From the Guidelines
Free water, also known as hypotonic fluid, is a type of fluid that has a lower concentration of solutes, such as sodium, compared to blood plasma.
Characteristics of Free Water
- It is an essential component of the human body, making up approximately 50-90% of body weight, depending on age and other factors 1
- Free water is found in various body compartments, including intracellular and extracellular fluids, and plays a crucial role in maintaining proper fluid balance and electrolyte homeostasis
- In the context of intravenous fluids, free water refers to fluids with a low sodium concentration, typically less than 135 mEq/L, which can lead to hyponatremia if not administered carefully 1
Clinical Implications of Free Water
- The administration of hypotonic fluids, which contain free water, can lead to hyponatremia, particularly in patients with elevated arginine vasopressin (AVP) concentrations, such as those with acute illness or postoperative states 1
- Hyponatremia can cause severe complications, including hyponatremic encephalopathy, which is a medical emergency that can be fatal or lead to irreversible brain injury if inadequately treated 1
- The use of isotonic fluids, which have a sodium concentration similar to that of blood plasma, is recommended for maintenance hydration in hospitalized children to reduce the risk of hyponatremia 1
Key Considerations for Fluid Management
- Fluid and electrolyte management is critical in the acutely ill child and in children in the operative setting, and should be tailored to individual needs 1
- Patients with edematous states, such as congestive heart failure, cirrhosis, and nephrotic syndrome, require careful fluid management to avoid volume overload and hyponatremia 1
From the Research
Definition of Free Water (Hypotonic Fluid)
- Free water, also known as hypotonic fluid, refers to a solution with a lower concentration of solutes (such as sodium) compared to blood plasma [(2,3,4)].
- Hypotonic fluids have a lower osmolality than blood plasma, which can lead to an imbalance of fluids and electrolytes in the body [(2,3,4)].
Examples of Hypotonic Fluids
- 5% glucose solution 4
- Darrow-glucose solution 4
- NaKglucose solution 4
- 0.45% NaCl in 5% glucose solution 4
Risks Associated with Hypotonic Fluids
- Hyponatremia, a condition where the sodium level in the blood is lower than normal [(2,3,4,5)]
- Hospital-acquired hyponatremia, which can be lethal 3
- Neurological morbidity and mortality 3
Prevention and Management of Hyponatremia
- Restricting free water and hypotonic fluid intake 2
- Using isotonic fluids, such as 0.9% NaCl, instead of hypotonic fluids [(3,4,5)]
- Monitoring plasma sodium levels and adjusting fluid replacement therapy accordingly [(2,6)]