Daily Maintenance Fluid Requirements for Adults
For adults, the recommended baseline maintenance fluid intake is 30-35 mL/kg/day, which translates to approximately 2,010-2,345 mL per day for a 67 kg patient, or more simply: women should receive at least 1.6-2.0 L/day and men should receive at least 2.0-2.5 L/day from beverages. 1, 2, 3
Standard Calculation Method
The most widely accepted approach uses 30-35 mL/kg/day as the baseline for adults 1, 2. This method is straightforward and clinically practical for most hospitalized patients.
For patients requiring parenteral nutrition, the Holliday-Segar formula can be applied: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 25 mL/kg/day for remaining weight 1. However, the simpler 30-35 mL/kg/day calculation is preferred for general adult maintenance 1.
Fluid Type Selection
Use isotonic crystalloid solutions (0.9% sodium chloride or balanced crystalloids) for maintenance therapy 1. Balanced crystalloids may be preferred over 0.9% saline to avoid hyperchloremic acidosis 1.
Standard electrolyte supplementation should include 1-3 mmol/kg/day of sodium, 1-3 mmol/kg/day of potassium, and 2-4 mmol/kg/day of chloride 1.
Critical Adjustments Required
Reduce Fluids (50-60% of calculated amount) for:
In heart failure specifically, fluid restriction of 1.5-2.0 L/day should be considered for patients with severe symptoms or hyponatremia 2. Routine fluid restriction in mild-to-moderate heart failure does not provide clinical benefit 2, 4.
Increase Fluids for:
- Fever: Add 2-2.5 mL/kg/day for each 1°C rise above 37°C 1
- High ambient temperatures 2, 3
- Increased physical activity 2, 3
- Excessive losses from diarrhea, vomiting, or hemorrhage 2
Age-Specific Considerations
For elderly patients (>60 years), the baseline remains 30-35 mL/kg/day, but do not rely on thirst as a guide 2, 3. Older women should be offered at least 1.6 L/day and older men at least 2.0 L/day 2. Thirst sensation diminishes with age, making proactive fluid offering essential 3.
Monitoring Requirements
Daily reassessment must include: 1
- Fluid balance calculation
- Serum sodium and electrolytes
- Clinical status (edema, mucous membranes, skin turgor)
- Urine output (should be at least 0.5 mL/kg/hour)
Critical Pitfalls to Avoid
Avoid fluid overload, which independently predicts prolonged mechanical ventilation, increased ICU length of stay, and higher mortality 1. This is particularly important in critically ill patients where aggressive fluid resuscitation may be harmful.
Avoid hypotonic maintenance fluids in acutely ill adults, as they significantly increase hyponatremia risk 1.
Do not use the same calculation for extremes of body weight without adjustment 5. For significantly underweight or overweight patients, the Holliday-Segar formula (which adjusts for weight extremes) may be more appropriate than simple mL/kg calculations 5.
In nursing home or institutionalized settings, inadequate staffing and poor supervision contribute to chronic dehydration 6. Residents with dysphagia, cognitive impairment, or language barriers require systematic fluid offering rather than relying on self-initiated intake 6.