From the Guidelines
Hypotonic, isotonic, and hypertonic solutions are differentiated by their solute concentration relative to body fluids, with hypotonic solutions having lower solute concentration, isotonic solutions having equal solute concentration, and hypertonic solutions having higher solute concentration, as defined by their osmolarity, which ranges from less than 280 mOsm/L for hypotonic, 280-310 mOsm/L for isotonic, and exceeding 310 mOsm/L for hypertonic solutions 1.
Key Characteristics of Each Solution
- Hypotonic solutions: have an osmolarity lower than 280 mOsm/L, causing water to move into cells, making them swell, examples include Ringer lactate 1.
- Isotonic solutions: have an osmolarity ranging from 280 to 310 mOsm/L, resulting in no net movement of water, examples include 0.9% NaCl and Plasma-Lyte1 1.
- Hypertonic solutions: have an osmolarity exceeding 310 mOsm/L, drawing water out of cells and causing them to shrink, examples include 3% NaCl and 7.5% NaCl 1.
Clinical Implications
The differences in solute concentration between hypotonic, isotonic, and hypertonic solutions have significant clinical implications, as they determine how fluids move between compartments in the body through osmosis, and can be used to manage various conditions, such as hypovolaemia, cerebral edema, and hyperkalaemia 1. For example, isotonic solutions like 0.9% NaCl are commonly used for fluid replacement without disturbing cellular fluid balance, while hypertonic solutions like 3% NaCl can be used to reduce cerebral edema, but may cause cellular dehydration if used inappropriately 1.
From the Research
Solution Types
- Hypotonic solutions have a lower concentration of solutes than blood, which can lead to swelling of cells as water moves into them [(2,3,4)].
- Isotonic solutions have the same concentration of solutes as blood, and do not cause significant changes in cell volume 4.
- Hypertonic solutions have a higher concentration of solutes than blood, which can lead to shrinkage of cells as water moves out of them [(5,4)].
Key Characteristics
- Hypotonic hyponatremia is a condition where the serum sodium level is low due to a low concentration of solutes in the blood [(2,3)].
- Hypertonic saline solutions, such as 3% NaCl, are used to treat severe hyponatremia and cerebral edema [(2,5)].
- The treatment of hyponatremia depends on the severity of symptoms, with rapid correction of serum sodium levels being necessary in some cases, but also carrying the risk of osmotic demyelination syndrome [(2,3,4,6)].
Clinical Implications
- The use of hypertonic saline solutions can lead to hyperchloremia, which is associated with an increased risk of acute kidney injury 5.
- The choice of fluid for treatment of hyponatremia should be based on the underlying pathophysiology and the clinical and biochemical severity of the condition [(3,4,6)].
- Clinical practice guidelines have been developed to provide a standardized approach to the diagnosis and treatment of hyponatremia 6.