# Respiratory alkalosis

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

Respiratory alkalosis is a medical condition in which increased respiration elevates the blood pH beyond the normal range (7.35-7.45) with a concurrent reduction in arterial levels of carbon dioxide. This condition is one of the four basic categories of disruption of acid-base homeostasis.

## Terminology

• Alkalosis refers to disorders that elevate cellular pH greater than 7.45.
• Alkalemia refers to an arterial blood pH of greater than 7.45.

## Classification

There are two types of respiratory alkalosis: chronic and acute as a result of the 3-5 day delay in kidney compensation of the abnormality.[1][2]

• 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.

## Signs and symptoms

Signs and 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.[3]

## Mechanism

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

Respiratory alkalosis may be produced as a result of medical treatment (iatrogenically) during excessive mechanical ventilation. Other causes include:

## In popular culture

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.