When do losses from the skin lead to hypovolemia?
Evaporation of water from the skin and respiratory tract totals about 700 to 1000 mL/day. These losses are called insensible water losses. Sweat is hypotonic (sodium concentration 15 to 65 mmol/L), and production of sweat is low in day-to-day life.
However, exercising in a hot environment will greatly increase sweat production and lead to deficits of sodium and water.
Burns can lead to large losses of fluid from the interstitial compartment to the external environment. This fluid has electrolyte concentrations similar to those of plasma.
