Nitrogen narcosis
Overview
 


Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect), is a reversible alteration in 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...

 that occurs while scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

 at depth. The Greek word ναρκωσις (narcosis) is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer
Homer
In the Western classical tradition Homer , is the author of the Iliad and the Odyssey, and is revered as the greatest ancient Greek epic poet. These epics lie at the beginning of the Western canon of literature, and have had an enormous influence on the history of literature.When he lived is...

 and Hippocrates
Hippocrates
Hippocrates of Cos or Hippokrates of Kos was an ancient Greek physician of the Age of Pericles , and is considered one of the most outstanding figures in the history of medicine...

. Narcosis produces a state similar to alcohol intoxication
Drunkenness
Alcohol intoxication is a physiological state that occurs when a person has a high level of ethanol in his or her blood....

 or nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

 inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 metres (98.4 ft).

Apart from helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

, and probably neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

, all gases that can be breathed
Breathing 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...

 have a narcotic effect, which is greater as the lipid solubility of the gas increases.
Encyclopedia
Some components of breathing gases, and their relative narcotic potentcies
Gas Relative narcotic potency
Ne
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

0.3
H2
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

0.6
N2
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

1.0
O2
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

1.7
Ar
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

2.3
Kr
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...

7.1
CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

20.0
Xe
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

25.6


Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect), is a reversible alteration in 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...

 that occurs while scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

 at depth. The Greek word ναρκωσις (narcosis) is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer
Homer
In the Western classical tradition Homer , is the author of the Iliad and the Odyssey, and is revered as the greatest ancient Greek epic poet. These epics lie at the beginning of the Western canon of literature, and have had an enormous influence on the history of literature.When he lived is...

 and Hippocrates
Hippocrates
Hippocrates of Cos or Hippokrates of Kos was an ancient Greek physician of the Age of Pericles , and is considered one of the most outstanding figures in the history of medicine...

. Narcosis produces a state similar to alcohol intoxication
Drunkenness
Alcohol intoxication is a physiological state that occurs when a person has a high level of ethanol in his or her blood....

 or nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

 inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 metres (98.4 ft).

Apart from helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

, and probably neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

, all gases that can be breathed
Breathing 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...

 have a narcotic effect, which is greater as the lipid solubility of the gas increases. As depth increases, the effects may become hazardous as the diver is increasingly impaired. Although divers can learn to cope with the effects, it is not possible to develop a tolerance. While narcosis affects all divers, predicting the depth at which narcosis will affect a diver is difficult, as susceptibility varies widely from dive to dive and amongst individuals.

The condition is completely reversed by ascending to a shallower depth with no long-term effects. For this reason, narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms and ascend to manage it. Diving beyond 40 m (131.2 ft) is considered outside the scope of recreational diving
Recreational diving
Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...

: as narcosis and oxygen toxicity
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...

 become critical factors, specialist training is required in the use of various gas mixtures such as trimix or heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...

.

Classification

Narcosis results from breathing gases under elevated pressure and may be classified by the principal gas involved. The noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

es, except helium and probably neon, as well as nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 cause a decrement in mental function
Mental function
Mental processes, mental functions and cognitive processes are terms often used interchangeably to mean such functions or processes as perception, introspection, memory, creativity, imagination, conception, belief, reasoning, volition, and emotion—in...

, but their effect on psychomotor
Psychomotor
Psychomotor can refer to:* Psychomotor learning* Psychomotor retardation* Psychomotor agitation...

 function (processes affecting the coordination of sensory or cognitive processes and motor activity) varies widely. The effects of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 consistently result in a decrease of both mental and psychomotor function. The noble gases argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

, krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...

, and xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

 are more narcotic than nitrogen at a given pressure, and xenon has so much anesthetic activity that it is actually a usable anesthetic at 80% concentration and normal atmospheric pressure. Xenon has historically been too expensive to be used very much in practice, but it has been successfully used for surgical operations, and xenon anesthesia systems are still being proposed and designed.

Signs and symptoms

Due to its perception-altering effects, the onset of narcosis may be hard to recognize. At its most benign, narcosis results in relief of anxiety - a feeling of tranquility and mastery of the environment. These effects are essentially identical to various concentrations of nitrous oxide. They also resemble (though not as closely) the effects of alcohol and the familiar benzodiazepine
Benzodiazepine
A benzodiazepine is a psychoactive drug whose core chemical structure is the fusion of a benzene ring and a diazepine ring...

 drugs such as diazepam
Diazepam
Diazepam , first marketed as Valium by Hoffmann-La Roche is a benzodiazepine drug. Diazepam is also marketed in Australia as Antenex. It is commonly used for treating anxiety, insomnia, seizures including status epilepticus, muscle spasms , restless legs syndrome, alcohol withdrawal,...

 and alprazolam
Alprazolam
Alprazolam is a short-acting anxiolytic of the benzodiazepine class of psychoactive drugs. Alprazolam, like other benzodiazepines, binds to specific sites on the GABAA gamma-amino-butyric acid receptor...

. Such effects are not harmful unless they cause some immediate danger not to be recognized and addressed. Once stabilized, the effects generally remain the same at a given depth, only worsening if the diver ventures deeper.

The most dangerous aspects of narcosis are the loss of decision-making ability and focus, and impaired judgement, multi-tasking and coordination. Other effects include vertigo
Vertigo (medical)
Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...

, and visual or auditory disturbances. The syndrome
Syndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...

 may cause exhilaration, giddiness, extreme anxiety, depression, or paranoia
Paranoia
Paranoia [] is a thought process believed to be heavily influenced by anxiety or fear, often to the point of irrationality and delusion. Paranoid thinking typically includes persecutory beliefs, or beliefs of conspiracy concerning a perceived threat towards oneself...

, depending on the individual diver and the diver's medical or personal history. When more serious, the diver may feel overconfident, disregarding normal safe diving practices.

The relation of depth to narcosis is sometimes informally known as "Martini's law". This is the idea that narcosis results in the feeling of one martini
Martini (cocktail)
The martini is a cocktail made with gin and vermouth, and garnished with an olive or a lemon twist. Over the years, the martini has become one of the best-known mixed alcoholic beverages. H. L. Mencken called the martini "the only American invention as perfect as the sonnet" and E. B...

 for every 10 m (32.8 ft) below 20 m (65.6 ft) depth. This is a very rough guide, and not a substitute for an individual diver's known susceptibility
Susceptible individual
In epidemiology a susceptible individual is a member of a population who is at risk of becoming infected by a disease, or can not take a certain medicine, antibiotic, etc if he or she is exposed to the infectious agent....

, or for standard diving safety guides. Professional divers use such a calculation only as a rough guide to give new divers a metaphor, comparing a situation they may be more familiar with.

Reported signs and symptoms are summarized against typical depths in meters and feet of sea water in the following table:
Signs and symptoms of narcosis (breathing air)
Pressure (bar) Depth (m) Depth (ft) Comments
1–2 0–10 0-33 Unnoticeable small symptoms, or no symptoms at all.
2–4 10–30 33–100 Mild impairment of performance of unpracticed tasks.
Mildly impaired reasoning.
Mild euphoria
Euphoria (emotion)
Euphoria is medically recognized as a mental and emotional condition in which a person experiences intense feelings of well-being, elation, happiness, ecstasy, excitement and joy...

 possible.
4–6 30–50 100–165 Delayed response to visual and auditory stimuli.
Reasoning and immediate memory affected more than motor coordination.
Calculation errors and wrong choices.
Idea fixation.
Over-confidence and sense of well-being.
Laughter and loquacity (in chambers) which may be overcome by self control.
Anxiety (common in cold murky water).
6–8 50–70 165–230 Sleepiness, impaired judgment, confusion.
Hallucinations.
Severe delay in response to signals, instructions and other stimuli.
Occasional dizziness.
Uncontrolled laughter, hysteria
Hysteria
Hysteria, in its colloquial use, describes unmanageable emotional excesses. People who are "hysterical" often lose self-control due to an overwhelming fear that may be caused by multiple events in one's past that involved some sort of severe conflict; the fear can be centered on a body part, or,...

 (in chamber).
Terror in some.
8–10 70–90 230–300 Poor concentration and mental confusion.
Stupefaction with some decrease in dexterity and judgment.
Loss of memory, increased excitability.
10+ 90+ 300+ Hallucinations.
Increased intensity of vision and hearing.
Sense of impending blackout, euphoria, dizziness, manic
Mania
Mania, the presence of which is a criterion for certain psychiatric diagnoses, is a state of abnormally elevated or irritable mood, arousal, and/ or energy levels. In a sense, it is the opposite of depression...

 or depressive states, a sense of levitation
Levitation
Levitation is the process by which an object is suspended by a physical force against gravity, in a stable position without solid physical contact...

, disorganization of the sense of time, changes in facial appearance.
Unconsciousness. Death.

Causes

The cause of narcosis is related to the increased solubility of gases in body tissues, as a result of the elevated pressures at depth (Henry's law
Henry's law
In physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid...

).
Modern theories have suggested that inert gases dissolving in the lipid bilayer
Lipid bilayer
The lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus...

 of cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

s cause narcosis.
More recently, researchers have been looking at neurotransmitter receptor
Neurotransmitter receptor
A Neurotransmitter receptor is a membrane receptor protein that is activated by a Neurotransmitter. A membrane protein interacts with the lipid bilayer that encloses the cell and a membrane receptor protein interacts with a chemical in the cells external environment, which binds to the cell...

 protein mechanisms as a possible cause of the narcosis.
The breathing gas mix entering the diver's lung
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...

s will have the same pressure as the surrounding water, known as the ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....

. For any given depth, the pressure of gases in the blood passing through the brain catches up with ambient pressure within a minute or two and this produces a delay in narcotic effect after coming to a new depth.
Rapid compression potentiates narcosis, owing to carbon dioxide retention.

A divers' cognition
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...

 may be affected on dives as shallow as 10 m (32.8 ft), but the changes are not usually noticeable.
However there is no reliable method to predict the depth at which narcosis becomes noticeable, or the severity of the effect on an individual diver, as the effect may vary from dive to dive (even on the same day).

Significant impairment due to narcosis is an increasing risk below depths of about 30 m (98.4 ft), corresponding to an ambient pressure of about 4 bar (400,000 Pa). Most sport scuba training organizations recommend depths of no more than 40 m (131.2 ft) because of risk of narcosis. When breathing air at depths of 90 m (295.3 ft)—an ambient pressure of about 10 bar (1,000,000 Pa)—narcosis in most divers leads to hallucinations, loss of memory, and unconsciousness. A number of divers have died in attempts to set air depth records below 120 m (393.7 ft). Because of these incidents, the Guinness Book of World Records no longer reports on this figure.

Narcosis has been compared with altitude sickness
Altitude sickness
Altitude sickness—also known as acute mountain sickness , altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude...

 insofar as its variability (though not its symptoms); its effects depend on many factors, with variations between individuals. Thermal cold, stress
Stress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...

, heavy work, fatigue, and carbon dioxide retention all increase the risk and severity of narcosis. Carbon dioxide has a high narcotic potential and also causes increased blood flood to the brain, increasing the effects of other gases. Increased risk of narcosis results from increasing the amount of carbon dioxide retained through heavy exercise, shallow or skip breathing, or because of poor gas exchange in the lungs.

Narcosis is known to be additive to even minimal alcohol intoxication, and also to the effects of other drugs such as marijuana
Cannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...

 (which is more likely than alcohol to have effects which last into a day of abstinence from use). Other sedative
Sedative
A sedative or tranquilizer is a substance that induces sedation by reducing irritability or excitement....

 and analgesic
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

 drugs, such as opiate
Opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...

 narcotics and benzodiazepines, add to narcosis.

Mechanism

The precise mechanism is not well understood, but it appears to be the direct effect of gas dissolving into nerve membranes and causing temporary disruption in nerve transmissions. While the effect was first observed with air, other gases including argon, krypton and hydrogen cause very similar effects at higher than atmospheric pressure. Some of these effects may be due to antagonism
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

 at NMDA
NMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...

 receptors and potentiation of GABAA receptors, similar to the mechanism of nonpolar anesthetics such diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

 or ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

. However, their reproduction by the very chemically inactive gas argon makes them unlikely to be a strictly chemical bonding to receptors in the usual sense of a chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

. An indirect physical effect—such as a change in membrane volume—would therefore be needed to affect the ligand-gated ion channel
Ligand-gated ion channel
Ligand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...

s of nerve cells. Trudell et al. have suggested non-chemical binding due to the attractive van der Waals force
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

 between proteins and inert gases.

Similar to the mechanism of ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

's effect, the increase of gas dissolved in nerve cell membranes may cause altered ion permeability
Semipermeable membrane
A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...

 properties of the neural cells' lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

 bilayers. The partial pressure of a gas required to cause a measured degree of impairment correlates well with the lipid solubility of the gas: the greater the solubility, the less partial pressure is needed.

An early theory, the Meyer-Overton hypothesis suggested that narcosis happens when the gas penetrates the lipids of the brain's nerve cells, causing direct mechanical interference with the transmission of signals from one nerve cell to another. More recently, specific types of chemically-gated receptors in nerve cells have been identified as being involved with anesthesia and narcosis. However, the basic and most general underlying idea, that nerve transmission is altered in many diffuse areas of the brain as a result of gas molecules dissolved in the nerve cells' fatty membranes, remains largely unchallenged.

Diagnosis and management

The symptoms described may be caused by other factors during a dive: ear problems causing disorientation or nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

; early signs of oxygen toxicity causing visual disturbances; or hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

 causing rapid breathing and shivering. Nevertheless the presence of any of these symptoms should imply narcosis. Alleviation of the effects upon ascending to a shallower depth will confirm the diagnosis. Given the setting, other likely conditions do not produce reversible effects. In the rare event of misdiagnosis when another condition is causing the symptoms, the initial management—ascending closer to the surface—is still essential.

The management of narcosis is simply to ascend to shallower depths; the effects then disappear within minutes. In the event of complications or other conditions being present, ascending is always the correct initial response. Should problems remain, then it is necessary to abort the dive. The decompression schedule can still be followed unless other conditions require emergency assistance.

Prevention

The most straightforward way to avoid nitrogen narcosis is for a diver to limit the depth of dives. If narcosis does occur, the effects disappear almost immediately upon ascending to a shallower depth. Since narcosis becomes more severe as depth increases, a diver keeping to shallower depths can avoid serious narcosis. Most recreational dive schools will only certify basic divers to depths of 18 m (59.1 ft), and at these depths narcosis does not present a large risk. Further training is normally required for certification up to 30 m (98.4 ft) on air, and this training should include a discussion of narcosis, its effects, and cure. Some diver training agencies offer specialty training to prepare recreational divers to go to depths of 40 m (131.2 ft), often consisting of further theory and some practice in deep dives with close supervision.A number of technical diving agencies, such as TDI
Technical Diving International
Technical Diving International is the largest technical diving certification agency in the world. As one of the first agencies to provide training in mixed gas diving and rebreathers, TDI is seen as an innovator of new diving techniques and programs which previously were not available to the...

 and IANTD
International Association of Nitrox and Technical Divers
International Association of Nitrox and Technical Divers is a SCUBA diving organization concerned with certification and training in Enriched Air Nitrox diving, Technical diving and Free diving.- History :...

 teach "extended range" or "deep air" courses which teach diving to depths of up to 55 m (180.4 ft) without helium.

Scuba organizations which train for diving beyond recreational depths,BSAC, SAA
Sub-Aqua Association
The Sub-Aqua Association or SAA is a diver training organization for scubadivers in the United Kingdom. The association and some other UK-based diving groups have traditionally used a club-based system with unpaid instructors, while the other principal training agency, PADI, organises most of its...

 and other European training agencies teach recreational diving to a depth limit of 50 m (164 ft).
may forbid diving with gases that cause too much narcosis at depth in the average diver, and strongly encourage the use of other breathing gas
Breathing 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...

 mixes containing helium in place of some or all of the nitrogen in air—such as trimix and heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...

—because helium has no narcotic potential. The use of these gases forms part of technical diving
Technical diving
Technical diving is a form of scuba diving that exceeds the scope of recreational diving...

 and requires further training and certification.

While the individual diver cannot predict exactly at what depth the onset of narcosis will occur on a given day, the first symptoms of narcosis for any given diver are often more predictable and personal. For example, one diver may have trouble with eye focus (close accommodation for middle-aged divers), another may experience feelings of euphoria, and another feelings of claustrophobia
Claustrophobia
Claustrophobia is the fear of having no escape and being closed in small spaces or rooms...

. Some divers report that they have hearing changes, and that the sound which their exhaled bubbles make becomes different. Specialist training may help divers to identify these personal onset signs, and these may then be used as a signal to ascend to shallower depths. Although severe narcosis may interfere with the judgment necessary to take preventive action, a diver who remains calm and is alert to the danger will be capable of resolving these problems at an earlier stage.

Deep dives should be made only after a gradual training to gradually test the individual diver's sensitivity to increasing depths, with careful supervision and logging of reactions. Diving organizations such as Global Underwater Explorers
Global Underwater Explorers
Global Underwater Explorers is a scuba diving organization that provides education within recreational, technical and cave diving. It is a not-for-profit, membership organization, based in High Springs, Florida, United States....

 (GUE) emphasize that such sessions are for the purpose of gaining experience in recognizing the onset symptoms of narcosis for an individual, which are somewhat more repeatable than for the average group of divers. Scientific evidence does not show that a diver can train to overcome any measure of narcosis at a given depth or become tolerant of it.

Equivalent narcotic depth
Equivalent narcotic depth
Equivalent narcotic depth is used in technical diving as a way of estimating the narcotic effect of a breathing gas mixture, such as heliox and trimix...

 (END) is a commonly used way of expressing the narcotic effect of different breathing gases.
The National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 (NOAA) Diving Manual now states that both oxygen and nitrogen should be considered equally narcotic.
Standard tables, based on relative lipid solubilities, list conversion factors for narcotic effect of other gases. For example, neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

 at a given pressure has a narcotic effect equivalent to nitrogen at 0.28 times that pressure, so in principle it should be usable at nearly four times the depth. Argon, however, has 2.33 times the narcotic effect of nitrogen, and is not suitable as a breathing gas for diving (it is used as a drysuit inflation gas, owing to its low thermal conductivity). Some gases have other dangerous effects when breathed at pressure; for example, high-pressure oxygen can lead to oxygen toxicity
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...

. Although helium is the least intoxicating of the breathing gases, at greater depths it can cause high pressure nervous syndrome
High pressure nervous syndrome
High-pressure nervous syndrome is a neurological and physiological diving disorder that results when a commercial diver or scuba diver descends below about while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth...

, a still-mysterious but apparently unrelated phenomenon. Inert gas narcosis is only one factor which influences the choice of gas mixture; the risks of decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...

 and oxygen toxicity, cost, and other factors are also important.

Because of similar and additive effects, divers should avoid sedating medications and drugs, such as marijuana and alcohol before any dive. A hangover, combined with the reduced physical capacity that goes with it, makes nitrogen narcosis more likely. Experts recommend total abstinence from alcohol at least 12 hours before diving, and longer for other drugs. Abstinence time needed for marijuana is unknown, but due to the much longer half-life of the active agent of this drug in the body, it is likely to be longer than for alcohol.

Prognosis and epidemiology

Narcosis is potentially one of the most dangerous conditions to affect the scuba diver below about 30 m (98.4 ft). Except for occasional amnesia of events at depth, the effects of narcosis are entirely reversible by ascending and therefore pose no problem in themselves, even for repeated, chronic or acute exposure. Nevertheless, the severity of narcosis is unpredictable and it can be fatal while diving, as the result of illogical behavior in a dangerous environment.

Tests have shown that all divers are affected by nitrogen narcosis, though some are less affected than others.
Even though it is possible that some divers can manage better than others because of learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...

 to cope with the subjective
Subjectivity
Subjectivity refers to the subject and his or her perspective, feelings, beliefs, and desires. In philosophy, the term is usually contrasted with objectivity.-Qualia:...

 impairment, the underlying behavioral effects remain. These effects are particularly dangerous because a diver may feel they are not experiencing narcosis, yet still be affected by it.

History


French researcher Victor T. Junod was the first to describe symptoms of narcosis in 1834, noting "the functions of the brain are activated, imagination is lively, thoughts have a peculiar charm and, in some persons, symptoms of intoxication are present." Junod suggested that narcosis resulted from pressure causing increased blood flow and hence stimulating nerve centers.
Walter Moxon (1836–1886), a prominent Victorian physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...

, hypothesized in 1881 that pressure forced blood to inaccessible parts of the body and the stagnant blood then resulted in emotional changes.
The first report of anesthetic potency being related to lipid solubility was published by Hans H. Meyer in 1899, entitled Zur Theorie der Alkoholnarkose. Two years later a similar theory was published independently by Charles Ernest Overton. What became known as the Meyer-Overton Hypothesis is illustrated in the diagram to the right.

In 1939, Albert R. Behnke
Albert R. Behnke
Captain Albert Richard Behnke Jr. USN was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute...

 and O. D. Yarborough demonstrated that gases other than nitrogen also could cause narcosis.
For an inert gas the narcotic potency was found to be proportional to its lipid solubility. As hydrogen has only 0.55 the solubility of nitrogen, deep diving experiments using hydrox
Hydrox (breathing gas)
Hydrox, a gas mixture of hydrogen and oxygen, is used as a breathing gas in very deep diving. It allows divers to descend several hundred metres....

 were conducted by Arne Zetterström
Arne Zetterström
Arne Zetterström is best known for his research with the breathing mixture hydrox for the Swedish Navy.Zetterström first described the use of hydrogen as a breathing gas in 1943...

 between 1943 and 1945. Jacques-Yves Cousteau
Jacques-Yves Cousteau
Jacques-Yves Cousteau was a French naval officer, explorer, ecologist, filmmaker, innovator, scientist, photographer, author and researcher who studied the sea and all forms of life in water...

 in 1953 famously described it as "l’ivresse des grandes profondeurs" or the "rapture of the deep".

Further research into the possible mechanisms of narcosis by anesthetic action led to the "minimum alveolar concentration
Minimum alveolar concentration
Minimum alveolar concentration or MAC is a concept used to compare the strengths, or potency, of anaesthetic vapours; in simple terms, it is defined as the concentration of the vapour in the lungs that is needed to prevent movement in 50% of subjects in response to surgical stimulus...

" concept in 1965. This measures the relative concentration of different gases required to prevent motor response
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

 in 50% of subjects in response to stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

, and shows similar results for anesthetic potency as the measurements of lipid solubility. The (NOAA) Diving Manual was revised to recommend treating oxygen as if it were as narcotic as nitrogen, following research by Christian J. Lambertsen
Christian J. Lambertsen
Christian James Lambertsen was an American environmental medicine and diving medicine specialist who was principally responsible for developing the United States Navy frogmen's rebreathers in the early 1940s for underwater warfare...

et al. in 1977 and 1978.

External links

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