Metabolic alkalosis
Encyclopedia
Metabolic alkalosis
is a metabolic condition in which the pH
of tissue is elevated beyond the normal range ( 7.35-7.45 ). This is the result of decreased hydrogen ion
concentration, leading to increased bicarbonate
, or alternatively a direct result of increased bicarbonate
concentrations.
These can be divided into two categories, depending upon urine chloride
levels.
(CO2) through slower breathing, or hypoventilation
(respiratory compensation
). CO2 is then consumed toward the formation of the carbonic acid
intermediate, thus decreasing pH. Respiratory compensation, though, is incomplete. The decrease in [H+] suppresses the peripheral chemoreceptors, which are sensitive to pH. But, because respiration slows, there's an increase in PCO2 which would cause an offset of the depression because of the action of the central chemoreceptors which are sensitive to the partial pressure of CO2 in the blood. So, because of the central chemoreceptors, respiration rate would be increased.
Renal compensation
for metabolic alkalosis, less effective than respiratory compensation, consists of increased excretion of HCO3- (bicarbonate), as the filtered load of HCO3- exceeds the ability of the renal tubule to reabsorb it.
Alkalosis
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
is a metabolic condition in which the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of tissue is elevated beyond the normal range ( 7.35-7.45 ). This is the result of decreased hydrogen ion
Hydrogen ion
Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes.Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions....
concentration, leading to increased bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
, or alternatively a direct result of increased bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
concentrations.
Terminology
- Alkalosis refers to a high pH in tissue.
- Alkalemia refers to a high pH in the blood.
Causes
There are five main causes of metabolic alkalosis.These can be divided into two categories, depending upon urine chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
levels.
Chloride-responsive (<10 mEq/L)
- Loss of hydrogen ions - Most often occurs via two mechanisms, either vomiting or via the kidney.
- VomitingVomitingVomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
results in the loss of hydrochloric acidHydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
(hydrogen and chloride ions) with the stomach contents. In the hospital setting this can commonly occur from nasogastric suction tubes. - Severe vomitting also causes loss of potassium (hypokalaemia) and sodium (hyponatraemia). The kidneys compensate for these losses by retaining sodium in the collecting ducts at the expense of hydrogen ions (sparing sodium/potassium pumps to prevent further loss of potassium), leading to metabolic alkalosis.
- Vomiting
- Congenital chloride diarrheaCongenital chloride diarrheaCongenital chloride diarrhea is a genetic disorder due to an autosomal recessive mutation on chromosome 7. The mutation is in downregulated-in-adenoma , a gene that encodes a membrane protein of intestinal cells. The protein belongs to the solute carrier 26 family of membrane transport proteins...
- rare for being a diarrhea that causes alkalosis instead of acidosis. - Contraction alkalosisContraction alkalosisContraction alkalosis refers to the increase in blood pH that occurs as a result of fluid losses . The change in pH is especially pronounced with acidic fluid losses caused by problems like vomiting.-Pathophysiology:...
- This results from a loss of water in the extracellular space which is poor in bicarbonate, typically from diuretic use. Since water is lost while bicarbonate is retained, the increased concentration of bicarbonate "mops up" more of the hydrogen ions and raises the blood pH.- Diuretic therapy - loop diuretics and thiazides can both initially cause increase in chloride, but once stores are depleted, urine excretion will be below < 25 mEq/L. The loss of fluid from sodium excretion causes a contraction alkalosis.
- Posthypercapnia - Hypercapnia causes respiratory acidosis. Renal compensation with excess bicarbonate occurs to lessen the affect of the acidosis. Once carbon dioxide levels return to base line, the higher bicarbonate levels reveal themselves putting the patient into metabolic alkalosis
Chloride-resistant (>20 mEq/L)
- Retention of bicarbonateBicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
- Shift of hydrogen ions into intracellular space - Seen in hypokalemiaHypokalemiaHypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
. Due to a low extracellular potassium concentration, potassium shifts out of the cells. In order to maintain electrical neutrality, hydrogen shifts into the cells, raising blood pH.
- Alkalotic agents - Alkalotic agents, such as bicarbonate (administrated in cases of peptic ulcerPeptic ulcerA peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
or hyperacidityHyperacidityHyperacidity, also known as acid dyspepsia is the condition of excreting more than the normal amount of hydrochloric acid in the stomach.Some causes for hyperacidity are peptic ulcers, gastroesophageal reflux disease, stomach cancer and certain types of diet that contains spicy food.Hyperacidity or...
) or antacids, administered in excess can lead to an alkalosis. - Hyperaldosteronism - Renal loss of hydrogen ions occurs when excess aldosteroneAldosteroneAldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
(Conn's syndromeConn's syndromePrimary aldosteronism, also known as primary hyperaldosteronism, is characterized by the overproduction of the mineralocorticoid hormone aldosterone by the adrenal glands., when not a result of excessive renin secretion. Aldosterone causes increase in sodium and water retention and potassium...
) increases the activity of a sodium-hydrogen exchange protein in the kidney. This increases the retention of sodium ions whilst pumping hydrogen ions into the renal tubule. Excess sodium increases extracellular volume and the loss of hydrogen ions creates a metabolic alkalosis. Later, the kidney responds through the aldosterone escapeAldosterone escapeIn physiology, aldosterone escape is a term that has been used to refer to 2 distinct phenomena involving aldosterone that are exactly opposite each other:...
to excrete sodium and chloride in urine. - Licorice
- Bartter syndromeBartter syndromeBartter syndrome is a rare inherited defect in the thick ascending limb of the loop of Henle. It is characterized by low potassium levels , increased blood pH , and normal to low blood pressure. There are two types of Bartter syndrome: neonatal and classic...
- a syndrome analogous to taking loop diuretics characterized with normotensive patients - Liddle syndrome - a syndrome from defect sodium channel deletion characterized by hypertension and hypoaldosteronism.
- 11β-hydroxylase deficiency and 17 alpha-hydroxylase deficiencyCongenital adrenal hyperplasia due to 17 alpha-hydroxylase deficiencyCongenital adrenal hyperplasia due to 17α-hydroxylase deficiency is an uncommon form of congenital adrenal hyperplasia resulting from a defect in the gene for the enzyme CYP17A1. It produces decreased synthesis of both cortisol and sex steroids, with resulting increase in mineralocorticoid production...
- both characterized by hypertension
Compensation
Compensation for metabolic alkalosis occurs mainly in the lungs, which retain carbon dioxideCarbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) through slower breathing, or hypoventilation
Hypoventilation
In medicine, hypoventilation occurs when ventilation is inadequate to perform needed gas exchange...
(respiratory compensation
Respiratory compensation
Respiratory compensation is a mechanism by which plasma pH can be altered by varying the respiratory rate. It is faster than renal compensation, but has less ability to restore normal values....
). CO2 is then consumed toward the formation of the carbonic acid
Carbonic acid
Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
intermediate, thus decreasing pH. Respiratory compensation, though, is incomplete. The decrease in [H+] suppresses the peripheral chemoreceptors, which are sensitive to pH. But, because respiration slows, there's an increase in PCO2 which would cause an offset of the depression because of the action of the central chemoreceptors which are sensitive to the partial pressure of CO2 in the blood. So, because of the central chemoreceptors, respiration rate would be increased.
Renal compensation
Renal compensation
Renal compensation is a mechanism by which the kidneys can regulate the plasma pH. It is slower than respiratory compensation, but has a greater ability to restore normal values....
for metabolic alkalosis, less effective than respiratory compensation, consists of increased excretion of HCO3- (bicarbonate), as the filtered load of HCO3- exceeds the ability of the renal tubule to reabsorb it.
See also
- hypokalemiaHypokalemiaHypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
- Metabolic acidosisMetabolic acidosisIn medicine, metabolic acidosis is a condition that occurs when the body produces too much acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low due to increased production of hydrogen by the body or the...
- Respiratory acidosisRespiratory acidosisRespiratory acidosis is a medical condition in which decreased ventilation causes increased blood carbon dioxide concentration and decreased pH ....
- Respiratory alkalosisRespiratory alkalosisRespiratory alkalosis is a medical condition in which increased respiration elevates the blood pH...