Intravenous Fluid Administration and Classification

Study Notes

Intravenous fluid administration should be treated like any other pharmacological prescription.
Three main indications include resuscitation, replacement, and maintenance
Intravenous fluid administration should follow the four Ds: Drug, Dosing, Duration, De-escalation.
Drug—consider the indication and desired effect
Dosing—consider the appropriate amount of fluid to be given
Duration—consider appropriate start and stop times for therapy
De-escalation—consider if the fluid therapy is no longer needed or effective

Osmolarity of a solution is equal to the number of osmoles per liter of solution.
Tonicity refers to the effect a solution has on cell volume
Isotonic solutions have no effect on cell volume
Hypotonic solutions increase cell volume.
Hypertonic solutions decrease cell volume.
Tonicity describes the effective osmolality of a fluid.

IV fluids are classified as crystalloids or colloids based on their ability to diffuse through barriers separating body fluid compartments (intravascular and extravascular).
Crystalloids pass readily through the membrane, while colloids do not.

Crystalloid solutions are aqueous solutions with water and small solutes (electrolytes and glucose).
Crystalloids are categorized as hypotonic, isotonic, or hypertonic.
Colloid solutions have large molecular weight particles (proteins or hydroxyethyl starches) suspended in a crystalloid solution.
Intravascular half-life of crystalloids is 20-30 minutes, while colloids are 3–6 hours.
Crystalloids are just as effective as colloids in restoring intravascular volume.
Crystalloids can rapidly correct severe intravascular fluid deficits.
Rapid administration of >4-5L of crystalloids can cause tissue edema.
Excessive edema may impair oxygen transport, impair tissue healing, and impact bowel function recovery after major surgery.

A table comparing various fluids based on Na+, Cl-, K+, Ca++, Mg++, buffers, pH, and osmolarity.
Infusion of 1 L of 0.9% NaCl increases plasma volume by 275 mL and interstitial volume by 825 mL.

FDA-approved indications include extracellular fluid replacement (dehydration, hemorrhage, sepsis), treatment of metabolic alkalosis with fluid loss, and mild sodium depletion.
Also used for traumatic brain injury and brain edema, and as a replacement fluid in hyperkalemia and for diluting packed red blood cells prior to transfusion.
Used in diabetic ketoacidosis (DKA) with severe hypovolemia and serum sodium less than 140 mEq/L.

Hypotonic concentration of sodium chloride.
Best for parenteral maintenance fluids rather than aggressive intravascular volume repletion.

Introduced by Sydney Ringer in 1880.
Designed to promote contraction of isolated frog hearts.
Contains Ca+ and K+ in a sodium chloride diluent.
In the 1930s, Alexis Hartmann added sodium lactate buffer, creating Hartmann's solution.
Contains sodium, potassium, and chloride contents similar to extracellular fluid.
Has fewer adverse effects on acid-base balance.
Used in burn patients with BSA >20% (Parkland formula).
Calcium binding to citrated anticoagulant in blood products can inactivate anticoagulant and promote clot formation, so contraindicated for blood transfusions.

D5% prevents protein breakdown in NPO patients.
D5% is used for pure water deficit replacement and for patients with hypernatremia.
D10%, D20%, or D50% are used in hypoglycemia.
Providing calories with 5% dextrose solutions is considered obsolete
Distribution—less than 10% in intravascular space, less than 30% in interstitial space, more than 50% in intracellular space—cellular swelling can occur.
5% dextrose-in-water solution is not an effective volume expander.
Lactate production is increased in response to glucose load; greater in critically ill patients, can be a source of toxin production.

Do not pass across diffusional barriers as readily as crystalloids.
Natural colloids include human albumin (responsible for 75% of plasma oncotic pressure, antioxidant, transport protein).
Synthetic colloids include dextran, gelatin, and hydroxyethyl starch (HES).

Rule of 4:2:1 (infusion per hour):
- 4 mL/kg/hr for kg 1-10
- - 2 mL/kg/hr for kg 10–20
- - 1 mL/kg/hr for kg >20

Fluid resuscitation in patients with severe intravascular fluid deficits (e.g., hemorrhagic shock) prior to blood transfusion.
Fluid resuscitation in patients with severe hypoalbuminemia or conditions associated with large protein losses (e.g., burns).

Crystalloids are inexpensive and readily available; but only 25% remains in circulation and most goes to the interstitial space resulting in less resuscitation volume.
Colloids are more expensive and have a higher risk of adverse effects but have a longer half-life in the intravascular space. Fluid resuscitation is more rapid.