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Hypercapnia or Hypercapnea (from the Greek hyper = "above" and kapnos = "smoke"), also known as hypercarbia, is a condition where there is too much carbon dioxide (CO2) in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs.
Hypercapnia is the opposite of hypocapnia.
Additional recommended knowledge
Hypercapnia is generally caused by hypoventilation, lung disease, or diminished consciousness. It may also be caused by exposure to environments containing abnormally high concentrations of carbon dioxide (usually due to volcanic or geothermal causes), or by rebreathing exhaled carbon dioxide.
Symptoms of early hypercapnia, where arterial carbon dioxide pressure, PaCO2, is elevated but not extremely so, include flushed skin, full pulse, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure. In severe hypercapnia (generally PaCO2 greater than 10 kPa or 75 mmHg), symptomatology progresses to disorientation, panic, hyperventilation, convulsions, unconsciousness, and eventually death.
Hypercapnia is generally defined as a blood gas carbon dioxide level over 45 mmHg. Since carbon dioxide is in equilibrium with bicarbonate in the blood, hypercapnia can also result in a high serum bicarbonate (HCO3-) concentration. Normal bicarbonate concentrations vary from 22 to 28 milligrams per deciliter.
There are a variety of reasons for carbon dioxide not being expelled completely when the diver exhales:
Skip breathing is a controversial technique to conserve breathing gas when using open-circuit scuba, which consists of briefly holding one's breath between inhalation and exhalation (i.e. "skipping" a breath). It leads to CO2 not being exhaled efficiently. There is also an increased risk of burst lung from holding the breath while ascending.
Skip breathing is counter productive with a rebreather where the act of breathing pumps the gas around the "loop" pushing carbon dioxide through the scrubber and mixing freshly injected oxygen.
In closed circuit SCUBA (rebreather) diving, exhaled carbon dioxide must be removed from the breathing system, usually by a scrubber containing a solid chemical compound with a high affinity for CO2, such as soda lime. If not removed from the system, it may be re-inhaled, causing an increase in the inhaled concentration.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hypercapnia". A list of authors is available in Wikipedia.|