Normal distribution of body fluid is important for maintaining health through the balance of water metabolism. (1)
Bioelectrical impedance analysis (BIA) is a noninvasive rapid and simple bedside technique that can be used to predict total body water (TBW), extracellular water (ECW), and intracellular water (ICW) and identify altered fluid distribution following critical illness. (4)
Studies have shown that disease states and diuretics perturb the balance and then induce abnormal intracellular/extracellular fluid ratio. (1)
Body fluid volume imbalance is common in patients with kidney failure, and is associated with all‐cause mortality. The ECW/ICW ratio is independently associated with the level of albuminuria in patients with type 2 diabetes mellitus without kidney failure. This reinforces the importance of monitoring fluid balance in patients with type 2 diabetes mellitus.(3)
The importance of water in the body
Water is essential and necessary for development and survival. Water involve in the metabolism of body, modulate normal osmotic pressure, maintain electrolyte balance and regulate body temperature. Water is the largest constituent of body tissues. For babies within 0~6 months, total body water accounts for about 80% of body weight. The percentage gradually reduces with the growth of age. For adults, total body water accounts for about 60~70% of total body weight. For elders, the percentage gradually reduces as the reduction of muscle tissues.
The percentage in female is less than that in male. The body obtains water from drinking fluids, water in food and metabolic water. Water is lost from the body as urine, sweat, exhaled breath, and in feces.
Sources and losses of water are in dynamic balance and are maintained at approximately 2500 mL among adults.
The inner balance of water metabolism mainly depends on the body’s own homeostatic regulatory system, which is regulated by the thirst center in the brain, vasopressin secreted by the posterior pituitary gland and the kidneys. The thirst center is an important link in regulating the source of water in the body. The kidney regulates water balance by urination, dilution and concentration of urine.
Under normal circumstance, the body fluid is maintained in a dynamic balance, by osmotic pressure balance, through the osmotic action of solutes in the intracellular fluid (ICF) and extracellular fluid (ECF). The osmotic pressure balance of ICF and ECF mainly depends on the simple diffusion of water molecules inside and outside the cell. The balance between anionic and cationic electrolytes of ICF and ECF is regulated through exchange of these electrolytes. When water intake is insufficient or water loss is excessive, the osmotic pressure of ECF increases. Drinking behavior is stimulated aroused through the regulatory mechanism of nervous system. In addition, the secretion of antidiuretic hormone and aldosterone increase, which changes water permeability of the distal renal tubules and collecting tubules of the kidney to increase water reabsorption, reduce water discharge, and maintain normal osmotic pressure of body fluid. On the contrary, if too much water is taken, the secretion of these hormones are inhibited, resulting in increased urine output. Therefore, it is probable that fluid intake will influence the distribution of body fluid.
However, currently few studies have looked the relationship of water intake on the distribution of body fluid. Such studies have mainly focused on disease states including hepatitis, hepatocirrhosis, and kidney disease requiring dialysis .
Unbalanced shift in body fluid are not only effective indicators at diagnosing dehydration and water intoxication, but also risk indicators for some diseases, such as cardiovascular disease in hemodialysis patients, diabetic ketoacidosis, kidney diseases, and so on. The maintenance of the normal ECF/ICF ratio is important for heath. Body fluid is regulated through the balance of water metabolism, and the balance of water metabolism is closely related to the sources and loss of water. (1)
In hemodialysis patients, fluid overload and malnutrition are accompanied by extracellular fluid (ECF) expansion and intracellular fluid (ICF) depletion, respectively. We investigated the relationship between ECF/ICF ratio (as an integrated marker reflecting both fluid overload and malnutrition) and survival and cardiovascular disease (CVD) in the context of malnutrition-inflammation-arteriosclerosis (MIA) complex.
Hemodialysis patients with high ECF/ICF ratio are not only fluid overloaded, but malnourished and have stiff artery with more inflammation. The ECF/ICF ratio is highly related to the MIA complex, and is a major risk indicator for all-cause mortality and CVD. (2)