<prompt> Most common cause of hyponatremia in surgical practiceSmall intestinal obstructionDuodenal fistulaPancreatic fistulaIntussuception  <response>: Ans. a Small intestinal obstruction Ref. Bailey and Love Short textbook of surgery 24th ed., p 56The most frequent cause of sodium depletion in surgical practice is obstruction of the small intestine.SODIUM BALANCE Sodium is the principal cation content of the extracellular fluid. On average it is 1 mmolkg sodium chloride or 500 mL of isotonic 0.9 saline solution. An equivalent amount is excreted daily, mainly in the urine and some in the faeces.Sodium Depletion syn.HyponatremiaEtiology Small intestinal obstruction most frequent cause in surgical practice. Duodenal, total biliary, pancreatic and high intestinal external fistulae. Severe diarrhea will cause hyponatremia with acidosis. Hyponatremia with elevated potassium would suggest adrenocortical insufficiency. SIADH.Potassium Depletion It occurs most frequently in diabetic coma treated by insulin and prolonged infusion of saline solution. Diuretics. The diarrhoea from ulcerative colitis, villous tumours of the rectum and the loss from external fistulae of the alimentary tract are also common causes e.g., duodenal fistula, ileostomy;Clinical features risk of cardiac arrhythmias. Symptoms of severe hypokalemia include listlessness and slurred speech, muscular hypotonia, depressed reflexes and abdominal distension as a result of a paralytic ileus. ECG:Prolonged QT interval, depression of ST segment and flattening or inversion of the T-wave.Rx Oral potassium. Potassium can be given in the form of milk, meat extracts, fruit juices and honey. However, in hospital practice, effervescent tablets of potassium chloride 2 g can be given by mouth 6-hourly. IV potassium. Rapid IV supplementation especially when renal function is impaired carries the risk of dysrhythmias and cardiac arrest if the serum concentration rises to a dangerous level. When there is no associated alkalosis, potassium deficit can be restored by adding 40 mmol KCL to each litre of 5 glucose, glucose-saline or 0.9 saline solution, given 6-8-hrly.Sodium Excess syn. HypernatremiaEtiology excessive amount of 0.9 saline solution given intravenously during the early postoperative period.Clinical Features Slight puffiness of the face is the only early sign.POTASSIUM BALANCE Potassium is almost entirely intracellular. No less than 98 is intracellular, and only 2 is present in the extracellular fluid. Three-quarters of the total body potassium approximately 3500 mmol is found in skeletal muscles. 