Contraction alkalosis refers to the increase in blood pH that occurs as a result of fluid losses (
volume contraction
Volume contraction is a decrease in the volume of body fluid, including the dissolved substances that maintain osmotic balance (osmolytes). The loss of the water component of body fluid is specifically termed dehydration.
By body fluid compartment ...
). The change in pH is especially pronounced with acidic fluid losses caused by problems like
vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
.
Pathophysiology
There are several possible explanations for the process of alkalosis observed after volume contraction.
One popular theory is that alkalosis is simply the loss of solvent volume without a proportional loss in bicarbonate concentration or increase in carbon dioxide concentration. This explanation may be especially appropriate for the very short term after volume loss.
Another suggests that the alkalosis is due to renal compensatory mechanisms used to correct volume loss.
Extracellular fluid (ECF) volume contraction is associated with decreased blood volume and decreased renal perfusion pressure. Three compensation mechanisms engage as a result:
#
renin
Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the r ...
secretion is increased,
# production of
angiotensin II
Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adre ...
is increased, and
# secretion of
aldosterone
Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
is increased.
Increases in angiotensin II cause increased Na
+–H
+ exchange in the proximal tubule and increased HCO
3− (bicarbonate) reabsorption in the
proximal tubule
The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle. It can be further classified into the proximal convoluted tubule (PCT) and the proximal straig ...
due to increased luminal H
+. Increased aldosterone secretion stimulates the H-ATPase of alpha-intercalated cells of the collecting duct, which causes 1) increased
distal tubule
The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule.
Physiology
It is partly responsible for the regulation of potassium, sodium, calcium, and pH.
On its apical surface (lumen ...
H
+ secretion, worsening the metabolic alkalosis, and 2) increased generation of "new" bicarbonate within these same cells, which will be reabsorbed.
Additionally, increased
aldosterone
Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
secretion causes increased collecting duct K
+ secretion, in turn causing the
hypokalemia
Hypokalemia is a low level of potassium (K+) in the blood serum. Mild low potassium does not typically cause symptoms. Symptoms may include feeling tired, leg cramps, weakness, and constipation. Low potassium also increases the risk of an abno ...
seen with contraction alkalosis.
Finally, it has been suggested that the term "contraction alkalosis" is actually a misnomer, and that the alkalosis observed during volume contraction is actually attributable entirely to chloride depletion, which leads to a failure of
pendrin
Pendrin is an anion exchange protein that in humans is encoded by the ''SLC26A4'' gene (solute carrier family 26, member 4).
Pendrin was initially identified as a sodium-independent chloride-iodide exchanger with subsequent studies showing that i ...
, a chloride/bicarbonate exchanger in the collecting duct.
Diagnosis
Diagnosis of contraction alkalosis is made by correlating laboratory data with clinical history and examination. Metabolic alkalosis in the presence of decreased effective circulatory volume, loop diuretic use, or other causes of intravascular depletion such as profound diarrhea should raise suspicion for contraction alkalosis as a likely etiology in the absence of other causes.
Treatment
Treatment consists of
NaCl
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
infusion to correct ECF volume contraction and administration of K
+ to replace urinary losses.
References
Further reading
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{{Water-electrolyte imbalance and acid-base imbalance
Electrolyte disturbances