abnormal skin turgor, and abnormal respiratory pattern A combination of examination signs provided the best predictive data In the setting of severe dehydration (greater than or equal to 10% volume loss), evidence of shock may be apparent, with hypotension, poor peripheral perfusion with prolonged capillary refill time, cool or mottled extremities, lethargy, and rapid deep respirations Severe hypovolemia requires immediate attention with aggressive isotonic fluid resuscitation, especially in patients with sepsis (see Chapter 10 Shock ) Though laboratory assessment has been shown to be less useful than physical findings when predicting the degree of volume depletion, laboratory testing can identify associated electrolyte and acid–base abnormalities Classification of the type of hypovolemia based upon the serum sodium may impact subsequent fluid therapy and monitoring Solute is primarily composed of sodium salts in the extracellular fluid (ECF) and potassium salts in the intracellular fluid (ICF) The presenting serum sodium in the child with hypovolemia results from the loss of solute relative to water during the illness Determinants of the serum sodium include the type of fluid lost, the composition of fluid provided prior to presentation, and the ability to excrete water during the illness Hyponatremic hypovolemia (serum sodium less than 135 mEq/L) reflects the net loss of solute in excess of water Isonatremic hypovolemia (serum sodium 135 to 145 mEq/L) results when solute is lost in proportion to water, and hypernatremic hypovolemia (serum sodium greater than 145 mEq/L) reflects net loss of water in excess of solute Other biochemical abnormalities that may develop during hypovolemia include disorders of potassium homeostasis, acid–base abnormalities, and increased blood urea nitrogen (BUN) and creatinine, reflecting a decline in glomerular filtration rate (GFR) Though hyperkalemia may result, hypokalemia is more commonly seen in children with gastroenteritis given the loss of potassium in diarrheal fluid and urine Urine losses of potassium may be significant and driven by aldosterone The effect of aldosterone is to conserve urinary sodium to maintain effective intravascular volume and promote potassium excretion Management Initial management will depend on the severity of hypovolemia and presence of abnormalities of serum sodium, but the aims of treatment are to restore perfusion and maintain adequate volume in the