4. Fluid Balance and Electrolytes
Fluid Balance and Electrolytes Sri Lankan Surgery MD Part One — exam-directed master note This topic commonly appears through: Perioperative fluid prescriptions. Postoperative oliguria. Vomiting, diarrhoea, intestinal obstruction and fistulae. Sodium and potassium interpretation. ECG changes. Emergency electrolyte correction. Burns, sepsis, trauma and renal failure. Data interpretation and OSCE prescribing stations. The central principle is: Do not treat a fluid chart or electrolyte value in isolation. Treat the patient, the physiological disturbance and its cause. 1. Essential physiology Body-fluid compartments In a typical non-obese adult: Total body water: approximately 60% of body weight in a younger man and 50–55% in a woman. It is lower in older people and obesity. Intracellular fluid: approximately two-thirds of total body water. Extracellular fluid: approximately one-third. Extracellular fluid is divided into: Interstitial fluid: approximately three-quar...