Using the 4-2-1 rule, what is the hourly maintenance rate for an 8 kg infant?

• A. 16 mL/hr
• B. 32 mL/hr
• C. 64 mL/hr
• D. 8 mL/hr

Answer: (B)

The main idea here is the 4-2-1 rule for pediatric maintenance fluids: use 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg (11–20 kg), and 1 mL/kg/hr for each kg over 20 kg. An 8 kg infant lies entirely in the first 10 kg bracket, so you multiply 8 by 4, giving 32 mL per hour. The other numbers come from applying a different tier that doesn’t apply to this weight. For example, 16 mL/hr would come from using 2 mL/kg/hr, which is only for weights in the 11–20 kg range; 64 mL/hr would require an 8 mL/kg/hr rate (not applicable here); and 8 mL/hr would imply using a 1 mL/kg/hr rate in a situation that doesn’t fit the 8 kg infant’s weight. So 32 mL/hr is the correct maintenance rate.