(See also Water and Sodium Balance Water and Sodium Balance Body fluid volume and electrolyte concentration are normally maintained within very narrow limits despite wide variations in dietary intake, metabolic activity, and environmental stresses. Homeostasis... read more and Overview of Disorders of Fluid Volume Overview of Disorders of Fluid Volume Because sodium is the major osmotically active ion in the extracellular fluid (ECF), total body sodium content determines ECF volume. Deficiency or excess of total body sodium content causes... read more .)
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 Edema Edema is swelling of soft tissues due to increased interstitial fluid. The fluid is predominantly water, but protein and cell-rich fluid can accumulate if there is infection or lymphatic obstruction... read more develops.
Among the most common causes of ECF volume overload are the following:
Symptoms of volume overload are mainly those of the underlying disorder, but excess fluid may manifest as visible and palpable pitting edema Edema Edema is swelling of soft tissues due to increased interstitial fluid. The fluid is predominantly water, but protein and cell-rich fluid can accumulate if there is infection or lymphatic obstruction... read more in dependent soft tissue, as ascites Ascites Ascites is free fluid in the peritoneal cavity. The most common cause is portal hypertension. Symptoms usually result from abdominal distention. Diagnosis is based on physical examination and... read more in the abdomen, and as dyspnea Dyspnea Dyspnea is unpleasant or uncomfortable breathing. It is experienced and described differently by patients depending on the cause. Although dyspnea is a relatively common problem, the pathophysiology... read more and crackles from interstitial fluid in the lungs.
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 Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more , cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic fibrosis that has resulted in widespread distortion of normal hepatic architecture. Cirrhosis is characterized by regenerative nodules surrounded by dense... read more , and nephrotic syndrome Overview of Nephrotic Syndrome Nephrotic syndrome is urinary excretion of > 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary... read more .
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 Overview of Renal Replacement Therapy Renal replacement therapy (RRT) replaces nonendocrine kidney function in patients with renal failure and is occasionally used for some forms of poisoning. Techniques include continuous hemofiltration... read more 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.