Neonatal Nephrology
"Puppies are not just small dogs and
kittens are not just small cats." Nephrons are not functionally mature
in the neonate. The formation of new nephrons continues at least 3 weeks post partum in
dogs. There is a gradual transition from neonatal to adult metabolism. The ages listed
below are not absolute, but are guidelines.
The glomerular filtration rate (GFR) of neonates is 1/3 -
1/4 of the mature individual.
Tubular immaturity exists. The neonate can only concentrate
urine to an osmolality 1 & 1/2 times plasma osmolality whereas adult dogs and cats can
concentrate urine to several times the osmolality of plasma.
Fluid intake and excretion of fluids are 5 - 7 times as
great in relationship to weight compared to adults making the neonate more susceptible to
fluid depletion.
The metabolic rate of the neonate is 2 - 2 1/2 times
greater than adults in relation to body mass
Water consumption of the neonate is ~60 - 90 ml/lb/day
compared to the average water intake of the adult which is ~20-30 ml/lb/day. This needs to
be taken into consideration when formulating a fluid therapy plan for a neonatal animal.
Until 8 weeks of age the urine specific gravity is in the
range of 1.006 - 1.017. Adult animals often have a urine specific gravity in excess of
1.035.
A small amount of glucose may be present in the urine of
puppies and kittens (glucosuria) up to 8 weeks of age despite the presence of a normal
blood glucose.
Because of renal immaturity and high water turnover,
neonates are very susceptible to fluid imbalance and intoxication with renally excreted
substances. These factors must be taken into consideration when formulating a fluid
therapy plan for a neonatal animal. If you have a choice of drugs to use when treating a
neonatal animal, avoid potentially nephrotoxic drugs. If nephrotoxic drugs must be used,
maintain hydration and keep the duration of treatment as short as possible.
Last Edited: Jul 26, 2007 2:20 PM
