Chapter 10
RENAL PHYSIOLOGY, ACUTE RENAL FAILURE AND RENAL
REPLACEMENT THERAPY IN CHILDREN
Faisal Quareshi, MD
Felix C Blanco, MDPhysiology of the pediatric kidney
During the first days of life, the newborn is faced with the challenge of adapting to
the extra-uterine environment and not depending on maternal regulatory
mechanisms. This adaptation includes, in part, a tight homeostasis of water and
electrolytes.
One of the early events in the newborn life is the “physiologic weight loss” by
which a normal neonate loses approximately 10% of the body weight in the first
week of life. This loss is the result of the elimination of excess total body water
and sodium accumulated in-utero, and represents a loss primarily from the
extravascular extracellular (EC) compartment through the kidney. As expected, a
decrease in the EC water is undertaken without compromising the circulatory
volume; homeostasis achieved by slow replenishment of the intravascular
compartment from existing reservoirs of water in skin and muscle. This important
phenomenon is believed to be regulated by prolactin.
Failure to recognize this normal process by replacing water and sodium losses
would predispose to fluid overload leading to persistent ductus arteriosus (PDA),
cardiac failure, necrotizing enterocolitis (NEC) and bronchopulmonary dysplasia
(BPD). [1, 2]
Neonates have a limited ability to manage loads or restriction of sodium because
they have a decreased area of renal reabsorption (small and immature proximal
tubules), ineffective interstitial reabsorptive capacity and immature sodium