An increase in total body sodium is the key pathophysiologic event. It increases osmolality, which triggers compensatory mechanisms that cause water retention. When sufficient fluid accumulates in the ECF (usually >2.5 L), edema develops.
Among the most common causes of ECF volume overload are the following:
Diagnosis is mainly clinical. Key features include weight gain and edema. The location and amount of edema are dependent on many factors, including whether the patient has been sitting, lying, or standing recently.
Clinical findings vary significantly depending on the cause and are discussed in detail elsewhere in THE MANUAL.
Serum sodium concentration can be high, low, or normal in volume-overloaded patients (despite the increased total body sodium content). Urinary sodium may help differentiate acute kidney injury from other (non-renal related) acute causes of volume overload. In renal failure, the urinary sodium is > 20mEq/L (> 20 mmol/L) as compared to < 10 mEq/L (< 10 mmol/L) in heart failure, cirrhosis, and nephrotic syndrome.
Treatment aims to correct the cause. Treatment of heart failure, cirrhosis, kidney failure, and nephrotic syndrome are addressed elsewhere in THE MANUAL, but in general treatment includes diuretics and sometimes mechanical fluid removal via methods such as dialysis and paracentesis.
Dietary sodium intake is restricted. Diuretics are given in heart failure, cirrhosis, renal insufficiency, and nephrotic syndrome.
Daily weights are the best way to follow the progress of therapy for ECF volume overload. The speed of correction of ECF volume overload should be limited to 0.25 to 0.5 kg body weight/day, depending on the degree of volume overload (faster with a copious excess, slower with less excess) and the patient's other medical problems (slower with hypotension and renal insufficiency).
Outpatients should be monitored closely when undergoing active diuresis. When there is more severe organ system dysfunction or multiple organ systems are involved or little progress is being made with oral diuretics, inpatient treatment and monitoring are needed.