidity compared to dextrans or gelatins.

• As a class, starch is safer than other colloid and is a near – ideal resuscitation fluid.

How to get

amylopectin rich corn• Amylases glucose molecules • Hydroxy ethylation • neutralised with alkali and further purified

• HES

Voluven

HES

• Concentration: low (6%) or high (10%).• Molecular Weight (MW): low ( 70 kDa), medium

( 200 kDa), or high ( 450 kDa).

• Polydisperse • Small excreted • Large fragmented to small• continuous supply of oncotically active molecules

• Molar substitution (MS): low (0.45–0.58) or high (0.62–0.70)

• A varying number of hydroxyethyl residues attached to the anhydrous glucose particles within the polymer.

• increases the solubility of the starch in water, inhibits the rate of destruction of the starch polymer by amylase.

MS !! What is this ??

• The figure 0.7 in the description of a HES preparation indicates that there are seven hydroxyethyl residues on average per 10 glucose subunits.(hetastarches)

• hexastarch (MS 0.6),• pentastarch (MS 0.5), • tetrastarch (MS 0.4).

• C2/C6 ratio: low (<8) or high (>8).• The C2/C6 ratio refers to the site where

substitution has occurred on the initial glucose molecule.

• The higher the C2/C6 ratio, longer the half-life and hence, longer persistence in the blood

Metabolism

• initially a rapid amylase-dependent breakdown and renal excretion.

• Plasma half life is 5 days and 90% is eliminated in 42 days.• Smaller HES molecules (<50,000 to 60,000 Dalton) are

eliminated rapidly by glomerular filtration. • Medium sized molecules get excreted into the bile and

faeces. • Another fraction - taken up by the reticuloendothelial

system where the starch is slowly broken down. Detected for several weeks after administration

Advantages

• Volume expansion 100% • Duration 8-12 hours

• Shock • Endotoxemia • Maximal – 50 ml/kg • Cost less than albumin

Problems

• Coagulation • Renal impairment • Accumulation and itching • Anaphylactoid reactions

• But ? Found in third generation – tetrastarch !!

pharmacokinetics

• Clearance of the latest generation (third generation) 130/0.4) is 20 to 30 fold higher compared to first generation HES

• therapeutic safety index of third generation HES (130/0.4) (C2-C6 >8) is higher compared with all other HES solutions

Third-generation HES: tetrastarch

• Reductions in MW and MS have led to products with shorter half-lives,

• improved pharmacokinetic• pharmacodynamic properties, • fewer side effects

v

Benefits over older starches

• reduced effect on the coagulation process compared to older products

• rapid clearance of the latest generation of tetrastarches, - less accumulation

• Less tissue persistence – less itching

Benefits over older starches (130/0.4)

• Waxy maize better over potato derived in liver dysfunction

• Renal dysfunction, elderly, hepatic dysfunction ,Cardiac surgery, abdominal aortic surgery

• Also children

Effects on Microcirculation and Oxygenation

• beneficial effects on organ perfusion,

microcirculation, tissue oxygenation,

inflammation, endothelial activation, capillary

leakage, and tissue edema over and above

their volume replacement effects• We are using them in shock states

Crystalloids Vs colloids

• Intravascular persistence • Volume expansion

• Anaphylaxis,• Renal• Cost• Coagulation

Trials

• 1989 – may be more deaths with colloids • no difference in outcome among patients treated

with colloids or crystalloids (BMJ – 1998)• SAFE (Saline versus Albumin Fluid Evaluation) trial • 7000 critically ill patients requiring fluid

resuscitation to receive isooncotic albumin or isotonic crystalloid.

• There was no overall difference in outcome

The danger starts

FDA recommendations – June 2013

• Do not use HES solutions in critically ill adult patients including those with sepsis, and those admitted to the ICU.

• Avoid use in patients with pre-existing renal dysfunction.• Discontinue use of HES at the first sign of renal injury.• Need for renal replacement therapy has been reported

up to 90 days after HES administration.• Avoid use in patients undergoing open heart surgery in

association with cardiopulmonary bypass due to excess bleeding.

• Discontinue use of HES at the first sign of coagulopathy.

• This is an overview

• Read well for more details

• Are colloids – boon to gloom !!

Thank you all