A preterm neonate at 29 weeks develops hypernatremic dehydration on exclusive enteral feeds. Compared with a term infant, the key renal limitation predisposing to this is:
- A Low maximal urinary concentrating ability due to short loops of Henle and low medullary urea gradient ✓
- B Excessive glomerular filtration of sodium with tubular loss
- C Absence of aldosterone responsive sodium channels
- D Obligate polyuria from immature aquaporin 2 receptors only
Correct answer: A. Low maximal urinary concentrating ability due to short loops of Henle and low medullary urea gradient
Explanation
The neonatal kidney can concentrate urine to only about 600 mOsm/kg versus 1200 mOsm/kg in adults, because loops of Henle are short, medullary thickness is low, and the urea gradient is undeveloped. Preterm infants are even more limited. To excrete a solute load they must pass larger water volumes, so high-protein or high-solute feeds cause hypernatremic dehydration. ADH responsiveness is present but cannot compensate fully.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.