Water and electrolyte balance 294 2 Definition 295 2.1 States of hydration 295 2.2 Oedema and anasarca 295 2.3 Ascites 296 3 Pathogenesis 296 3.1 Oedematization 296 3.2 Formation of ascites 297 3.2.1 Mechanical factors 297 3.2.2 Biochemical factors 298 3.2.3 Increase in renal sodium retention 300 3.2.4 Theories of ascites formation 300 4 Aetiology of ascites 302 4.1 Differential diagnosis 302 4.2 Hepatogenic ascites 302 5 Diagnosis of ascites 303 5.1 Clinical findings 303 5.2 Imaging procedures 304 5.3 Laboratory diagnosis 305 6 Complications of ascites 308 7 Spontaneous bacterial peritonitis 308 7.1 Definition 3 0 8 7.2 Forms and frequency 308 7.3 Pathogenesis and predisposing factors 309 7.4 Clinical aspects 309 7.5 Prophylaxis and therapy 309 8 Conservative therapy of ascites 310 8.1 Prophylaxis 310 8.2 Basic therapy (stage I) 311 8.3 Diuretic therapy (stage II) 312 8.3.1 Pharmacology of diuretics 312 8.3.2 Side effects 314 8.3.3 Hyponatraemia 314 8.3.4 Resistance to diuretics 314 8.4 Osmotic diuresis (stage III) 314 8.5 Paracentesis (stage IV) 315 9 Refractory ascites 316 10 Invasive therapeutic procedures 316 10.1 Ascites reinfusion 316 10.2 Peritoneovenous shunt 317 10.3 TIPS 320 11 Surgical treatment 321 12 Liver transplantation 322 ț References (1Ϫ240) 323 (Figures 16.1Ϫ16.17; tables 16.1Ϫ16.19) 16 Oedema and ascites 1 Water and electrolyte balance ᭤ Water is an indispensable factor of life. By means of carefully coordinated regulatory mechanisms, the water equilibrium and hence the reservoir of body water is held constant. It is important to keep water intake and output in balance to maintain isovolaemia. (s. fig. 16.1) Water is present in a free (non-osmotically bound) state and as a chemically bound hydrate solid structure. • The clearance of freewater is controlled by vasopressin; it is calculated from the volume of urine/minute minus the osmolal clearance. A normal daily fluid intake of 1,700Ϫ2,200 ml (25Ϫ30 ml/kg BW) in addition to some 300 ml oxidation water is balanced by a fluid discharge of approximately 1,500 ml as urine, about 100 ml in stools, roughly 600 ml as perspiration and some 400 ml as expired air. (s. fig. 16.1) About 60% of the body's weight (ca. 55% in women) consists of water. The reservoir of body water is distributed between the intracellular space (ca. 40% of BW) and the extracellular space (ca. 20% of BW). The extracellular compartment consists of plasma fluids (ca. 4% of BW) and interstitial water (ca. 16% of BW), the latter also containing transcellular water (ca. 2.5% of BW). Because of its high degree of permeability, the body water is evenly shared between the intracellular and extracellular compartments. The water distribution between plasma and interstitium, regulated by Starling's forces, depends on the hydrostatic and colloidosmotic pressure gradients along the capillary walls. • Disturbances in the excretion of water are derived from (1.) an increase in ADH activity, (2 ( ( .) a reduction in distal filtrates available in the nephron, and (3.) greater absorption of wat...
