Dehydration in children denotes loss of TBW from extracellular and! or intracellular compartments, due to reduced intake or more likely, excessive losses via urine, stools, lungs or skin. As these losses are predominantly from ECF compartment, ECF dehydration is dominates in early stages. ICE dehydration usually develops after redistribution of fluids.
Acute Diarrhea or vomiting is the commonest cause of dehydration, apart from other causes.
As water loss is almost always associated with loss of other electrolytes, specially Na, pathophysiological changes in dehydration can be broadly divided into three categories.
a) Isonatremic dehydration (50%) i.e. proportionate loss of water and sodium e.g. in osmotic diarrhea, with normal serum osmolality. In established isotonic dehydration, usually 60% of fluid loss is from ECF and remaining 40% is from ICE
b) Hyponatrernic dehydration in children (30-40%) i.e. disproportionately higher loss of sodium than water, e.g. in secretory diarrhea. Serum osmolality falls with consequent movement of water from ECF to ICF, leading to
a) further ECF depletion
b) cellular overhydration e.g. cerebral edema. (*Clinical signs of dehydration in these cases are disproportionately more than the estimated fluid loss).
c) Hypernatremic dehydration is rare (<5%), usually attributed to erroneous fluid therapy with concentrated ORS or hypertonic parenteral fluids.
In these cases, higher serum osmolality leads to movement of water from ICF to ECF with partial compensation of ECF loss by ICF fluids* and cellular dehydration. (*Signs of dehydration in these cases are disproportionately less than estimated fluid loss)
Clinical features depend on its severity and indicate Compensatory mechanisms to restore/conserve body water e.g. excessive thirst, oliguria, dry skin/mucus membranes etc.; Circulatory decompensation e.g. weak & thready pulse, hypotension and shock; and Cellular dehydration e.g. loss of skin turgor and mental changes.
Note that the severity of dehydration is likely to be overestimated in marasmic children due to severe wasting (confused with turgor) or under-estimated in obese children or kwashiorkor.
Urine output is the most reliable indicator in these cases. Severity may also be misinterpreted in cases with hyponatremic or hypematermic dehydration. Hypernatremic dehydration in children is characterized by typical doughy skin and excessive irritability, rather than drowsiness in iso-/hypo-natremic dehydration.
Although clinical signs are cornerstones to evaluate the presence and severity of dehydration, following investigations are essential at least in severe cases to assess co-existing electrolyte imbalance and renal dysfunction.
a) S. electrolyte e.g. Nat, K, HCO and Cl-,
b) Renal parameters e.g. blood urea and s.creatinine.
c) Urinalysis, including specific gravity.
d) Hemogram, specially Hb, Hematocrit.
e) Relevant etiological investigations.
Management of dehydration in children involves oral or parenteral fluid therapy.