A breathing gas is a mixture of gaseous chemical elements and compounds used for
respiration
Respiration may refer to:
Biology
* Cellular respiration, the process in which nutrients are converted into useful energy in a cell
** Anaerobic respiration, cellular respiration without oxygen
** Maintenance respiration, the amount of cellul ...
. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats such as
scuba equipment,
surface supplied diving equipment,
recompression chambers,
high-altitude mountaineering, high-flying
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...
,
submarines,
space suit
A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...
s,
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
,
medical life support and first aid equipment, and
anaesthetic machines.
Oxygen is the essential component for any breathing gas, at a
partial pressure of between roughly 0.16 and 1.60
bar at the
ambient pressure
Ambient or Ambiance or Ambience may refer to:
Music and sound
* Ambience (sound recording), also known as atmospheres or backgrounds
* Ambient music, a genre of music that puts an emphasis on tone and atmosphere
* ''Ambient'' (album), by Moby
* ...
. The oxygen is usually the only
metabolically active component unless the gas is an anaesthetic mixture. Some of the oxygen in the breathing gas is consumed by the metabolic processes, and the inert components are unchanged, and serve mainly to dilute the oxygen to an appropriate concentration, and are therefore also known as diluent gases. Most breathing gases therefore are a mixture of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and one or more metabolically
inert gas
An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
es.
[ Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of ]decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
, reducing the duration of decompression stops
The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body, which occurs during the ascent, largely during ...
, reducing nitrogen narcosis
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain g ...
or allowing safer deep diving
Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, an ...
.[
A safe breathing gas for ]hyperbaric
Hyperbaric medicine is medical treatment in which an ambient pressure greater than sea level atmospheric pressure is a necessary component. The treatment comprises hyperbaric oxygen therapy (HBOT), the medical use of oxygen at an ambient pressure ...
use has four essential features:
* It must contain sufficient oxygen to support life, consciousness and work rate of the breather.[
* It must not contain harmful contaminants. ]Carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
and carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
are common poisons which may contaminate breathing gases. There are many other possibilities.[
* It must not become toxic when being breathed at high ]pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
such as when underwater. Oxygen and nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
are examples of gases that become toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
under pressure.[
* It must not be too dense to breathe. ]Work of breathing
Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not parti ...
increases with density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
and viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
. Maximum ventilation drops by about 50% when density is equivalent to air at 30 msw, and carbon dioxide levels rise unacceptably for moderate exercise with a gas density exceeding 6 g/litre. Breathing gas density of 10 g/litre or more may cause runaway hypercapnia
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
even at very low work levels, with potentially fatal effects.
The techniques used to fill diving cylinder
A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a sc ...
s with gases other than air are called gas blending
Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled.
A wide range of applications include scientific and industrial processes, food production and storage and ...
.
Breathing gases for use at ambient pressures below normal atmospheric pressure are usually pure oxygen or air enriched with oxygen to provide sufficient oxygen to maintain life and consciousness, or to allow higher levels of exertion than would be possible using air. It is common to provide the additional oxygen as a pure gas added to the breathing air at inhalation, or though a life-support system.
For diving and other hyperbaric use
These common diving breathing gases are used:
* Air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
is a mixture of 21% oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, 78% nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, and approximately 1% other trace gases, primarily argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
; to simplify calculations this last 1% is usually treated as if it were nitrogen. Being freely available and simple to use, it is the most common diving gas.[ As its nitrogen component causes ]nitrogen narcosis
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain g ...
, it is considered to have a safe depth limit of about 40 metres (130 feet) for most divers, although the maximum operating depth
In underwater diving activities such as saturation diving, technical diving and nitrox diving, the maximum operating depth (MOD) of a breathing gas is the depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable ...
of air taking an allowable oxygen partial pressure of 1,6 bar is 66.2 metres (218 feet). Breathing air is air meeting specified standards for contaminants.
* Pure oxygen is mainly used to speed the shallow decompression stops at the end of a military
A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...
, commercial
Commercial may refer to:
* a dose of advertising conveyed through media (such as - for example - radio or television)
** Radio advertisement
** Television advertisement
* (adjective for:) commerce, a system of voluntary exchange of products and s ...
, or technical dive. Risk of acute oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lu ...
increases rapidly at pressures greater than 6 metres sea water.[ It was much used in frogmen's ]rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
s, and is still used by attack swimmers.
* ''Nitrox
Nitrox refers to any breathing gas, gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual applicatio ...
'' is a mixture of oxygen and air, and generally refers to mixtures which are more than 21% oxygen. It can be used as a tool to accelerate in-water decompression stops or to decrease the risk of decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
and thus prolong a dive (a common misconception is that the diver can go deeper, this is not true owing to a shallower maximum operating depth than on conventional air).
* '' Trimix'' is a mixture of oxygen, nitrogen and helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
and is often used at depth in technical diving
Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally ...
and commercial diving
Commercial diving may be considered an application of professional diving where the diver engages in underwater work for industrial, construction, engineering, maintenance or other commercial purposes which are similar to work done out of the wate ...
instead of air to reduce nitrogen narcosis and to avoid the dangers of oxygen toxicity.[
* '']Heliox
Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because mixture generates less resistance than atmospheric air when passing through the airways of the lung ...
'' is a mixture of oxygen and helium and is often used in the deep phase of a commercial deep dive to eliminate nitrogen narcosis.
* '' Heliair'' is a form of trimix that is easily blended from helium and air without using pure oxygen. It always has a 21:79 ratio of oxygen to nitrogen; the balance of the mix is helium.
* '' Hydreliox'' is a mixture of oxygen, helium, and hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and is used for dives below 130 metres in commercial diving.
* ''Hydrox
Hydrox is a cream-filled chocolate sandwich cookie currently owned and manufactured by Leaf Brands. It debuted in the United States in 1908, and was manufactured by Sunshine Biscuits for over 90 years. Hydrox was largely discontinued in 1999, ...
'', a gas mixture of hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, is used as a breathing gas in very deep diving
Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, an ...
.
* ''Neox'' (also called neonox) is a mixture of oxygen and neon sometimes employed in deep commercial diving. It is rarely used due to its cost. Also, DCS symptoms produced by neon ("neox bends") have a poor reputation, being widely reported to be more severe than those produced by an exactly equivalent dive-table and mix with helium.
Breathing air
Breathing air is atmospheric air with a standard of purity suitable for human breathing in the specified application. For hyperbaric use the partial pressure of contaminants is increased in proportion to the absolute pressure, and must be limited to a safe composition for the depth or pressure range in which it is to be used.
Classification by oxygen fraction
Breathing gases for diving are classified by oxygen fraction. The boundaries set by authorities may differ slightly, as the effects vary gradually with concentration and between people, and are not accurately predictable.
;Normoxic: where the oxygen content does not differ greatly from that of air and allows continuous safe use at atmospheric pressure.
;Hyperoxic, or oxygen enriched: where the oxygen content exceeds atmospheric levels, generally to a level where there is some measurable physiological effect over long term use, and sometimes requiring special procedures for handling due to increased fire hazard. The associated risks are oxygen toxicity at depth and fire, particularly in the breathing apparatus.
;Hypoxic: where the oxygen content is less than that of air, generally to the extent that there is a significant risk of measurable physiological effect over the short term. The immediate risk is usually hypoxic incapacitation at or near the surface.
Individual component gases
Breathing gases for diving are mixed from a small number of component gases which provide special characteristics to the mixture which are not available from atmospheric air.
Oxygen
Oxygen (O2) must be present in every breathing gas.[ This is because it is essential to the human body's metabolic process, which sustains life. The human body cannot store oxygen for later use as it does with food. If the body is deprived of oxygen for more than a few minutes, unconsciousness and death result. The tissues and organs within the body (notably the heart and brain) are damaged if deprived of oxygen for much longer than four minutes.
Filling a diving cylinder with pure oxygen costs around five times more than filling it with compressed air. As oxygen supports combustion and causes rust in ]diving cylinder
A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a sc ...
s, it should be handled with caution when gas blending
Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled.
A wide range of applications include scientific and industrial processes, food production and storage and ...
.[
Oxygen has historically been obtained by fractional distillation of ]liquid air
Liquid air is air that has been cooled to very low temperatures ( cryogenic temperatures), so that it has condensed into a pale blue mobile liquid. To thermally insulate it from room temperature, it is stored in specialized containers ( vacuum in ...
, but is increasingly obtained by non-cryogenic technologies such as pressure swing adsorption
Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases (typically air) under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at ne ...
(PSA) and vacuum swing adsorption (VSA) technologies.
The fraction of the oxygen component of a breathing gas mixture is sometimes used when naming the mix:
* ''hypoxic'' mixes, strictly, contain less than 21% oxygen, although often a boundary of 16% is used, and are designed only to be breathed at depth as a "bottom gas" where the higher pressure increases the partial pressure of oxygen to a safe level.[ Trimix, ]Heliox
Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because mixture generates less resistance than atmospheric air when passing through the airways of the lung ...
and Heliair are gas blends commonly used for hypoxic mixes and are used in professional and technical diving
Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally ...
as deep breathing gases.[
* ''normoxic'' mixes have the same proportion of oxygen as air, 21%.][ The maximum operating depth of a normoxic mix could be as shallow as 47 metres (155 feet). Trimix with between 17% and 21% oxygen is often described as normoxic because it contains a high enough proportion of oxygen to be safe to breathe at the surface.
* ''hyperoxic'' mixes have more than 21% oxygen. Enriched Air Nitrox (EANx) is a typical hyperoxic breathing gas.][ Hyperoxic mixtures, when compared to air, cause ]oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lu ...
at shallower depths but can be used to shorten decompression stop
The practice of decompression by divers comprises the planning and monitoring of the profile indicated by the algorithms or tables of the chosen decompression model, to allow asymptomatic and harmless release of excess inert gases dissolved in ...
s by drawing dissolved inert gases out of the body more quickly.[
The fraction of the oxygen determines the greatest depth at which the mixture can safely be used to avoid ]oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lu ...
. This depth is called the maximum operating depth
In underwater diving activities such as saturation diving, technical diving and nitrox diving, the maximum operating depth (MOD) of a breathing gas is the depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable ...
.[
The concentration of oxygen in a gas mix depends on the fraction and the pressure of the mixture. It is expressed by the partial pressure of oxygen (PO2).][
The partial pressure of any component gas in a mixture is calculated as:
:''partial pressure = total absolute pressure × volume fraction of gas component''
For the oxygen component,
:PO2 = P × FO2
where:
:PO2 = partial pressure of oxygen
:P = total pressure
:FO2 = volume fraction of oxygen content
The minimum safe partial pressure of oxygen in a breathing gas is commonly held to be 16 ]kPa
KPA may refer to:
* Keele Postgraduate Association, Keele University, UK, formerly Keele Research Association (KRA)
* Kensington (Olympia) station, London, England, National Rail station code
* Kenya Ports Authority
* ''Kiln phosphoric acid'', a ...
(0.16 bar). Below this partial pressure the diver may be at risk of unconsciousness and death due to hypoxia, depending on factors including individual physiology and level of exertion. When a hypoxic mix is breathed in shallow water it may not have a high enough PO2 to keep the diver conscious. For this reason normoxic or hyperoxic "travel gases" are used at medium depth between the "bottom" and "decompression" phases of the dive.
The maximum safe PO2 in a breathing gas depends on exposure time, the level of exercise and the security of the breathing equipment being used. It is typically between 100 kPa (1 bar) and 160 kPa (1.6 bar); for dives of less than three hours it is commonly considered to be 140 kPa (1.4 bar), although the U.S. Navy has been known to authorize dives with a PO2 of as much as 180 kPa (1.8 bar).[ At high PO2 or longer exposures, the diver risks oxygen toxicity which may result in a ]seizure
An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with l ...
.[ Each breathing gas has a ]maximum operating depth
In underwater diving activities such as saturation diving, technical diving and nitrox diving, the maximum operating depth (MOD) of a breathing gas is the depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable ...
that is determined by its oxygen content.[ For therapeutic recompression and hyperbaric oxygen therapy partial pressures of 2.8 bar are commonly used in the chamber, but there is no risk of drowning if the occupant loses consciousness.] For longer periods such as in saturation diving
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
, 0.4 bar can be tolerated over several weeks.
Oxygen analysers are used to measure the oxygen partial pressure in the gas mix.[
Divox is breathing grade oxygen labelled for diving use. In the ]Netherlands
)
, anthem = ( en, "William of Nassau")
, image_map =
, map_caption =
, subdivision_type = Sovereign state
, subdivision_name = Kingdom of the Netherlands
, established_title = Before independence
, established_date = Spanish Netherl ...
, pure oxygen for breathing purposes is regarded as medicinal as opposed to industrial oxygen, such as that used in welding
Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
, and is only available on medical prescription
A prescription, often abbreviated or Rx, is a formal communication from a physician or other registered health-care professional to a pharmacist, authorizing them to dispense a specific prescription drug for a specific patient. Historicall ...
. The diving industry registered Divox as a trademark
A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from othe ...
for breathing grade oxygen to circumvent the strict rules concerning medicinal oxygen thus making it easier for (recreational) scuba divers to obtain oxygen for blending their breathing gas.
In most countries, there is no difference in purity in medical oxygen and industrial oxygen, as they are produced by exactly the same methods and manufacturers, but labeled and filled differently. The chief difference between them is that the record-keeping trail is much more extensive for medical oxygen, to more easily identify the exact manufacturing trail of a "lot" or batch of oxygen, in case problems with its purity are discovered. Aviation grade oxygen is similar to medical oxygen, but may have a lower moisture content.
Diluent gases
Gases which have no metabolic function in the breathing gas are used to dilute the gas, and are therefore classed as diluent gases. Some of them have a reversible narcotic effect at high partial pressure, and must therefore be limited to avoid excessive narcotic effects at the maximum pressure at which they are intended to be breathed. Diluent gases also affect the density of the gas mixture and thereby the work of breathing
Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not parti ...
.
= Nitrogen
=
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(N2) is a diatomic gas and the main component of air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
, the cheapest and most common breathing gas used for diving. It causes nitrogen narcosis
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain g ...
in the diver, so its use is limited to shallower dives. Nitrogen can cause decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
.
Equivalent air depth is used to estimate the decompression requirements of a nitrox
Nitrox refers to any breathing gas, gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual applicatio ...
(oxygen/nitrogen) mixture. Equivalent narcotic depth is used to estimate the narcotic potency of trimix (oxygen/helium/nitrogen mixture). Many divers find that the level of narcosis caused by a dive, whilst breathing air, is a comfortable maximum.
Nitrogen in a gas mix is almost always obtained by adding air to the mix.
= Helium
=
Helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
(He) is an inert gas that is less narcotic than nitrogen at equivalent pressure (in fact there is no evidence for any narcosis from helium at all), and it has a much lower density, so it is more suitable for deeper dives than nitrogen.[ Helium is equally able to cause ]decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
. At high pressures, helium also causes high-pressure nervous syndrome, which is a central nervous system irritation syndrome which is in some ways opposite to narcosis.
Helium mixture fills are considerably more expensive than air fills due to the cost of helium and the cost of mixing and compressing the mix.
Helium is not suitable for dry suit
A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold or contaminated ...
inflation owing to its poor thermal insulation
Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with ...
properties – compared to air, which is regarded as a reasonable insulator, helium has six times the thermal conductivity. Helium's low molecular weight (monatomic MW=4, compared with diatomic nitrogen MW=28) increases the timbre of the breather's voice, which may impede communication. This is because the speed of sound is faster in a lower molecular weight gas, which increases the resonance frequency of the vocal cords.[ Helium leaks from damaged or faulty ]valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s more readily than other gases because atoms of helium are smaller allowing them to pass through smaller gaps in seals.
Helium is found in significant amounts only in natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, from which it is extracted at low temperatures by fractional distillation.
= Neon
=
Neon (Ne) is an inert gas sometimes used in deep commercial diving
Commercial diving may be considered an application of professional diving where the diver engages in underwater work for industrial, construction, engineering, maintenance or other commercial purposes which are similar to work done out of the wate ...
but is very expensive.[ Like helium, it is less narcotic than nitrogen, but unlike helium, it does not distort the diver's voice. Compared to helium, neon has superior thermal insulating properties.]
= Hydrogen
=
Hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
(H2) has been used in deep diving gas mixes but is very explosive when mixed with more than about 4 to 5% oxygen (such as the oxygen found in breathing gas).[ This limits use of hydrogen to deep dives and imposes complicated protocols to ensure that excess oxygen is cleared from the breathing equipment before breathing hydrogen starts. Like helium, it raises the timbre of the diver's voice. The hydrogen-oxygen mix when used as a diving gas is sometimes referred to as ]Hydrox
Hydrox is a cream-filled chocolate sandwich cookie currently owned and manufactured by Leaf Brands. It debuted in the United States in 1908, and was manufactured by Sunshine Biscuits for over 90 years. Hydrox was largely discontinued in 1999, ...
. Mixtures containing both hydrogen and helium as diluents are termed Hydreliox.
Unwelcome components of breathing gases for diving
Many gases are not suitable for use in diving breathing gases. Here is an incomplete list of gases commonly present in a diving environment:
Argon
Argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
(Ar) is an inert gas that is more narcotic than nitrogen, so is ''not'' generally suitable as a diving breathing gas. Argox is used for decompression research. It is sometimes used for dry suit
A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold or contaminated ...
inflation by divers whose primary breathing gas is helium-based, because of argon's good thermal insulation properties. Argon is more expensive than air or oxygen, but considerably less expensive than helium. Argon is a component of natural air, and constitutes 0.934% by volume of the Earth's atmosphere.
Carbon dioxide
Carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(CO2) is produced by the metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...
in the human body and can cause carbon dioxide poisoning. When breathing gas is recycled in a rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
or life support system, the carbon dioxide is removed by scrubbers
''Scrubbers'' is a 1982 British drama film directed by Mai Zetterling and produced by Don Boyd starring Amanda York, Kathy Burke, and Chrissie Cotterill. It was shot primarily in Virginia Water, Surrey, England
Surrey () is a ceremonia ...
before the gas is re-used.
Carbon monoxide
Carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
(CO) is a highly toxic gas that competes with dioxygen for binding to hemoglobin, thereby preventing the blood from carrying oxygen (see carbon monoxide poisoning
Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...
). It is typically produced by incomplete combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
.[ Four common sources are:
* ]Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
containing CO in the air being drawn into a diving air compressor
A diving air compressor is a gas compressor that can provide breathing air directly to a surface-supplied diver, or fill diving cylinders with high-pressure air pure enough to be used as a breathing gas. A low pressure diving air compressor us ...
. CO in the intake air cannot be stopped by any filter. The exhausts of all internal combustion engines running on petroleum fuels contain some CO, and this is a particular problem on boats, where the intake of the compressor cannot be arbitrarily moved as far as desired from the engine and compressor exhausts.
* Heating of lubricants inside the compressor may vaporize them sufficiently to be available to a compressor intake or intake system line.
* In some cases hydrocarbon lubricating oil may be drawn into the compressor's cylinder directly through damaged or worn seals, and the oil may (and usually will) then undergo combustion, being ignited by the immense compression ratio and subsequent temperature rise. Since heavy oils don't burn well – especially when not atomized properly – incomplete combustion will result in carbon monoxide production.
*A similar process is thought to potentially happen to any particulate material, which contains "organic" (carbon-containing) matter, especially in cylinders which are used for hyperoxic gas mixtures. If the compressor air filter(s) fail, ordinary dust
Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ho ...
will be introduced to the cylinder, which contains organic matter (since it usually contains humus). A more severe danger is that air particulates on boats and industrial areas, where cylinders are filled, often contain carbon-particulate combustion products (these are what makes a dirt rag black), and these represent a more severe CO danger when introduced into a cylinder.
Carbon monoxide is generally avoided as far as is reasonably practicable by positioning of the air intake in uncontaminated air, filtration of particulates from the intake air, use of suitable compressor design and appropriate lubricants, and ensuring that running temperatures are not excessive. Where the residual risk is excessive, a hopcalite
Hopcalite is the trade name for a number of mixtures that mainly consist of oxides of copper and manganese, which are used as catalysts for the conversion of carbon monoxide to carbon dioxide when exposed to the oxygen in the air at room temperatu ...
catalyst can be used in the high pressure filter to convert carbon monoxide into carbon dioxide, which is far less toxic.
Hydrocarbons
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s (C''x''H''y'') are present in compressor lubricants and fuels. They can enter diving cylinders as a result of contamination, leaks, or due to incomplete combustion near the air intake.
* They can act as a fuel in combustion increasing the risk of explosion, especially in high-oxygen gas mixtures.
* Inhaling oil mist can damage the lungs and ultimately cause the lungs to degenerate with severe lipid pneumonia or emphysema.
Moisture content
The process of compressing gas into a diving cylinder removes moisture from the gas.[ This is good for ]corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
prevention in the cylinder but means that the diver inhales very dry gas. The dry gas extracts moisture from the diver's lungs while underwater contributing to dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
, which is also thought to be a predisposing risk factor of decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
. It is also uncomfortable, causing a dry mouth and throat and making the diver thirsty. This problem is reduced in rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
s because the soda lime reaction, which removes carbon dioxide, also puts moisture back into the breathing gas,[ and the relative humidity and temperature of exhaled gas is relatively high and there is a cumulative effect due to rebreathing.] In hot climates, open circuit diving can accelerate heat exhaustion Heat exhaustion is a severe form of heat illness. It is a medical emergency. Heat exhaustion is caused by the loss of water and electrolytes through sweating.
The United States Department of Labor makes the following recommendation, "Heat illness ...
because of dehydration. Another concern with regard to moisture content is the tendency of moisture to condense as the gas is decompressed while passing through the regulator; this coupled with the extreme reduction in temperature, also due to the decompression, can cause the moisture to solidify as ice. This icing up in a regulator can cause moving parts to seize and the regulator to fail or free flow.
This is one of the reasons that scuba regulators are generally constructed from brass, and chrome plated (for protection). Brass, with its good thermal conductive properties, quickly conducts heat from the surrounding water to the cold, newly decompressed air, helping to prevent icing up.
Gas analysis
Gas mixtures must generally be analysed either in process or after blending for quality control. This is particularly important for breathing gas mixtures where errors can affect the health and safety of the end user. It is difficult to detect most gases that are likely to be present in diving cylinders because they are colourless, odourless and tasteless. Electronic sensors exist for some gases, such as oxygen analyser
An electro-galvanic fuel cell is an electrochemical device which consumes a fuel to produce an electrical output by a chemical reaction. One form of electro-galvanic fuel cell based on the oxidation of lead is commonly used to measure the concen ...
s, helium analyser, carbon monoxide detector
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas to prevent carbon monoxide poisoning. In the late 1990s Underwriters Laboratories changed the definition of a single station CO de ...
s and carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
detectors.[ Oxygen analysers are commonly found underwater in ]rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
s.[ Oxygen and helium analysers are often used on the surface during ]gas blending
Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled.
A wide range of applications include scientific and industrial processes, food production and storage and ...
to determine the percentage of oxygen or helium in a breathing gas mix.[ Chemical and other types of gas detection methods are not often used in recreational diving, but are used for periodic quality testing of compressed breathing air from diving air compressors.]
Breathing gas standards
Standards for breathing gas quality are published by national and international organisations, and may be enforced in terms of legislation. In the UK, the Health and Safety Executive indicate that the requirements for breathing gases for divers are based on the BS EN 12021:2014.
The specifications are listed for oxygen compatible air, nitrox mixtures produced by adding oxygen, removing nitrogen, or mixing nitrogen and oxygen, mixtures of helium and oxygen (heliox), mixtures of helium, nitrogen and oxygen (trimix), and pure oxygen, for both open circuit and reclaim systems, and for high pressure and low pressure supply (above and below 40 bar supply).
Oxygen content is variable depending on the operating depth, but the tolerance depends on the gas fraction range, being ±0.25% for an oxygen fraction below 10% by volume, ±0.5% for a fraction between 10% and 20%, and ±1% for a fraction over 20%.
Water content is limited by risks of icing of control valves, and corrosion of containment surfaces – higher humidity is not a physiological problem – and is generally a factor of dew point
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...
.
Other specified contaminants are carbon dioxide, carbon monoxide, oil, and volatile hydrocarbons, which are limited by toxic effects. Other possible contaminants should be analysed based on risk assessment, and the required frequency of testing for contaminants is also based on risk assessment.
In Australia breathing air quality is specified by Australian Standard 2299.1, Section 3.13 Breathing Gas Quality.
Diving gas blending
Gas blending (or gas mixing) of breathing gases for diving is the filling of gas cylinders with non-air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
breathing gases.
Filling cylinders with a mixture of gases has dangers for both the filler and the diver. During filling there is a risk of fire due to use of oxygen and a risk of explosion due to the use of high-pressure gases. The composition of the mix must be safe for the depth and duration of the planned dive. If the concentration of oxygen is too lean the diver may lose consciousness due to hypoxia and if it is too rich the diver may develop oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lu ...
. The concentration of inert gases, such as nitrogen and helium, are planned and checked to avoid nitrogen narcosis and decompression sickness.
Methods used include batch mixing by partial pressure or by mass fraction, and continuous blending processes. Completed blends are analysed for composition for the safety of the user. Gas blenders may be required by legislation to prove competence if filling for other persons.
Density
Excessive density of a breathing gas can raise the work of breathing to intolerable levels, and can cause carbon dioxide retention at lower densities. Helium is used as a component to reduce density as well as to reduce narcosis at depth. Like partial pressure, density of a mixture of gases is in proportion to the volumetric fraction of the component gases, and absolute pressure. The ideal gas laws are adequately precise for gases at respirable pressures.
The density of a gas mixture at a given temperature and pressure can be calculated as:
:ρm = (ρ1 V1 + ρ2 V2 + .. + ρn Vn) / (V1 + V2 + ... + Vn)
where
:ρm = density of the gas mixture
:ρ1 ... ρn = density of each of the components
:V1 ... Vn = partial volume of each of the component gases
Since gas fraction Fi (volumetric fraction) of each gas can be expressed as Vi / (V1 + V2 + ... + Vn )
by substitution,
:ρm = (ρ1 F1 + ρ2 F2 + .. + ρn Fn)
Hypobaric breathing gases
Breathing gases for use at reduced ambient pressure are used for high altitude flight in unpressurised aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...
, in space flight
Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in ...
, particularly in space suits
A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...
, and for high altitude mountaineering. In all these cases, the primary consideration is providing an adequate partial pressure of oxygen. In some cases the breathing gas has oxygen added to make up a sufficient concentration, and in other cases the breathing gas may be pure or nearly pure oxygen. Closed circuit systems may be used to conserve the breathing gas, which may be in limited supply – in the case of mountaineering the user must carry the supplemental oxygen, and in space flight the cost of lifting mass into orbit is very high.
Medical breathing gases
Medical use of breathing gases other than air include oxygen therapy and anesthesia applications.
Oxygen therapy
upA person wearing a simple face mask for ">oxygen therapy
Oxygen is required by people for normal cell metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. Air is typically 21% oxygen by volume. This is normally sufficient, but in some circumstances the oxygen supply to tissues is compromised.
Oxygen therapy, also known as supplemental oxygen, is the use of oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
as a medical treatment. This can include for low blood oxygen, carbon monoxide toxicity, cluster headache
Cluster headache (CH) is a neurological disorder characterized by recurrent severe headaches on one side of the head, typically around the eye(s). There is often accompanying eye watering, nasal congestion, or swelling around the eye on the af ...
s, and to maintain enough oxygen while inhaled anesthetics
An inhalational anesthetic is a chemical compound possessing general anesthetic properties that can be delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vapo ...
are given. Long term oxygen is often useful in people with chronically low oxygen such as from severe COPD
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
or cystic fibrosis.[ Oxygen can be given in a number of ways including ]nasal cannula
The nasal cannula (NC) is a device used to deliver supplemental oxygen or increased airflow to a patient or person in need of respiratory help. This device consists of a lightweight tube which on one end splits into two prongs which are place ...
, face mask, and inside a hyperbaric chamber
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
.
High concentrations of oxygen can cause oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lu ...
such as lung damage or result in respiratory failure
Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
in those who are predisposed.[ It can also dry out the nose and increase the risk of fires in those who ]smoke
Smoke is a suspension of airborne 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-produc ...
. The target oxygen saturation
Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
recommended depends on the condition being treated. In most conditions a saturation of 94-98% is recommended, while in those at risk of carbon dioxide retention
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pr ...
saturations of 88-92% are preferred, and in those with carbon monoxide toxicity or cardiac arrest
Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and poss ...
the saturation should be as high as possible.[
The use of oxygen in medicine become common around 1917.] It is on the World Health Organization's List of Essential Medicines
The WHO Model List of Essential Medicines (aka Essential Medicines List or EML), published by the World Health Organization (WHO), contains the medications considered to be most effective and safe to meet the most important needs in a health s ...
. The cost of home oxygen is about US$150 a month in Brazil and US$400 a month in the United States. Home oxygen can be provided either by oxygen tanks
An oxygen tank is an oxygen storage vessel, which is either held under pressure in gas cylinders, or as liquid oxygen in a cryogenic storage tank.
Uses
Oxygen tanks are used to store gas for:
* medical breathing at medical facilities and at home ...
or an oxygen concentrator
An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream. They are used industrially and as medical devices for oxy ...
.[ Oxygen is believed to be the most common treatment given in hospitals in the ]developed world
A developed country (or industrialized country, high-income country, more economically developed country (MEDC), advanced country) is a sovereign state that has a high quality of life, developed economy and advanced technological infrastruct ...
.[
]
Anaesthetic gases
upAn anaesthetic machine.
The most common approach to general anaesthesia is through the use of inhaled general anesthetics. Each has its own potency which is correlated to its solubility in oil. This relationship exists because the drugs bind directly to cavities in proteins of the central nervous system, although several theories of general anaesthetic action
A general anaesthetic (or anesthetic) is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anesthesiologist in order to induce or maintain general anaesthesia to facilitate surge ...
have been described. Inhalational anesthetics are thought to exact their effects on different parts of the central nervous system. For instance, the immobilizing effect of inhaled anesthetics results from an effect on the spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
whereas sedation, hypnosis and amnesia involve sites in the brain.
An inhalational anaesthetic is a chemical compound possessing general anaesthetic
General anaesthetics (or anesthetics, see spelling differences) are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced com ...
properties that can be delivered via inhalation. Agents of significant contemporary clinical interest include volatile anaesthetic agents such as isoflurane, sevoflurane and desflurane, and anaesthetic gases such as nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has ...
and xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
.
Administration
Anaesthetic gases are administered by anaesthetists (a term which includes anaesthesiologists, nurse anaesthetists, and anaesthesiologist assistants) through an anaesthesia mask, laryngeal mask airway
A laryngeal mask airway (LMA), also known as laryngeal mask, is a medical device that keeps a patient's Respiratory tract, airway open during anaesthesia or while they are Unconsciousness, unconscious. It is a type of supraglottic airway device. ...
or tracheal tube
A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide.
Many different types of tracheal tubes are ...
connected to an anaesthetic vaporiser
An anesthetic vaporizer (American English) or anaesthetic vaporiser (British English) is a device generally attached to an anesthetic machine which delivers a given concentration of a volatile anesthetic agent. It works by controlling the vap ...
and an anaesthetic delivery system.
The anaesthetic machine (UK English) or anesthesia machine (US English) or Boyle's machine is used to support the administration of anaesthesia
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), a ...
. The most common type of anaesthetic machine in use in the developed world is the continuous-flow anaesthetic machine, which is designed to provide an accurate and continuous supply of medical gases (such as oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has ...
), mixed with an accurate concentration of anaesthetic vapour (such as isoflurane), and deliver this to the patient at a safe pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
and flow. Modern machines incorporate a ventilator
A ventilator is a piece of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. Ventilators ...
, suction unit, and patient monitoring devices. Exhaled gas is passed through a scrubber to remove carbon dioxide, and the anaesthetic vapour and oxygen are replenished as required before the mixture is returned to the patient.
See also
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References
External links
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{{DEFAULTSORT:Breathing Gas
Industrial gases