Fluids decreased intake/excess loss

TBW depletion (often referred to as dehydration ) is typically a more gradual, chronic problem compared to ECF depletion. Because TBW depletion represents a loss of hypotonic fluid (proportionally more water is lost than sodium) from all body compartments, a primary disturbance of osmolality is usually seen. The signs and symptoms of TBW depletion include CNS disturbances (mental status changes, seizures, and coma), excessive thirst, dry mucous membranes, decreased skin turgor, elevated serum sodium, increased plasma osmolality, concentrated urine, and acute weight loss. Common causes of TBW depletion include insufficient oral intake, excessive insensible losses, diabetes insipidus, excessive osmotic diuresis, and impaired renal concentrating mechanisms. Long-term care residents are frequently admitted to the acute care hospital with TBW depletion secondary to lack of adequate oral intake, often with concurrent excessive insensible losses. 

Situations that predispose patients to lithium toxicity include sodium restriction, dehydration, vomiting, diarrhea, and drng interactions that decrease lithinm clearance. Heavy exercise, sanna baths, hot weather, and fever may promote sodinm loss. Patients shonld be cautioned to maintain adeqnate sodinm and flnid intake (2.5 to 3 quarts per day of fluids) and to avoid the excessive use of coffee, tea, cola, and other caffeine-containing beverages and alcohol. 

Relative hypovolemia can occur when a large portion of the body s fluids escape into the tissues, most often owing to low oncotic pressures as a result of decreased protein. The circulating blood volume is decreased, which reduces venous return and results in symptoms similar to those of inadequate intake or fluid loss from the body. Symptoms of hypovolemia can occur when the total volume of fluid in the body is adequate. If an excess amount of fluid volume remains in the tissues, decreased volume in the blood vessels will result. 

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