The importance of fluid and electrolyte replacement for promoting tissue perfusion and ionic equilibrium is self-evident. In addition, it is necessary to give potassium, magnesium, phosphate, and zinc to ensure optimum nitrogen retention.

Sodium and chloride

Foods high in sodium are often high in chloride. Sodium and chloride are the most abundant extracellular ions and are responsible for maintaining the osmolality of the extracellular fluid. In a cold climate balance can be maintained with as little as 5 mmol/day, but this rises to 20 mmol/day in hot weather.


Potassium, which is the main intracellular cation, is present in a variety of foods. Traditionally, orange juice and bananas are given as rich sources of potassium. The range of normal dietary intake is determined by the fact that potassium is not as well conserved as sodium and there are significant fecal and renal losses. To maintain body stores and normal plasma levels 40 to 50 mmol/day must be given.


Magnesium is the second most abundant intracellular cation. It is necessary for mitochondrial integrity and stability of nuclear DNA. It is also necessary for control of neuromuscular excitability. The amount of magnesium required to maintain balance in normal subjects has been estimated to vary from 0.125 to 0.187 mmol/kg/day. During pregnancy and lactation the requirements are increased to 0.25 mmol/kg/day.


About 98 per cent of the total body calcium is in the skeleton. The intracellular concentration of calcium is extremely low as it is toxic to the cell. The concentration of extracellular calcium plays a very important part in nerve and muscle cell excitability. The calcium requirement is 60 mmol/day during adolescence up to the age of 24 and is reduced to 40 mmol/day for older persons. During pregnancy and lactation 60 mmol/day is considered a prudent intake.


Phosphorus is the major intracellular anion. In the cell, among other functions, it is a part of buffer systems of energy-storing nucleotides (ATP), membranes (as phospholipids), and oxygen transfer systems in the form of erythrocyte 2,3-diphosphoglycerate. Phosphorus requirement is set at a 1:1 ratio with calcium. Therefore the phosphorus intake in normal subjects and orally fed patients should approximate the calcium intake.

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