Regulation of extracellular fluid volume and renal function.

Normal fluid homoeostasis includes dynamic shifts in water,
crystalloids, and proteins between the various compartments of the
body (1–3). The fluid dynamics are controlled by refined mechanisms
that include water and solute intake, renal handling, haemodynamic/
oncotic forces, and neurohumoral regulation (4, 5). Fluid
retention is a characteristic feature in the progressive state of cirrhosis,
where the accumulation of fluid in the peritoneal cavity occurs in a
substantial number of patients (6–8). Over the last decade, much effort
has been devoted to the role of vasodilation, abnormal blood volume
distribution, hyperdynamic cardiovascular decompensation, and kidney
dysfunction in the formation of hepatic ascites (9–15). A considerable
advance in the understanding of the microvascular dynamics and pathophysiology
of the extravascular volume regulation has been achieved by
studies with indicators of different molecular size (16–19). Advances
in the insight of the dynamics of lymphatics and the peritoneal space
have in part been attained by studies on patients undergoing peritoneal
dialysis (20, 21). Renal dysfunction in patients with advanced cirrhosis
has been intensively studied over several decades (22–27). The present
chapter will deal with the regulation of the extracellular fluid volume,
kidney function, and aspects of the pathophysiology of the hepatorenal
syndromes. Some cornerstones and recent advances in the understanding
of the normal state, especially with respect to the regulation of
transvascular exchange at the local level, are also considered.