IV Fluids - Pharmacology

The osmolality of many IV fluids is similar to serum osmolality,which is 290 mOsm/kg H2O. IV fluids are:

  • Isotonic. This is in the iso-osmolar range (240 to 340 mOsm/L) where the concentration of the IV fluid is the same as concentration of intracellular fluid (NaCl 0.9%, normal saline).
  • Hypotonic. This is in the hypo-osmolar range (< 240 mOsm/L) where the concentration of the IV fluid is less than the concentration of intracellular fluid (NaCl 0.45%, sodium chloride).
  • Hypertonic. This is in the hyper-osmolar range (> 340 mOsm/L) where the concentration of the IV fluid is more than the concentration of intracellular fluid (Dextrose 5% in 0.45% saline).

IV solutions are classified as crystalloids, colloids, or lipids.

CRYSTALLOIDS

Crystalloids are used for replacement and maintenance of fluid balance therapy. These include dextrose, saline, and lactated Ringer’s solution.

COLLOIDS

Colloids are volume expanders that increase the patient’s fluid volume. These include Dextran, amino acids, hetastarch, and plasmanate.

  • Dextran is not a substitute for whole blood because it does not have components that carry oxygen. Dextran 40 tends to interfere with platelet function resulting in prolonged bleeding times.
  • Amino acids provide protein, calories, and fluid for the body. It is helpful for patients who are old and malnourished and for those with hypopro-teinemia resulting from other causes.
  • Hetastarch is a non-antigenic used to treat or prevent shock following serious injury, surgery, or for burn patients when blood is not available for transfusion. This too isn’t a substitute for whole blood. In an isotonic solution (310 mOsm/L), hetastarch decreases platelet and hematocrit counts and must not be used for patients who have bleeding disorders, congestive heart failure (CHF), and renal dysfunction.
  • Plasmanate is a protein-containing fluid that is derived from human plasma and is used to treat shock that results from burns, crushing injuries, abdomi¬nal emergencies, or any emergency where there is a loss of plasma, but not red blood cells. Plasmanate is non-antigenic and must not be given to patients who have anemia, increased blood volume, or congestive heart failure.

LIPIDS

Lipids are a fat emulsion that is given when IV therapy extends for longer than five days. This is used for prolonged parenteral nutrition to provide essential fatty acids.


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