Water intoxication refers to a condition where water retention significantly increases body fluid volume, leading to serum sodium concentration <130 mmol/L and plasma osmolality <280 mOsm/(kg·H2O), while total body sodium is normal or elevated. Edema refers to the accumulation of excessive fluid in the interstitial spaces or body cavities.
Etiology
Water Intoxication
It may result from acute renal failure or excessive secretion of antidiuretic hormone (ADH) triggered by various factors. Water intoxication most commonly occurs in patients with renal insufficiency. Persistent excessive water intake or rapid intravenous infusion of hypotonic or low-salt solutions that exceed renal excretion capacity can also cause water intoxication.
Edema
Generalized edema is often observed in conditions such as congestive heart failure (commonly referred to as heart failure), nephrotic syndrome, nephritis, liver diseases, malnutrition, and certain endocrine disorders. Localized edema may occur due to local inflammation in tissues, or due to venous or lymphatic obstruction.
Clinical Manifestations
Acute water intoxication typically has a rapid onset. The excessive water can cause brain cell swelling, leading to increased intracranial pressure and a range of neurological and psychiatric symptoms such as headache, drowsiness, agitation, confusion, disorientation, delirium, or even coma. In cases where brain herniation occurs, corresponding neurological signs of localized brain damage may appear. Chronic water intoxication symptoms are often masked by those of the underlying disease and may include weakness, nausea, vomiting, and drowsiness. Significant weight gain, pale and moist skin are also common signs.
Laboratory findings may reveal decreases in red blood cell count, hemoglobin concentration, hematocrit, and plasma protein levels, along with reduced plasma osmolality. Increased mean corpuscular volume and decreased mean corpuscular hemoglobin concentration indicate an overall increase in both intracellular and extracellular fluid volumes.
Subcutaneous edema is a key clinical feature of edema. When fluid accumulates excessively in the subcutaneous tissues, the skin appears swollen and has reduced elasticity. Pressing the skin with a finger may produce an indentation, known as pitting edema. The location of the edema varies depending on the underlying cause. Cardiac edema usually appears first in dependent areas, renal-related edema often manifests as swelling of the eyelids or face, and hepatic edema is primarily characterized by ascites.
Treatment
The prevention and treatment of the underlying conditions are of paramount importance. Patients with acute renal failure or heart failure should strictly limit water intake to prevent water intoxication. Factors such as pain, hemorrhage, shock, trauma, and major surgeries can trigger excessive ADH secretion, and in these patients, attention should be given to avoid overhydration during intravenous therapy.
Mild cases of water intoxication can resolve when excess water is excreted by the body after stopping or reducing water intake. In severe cases, water intake should not only be carefully restricted but diuretics also need to be administered to promote water excretion. Osmotic diuretics like 20% mannitol can be intravenously infused to reduce brain cell swelling and increase water excretion. Intravenous administration of potent diuretics such as furosemide can further enhance water elimination from the body.