General Factors affecting Acid-Base Balance in Infants

Low Bicarbonate depends on Gestational Age

• As compared to normal adults, the plasma [HCO3] in neonates is lower due to the lower renal threshold and lower capacity to reabsorb bicarbonate.
• The more immature the neonate, the lower the level.
• Very low birth weight babies have bicarbonate levels of 12-16 mmoles/l but term babies have levels of 20-22 mmol/l

Low Reserve to excrete an Acid Load

• At birth in term infants, acid excretion is working near maximum capacity and there is little reserve to deal with acidosis.
• The lower bicarbonate levels in preterm babies means they have even less capacity than a term neonate to buffer an acid load
• The ability to excrete an acid load improves over the first couple of months of life

Other Factors

• Growth results in deposition of base in new bone as the calcium salts in bone are alkaline salts
• On a weight basis, fixed acid production is higher than in adults (eg neonates and children < 12 months : fixed acid production is 2 to 3 mmol/kg/day).

NB:

• As opposed to 1-1.5mmol/kg/day