Peri-Operative Fluid Therapy (Crystalloids, Colloids) and Blood Transfusion

Definition: Aqueous solutions of low molecular weight ions (<30,000 Daltons) with intravascular half-lives of 20-30 minutes.

Types:

1. Hypotonic solutions (Maintenance-Type solutions): Used for the replacement of pure water deficits (losses) and as maintenance fluid for patients on Na+ restriction. Example: Dextrose 5% in water.
2. Isotonic solution (Replacement-Type solutions): Used for replacement of losses that involve both water and electrolyte deficits, as seen in most intra-operative losses. Example: Normal saline (NS). When used in large amounts, NS can produce dilutional hyperchloremic acidosis due to its high chloride content (154mmol/L). Plasma HCO3 concentration decreases as chloride concentration increases. NS is the preferred solution for hypochloremic metabolic acidosis and for diluting packed RBCs prior to transfusion.

Lactated Ringer's Solution

It is the most physiologic solution. Its lactate content is converted by the liver into bicarbonate.

Ringer Acetate Solution

This solution was recently introduced and is considered better than Ringer Lactate for the following reasons:

• It improves acid-base parameters in hypovolemic shock.
• It is metabolized in the muscles, unlike lactate, which is mainly in the liver.
• It is recommended in lactic acidosis.
• It improves cardiac output in burned patients.
• It does not decrease ketone bodies uptake with liver insufficiency.
3. Hypertonic SolutionsHypertonic solutions should be given slowly through a central venous line to avoid rapid hemolysis. Examples include:
• 3% Saline: Used in the treatment of severe symptomatic hyponatremia.
• 7.5% Saline: Used in the resuscitation of patients in hypovolemic shock.
• 20% Mannitol:...

Colloid solutions contain high molecular weight substances (>30,000 Daltons) with intravascular half-lives of 4-6 hours. They are used for various purposes:

1. Fluid Resuscitation:
   • Patients with severe intravascular fluid deficits, e.g., hemorrhagic shock, before the arrival of blood for transfusion.
   • Conditions associated with severe hypo-albuminemia or large protein loss, such as burns.
2. Blood-Derived Colloids:
   • Human albumin (5%, 25%).
   • Plasma protein fraction (PPF) (5%).
3. Synthetic Colloids:
1. Dextrose Starches (maximal doses 1.5L): e.g., Dextran 70 and Dextran 40.
   • Disadvantages:
     • Anti-platelet effects and prolongation of bleeding time.
     • Interference with blood typing and compatibility due to the formation of rouleaux.
     • Association with renal failure.
     • Antigenic effects leading to anaphylactoid reactions.
2. Gelatins (maximal dose is 1.5L): Types: Succinylated Gelatin (Gelofusine), Polygeline (Haemaccel or Hemagel).
   • Disadvantages:
     • Histamine-mediated allergic reactions.
   • Advantages:
     • Does not interfere with blood grouping or compatibility.
     • Does not affect renal functions.
3. Hydroxyl-Ethyl Starch (maximal dose is 1L)
• Group of polydisperse synthetic colloids resembling glycogen structurally.
• Examples:
  • Heta-starch: Average MW is 450,000, half-life is 48 hours.
  • Penta-starch: Average MW is 20,000, shorter half-life (90% eliminated within 24 hours).
  • Hextend: High MW and longer half-life.
• Advantages:
  1. Do not affect coagulation studies or bleeding times.
  2. Not antigenic, but only cause very rare anaphylactoid reactions.
  3. Very effective as plasma expanders.
  4. Less expensive than human albumin.

1. Crystalloids, when given in sufficient amounts, can be as effective as colloids in restoring intravascular volume. Therefore, they are used for initial resuscitation.
2. Replacing an intravascular volume deficit with crystalloids generally requires 3-4 times the volume needed when using colloids.
3. Severe intravascular fluid deficits can be more rapidly corrected using colloid solutions.
4. The rapid administration of large amounts of crystalloids (>4-5L) is more frequently associated with decreased plasma oncotic pressure, leading to significant tissue edema. Therefore, continued fluid resuscitation should include colloids.