DISORDERS OF WATER BALANCE
GENERAL PRINCIPLES OF DISORDERS OF WATER BALANCE (HYPONATREMIA AND HYPERNATREMIA) AND SODIUM BALANCE (HYPOVOLEMIA AND EDEMA)
Literature review current through: Sep 2013. | This topic last updated: ene 15, 2013.
1. INTRODUCTION —
The plasma sodium concentration is regulated by changes in water intake and excretion, not by changes in sodium balance. hyponatremia is primarily due to the intake of water that cannot be excreted hypernatremia is primarily due to the loss of water that has not been replaced hypovolemia represents the loss of sodium and water edema is primarily due to sodium and water retention.
Understanding these basic principles is essential for appropriate diagnosis and treatment.
2. DEFINITIONS —
2.1. Total body water — The total body water (TBW) as a percentage of lean body weight varies with age.
80 percent in premature infants
70 to 75 percent in term infants
65 to 70 percent in toddlers
60 percent after puberty
These values vary with the amount of fat since fat has a much lower water content than muscle. Thus, the TBW as a percentage of total body weight is lower in individuals with more fat and becomes progressively lower with increasing obesity or with loss of muscle mass. young adult females (50 %) young adult males (60 %)
The TBW (60%) has two main compartment, which are separated by the cell membrane. The relative size of the two main compartments varies with age. (FIGURA 1)
FIGURA 1. TOTAL BODY WATER AND ITS MAJOR SUBDIVISIONS AS A FUNCTION OF AGE
The cell membranes are freely permeable to water but not electrolytes and therefore help to maintain the different solute composition of the two compartments: sodium salts in the extracellular fluid, with chloride and bicarbonate being the major anions; and potassium salts in the intracellular fluid, with large macromolecular organic phosphates being the main anions.
The extracellular fluid (20%)(1/3 TBW):
The ECF volume is regulated by
Literature review current through: Sep 2013. | This topic last updated: ene 15, 2013.
1. INTRODUCTION —
The plasma sodium concentration is regulated by changes in water intake and excretion, not by changes in sodium balance. hyponatremia is primarily due to the intake of water that cannot be excreted hypernatremia is primarily due to the loss of water that has not been replaced hypovolemia represents the loss of sodium and water edema is primarily due to sodium and water retention.
Understanding these basic principles is essential for appropriate diagnosis and treatment.
2. DEFINITIONS —
2.1. Total body water — The total body water (TBW) as a percentage of lean body weight varies with age.
80 percent in premature infants
70 to 75 percent in term infants
65 to 70 percent in toddlers
60 percent after puberty
These values vary with the amount of fat since fat has a much lower water content than muscle. Thus, the TBW as a percentage of total body weight is lower in individuals with more fat and becomes progressively lower with increasing obesity or with loss of muscle mass. young adult females (50 %) young adult males (60 %)
The TBW (60%) has two main compartment, which are separated by the cell membrane. The relative size of the two main compartments varies with age. (FIGURA 1)
FIGURA 1. TOTAL BODY WATER AND ITS MAJOR SUBDIVISIONS AS A FUNCTION OF AGE
The cell membranes are freely permeable to water but not electrolytes and therefore help to maintain the different solute composition of the two compartments: sodium salts in the extracellular fluid, with chloride and bicarbonate being the major anions; and potassium salts in the intracellular fluid, with large macromolecular organic phosphates being the main anions.
The extracellular fluid (20%)(1/3 TBW):
The ECF volume is regulated by