Crystalloid vs. colloid solutions

Crystalloid vs. colloid solutions

Crystalloid vs. colloid solutions

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Body Fluid Compartments - The Battlefield

  • Total Body Water (TBW) constitutes ~60% of lean body weight.
  • 📌 Rule of 60-40-20 (% of body weight):
    • 60% Total Body Water
    • 40% Intracellular Fluid (ICF) (~2/3 of TBW)
    • 20% Extracellular Fluid (ECF) (~1/3 of TBW)
  • ECF is further divided:
    • Interstitial Fluid: 3/4 of ECF
    • Plasma Volume: 1/4 of ECF

⭐ Third-spacing is the sequestration of ECF into serosal cavities (e.g., ascites) or injured tissue, rendering it non-contributory to circulation.

Crystalloids - Salty Water Squad

  • Aqueous solutions of mineral salts or other water-soluble molecules. The go-to initial fluid for resuscitation.
  • Mechanism: ↑ intravascular volume, but fluid rapidly redistributes to the entire extracellular space. Only ~25% remains intravascular after 1 hour.

Major Types

  • Normal Saline (NS - 0.9% NaCl)

    • Composition: 154 mEq/L Na⁺, 154 mEq/L Cl⁻.
    • Use: General fluid resuscitation, especially in metabolic alkalosis or hyponatremia.
    • ⚠️ Warning: Large volumes can cause non-anion gap hyperchloremic metabolic acidosis.
  • Lactated Ringer’s (LR)

    • Composition: More "balanced" or physiologic. Contains Na⁺, Cl⁻, K⁺, Ca²⁺, and lactate (buffer).
    • Use: Trauma, burns, sepsis, GI fluid loss. Preferred for most resuscitations.
    • 💡 Traditionally avoided in hyperkalemia, but K⁺ content is low (4 mEq/L).

⭐ In patients with diabetic ketoacidosis (DKA), using balanced crystalloids like Lactated Ringer's instead of Normal Saline is associated with a faster resolution of the acidosis.

Colloids - The Plasma Protectors

  • Mechanism: Solutions with large, osmotically active molecules (e.g., proteins, starches) that are retained in the intravascular space, increasing plasma oncotic pressure.
  • Primary Function: Potent volume expanders; maintain circulatory volume for a longer duration than crystalloids.
  • Types & Characteristics:
    • Albumin (5%, 25%): Natural plasma protein. Used in hypoalbuminemia, spontaneous bacterial peritonitis (SBP), and hepatorenal syndrome. Less immunogenic.
    • Dextrans: Glucose polymers. Risk of anaphylaxis and interference with blood cross-matching.
    • Hydroxyethyl Starches (HES): Synthetic. ⚠️ Warning: Associated with ↑ risk of acute kidney injury and coagulopathy; use is now restricted.
  • Clinical Use: Reserved for specific indications where rapid, sustained volume expansion is critical and crystalloids are insufficient.

Exam Favorite: The SAFE trial (Saline versus Albumin Fluid Evaluation) showed that in a general ICU population, albumin was as safe as saline for resuscitation but offered no survival benefit. However, a subgroup analysis suggested potential benefit in patients with severe sepsis.

The Showdown - Clash of the Solutions

FeatureCrystalloids (e.g., Normal Saline, LR)Colloids (e.g., Albumin, Starches)
CompositionWater, electrolytes, small solutesLarge, osmotically active molecules
DistributionDistributes throughout ECFStays intravascularly (↑ oncotic pressure)
VolumeRequires larger volumes (approx. 3:1 ratio)Smaller volume for same plasma expansion
Use/RisksInitial resuscitation; risk of edemaSpecific uses (burns); expensive, anaphylaxis risk

High‑Yield Points - ⚡ Biggest Takeaways

  • Crystalloids (e.g., Normal Saline, Lactated Ringer's) are the first-line choice for most initial fluid resuscitation.
  • They rapidly distribute throughout the entire extracellular fluid (ECF), requiring larger volumes for intravascular expansion.
  • Colloids (e.g., Albumin) contain large molecules that remain in the intravascular space, making them more potent volume expanders.
  • Colloid use is generally reserved for specific conditions like severe burns or hypoalbuminemia.
  • Primary risk of crystalloids is edema; colloids carry risks of anaphylaxis and coagulopathy.

Practice Questions: Crystalloid vs. colloid solutions

Test your understanding with these related questions

A 28-year-old research assistant is brought to the emergency department for severe chemical burns 30 minutes after accidentally spilling hydrochloric acid on himself. The burns cover both hands and forearms. His temperature is 37°C (98.6°F), pulse is 112/min, respirations are 20/min, and blood pressure is 108/82 mm Hg. Initial stabilization and resuscitation is begun, including respiratory support, fluid resuscitation, and cardiovascular stabilization. The burned skin is irrigated with saline water to remove the chemical agent. Which of the following is the most appropriate method to verify adequate fluid infusion in this patient?

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Flashcards: Crystalloid vs. colloid solutions

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An entire abdomen burn is _____% of the body surface area.

TAP TO REVEAL ANSWER

An entire abdomen burn is _____% of the body surface area.

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