What type of fluid should I start a dehydrated patient on?

Fluid Selection for Dehydrated Patients

Isotonic fluids (0.9% normal saline or lactated Ringer's) should be the first-line choice for rehydration in dehydrated patients. 1, 2

Assessment of Dehydration

Before initiating fluid therapy, assess the severity of dehydration:

Mild Dehydration

• Minimal clinical signs
• Alert and oriented
• Normal vital signs
• Mild thirst

Moderate Dehydration

• Dry mucous membranes
• Reduced skin turgor
• Tachycardia
• Postural hypotension
• Concentrated urine

Severe Dehydration

• Altered mental status
• Hypotension
• Tachycardia >30 beats/min from baseline
• Severe postural dizziness/inability to stand
• Oliguria/anuria
• In older adults: confusion, non-fluent speech, extremity weakness, dry mucous membranes, dry tongue, furrowed tongue, sunken eyes (≥4 signs indicates moderate-severe dehydration) 1

Fluid Selection Algorithm

1. Oral Rehydration (Mild to Moderate Dehydration)

• First choice: Oral rehydration solution (ORS) containing sodium (65-70 mEq/L) and glucose (75-90 mmol/L) 1
• Commercial options: Pedialyte, CeraLyte, Enfalac Lytren 1
• Do not use: Apple juice, Gatorade, or commercial soft drinks (inappropriate electrolyte content) 1
• Total fluid volume: 2200-4000 mL/day 1

2. Intravenous Rehydration (Moderate to Severe Dehydration)

• First choice: Isotonic fluids - 0.9% normal saline or lactated Ringer's 1, 2
• For severe dehydration with signs of shock: Initial fluid bolus of 20 mL/kg 1
• Continue rapid infusion until clinical signs of hypovolemia improve (blood pressure, urine output, mental status) 1
• Target urine output >0.5 mL/kg/h 1

Special Considerations

Pediatric Patients

• Isotonic fluids are safer than hypotonic fluids for maintenance therapy 3, 4, 5
• Hypotonic fluids significantly increase the risk of hospital-acquired hyponatremia 4
• In one study, hyponatremia occurred in 20.6% of children receiving hypotonic fluids vs. only 5.1% with isotonic fluids 3

Elderly Patients

• Isotonic fluids are recommended for volume depletion in older adults 1
• Consider subcutaneous hydration (hypodermoclysis) for mild to moderate dehydration when IV access is difficult 1, 6
• Monitor for fluid overload, especially in patients with heart or kidney failure 1

High-Output Stoma

• Restrict hypotonic/hypertonic fluids to <1000 mL daily 1
• Remaining fluid requirements should be met with isotonic glucose-saline solution 1
• Consider modified WHO cholera solution (St. Mark's solution): sodium chloride 60 mmol, sodium bicarbonate 30 mmol, glucose 110 mmol in 1L water 1

Monitoring and Adjustments

• Regularly reassess hydration status
• Monitor electrolytes, especially in severe dehydration
• Check urine output (target >0.5 mL/kg/h)
• For ongoing losses (diarrhea, vomiting), replace with additional ORS after each episode 2
• Consider central venous pressure monitoring and urinary catheter in severe cases 1

Common Pitfalls to Avoid

1. Using hypotonic fluids: Increases risk of iatrogenic hyponatremia, especially in children 3, 4, 5
2. Overhydration: Particularly dangerous in elderly patients with cardiac or renal disease 1
3. Inadequate replacement: Fluid administration rate must exceed ongoing losses 1
4. Inappropriate oral rehydration: Using sports drinks or juices instead of proper ORS 1
5. Failing to monitor electrolytes: Especially important with severe dehydration or ongoing losses 1

By following this evidence-based approach to fluid selection, you can effectively and safely rehydrate patients while minimizing the risk of complications such as hyponatremia or fluid overload.