Which patient requires the greatest amount of maintenance intravenous (IV) fluids?

Maintenance IV Fluid Requirements by Patient Type

The 21-year-old male athlete (option a) requires the greatest amount of maintenance intravenous fluids due to higher metabolic rate, greater lean body mass, and increased insensible losses compared to the other patient populations.

Physiological Basis for Fluid Requirements

Maintenance IV fluid calculations are fundamentally based on metabolic rate and body composition, which directly correlate with fluid needs 1:

• Daily fluid maintenance for adults is estimated at approximately 30 mL per kilogram of body weight 1
• Younger individuals with higher metabolic rates require proportionally more fluid per kilogram than older adults
• Lean body mass (not total body weight including adipose tissue) is the primary determinant of metabolic water requirements

Analysis of Each Patient Option

Option A: 21-Year-Old Male Athlete (HIGHEST REQUIREMENT)

This patient has the greatest maintenance fluid needs due to:

• Highest basal metabolic rate among all options, as young adult males have peak metabolic activity 1
• Greatest lean body mass, which is the metabolically active tissue requiring fluid maintenance
• Higher insensible losses through respiration and skin due to increased metabolic activity
• Athletes typically have lower body fat percentages, meaning a higher proportion of their weight represents metabolically active tissue requiring fluid support

Option B: 55-Year-Old Obese Male Office Worker (LOWER REQUIREMENT)

This patient requires less maintenance fluid because:

• Adipose tissue is metabolically inactive and does not require proportional fluid maintenance 1
• Maintenance fluid calculations should be based on ideal body weight or lean body mass, not total body weight in obese patients
• Middle-aged individuals have lower basal metabolic rates than young adults
• Sedentary lifestyle results in lower overall metabolic demands

Option C: 21-Year-Old Housewife (MODERATE REQUIREMENT)

This patient has intermediate fluid requirements:

• Young age maintains relatively high metabolic rate
• However, females typically have lower lean body mass than males of equivalent age and weight
• Lower basal metabolic rate compared to male athletes
• Likely lower activity level than a trained athlete

Option D: 75-Year-Old Female with Recent Weight Loss (LOWEST REQUIREMENT)

This patient requires the least maintenance fluid:

• Elderly patients have significantly reduced metabolic rates compared to younger adults 1
• Recent weight loss further reduces total body mass requiring maintenance
• Geriatric patients often require fluid restriction rather than liberal administration 1
• Older adults are at higher risk for fluid overload and should be monitored carefully for volume status 1

Clinical Application

When calculating maintenance IV fluids:

• Use actual body weight for lean individuals (athletes, normal weight patients) 1
• Use ideal body weight for obese patients, as adipose tissue does not contribute proportionally to fluid requirements 1
• Adjust for age-related metabolic decline in elderly patients, who may require 20-30% less than calculated standard maintenance 1
• Monitor for euvolemia as the goal, avoiding both hypovolemia and hypervolemia 1

Important Caveats

• These calculations assume euvolemic patients requiring only maintenance fluids, not resuscitation or replacement of ongoing losses 1
• Isotonic solutions (0.9% saline or balanced crystalloids) should be used for maintenance in adults to avoid complications 1
• Patients with specific conditions (heart failure, renal failure, hepatic failure) require individualized fluid restriction regardless of baseline metabolic needs 1
• Daily reassessment of fluid balance and electrolytes is essential for all patients receiving IV maintenance fluids 1