Respiratory alkalosis

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Respiratory alkalosis
Classification and external resources
Davenport Fig 11.jpg
ICD-10 E87.3
ICD-9 276.3
DiseasesDB 406
MedlinePlus 000111
eMedicine med/2009
MeSH D000472

Respiratory alkalosis is a medical condition in which increased respiration elevates the blood pH (a condition generally called alkalosis). It is one of four basic categories of disruption of acid-base homeostasis. This condition is commonly associated with a decrease in PaCO2 (hyperventilation).

Terminology[edit]

  • Alkalosis refers to disorders that elevate cellular pH to > 7.45.
  • Alkalemia refers to an arterial pH > 7.45.

Types[edit]

There are two types of respiratory alkalosis: chronic and acute.

  • Acute respiratory alkalosis occurs rapidly. For every 10 mmHg drop in PCO2 in arterial blood, there is a corresponding 2 mEq/L drop in bicarbonate ion due to acute compensation. During acute respiratory alkalosis, the person may lose consciousness where the rate of ventilation will resume to normal.
  • Chronic respiratory alkalosis is a more long-standing condition. For every 10 mmHg drop in PCO2 in arterial blood, there is a corresponding 5 mEq/L drop in bicarbonate ion. The drop of 5 mEq/L of bicarbonate ion is a compensation effect which reduces the alkalosis effect of the drop in PCO2 in blood. This is termed metabolic compensation.

Mechanism[edit]

Respiratory alkalosis generally occurs when some stimulus (see "Causes" below) makes a person hyperventilate. The increased breathing produces increased alveolar respiration, expelling CO2 from the circulation. This alters the dynamic chemical equilibrium of carbon dioxide in the circulatory system, and the system reacts according to Le Chatelier's principle. Circulating hydrogen ions and bicarbonate are shifted through the carbonic acid (H2CO3) intermediate to make more CO2 via the enzyme carbonic anhydrase according to the following reaction:

\rm HCO_3^- + H^+ \rightarrow H_2CO_3 \rightarrow CO_2 + H_2O

The net result of this is decreased circulating hydrogen ion concentration, and thus increased pH (alkalosis). There is also a decrease in ionized blood calcium concentration.

Causes[edit]

Respiratory alkalosis may be produced accidentally (iatrogenically) during excessive mechanical ventilation. Other causes include:

Symptoms[edit]

Symptoms of respiratory alkalosis are related to the decreased blood carbon dioxide levels, and include peripheral paraesthesiae. In addition, the alkalosis may disrupt calcium ion balance, and cause the symptoms of hypocalcaemia (such as tetany and fainting) with no fall in total serum calcium levels. However, chronic respiratory alkalosis leads to hyperphosphatemia and hypocalcemia, by inducing renal PTH-resistance.[1]

In popular culture[edit]

In The Andromeda Strain, Michael Crichton's first novel published under his real name, only two people exposed to a pathogenic extraterrestrial microbe survive. Scientists investigating these survivors discover that each had abnormal blood pH. One, a baby, had respiratory alkalosis due to constant crying; the other, an old man, drinks Sterno. As a result, it becomes clear that the microbe cannot survive outside a narrow pH range.

See also[edit]

References[edit]

  1. ^ Krapf, Reto; Jaeger, Philippe; Hulter, Henry N (10 April 1992), "Chronic respiratory alkalosis induces renal PTH-resistance, hyperphosphatemia and hypocalcemia in humans", Kidney International (42): 727–734, doi:10.1038/ki.1992.340, ISSN 0085-2538