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Hypercapnia
 
 
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Hypercapnia or hypercapnea (from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 hyper = "above" and kapnos = "smoke
Smoke

File:Bling-Bling Skywriting David Shankbone.jpgSmoke is the collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrainment or otherwise mixed into the mass....
"), also known as hypercarbia, is a condition where there is too much carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
 (CO2) in the blood. Carbon dioxide is a gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
eous product of the body's
Human body

The human body is the entire physical and mental structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 10 trillion Cell , the basic unit of life....
 metabolism
Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
 and is normally expelled through the lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s.

Hypercapnia is the opposite of hypocapnia
Hypocapnia

Hypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood....
.

rcapnia is generally caused by hypoventilation
Hypoventilation

In medicine, hypoventilation occurs when Ventilation is inadequate to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide and respiratory acidosis....
, lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
 disease, or diminished consciousness
Consciousness

Consciousness is a difficult term to define, because the word is used and understood in a wide variety of ways, so that it frequently happens that what one person sees as a definition of consciousness is seen by others as about something else altogether....
.






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Hypercapnia or hypercapnea (from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 hyper = "above" and kapnos = "smoke
Smoke

File:Bling-Bling Skywriting David Shankbone.jpgSmoke is the collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrainment or otherwise mixed into the mass....
"), also known as hypercarbia, is a condition where there is too much carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
 (CO2) in the blood. Carbon dioxide is a gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
eous product of the body's
Human body

The human body is the entire physical and mental structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 10 trillion Cell , the basic unit of life....
 metabolism
Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
 and is normally expelled through the lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s.

Hypercapnia is the opposite of hypocapnia
Hypocapnia

Hypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood....
.

Causes

Hypercapnia is generally caused by hypoventilation
Hypoventilation

In medicine, hypoventilation occurs when Ventilation is inadequate to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide and respiratory acidosis....
, lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
 disease, or diminished consciousness
Consciousness

Consciousness is a difficult term to define, because the word is used and understood in a wide variety of ways, so that it frequently happens that what one person sees as a definition of consciousness is seen by others as about something else altogether....
. 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
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
. It can also be an initial effect of administering supplemental oxygen on a patient with sleep apnea. In this situation the hypercapnia can also be accompanied by respiratory acidosis
Respiratory acidosis

Respiratory acidosis is acidosis due to decreased Ventilation of the lung alveoli, leading to elevated artery carbon dioxide concentration ....
.

Symptoms

Symptoms of early hypercapnia, where arterial carbon dioxide pressure, PaCO2, is elevated but not extremely so, include flushed skin, full pulse
Pulse

In medicine, a person's pulse is the throbbing of their artery. It can be palpated in any place that allows for an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the ankle joint ....
, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure
Blood pressure

Blood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs. The pressure of the circulating blood decreases as it moves away from the heart through artery and capillary, and toward the heart through veins....
. In severe hypercapnia (generally PaCO2 greater than 100 hPa
Pascal (unit)

The pascal is the SI derived unit of pressure, stress , Young's modulus and tensile strength. It is a measure of force per unit area i.e. equivalent to one newton per square meter or one joule per cubic meter....
 or 75 mmHg), symptomatology progresses to disorientation, panic
Panic

Panic is a sudden fear which dominates or replaces thinking and often affects groups of people or animals. Panics typically occur in disaster situations, or violent situations which may endanger the overall health of the affected group....
, hyperventilation
Hyperventilation

In medicine, hyperventilation is the state of breathing faster and/or deeper than necessary, bringing about lightheadedness and other undesirable symptoms often associated with panic attacks....
, convulsions, unconsciousness
Unconsciousness

Unconsciousness, more appropriately referred to as loss of consciousness or lack of consciousness, is a dramatic alteration of mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli....
, and eventually death
Death

Death is the permanent termination of the biological functions that define a life organism. It refers to both a particular event and to the condition that results thereby....
.

Laboratory values

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.

During diving

Normal respiration in divers results in alveolar
Pulmonary alveolus

An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood....
 hypoventilation
Hypoventilation

In medicine, hypoventilation occurs when Ventilation is inadequate to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide and respiratory acidosis....
 resulting in inadequate CO2 elimination or hypercapnia. Lanphier's work at the US Naval Experimental Diving Unit
United States Navy Experimental Diving Unit

The United States Navy Experimental Diving Unit is the primary source of Commercial diving#Military and naval diving and Diving chamber operational guidance for the US Navy....
 answered the question "why don't divers breathe enough?":
  • Higher Inspired Oxygen (PiO2) at 4 ata (404 kPa) accounted for not more than 25% of the elevation in End Tidal CO2 (etCO2) above values found at the same work rate when breathing air just below the surface.
  • Increased Work of Breathing accounted for most of the elevation of PACO2 (alveolar gas equation
    Alveolar gas equation

    The alveolar pO2 is not routinely measured but is calculated from blood gas measurements by the Alveolar gas equation.It was first characterized in 1946....
    ) in exposures above 1 ata (101 kPa), as indicated by the results when helium was substituted for nitrogen at 4 ata (404 kPa).
  • Inadequate ventilatory response to exertion was indicated by the fact that, despite resting values in the normal range, PetCO2 rose markedly with exertion even when the divers breathed air at a depth of only a few feet.


Additional Sources of CO2 in diving

There are a variety of reasons for carbon dioxide not being expelled completely
CO2 retention

CO2 retention is a pathophysiology process in which too little carbon dioxide is removed from the blood by the lungs. The end result is hypercapnia, an elevated level of carbon dioxide dissolved in the bloodstream....
 when the diver exhales:
  • The diver is exhaling into a vessel that does not allow all the CO2 to escape to the environment, such as a long snorkel
    Snorkeling

    Snorkeling is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually swimfins....
    , full face diving mask
    Full face diving mask

    A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece or demand valve that provides the diver with breathing gas....
    , or diving helmet
    Diving helmet

    File:Kask-nurka.jpgDiving helmets are worn mainly by professional diving engaged in surface supplied diving, though many models can be adapted for use with SCUBA equipment....
    . The diver then re-inhales from that vessel (Increased deadspace).
  • The carbon dioxide scrubber
    Soda lime

    Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO%E2%82%82_retention and carbon dioxide poisoning....
     in the diver's rebreather
    Rebreather

    A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere....
     is failing to remove sufficient carbon dioxide from the loop (Higher inspired CO2).
  • The diver is over-exercising, producing excess carbon dioxide due to elevated metabolic activity.
  • The density
    Density

    The density of a material is defined as its mass per unit volume. The symbol of density is ....
     of the breathing gas
    Breathing gas

    Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
     is higher at depth, so the effort required to fully inhale and exhale has increased, making breathing more difficult and less efficient (Work of breathing). The higher gas density also causes gas mixing within the lung to be less efficient, thus increasing the deadspace (wasted breathing).
  • The diver is deliberately hypoventilating
    Hypoventilation

    In medicine, hypoventilation occurs when Ventilation is inadequate to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide and respiratory acidosis....
    , known as "skip breathing" (see below).


Skip breathing

Skip breathing is a controversial technique to conserve breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
 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.

Rebreathers

In closed circuit SCUBA
Scuba set

A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving....
 (rebreather
Rebreather

A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere....
) diving, exhaled carbon dioxide must be removed from the breathing system, usually by a scrubber
Scrubber

Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams....
 containing a solid chemical compound with a high affinity for CO2, such as soda lime
Soda lime

Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO%E2%82%82_retention and carbon dioxide poisoning....
. If not removed from the system, it may be re-inhaled, causing an increase in the inhaled concentration.

See also

  • Hypocapnia
    Hypocapnia

    Hypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood....
    , decreased level of carbon dioxide
  • Ocean acidification
    Ocean acidification

    Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by their uptake of anthropogenic carbon dioxide from the Earth's atmosphere....
  • Permissive hypercapnia
    Permissive hypercapnia

    Permissive hypercapnia is hypercapnia, , in respiratory insufficiency patients in which oxygenation has become so difficult that the optimal mode of mechanical ventilation is not capable of exchanging enough carbon dioxide....
  • Respiratory Physiology
  • Sleep apnea
    Sleep apnea

    Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. Each episode, called an apnea , lasts long enough so that one or more breaths are missed, and such episodes occur repeatedly throughout sleep....