This IV fluid contains 0.9% NaCl in water. It is used to increase the volume of plasma when there is no hemorrhaging and there are enough red cells in the blood. Medical conditions treated with NS include fluid replacement for patients with diabetic ketoacidosis (DKA), treatment for too little sodium in the blood (hyponatremia), blood transfusions, metabolic alkalosis, and treatment for too much calcium in the blood (hypercalcemia). It is important to note that because NS replaces extracellular fluid, it isn’t used in patients with heart failure, too much sodium in their blood (hypernatremia), or fluid retention (edema).
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Lactated Ringer’s (LR)
LR is used to replace fluids and as a pH buffer. It is particularly useful in cases of acute blood loss, lower gastrointestinal tract fluid loss, burns, surgery, and dehydration. It’s the same as NS but also has the electrolytes K+ and Ca2+ and a buffer called lactate (a salt of lactic acid). LR is not used in patients with renal failure because it may cause too much K+ to build up in the body (hyperkalemia) or those with liver disease because they can’t metabolize the lactate.
This IV solution has a two-fold effect. It is an isotonic solution when it is administered but becomes hypotonic as the patient’s body metabolizes the 5% dextrose it contains. In other words, D5W is isotonic in the bag and “physiologically hypotonic.” Because of the hypotonicity, this IV fluid raises the total body fluid volume and is used rehydrate patients, assist with excretory processes, and treat hypernatremia.
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The image above shows a human red blood cell in an isotonic solution. When the extracellular solution has the same solute concentration as inside the cell, the solution is isotonic. The solute concentration of isotonic IV solutions is similar to the intracellular environment.