Hypercapnia
Encyclopedia
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 gas
eous product of the body's
metabolism
and is normally expelled through the lung
s.
Hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, as in sudden infant death syndrome
.
Hypercapnia is the opposite of hypocapnia
.
, 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
. 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
.
, tachypnea
, dyspnoea, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure
. According to other sources, symptoms of mild hypercapnia might include headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmias. In severe hypercapnia (generally PaCO2 greater than 10 kPa
or 75 mmHg), symptomatology progresses to disorientation, panic
, hyperventilation
, convulsions, unconsciousness
, and eventually death
.
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.
hypoventilation
resulting in inadequate CO2 elimination or hypercapnia. Lanphier's work at the US Navy Experimental Diving Unit
answered the question "why don't divers breathe enough?":
when the diver exhales:
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. It is counterproductive 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.
(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.
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
hyper = "above" and kapnos = "smoke
Smoke
Smoke is a 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 entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...
"), also known as hypercarbia, is a condition where there is too much carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) in the blood. Carbon dioxide is a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
eous product of the body's
Human body
The human body is the entire 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 100 trillion cells, the basic unit of life...
metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and is normally expelled through the lung
Lung
The lung is the essential respiration organ in many 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 near the backbone on either side of the heart...
s.
Hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, as in sudden infant death syndrome
Sudden infant death syndrome
Sudden infant death syndrome is marked by the sudden death of an infant that is unexpected by medical history, and remains unexplained after a thorough forensic autopsy and a detailed death scene investigation. An infant is at the highest risk for SIDS during sleep, which is why it is sometimes...
.
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. Hypocapnia usually results from deep or rapid breathing, known as hyperventilation....
.
Causes
Hypercapnia is generally caused by hypoventilationHypoventilation
In medicine, hypoventilation occurs when ventilation is inadequate to perform needed gas exchange...
, lung
Lung
The lung is the essential respiration organ in many 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 near the backbone on either side of the heart...
disease, or diminished consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
. 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 naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. 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 a medical condition in which decreased ventilation causes increased blood carbon dioxide concentration and decreased pH ....
.
Symptoms and signs
Symptoms and signs of early hypercapnia include flushed skin, full pulsePulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows 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...
, tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
, dyspnoea, 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 upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
. According to other sources, symptoms of mild hypercapnia might include headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmias. In severe hypercapnia (generally PaCO2 greater than 10 kPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
or 75 mmHg), symptomatology progresses to disorientation, panic
Panic
Panic is a sudden sensation of fear which is so strong as to dominate or prevent reason and logical thinking, replacing it with overwhelming feelings of anxiety and frantic agitation consistent with an animalistic fight-or-flight reaction...
, hyperventilation
Hyperventilation
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
, convulsions, unconsciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
, and eventually death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
.
Laboratory values
Hypercapnia is generally defined as a blood gasBlood gas
Blood gas is a term used to describe a laboratory test of blood where the purpose is primarily to measure ventilation and oxygenation. The source is generally noted by an added word to the beginning; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood...
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 alveolarPulmonary alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...
hypoventilation
Hypoventilation
In medicine, hypoventilation occurs when ventilation is inadequate to perform needed gas exchange...
resulting in inadequate CO2 elimination or hypercapnia. Lanphier's work at the US Navy Experimental Diving Unit
United States Navy Experimental Diving Unit
The United States Navy Experimental Diving Unit is the primary source of diving and hyperbaric operational guidance for the US Navy...
answered the question "why don't divers breathe enough?":
- Higher Inspired Oxygen (PiO2) at 4 atm (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 equationAlveolar gas equationThe partial pressure of oxygen in the pulmonary alveoli is required to calculate both the alveolar-arterial gradient of oxygen and the amount of right-to-left cardiac shunt, which are both clinically useful quantities. However it is not practical to take a sample of gas from the alveoli in order...
) in exposures above 1 atm (101 kPa), as indicated by the results when helium was substituted for nitrogen at 4 atm (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 carbon dioxide in diving
There is a variety of reasons for carbon dioxide not being expelled completelyCO2 retention
CO2 retention is a pathophysiological 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. Various diseases may lead to this state; disturbed gas exchange may lead to...
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 snorkelSnorkelingSnorkeling 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. In cooler waters, a wetsuit may also be worn...
, full face diving maskFull face diving maskA 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 helmetDiving helmetDiving helmets are worn mainly by professional divers engaged in surface supplied diving, though many models can be adapted for use with scuba equipment....
, and the diver then re-inhales from that vessel, causing increased deadspace. - The carbon dioxide scrubberSoda limeSoda 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 CO2 retention and carbon dioxide poisoning.It is made by treating...
in the diver's rebreatherRebreatherA 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...
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 densityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the breathing gasBreathing gasBreathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
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 hypoventilatingHypoventilationIn medicine, hypoventilation occurs when ventilation is inadequate to perform needed gas exchange...
, known as "skip breathing" (see below).
Skip breathing
Skip breathing is a controversial technique to conserve breathing gasBreathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural 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. It is counterproductive 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 SCUBAScuba 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. It is much used for sport diving and some sorts of work 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...
) 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. Traditionally, the term "scrubber" has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream...
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 CO2 retention and carbon dioxide poisoning.It is made by treating...
. If not removed from the system, it may be re-inhaled, causing an increase in the inhaled concentration.
See also
- HypocapniaHypocapniaHypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood. Hypocapnia usually results from deep or rapid breathing, known as hyperventilation....
, decreased level of carbon dioxide - Ocean acidificationOcean acidificationOcean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....
- Permissive hypercapniaPermissive hypercapniaPermissive hypercapnia is hypercapnia, , in respiratory insufficient 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 apneaSleep apneaSleep apnea is a sleep disorder characterized by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour. Similarly, each abnormally low...
- Animal euthanasiaAnimal euthanasiaAnimal euthanasia is the act of putting to death painlessly or allowing to die, as by withholding extreme medical measures, an animal suffering from an incurable, especially a painful, disease or condition. Euthanasia methods are designed to cause minimal pain and distress...
- Lake NyosLake NyosLake Nyos is a crater lake in the Northwest Region of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...