= Solution
\b[General <anasarca> is extensive interstitial fluid accumulation, produced when vascular filtration exceeds the capacity of <lymphatic drainage> and the body's regulation of salt and <water>.] Several mechanisms commonly act together.
Raised venous and capillary <hydrostatic pressure> promotes filtration. <Heart failure>, especially when systemic venous pressure is elevated, is a major example; renal retention of <sodium> and <water> reinforces the swelling. Severe <kidney failure> can itself cause general fluid overload when salt and water cannot be excreted adequately. Acute <glomerulonephritis> may therefore cause widespread <oedema> without requiring the extremely low plasma protein concentration of every nephrotic case.<Edema by Merck Manual Professional Edition>[Etiology and Some Causes of Edema: cardiac, renal and hydrostatic mechanisms]{ref}
Reduced plasma <oncotic pressure> contributes when circulating <albumin> is markedly depleted. Causes include heavy urinary protein loss in <nephrotic syndrome>, reduced synthesis in advanced <liver disease>, protein loss through the <intestine>, and severe <malnutrition>. In <cirrhosis>, altered circulation and renal salt retention add to reduced protein synthesis; the mechanism cannot be reduced to a single blocked vein. Likewise, <nephrotic syndrome> can include primary renal salt retention as well as a fall in <oncotic pressure>.<Anasarca in StatPearls>[Etiology: cardiac, renal, hepatic and protein-losing conditions]{ref}
Increased vascular permeability during severe systemic <inflammation>, <sepsis> or extensive tissue injury can allow fluid and protein into the interstitium. Impaired <lymphatic drainage> can amplify systemic <oedema>, although a single obstructed lymphatic or vein ordinarily causes regional rather than general swelling. Excess administered fluid and some drugs can contribute by salt retention or altered vascular tone. Multiple mechanisms are particularly likely in a severely ill patient.
A nineteenth-century description would group much of this as cardiac, renal or hepatic “dropsy,” and might invoke an impoverished state of the <blood>. Modern physiology specifies the abnormalities that those broad descriptions leave unresolved. A general examination should distinguish pitting fluid accumulation from a predominantly non-pitting disorder such as <myxoedema>, and from isolated <ascites>. The distribution, jugular venous filling, heart and lung findings, urinary <albumin>, renal function and plasma <albumin> help distinguish causes. \b[Anasarca is a sign with several possible causes, not a diagnosis of renal disease by itself.]
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