D5W is Hypotonic, Not Hypertonic
D5W (5% Dextrose in Water) is a hypotonic solution, not a hypertonic solution. While D5W is initially isotonic in vitro, it becomes hypotonic in vivo as glucose is rapidly metabolized, leaving free water behind 1.
Understanding D5W's Tonicity
- D5W has an initial osmolarity of approximately 252-255 mOsm/L, making it isotonic when administered 1
- However, once the glucose is metabolized, D5W effectively becomes free water in the body, creating a hypotonic effect 2
- This is why D5W is avoided in acute ischemic stroke patients, as hypotonic solutions can exacerbate ischemic brain edema 2
Comparison with Other Solutions
- Normal saline (0.9% NaCl) has an osmolarity of 308 mOsm/L and an osmolality of 286 mOsm/kgH₂O, making it isotonic 1
- 3% hypertonic saline has an osmolarity of 1026 mOsm/L, making it truly hypertonic 3
- PlasmaLyte has an osmolarity of 294 mOsm/L, making it near-isotonic 4
Clinical Implications of D5W's Hypotonic Nature
- D5W administration can lead to decreased blood sodium levels and increased brain edema 5
- In patients with closed head trauma, D5W has been shown to worsen neurological outcomes and increase mortality rates 5
- The American Heart Association recommends avoiding glucose-containing solutions like D5W in acute ischemic stroke patients due to the risk of exacerbating brain edema 2
- Hypotonic solutions cause water to move from the extracellular space to the intracellular space, which can be particularly problematic for the brain 1
When D5W Is Used
- D5W is sometimes used for dilution of medications 2
- It can be used for correction of hypernatremia when free water deficit exists 6
- In specific cases, D5W may be used for treatment of dialysis-related muscle cramps, though 50% dextrose (D50W) has been shown to be more effective 7
Safety Considerations
- A decrease in plasma osmolality by only 3% can produce an increase in intracranial pressure of about 15 mmHg 1
- Larger volumes of hypotonic solutions like D5W should be avoided in patients with or at risk for increased intracranial pressure 1
- Pediatric studies have shown that isotonic fluids result in fewer cases of hyponatremia compared to hypotonic fluids 6
Understanding the hypotonic nature of D5W is crucial for safe fluid management in clinical practice, especially in neurological conditions where changes in osmolality can significantly impact outcomes.