Inert Gas Narcosis
   HOME

TheInfoList



OR:

Nitrogen narcosis (also known as narcosis while diving, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in
consciousness Consciousness, at its simplest, is awareness of a state or object, either internal to oneself or in one's external environment. However, its nature has led to millennia of analyses, explanations, and debate among philosophers, scientists, an ...
that occurs while
diving Diving most often refers to: * Diving (sport), the sport of jumping into deep water * Underwater diving, human activity underwater for recreational or occupational purposes Diving or Dive may also refer to: Sports * Dive (American football), ...
at depth. It is caused by the
anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...
effect of certain gases at high
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
. The Greek word (narkōsis), "the act of making numb", is derived from (narkē), "numbness, torpor", a term used by
Homer Homer (; , ; possibly born ) was an Ancient Greece, Ancient Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Despite doubts about his autho ...
and
Hippocrates Hippocrates of Kos (; ; ), also known as Hippocrates II, was a Greek physician and philosopher of the Classical Greece, classical period who is considered one of the most outstanding figures in the history of medicine. He is traditionally referr ...
. Narcosis produces a state similar to
drunkenness Alcohol intoxication, commonly described in higher doses as drunkenness or inebriation, and known in overdose as alcohol poisoning, is the behavior and physical effects caused by recent consumption of alcohol. The technical term ''intoxication ...
(alcohol intoxication), or
nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room te ...
inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than . Except for
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
and probably
neon Neon is a chemical element; it has symbol Ne and atomic number 10. It is the second noble gas in the periodic table. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with approximately two-thirds the density of ...
, all gases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higher lipid solubility, and although the mechanism of this phenomenon is still not fully clear, there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop a tolerance. Narcosis can affect all ambient pressure divers, although susceptibility varies widely among individuals and from dive to dive. The main modes of underwater diving that deal with its prevention and management are
scuba diving Scuba diving is a Diving mode, mode of underwater diving whereby divers use Scuba set, breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The word ''scub ...
and
surface-supplied diving Surface-supplied diving is a mode of underwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. ...
at depths greater than . Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond is generally considered outside the scope of
recreational diving Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasur ...
. To dive at greater depths, as narcosis and
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, lung ...
become critical risk factors, gas mixtures such as trimix or
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 this mixture generates less resistance than atmospheric air when passing through the airways of ...
are used. These mixtures prevent or reduce narcosis by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium. There is a synergy between carbon dioxide toxicity and inert gas narcosis which is recognised but not fully understood. Conditions where high work of breathing due to gas density occur tend to exacerbate this effect.


Classification

Narcosis results from breathing gases under elevated pressure, and may be classified by the principal gas involved. The
noble gas The noble gases (historically the inert gases, sometimes referred to as aerogens) are the members of Group (periodic table), group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and, in some ...
es, except
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
and probably
neon Neon is a chemical element; it has symbol Ne and atomic number 10. It is the second noble gas in the periodic table. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with approximately two-thirds the density of ...
, as well as
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
,
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
and
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
cause a decrement in
mental function Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, i ...
, but their effect on psychomotor function (processes affecting the coordination of sensory or cognitive processes and motor activity) varies widely. The effect of
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
is a consistent diminution of mental and psychomotor function. The noble gases
argon Argon is a chemical element; it has 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 abu ...
,
krypton Krypton (from 'the hidden one') is a chemical element; it has symbol (chemistry), symbol Kr and atomic number 36. It is a colorless, odorless noble gas that occurs in trace element, trace amounts in the Earth's atmosphere, atmosphere and is of ...
, and
xenon Xenon is a chemical element; it has 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 ...
are more narcotic than nitrogen at a given pressure, and xenon has so much
anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...
activity that it is 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 tranquillity 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 Benzodiazepines (BZD, BDZ, BZs), colloquially known as "benzos", are a class of central nervous system (CNS) depressant, depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed t ...
drugs such as
diazepam Diazepam, sold under the brand name Valium among others, is a medicine of the benzodiazepine family that acts as an anxiolytic. It is used to treat a range of conditions, including anxiety disorder, anxiety, seizures, alcohol withdrawal syndr ...
and
alprazolam Alprazolam, sold under the brand name Xanax among others, is a fast-acting, potent tranquilizer of moderate duration within the triazolobenzodiazepine group of chemicals called benzodiazepines. Alprazolam is most commonly prescribed in the ...
. Such effects are not harmful unless they cause some immediate danger to go unrecognized and unaddressed. 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 impairment of judgement, multi-tasking and coordination, and the loss of decision-making ability and focus. Other effects include
vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...
and visual or auditory disturbances. The
syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek language, Greek σύνδρομον, meaning "concurrence". When a sy ...
may cause exhilaration, giddiness, extreme anxiety, depression, or
paranoia Paranoia is an instinct or thought process that is believed to be heavily influenced by anxiety, suspicion, or fear, often to the point of delusion and irrationality. Paranoid thinking typically includes persecutory beliefs, or beliefs of co ...
, 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. Slowed mental activity, as indicated by increased reaction time and increased errors in cognitive function, are effects which increase the risk of a diver mismanaging an incident. Narcosis reduces both the perception of cold discomfort and shivering and thereby affects the production of body heat and consequently allows a faster drop in the core temperature in cold water, with reduced awareness of the developing problem. The relation of depth to narcosis is sometimes informally known as "Martini's law", the idea that narcosis results in the feeling of one martini for every below depth. This is a rough guide to give new divers a comparison with 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, closely adapted from ''Deeper into Diving'' by Lippman and Mitchell:


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 In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional at equilibrium to its partial pressure above the liquid. The proportionality factor is called Henry's law constant ...
). It has been suggested that inert gases dissolving in the
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cell (biology), cells. The cell membranes of almost all organisms and many viruses a ...
of
cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
s cause narcosis. More recently, researchers have been looking at
neurotransmitter receptor A neurotransmitter receptor (also known as a neuroreceptor) is a membrane receptor protein that is activated by a neurotransmitter. Chemicals on the outside of the cell, such as a neurotransmitter, can bump into the cell's membrane, in which the ...
protein mechanisms as a possible cause of narcosis. The breathing gas mix entering the diver's
lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
s will have the same pressure as the surrounding water, known as the
ambient pressure The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, in contact with the object. Atmosphere Within the atmosphere, the ambient pressure decreases as elevation increases. By measuring ambient atmosp ...
. After a change of depth, the partial pressure of inert gases in the blood passing through the brain catches up with ambient pressure within a minute or two, which results in a delayed change in narcotic effect after descending to a new depth. Rapid compression potentiates narcosis owing to carbon dioxide retention. A divers'
cognition Cognition is the "mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
may be affected on dives as shallow as , but the changes are not usually noticeable. 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 it may vary from dive to dive even on the same day. Significant impairment due to narcosis is an increasing risk below depths of about , corresponding to an ambient pressure of about . Most sport scuba training organizations recommend depths of no more than because of the risk of narcosis. When breathing air at depths of  – an ambient pressure of about  – 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 . Because of these incidents, ''
Guinness World Records ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a British reference book published annually, list ...
'' no longer reports on this figure. Narcosis has been compared with
altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is a harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People's bodies can respond to high altitude in different wa ...
regarding its variability of onset (though not its symptoms); its effects depend on many factors, with variations between individuals. Thermal cold, stress, 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 flow 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, high
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 ...
, or because of poor gas exchange in the lungs. Narcosis is known to be additive to even minimal alcohol intoxication. Other
sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or Psychomotor agitation, excitement. They are central nervous system (CNS) Depressant, depressants and interact with brain activity, causing its decelera ...
and
analgesic An analgesic drug, also called simply an analgesic, antalgic, pain reliever, or painkiller, is any member of the group of drugs used for pain management. Analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in s ...
drugs, such as
opiate An opiate is an alkaloid substance derived from opium (or poppy straw). It differs from the similar term ''opioid'' in that the latter is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain ( ...
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 at
NMDA ''N''-methyl--aspartic acid, or ''N''-methyl--aspartate (NMDA), is an amino acid derivative that acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor. Unl ...
receptors and potentiation of GABAA receptors, similar to the mechanism of
nonpolar In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar ...
anesthetics such
diethyl ether Diethyl ether, or simply ether, is an organic compound with the chemical formula , sometimes abbreviated as . It is a colourless, highly Volatility (chemistry), volatile, sweet-smelling ("ethereal odour"), extremely flammable liquid. It belongs ...
or
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
. 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 A chemical bond is the association of atoms or ions to form molecules, crystals, and other structures. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons a ...
. 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 channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as sodium, Na+, potassium, K+, calcium, Ca2+, and/or chloride, Cl− to ...
s of nerve cells. Trudell ''et al.'' have suggested non-chemical binding due to the attractive
van der Waals force In molecular physics and chemistry, the van der Waals force (sometimes van der Waals' force) is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical elec ...
between proteins and inert gases. Similar to the mechanism of
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
's effect, the increase of gas dissolved in nerve cell membranes may cause altered ion permeability properties of the neural cells'
lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
bilayers. The
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
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 of narcosis may be caused by other factors during a dive: ear problems causing disorientation or
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
; early signs of oxygen toxicity causing visual disturbances; carbon dioxide toxicity caused by rebreather scrubber malfunction, excessive work of breathing, or inappropriate breathing pattern, or
hypothermia Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...
causing rapid breathing and shivering. Nevertheless, the presence of any of these symptoms can 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 event of misdiagnosis when another condition is causing the symptoms, the initial management – ascending to a shallower depth – is still beneficial in most cases, as it is also the appropriate response for most of the alternative causes for the symptoms. The management of inert gas narcosis is usually simply to ascend to shallower depths, where much of the effect disappears within minutes. Divers carrying multiple gas mixtures will usually switch to a mixture with more helium before significant narcosis is noticeable during descent. In the event of complications or other conditions being present, ascending remains the correct initial response unless it would violate decompression obligations. Should problems persist, it may be necessary to abort the dive. The decompression schedule can and should still be followed unless other conditions require emergency assistance. Inert gas narcosis can follow a gas switch to a decompression gas with higher nitrogen fraction during ascent, which may be confused with symptoms of
decompression sickness Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
, in a rare example of a situation in which it is not advisable to ascend immediately. If this is suspected to be the problem, it is better to switch back to the less narcotic gas if practicable, and adjust the decompression schedule to suit. This problem can be aggravated by the possibility of inert gas counterdiffusion, which is most likely to affect the inner ear, and can usually be avoided by a better selection of gas mixtures and switching depths.


Prevention

The most straightforward way to avoid nitrogen narcosis is for a diver to limit the depth of dives. The other main preventive measure is properly informed selection/choice of which gas to use for the particular dive under consideration. Since narcosis becomes more severe as depth increases, a diver keeping to shallower depths can avoid serious narcosis. Most recreational training agencies will only certify entry level divers to depths of , and at these depths narcosis does not present a significant risk. Further training is normally required for certification up to on air, and this training should include a discussion of narcosis, its effects, and management. Some diver training agencies offer specialized training to prepare recreational divers to go to depths of , often consisting of further theory and some practice in deep dives under close supervision. Scuba organizations that train for diving beyond recreational depths, may exclude diving with gases that cause too much narcosis at depth in the average diver (such as the typical widely used
nitrox Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. It is usually used for mixtures that contain less than 78% nitrogen by volume. In the usual application, underwater diving, nitrox is normally distinguished ...
mixtures used for most recreational diving), and strongly encourage the use of other
breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. 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 ...
mixes containing helium in place of some or all of the nitrogen in air – such as trimix and
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 this mixture generates less resistance than atmospheric air when passing through the airways of ...
 – because helium has no narcotic effect. The use of these gases is considered to be
technical diving Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the List of diver certification organizations, agency-specified limits of recreational diving for non-Professional diver, professional purposes. Technica ...
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 is a fear of confined spaces. It is triggered by many situations or stimuli, including elevators, especially when crowded to capacity, windowless rooms, and hotel rooms with closed doors and sealed windows. Even bedrooms with a l ...
. Some divers report that they have hearing changes, and that the sound their exhaled bubbles make becomes different. Specialist training may help divers to identify these personal onset signs, which may then be used as a signal to ascend to avoid the narcosis, although severe narcosis may interfere with the judgement necessary to take preventive action. Deep dives should be made only after a gradual work-up to test the individual diver's sensitivity to increasing depths, taking note of reactions. Scientific evidence does not show that a diver can develop a resistance to the effects of narcosis at a given depth or become tolerant of it.
Equivalent narcotic depth Equivalent narcotic depth (END) (historically also equivalent nitrogen depth) is used in technical diving as a way of estimating the narcotic effect of a breathing gas mixture, such as nitrox, heliox or trimix. The method is used, for a given b ...
(END) is a commonly used way of expressing the narcotic effect of different breathing gases. The
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with Weather forecasting, forecasting weather, monitoring oceanic and atmospheric conditions, Hydrography, charting the seas, ...
(NOAA) Diving Manual now states that 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,
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
at a given pressure has a narcotic effect equivalent to nitrogen at 0.55 times that pressure, so in principle it should be usable at more than twice the depth. Argon, however, has 2.33 times the narcotic effect of nitrogen, and is a poor choice as a breathing gas for diving (it is used as a
drysuit 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 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 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, lung ...
. Although helium is the least intoxicating of the breathing gases, at greater depths it can cause
high-pressure nervous syndrome High-pressure nervous syndrome (HPNS – also known as high-pressure neurological syndrome) is a neurological and physiological diving disorder which can result when a diver descends below about using a breathing gas containing helium. The effe ...
, a still mysterious but apparently unrelated phenomenon. Inert gas narcosis is only one factor influencing the choice of gas mixture; the risks of
decompression sickness Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
and oxygen toxicity, work of breathing, cost, and other factors are also important. Because of similar and additive effects, divers should avoid sedating medications and drugs, such as cannabis 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 for at least 12 hours before diving, and longer for other drugs.


Prognosis and epidemiology

Narcosis is potentially one of the most dangerous conditions to affect the scuba diver below about . Except for occasional amnesia of events at depth, the effects of narcosis are entirely removed on ascent 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 inappropriate behavior in a dangerous environment. Tests have shown that all divers are affected by nitrogen narcosis, though some experience lesser effects than others. Even though it is possible that some divers can manage better than others because of learning to cope with the subjective 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 A physician, medical practitioner (British English), medical doctor, or simply doctor is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through the Medical education, study, Med ...
, 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 Charles Ernest Overton (1865–1933) was a British and Swedish physiologist and biologist, now regarded as a pioneer of the theory of the cell membrane. In the last years of the 19th century Overton did experimental work, allowing the distinctio ...
. What became known as the Meyer-Overton hypothesis may be illustrated by a graph comparing narcotic potency with solubility in oil. In 1939, Albert R. Behnke 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 is a creme-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, th ...
were conducted by Arne Zetterström between 1943 and 1945.
Jacques-Yves Cousteau Jacques-Yves Cousteau, (, also , ; 11 June 191025 June 1997) was a French naval officer, oceanographer, filmmaker and author. He co-invented the first successful open-circuit self-contained underwater breathing apparatus (SCUBA), called the A ...
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 or MAC is the concentration, often expressed as a percentage by volume, of a vapour in the alveoli of the lungs that is needed to prevent movement (motor response) in 50% of subjects in response to surgical (pain) sti ...
" concept in 1965. This measures the relative concentration of different gases required to prevent motor response in 50% of subjects in response to stimulus, 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 ''et al.'' in 1977 and 1978, but this hypothesis has been challenged by more recent work. A study on the effects of the environment on inert gas narcosis published by Lafère et al. in 2016 concluded that pressure and gas composition may be the only significant external factors influencing inert gas narcosis. It also found that the onset of narcosis follows a short period of raised alertness during descent, and some of the effects persist for at least 30 minutes after the dive. As of about 2020, research using critical flicker fusion frequency (CFFF) and EEG functional connectivity has shown sensitivity to nitrogen narcosis, but is not sensitive to helium partial pressure, in laboratory trials.


See also

* * * * * *


Footnotes


References


Notes


Sources

* * *


External links


Undersea and Hyperbaric Medical Society
Scientific body, publications about nitrogen narcosis.
Diving Diseases Research Centre (DDRC)
UK charity dedicated to treatment of diving diseases. * ScubaDoc's overview of marijuana and diving. * ScubaDoc's overview of alcohol and diving. * {{DEFAULTSORT:Nitrogen Narcosis Underwater diving safety Underwater diving disorders