Maintenance fluid requirements

Maintenance Fluids - The Daily Gulp

Calculates daily needs for water and electrolytes to prevent dehydration and ketoacidosis in a euvolemic patient who cannot eat or drink.

• Standard "4-2-1" Rule (Hourly Rate):
  • First 10 kg: $4$ mL/kg/hr
  • Next 10-20 kg: $2$ mL/kg/hr
  • Above 20 kg: $1$ mL/kg/hr

⭐ Increase maintenance fluids by 10-15% for each 1°C rise in body temperature above 38°C. Also account for other insensible losses like tachypnea.

Calculating Rates - Fluid Formula Fun

• "4/2/1 Rule" for Hourly Maintenance: A simple method to calculate maintenance fluid needs.
  • First 10 kg: $4$ mL/kg/hr
  • Next 10-20 kg: $2$ mL/kg/hr
  • Above 20 kg: $1$ mL/kg/hr
• Example (75 kg adult):
  • $(10 \times 4) + (10 \times 2) + (55 \times 1) = 40 + 20 + 55 = 115$ mL/hr.
• 📌 Mnemonic: "4-2-1, the fluid calculation is done!"

⭐ For febrile patients, increase maintenance fluid rates by 10-15% for each 1°C rise in body temperature above 38°C, as insensible losses are higher.

IV Fluid Types - What's in the Bag?

• Crystalloids: Salt & water solutions; primary for volume resuscitation & maintenance.
• Colloids: Large molecules (e.g., Albumin); remain in intravascular space longer.

Common Crystalloids Compared

• Hypertonic Fluids: e.g., 3% NaCl. Used for severe, symptomatic hyponatremia.

⭐ Exam Favorite: Lactated Ringer's is generally avoided in severe traumatic brain injury (TBI). Its relative hypotonicity (273 mOsm/L) compared to plasma can worsen cerebral edema.

Adjusting Fluids - Tricky Situations

• Hypermetabolic States: Increase maintenance fluids for:
  • Fever: Add 10-15% per 1°C over 37°C
  • Tachypnea, significant sweating, or large wounds/burns
• Fluid Restriction States: Decrease maintenance fluids in:
  • Congestive Heart Failure (CHF)
  • Renal Failure (especially oliguric)
  • Cirrhosis

⭐ In elderly patients or those with cardiac/renal disease, err on the side of caution. Iatrogenic fluid overload is a common and serious complication.

• The "4/2/1" rule is key for hourly maintenance: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr after.
• A common choice is D5 ½ NS + 20 mEq KCl to provide dextrose, prevent ketosis, and replace electrolytes.
• Increase fluids for factors like fever, tachypnea, and GI losses.
• Using hypotonic fluids alone risks iatrogenic hyponatremia, particularly in postoperative patients due to high ADH levels.
• Daily requirements are typically 1-2 mEq/kg for both sodium and potassium.
• Closely monitor urine output (>0.5 mL/kg/hr) and serum electrolytes.