I. BIOCHEMICAL BASIS OF FLUID THERAPY
When this ratio is disturbed, the result is either acidosis or alkalosis.
Since is the major buffering system in the body, respiratory and renal control of the blood CO2 and concentrations intends to keep body pH normal. Under normal physiological condition, the ratio of blood  and [H2CO3] is 20:1, where is the metabolic component and H2CO3 (or dissolved CO2) is the respiratory component. This ratio will change by addition or loss of CO2 and to the system. Figure 18-2 depicts changes in the ratio of  and [H2CO3] that might occur during simple acid–base disturbances.
During hypoventilation (respiratory acidosis), retention of CO2 will lower the ratio. In order to return the ratio to 20:1, the body must retain more through metabolic compensation.
During metabolic acidosis, loss of will decrease the ratio. In order to return the ratio to 20:1, body must expel more CO2 to lower the ratio through respiratory compensation.
These changes in also account for the compensatory processes during respiratory alkalosis (hyperventilation) and metabolic alkalosis (Figure 18-2).
II. GENERAL CONCEPTS OF FLUID AND ELECTROLYTE THERAPY
The clinical signs for detection of dehydration include: loss of skin elasticity, dry buccal mucosa and tongue, and sunken eyeballs should be taken into account.
Replacement volume (L) = %dehydration × body weight (kg)
H2CO3 + NaCl → NaHCO3 + HCl
HCl will then be absorbed from the small intestine. GI stasis will prevent/delay the absorption of HCl into the circulation, thereby resulting in metabolic alkalosis.
Alkalosis becomes apparent when a large amount of HCl is converted into NH4Cl.