• Clinical science

Intravenous fluid therapy (Parenteral fluid therapy)

Summary

Parenteral fluid therapy usually involves the intravenous administration of crystalloid solutions, colloidal solutions, and/or blood products. The choice of fluid, the amount of fluid to be infused, and the rate of infusion are determined by the indication for fluid therapy. Fluid therapy with crystalloid solutions is used to resuscitate patients who are hypovolemic, to correct free water deficits in the case of dehydrated patients, to replace ongoing fluid losses, and to meet the fluid requirements of patients who cannot take fluids orally. The use of colloidal solutions is now controversial. However, colloidal solutions (such as albumin solution) may be indicated either as a monotherapy or in combination with crystalloid solutions in severe cases of low oncotic pressure, especially in children. In the case of severe bleeding, the use of blood products must be considered. All patients on fluid therapy should be closely monitored using a combination of clinical parameters and laboratory tests to determine the end-point of fluid therapy.

General indications for parenteral fluid therapy

Fluid resuscitation

Patients who are in hypovolemic shock require rapid fluid infusions in the form of fluid challenges to maintain intravascular volume.

  1. Rapid infusion of a 500–1000 mL bolus; of normal (isotonic) saline (NS) or lactated Ringer's solution (RL) within 15 minutes
  2. Observe the patient for a clinical response
  3. Repeat the fluid bolus infusion if the clinical response is inadequate.
  4. If the patient does not respond to multiple fluid challenges:

Replacement of free water deficit

Replacement of ongoing fluid loss

  • Fluids are also indicated in the post-resuscitation phase when the patient is no longer hypovolemic but still has ongoing abnormal fluid loss that cannot be compensated for by oral intake alone.
  • Some common conditions associated with an ongoing fluid loss are:
  • The amount and rate of fluid infusion should ideally match the amount and rate of ongoing fluid loss.
  • The composition of fluid given should ideally match the composition of the bodily fluid lost.

Maintenance fluid therapy

The maintenance fluid requirement is higher in children than in adults!

Other indications

References:[1][2][3][4][5][6]

Types of parenteral fluids

Crystalloid solutions

  • Aqueous solutions with varying concentrations of electrolytes
  • The most commonly used fluids in a hospital setting
  • Crystalloids increase intravascular volume. The extent to which they do this depends on the effect on fluid compartments.
Type of crystalloid solution Crystalloid solution Effect on fluid compartments Specific Indications Risks
Hypertonic 3% NaCl
  • ↓ Intracellular volume
  • ↑ Extracellular volume
Hypotonic

½ normal saline (0.45% NaCl)

  • ↑ Intracellular volume
  • ↑ Extracellular volume
Isotonic

Normal saline (0.9% NaCl)

  • No change in intracellular volume
  • ↑ Extracellular volume

Ringer's lactate solution (RL or Hartmann solution)

  • ↑ Extracellular volume
  • Minimally elevated intracellular volume
  • Mild buffer action that counters acidosis
  • Lactic acidosis in patients with liver failure
  • Clumping of red cells if RL is co-administered with blood products
5% dextrose (D5W)
  • The sodium-free water becomes evenly distributed among both fluid compartments
    • ↑ Intracellular volume
    • ↑ Extracellular volume

Patients 28 days to 18 years of age requiring maintenance intravenous fluid therapy should receive isotonic solutions (which have a sodium concentration similar to plasma) with appropriate levels of potassium chloride and dextrose to reduce the risk of hyponatremia!

Colloidal solutions

  • A colloid is a high molecular weight substance; that mostly remains confined to the intravascular compartment; and thus generates oncotic pressure
  • Examples:
  • Effects
    • Colloids have a greater effect on intravascular volume than crystalloids
    • Decreased blood coagulability
    • Anti-inflammatory effect
  • Administration: : Their use is controversial, but they may be indicated in combination with crystalloids (for more information, see the table in extra information below).

Although colloids are much more effective than crystalloids as intravascular volume expanders, they are more expensive and are also associated with more side effects than crystalloids without being demonstrably superior. Their use is, therefore, controversial!

Blood products

The transfusion of packed RBC concentrate is indicated in the case of massive blood loss (see blood transfusion).

References:[7][6][8]

Route of parenteral fluid therapy

The flow rate is subject to Poiseuille's law: The flow rate is 16 times slower if a lumen's diameter is halved, but flow rate doubles if the catheter's length is halved!

References:[9]

Titration parameters for IV fluid therapy

References:[10]