Acid-base balance can be defined as homeostasis of the body fluids at a normal arterial blood pH ranging between 7.37 and 7.43.
Description
An acid is a substance that acts as a proton donor. In contrast, a base, also known as an alkali, is frequently defined as a substance that combines with a proton to form a chemical bond. Acid solutions have a sour taste and produce a burning sensation with skin contact. A base is any chemical compound that produces hydroxide ions when dissolved in water. Base solutions have a bitter taste and a slippery feel. Despite variations in metabolism, diet, and environmental factors, the body's acid-base balance, fluid volume, and electrolyte concentration are maintained within a narrow range.
Function
Many naturally occurring acids are necessary for life. For example, hydrochloric acid is secreted by the stomach to assist with digestion. The chemical composition of food in the diet can have an effect on the body's acid-base production. Components that affect acid-base balance include protein, chloride, phosphorus, sodium, potassium, calcium, and magnesium. In addition, the rate at which nutrients are absorbed in the intestine will alter acid-base balance.
Cells and body fluids contain acid-base buffers, which help prevent rapid changes in body fluid pH over short periods of time, until the kidneys pulmonary systems can make appropriate adjustments. The kidneys and pulmonary system then work to maintain acid-base balance through excretion in the urine or respiration. The partial pressure of carbon dioxide gas (PCO2) in the pulmonary system can be measured with a blood sample and correlates with blood carbon dioxide (CO2) levels. PCO2 can then be used as an indicator of the concentration of acid in the body. The concentration of base in the body can be determined by measuring plasma bicarbonate (HCO3-) concentration. When the acid-base balance is disturbed, the respiratory system can alter PCO2 quickly, thus changing the blood pH and correcting imbalances. Excess acid or base is then excreted in the urine by the renal system to control plasma bicarbonate concentration. Changes in respiration occur primarily in minutes to hours, while renal function works to alter blood pH within several days.
Role in human health
Production of CO2 is a result of normal body metabolism. Exercise or serious infections will increase the production of CO2 through increased respiration in the lungs. When oxygen (O2) is inhaled and CO2 is exhaled, the blood transports these gases to the lungs and body tissues. The body's metabolism produces acids that are buffered and then excreted by the lungs and kidneys to maintain body fluids at a neutral pH. Disruptions in CO2 levels and HCO3-create acid-base imbalances. When acid-base imbalances occur, the disturbances can be broadly divided into either acidosis (excess acid) or alkalosis (excess base/alkali).
Common diseases and disorders
Acid-base metabolism imbalances are often characterized in terms of the HCO3-/CO2 buffer system. Acid-base imbalances result primarily from metabolic or respiratory failures. An increase in HCO3-is called metabolic alkalosis, while a decrease in the same substance is called metabolic acidosis. An increase in PCO2, on the other hand, is known as respiratory acidosis, and a decrease in the same substance is called respiratory alkalosis.
Acidosis
Acidosis is a condition resulting from higher than normal acid levels in the body fluids. It is not a disease, but may be an indicator of disease. Metabolic acidosis is related to processes that transform food into energy and body tissues. Conditions such as diabetes, kidney failure, severe diarrhea, and poisoning can result in metabolic acidosis. Mild acidosis is often compensated by the body in a number of ways. However, prolonged acidosis can result in heavy or rapid breathing, weakness, and headache. Acidemia (arterial pH < 7.35) is an accumulation of acids in the bloodstream that may occur with severe acidosis when the acid load exceeds respiratory capacity. This condition can sometimes result in comaand, if the pH falls below 6.80, it will lead to death. Diabetic ketoacidosis is a condition where excessive glucagon and a lack of insulin contribute to the production of ketoacids in the liver. This condition can be caused by chronic alcoholism and poor carbohydrate utilization.
Respiratory acidosis is caused by the lungs's failure to remove excess carbon dioxide from the body, reducing
Acid-base disturbances, causes, and compensatory mechanisms
SOURCE: Pagana, K.D. and T.J. Pagana. Mosby's Diagnostic and Laboratory Test Reference. 3rd ed. St. Louis: Mosby, 1997.
Acid-base disturbance
Common cause
Mode of compensation
Respiratory acidosis
Respiratory depression (drugs, central nervous system trauma)
Kidneys will retain increased amounts of HCO3– to increase pH
the pH in the body. Several conditions, including chest injury, blockage of the upper air passages, and severe lung disease, may lead to respiratory acidosis. Blockage of the air passages may be caused by bronchitis, asthma, or airway obstruction, resulting in mild or severe acidosis. Regular, consistent retention of carbon dioxide in the lungs is referred to as chronic respiratory acidosis. This disorder results in only mild acidosis because it is balanced by increased bicarbonate production.
The predominant symptoms of acidosis are sometimes difficult to distinguish from symptoms of an underlying disease or disorder. Mild conditions of acidosis may be asymptomatic or may be accompanied by weakness or listlessness, nausea, and vomiting. Most often, severe metabolic acidosis (pH < 7.20) is associated with increased respiration to compensate for a shortage of HCO3-. This is followed by a secondary decrease in PCO2 that occurs as part of respiratory compensation process. Treatment options for acidosis typically require correction of the underlying condition by venous administration of sodium bicarbonate or another alkaline substance.
Alkalosis
Alkalosis is a condition resulting from a higher than normal level of base/alkali in the body fluids. An excessive loss of HCO3-in the blood causes metabolic alkalosis. The body can compensate for mild alkalinity, but prolonged alkalosis can result in convulsions, muscular weakness, and even death if the pH rises above 7.80. Alkalosis can be caused by drugs or disorders that upset the normal acid-base balance. Prolonged vomiting and hyperventilation (abnormally fast, deep breathing) can result in alkalosis.
The predominant symptoms of alkalosis are neuromuscular hyperexcitability and irritability. Alkalemia (abnormal blood alkalinity) increases protein binding of ionized calcium even though plasma total calcium does not change. Severe cases may induce hypocalcemia (a low level of plasma calcium). Low plasma potassiumleads to a condition called hypokalemic alkalosis. It is frequently accompanied by metabolic alkalosis, resulting in cramping, muscle weakness, polyuria, and ileus (obstruction of the intestines). Diuretic medications may cause hypokalemic alkalosis. Prolonged vomiting may induce hypochloremic alkalosis (a large loss of chloride). The kidneys may conserve bicarbonate in order to compensate for the chloride reduction. Compensated alkalosis results when the body has partially compensated for alkalosis, and has restored normal acid-base balances. However, in compensated alkalosis, abnormal bicarbonate and carbon dioxide levels persist.
Alkalosis requires correction of the underlying condition and may involve venous administration of a weak acid to restore normal balance. If the source of alkalosis is excessive drug intake, it may be appropriate to reduce intake to restore the normal acid-base balance.
Respiratory alkalosis results from decreased CO2 levels caused by conditions such as hyperventilation (a faster breathing rate), anxiety, and fever. The pH is elevated in the body. Hyperventilation causes the body to lose excess carbon dioxide in expired air and can be triggered by altitude or a disease that reduces the amount of oxygen in the blood. Symptoms of respiratory alkalosis may include dizziness, lightheadedness, and numbing of the hands and feet. Treatments include breathing into a paper bag or a mask that induces rebreathing of carbon dioxide.
KEY TERMS
Acid—(a) Any ionic or molecular substance that can act as a proton donor; (b) A sour-tasting sub-stance, like vinegar; (c) A chemical compound that can react with a base to form a salt.
Acidosis—A dangerous condition where the blood and body tissues are less alkaline (or more acidic) than normal.
Alkalosis—Excessive alkalinity of the blood and body tissue.
Alkalemia—Abnormal blood alkalinity.
Base—(a) Any ionic or molecular substance that can act as a proton acceptor; (b) A bitter-tasting substance which has a soapy feel; (c) A chemical compound that can react with an acid to form a salt. A base can also be called an alkali.
Bicarbonate—A salt of carbonic acid produced by neutralizing a hydrogen ion.
Diabetic ketoacidosis—A condition characterized by excessive thirst and urination. Other symptoms may include appetite loss, nausea, vomiting, and rapid deep breathing.
Diuretic—An agent or drug that eliminates excessive water in the body by increasing the flow of urine.
Electrolyte—A substance such as an acid, bases, or salt. An electrolyte's water solution will conduct an electric current and ionizes. Acids, bases, and salts are electrolytes.
Homeostasis—An organism's regulation of body processes to maintain internal equilibrium in temperature and fluid content.
