Rate of CO₂ production

СО2 release is indissolubly related to the oxygen consumption and СО2 generation in organism. СО2 is generated in organism as a result of biochemical transformations of glucose, amino acids, fats in the liver and blood under the influence of enzymes. Since glucose is one of the main oxygen source for a cell, its level is connected with СО2 generation and release in organism. Under the influence of glucose oxydase, glucose is oxidized by air oxygen to gluconic acid, and hydrogen peroxide in equimolecular quantities is formed. In this relation, СО2 generation rate must be lower than СО2 release rate, and total venous blood CO2 must be higher than total arterial blood CO2.

Clinical Significance

Clinically, transportation and elimination of carbon dioxide become especially crucial in regulating the pH of the blood. Should the partial pressure of carbon dioxide increase or decrease, the body’s pH will decrease or increase, respectively. This change can occur as a primary disorder, such as in the case of an individual who becomes apneic and develops acidosis because of the increased partial pressure of carbon dioxide, or as a compensatory reaction, such as in a person with diabetes who develops ketoacidosis and hyperventilates to decrease carbon dioxide levels and prevent the pH from dropping too low.[5]

Carbon dioxide is an important side product of the citric acid cycle (Krebs cycle). This oxidized carbon represents an end product of metabolism that, ultimately, needs to be removed using transport to the lungs and subsequent expiration out into the surrounding environment. Together with renal regulation, this complex process of carbon dioxide production, transport, and elimination is the principal means by which the body regulates the blood’s pH. Disorders in this delicate process can result in acid-base derangements and may be acute or chronic.

Cellular Level

Carbon dioxide production occurs in cells, mainly during the citric acid cycle in the cytoplasm and mitochondria, respectively. During these successive biochemical reactions, the energy stored in the reduced carbon bonds of fats, sugars, and proteins is gradually liberated in a series of stepwise reactions until the carbon atom is fully oxidized and bound to two oxygen atoms. This final product is carbon dioxide. Like other molecules, carbon dioxide always moves down its concentration gradient from sites of production in the mitochondria and cytosol through the phospholipid membrane and into the extracellular space. However, carbon dioxide diffuses readily, much quicker than oxygen. As the cells produce carbon dioxide, it dissolves into the water of the cytoplasm and continues to build up until it reaches a partial pressure greater than 40 to 45 mmHg. This buildup sets up a concentration gradient down which carbon dioxide can diffuse. From that extracellular space, carbon dioxide molecules freely diffuse through the capillary walls, rapidly equilibrating and increasing the partial pressure of carbon dioxide in the blood from about 40 mmHg on the arterial side of a capillary to 45 to 48 mmHg on the venous side.[1]

Once the venous blood returns to the lungs, the carbon dioxide diffuses out of the bloodstream, through the capillaries, and into the alveoli, from where it is expelled, during which time oxygen simultaneously binds with hemoglobin to be carried back to the tissues.

Too much CO2 in the blood can be a sign of many conditions, including:

• Lung diseases
• Cushing's syndrome
• Kidney failure
• Metabolic alkalosis, a condition in which your blood is not acidic enough. You may lose acid from conditions such as vomiting, dehydration, and anorexia.

Too little CO2 in the blood may be a sign of:

• Addison disease, a complication of type 1 and type 2 diabetes
• Diabetic ketoacidosis
• Shock
• Metabolic acidosis, a condition in which your blood is too acidic. It may be caused by many things, including kidney or liver disease, or long-lasting diarrhea.
• Respiratory alkalosis, a condition in which your blood is not acidic enough because of lung or breathing disorders, including hyperventilation (rapid, deep breathing).

1.

Geers C, Gros G. Carbon dioxide transport and carbonic anhydrase in blood and muscle. Physiol Rev. 2000 Apr;80(2):681-715. [PubMed]

2.

Hsia CC. Respiratory function of hemoglobin. N Engl J Med. 1998 Jan 22;338(4):239-47. [PubMed]

3.

Jensen FB. Red blood cell pH, the Bohr effect, and other oxygenation-linked phenomena in blood O2 and CO2 transport. Acta Physiol Scand. 2004 Nov;182(3):215-27. [PubMed]

4.

Dash RK, Bassingthwaighte JB. Erratum to: Blood HbO2 and HbCO2 dissociation curves at varied O2, CO2, pH, 2,3-DPG and temperature levels. Ann Biomed Eng. 2010 Apr;38(4):1683-701. [PMC free article] [PubMed]

5.

Berend K, de Vries AP, Gans RO. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2015 Jan 08;372(2):195. [PubMed]

https://www.ncbi.nlm.nih.gov/books/NBK532988/

https://medlineplus.gov/lab-tests/carbon-dioxide-co2-in-blood/

https://www.nps.org.au/assets/AP/pdf/The-interpretation-of-arterial-blood-gases.pdf

https://acutecaretesting.org/en/articles/parameters-that-reflect-the-carbon-dioxide-content-of-blood