Use 0.9% Normal Saline (NS) for Severe Dehydration Requiring IV Therapy
For severe dehydration requiring intravenous rehydration, use 0.9% normal saline (isotonic fluid) as the initial resuscitation fluid, not 0.45% NS (hypotonic saline). 1
Clinical Context and Fluid Selection
Severe Dehydration (IV Therapy Required)
Isotonic intravenous fluids such as lactated Ringer's and normal saline solution should be administered when there is severe dehydration, shock, or altered mental status. 1 The evidence supports 0.9% NS as safe and effective:
0.9% NS is a safe initial rehydration fluid in children with diarrhea-related dehydration, with a satisfactory rate of sodium correction and relatively low incidence of morbidity. 2
Administer 20 mL/kg IV boluses until pulse, perfusion, and mental status normalize. 3
Continue IV rehydration until the patient awakens, has no risk factors for aspiration, and has no evidence of ileus. 1
Mild to Moderate Dehydration (Oral Therapy Preferred)
For mild to moderate dehydration, oral rehydration solution (ORS) is the first-line therapy, not IV fluids. 1 Administer:
- 50-100 mL/kg of ORS over 2-4 hours for moderate dehydration 3, 4
- Replace ongoing losses with 10 mL/kg ORS for each diarrheal stool and 2 mL/kg for each vomiting episode 4
Critical Safety Consideration: Avoid 0.45% NS in Specific Contexts
Hypernatremic Dehydration Warning
In nephrogenic diabetes insipidus (NDI) with hypernatremic dehydration, salt-containing solutions, especially NaCl 0.9% solutions, should be avoided because their tonicity (300 mOsm/kg H₂O) exceeds typical urine osmolality in NDI (100 mOsm/kg H₂O) by about 3-fold, requiring approximately 3 liters of urine to excrete the renal osmotic load from 1 liter of isotonic fluid, risking serious hypernatremia. 1
- In this specific scenario, use 5% dextrose in water instead, calculating initial fluid administration based on physiological demand. 1
However, this is a rare, specialized scenario—for typical dehydration from gastroenteritis, vomiting, or diarrhea, 0.9% NS remains appropriate.
Evidence Comparison: 0.9% NS vs Balanced Solutions
While balanced crystalloid solutions (Ringer's lactate, Plasma-Lyte) have been studied as alternatives:
Balanced solutions likely result in a slight reduction in hospital time (mean difference -0.35 days) compared to 0.9% NS. 5
Balanced solutions probably produce higher increases in blood pH and bicarbonate levels, and likely reduce the risk of hypokalemia. 5, 6
However, no significant difference exists in mortality, need for additional fluids, or most biochemical measures between 0.9% NS and balanced solutions. 5, 7
0.9% NS is more cost-effective and widely available than balanced solutions. 7
Practical Algorithm for Fluid Selection
Step 1: Assess Dehydration Severity
- Severe (shock, altered mental status, poor perfusion): Requires IV therapy 1
- Mild to moderate (normal mental status, able to drink): Use ORS 1, 3
Step 2: Choose IV Fluid for Severe Dehydration
- Standard dehydration: 0.9% NS at 20 mL/kg boluses 3, 2
- Hypernatremic dehydration with NDI: 5% dextrose in water 1
Step 3: Monitor and Transition
- Reassess after each bolus until vital signs normalize 3
- Once stabilized, transition to ORS for remaining deficit 1
Common Pitfalls to Avoid
- Do not use 0.45% NS as initial resuscitation fluid for severe dehydration—it is hypotonic and insufficient for volume expansion
- Do not use sports drinks, juice, or soda for rehydration due to inappropriate electrolyte content 3, 4
- Avoid excessive IVE volumes (≥40 mL/kg) when possible, as this is associated with higher mortality risk 2
- Monitor sodium drop carefully—aim for <0.5 mEq/L/hour to avoid neurological complications 2