tailieunhanh - Chapter 046. Sodium and Water (Part 4)

Extrarenal Nonrenal causes of hypovolemia include fluid loss from the gastrointestinal tract, skin, and respiratory system and third-space accumulations (burns, pancreatitis, peritonitis). Approximately 9 L of fluid enters the gastrointestinal tract daily, 2 L by ingestion and 7 L by secretion. Almost 98% of this volume is reabsorbed so that fecal fluid loss is only 100–200 mL/d. Impaired gastrointestinal reabsorption or enhanced secretion leads to volume depletion. Since gastric secretions have a low pH (high H+ concentration) and biliary, pancreatic, and intestinal secretions are alkaline (high HCO3– concentration), vomiting and diarrhea are often accompanied by metabolic alkalosis and acidosis, respectively. Water. | Chapter 046. Sodium and Water Part 4 Extrarenal Nonrenal causes of hypovolemia include fluid loss from the gastrointestinal tract skin and respiratory system and third-space accumulations burns pancreatitis peritonitis . Approximately 9 L of fluid enters the gastrointestinal tract daily 2 L by ingestion and 7 L by secretion. Almost 98 of this volume is reabsorbed so that fecal fluid loss is only 100-200 mL d. Impaired gastrointestinal reabsorption or enhanced secretion leads to volume depletion. Since gastric secretions have a low pH high H concentration and biliary pancreatic and intestinal secretions are alkaline high HCO3- concentration vomiting and diarrhea are often accompanied by metabolic alkalosis and acidosis respectively. Water evaporation from the skin and respiratory tract contributes to thermoregulation. These insensible losses amount to 500 mL d. During febrile illnesses prolonged heat exposure exercise or increased salt and water loss from skin in the form of sweat can be significant and lead to volume depletion. The Na concentration of sweat is normally 20-50 mmol L and decreases with profuse sweating due to the action of aldosterone. Since sweat is hypotonic the loss of water exceeds that of Na . The water deficit is minimized by enhanced thirst. Nevertheless ongoing Na loss is manifest as hypovolemia. Enhanced evaporative water loss from the respiratory tract may be associated with hyperventilation especially in mechanically ventilated febrile patients. Certain conditions lead to fluid sequestration in a third space. This compartment is extracellular but is not in equilibrium with either the ECF or the ICF. The fluid is effectively lost from the ECF and can result in hypovolemia. Examples include the bowel lumen in gastrointestinal obstruction subcutaneous tissues in severe burns retroperitoneal space in acute pancreatitis and peritoneal cavity in peritonitis. Finally severe hemorrhage from any source can result in volume depletion. .