The basic characteristics of hypotonic dehydration are that sodium loss is more than water loss, extracellular fluid is hypotonic, serum sodium concentration is less than135 mol/L, and plasma osmotic pressure is less than 280 mosm/L. The basic characteristics of hypertonic dehydration are that water loss is more than sodium loss, extracellular fluid is hypertonic, serum sodium is greater than150mmol/L, and plasma osmotic pressure is greater than 310mosm/L..