Postgrad Med J: first published as 10.1136/pgmj.42.488.378 on 1 June 1966. Downloaded from POSTGRAD. MED. J., (1966), 42, 378 INERT GAS NARCOSIS -AN INTRODUCTION 1. P. UNSWORTH, B.M., B.Ch., L.R.C.P., Walton Hospital, Liverpool INERT gas narcosis is the physical and mental peculiar charm and in some persons, symptoms disturbance, both sulbjective and objective, that of intoxication are present". It was not until occurs when breathing gas mixtures containing 1861 that a professional diver described his certain members of the inert gases under pres- own signs and sym,ptoms, and suggested a pre- sure. These include krypton, argon, xenon, nitro- cautionary measure. J. B. Green, an American, gen and possilbly neon. The phenomenon of reported that on his deep dives of 150 feet or narcosis associated with nitrogen has been more, 'he noticed a feeling of excitement fol- alternatively termed "nitrogen intoxication" lowd by drowsiness, and he considered it im- though "narcosis" is the generally accepted portant that at this stage, the diver should be name. (Unsworth, 1960; Miles, 1962.) brought u'p. From Green's full description it It is more than a hundred years since the is clear that he noted hallucinatory changes first report in print of the problem that has been and impairment of a diver's judgement. Paul facing divers ever since their descents went Bert (1878) remarked upon the objective signs deeper than 100 feet or the ambient pressure when nitrogen is 'breathed under pressure but at by copyright. increased above 4 atmosiphere-nitrogen nar- that time did not pursue their cause though he cosis. For many years, it was only helmeted established that dissolved nitrogen was the divers and caisson workers who were 'sulbject aetiological factor in decompression sickness or to this condition, but With the introduction dur- the "bends". ing the last three decades of self-contalined The next report of nitrogen narcosis came underwater 'breathing apparatus, free divers are from Damant (1930) d-uring the British Ad- even more liable to the serious and fatal side miralty IDeep Sea diving trials to 320 feet. effects of nitrogen narcosis. Damant described the findings of 'Hill and Selby, The signiificance of inert gas narcosis has a that although the dlivers were all 'picked men http://pmj.bmj.com/ bearing not only on naval diving in warfare but who had 'been put through a specially searching also undersea salvage and exploration. With medical examination, some of them became the introduction of ihigh pressure chambers into abnormal mentally or emotionally. The effect the field of anaesthesia and surgery, the in- was attributed at first to the high ambient air herent properties of nitrogen narcosis may have pressure and oxygen poisoning, or to ilmpurities wider implications, as, 'for example, the pos- such as carbon dioxide or monoxide. But care- si'ble use of nitrogen or other inert gas, under ful work ruled these out, and though oxygen on September 26, 2021 by guest. Protected pressure as an anaesthetic agent, or as a side- and carbon diox'ide were no 'longer held res- effect when 'high pressures of compressed air ponsilble, no incrimination of nitrogen was made. are used. The first definiitive theory that nitrogen was t-he aetiological factor in mental changes while Historical under air pressure was put forward in 1935 In 1826 Colladon, a French physician, descriib- by Behnke, Thompson and Motley. They stated ing a prolonged descent in a dliving bell, re- that air at, and higher than, 3 atmospheres, pres- marked u'pon !his "state of excitement as if I sure exerted a narcotic effect on man, with had drunk some alcoholic liquor". It is doubt- euphoria, mental retardation and loss of neuro- ful if, 'in fact, Colladon did suffer from narcosis muscular control, with coma intervening at as the bell only descended to 20 metres although higher 'pressures. his comparison with alcohol would suggest it. Since the end of the 'war, research on substi- Another Frenchman, Junod, in 1835, noted that tution diluents continued and in 1948 the oxy- under pressure "the functions of the brain are hydrogen mix,ture was introduced (Zetterstrom: activated, imagination is lively, thoughts have a Burjstedt and Severin). Ten years earlier, how- Postgrad Med J: first published as 10.1136/pgmj.42.488.378 on 1 June 1966. Downloaded from June, 1966 UNSWORTH: Inert Gas Narcosis 379 ever, Behnke and Yaribrough, and End (1938) becomes dtifficult and 'the recollcstion of ideas had used helium as diluent in gas mixtures. This requires great effort. Other symptoms noticed eliminated nitrogen narcosis from deep dives 'include perilpherall numbness, lip 'trebling not though both hydrogen and helium had difficult undlike that of oxygen poisoning, and hallucin-a- features, the former being explosive with a tions. Occasionally ithis iiniltial ph,ase of nibrogen higher oxygen concentration that 4 per cent, stimulation may be passed very rapidly and and the latter posing problems of decompres- almost ,unnldiced, ,the diverithen being affected sion, voice distortion and thermal conductivity. very profoundly by the phase of exitreme Considerable experimental work has been lethargy and drowsiness. carried out on the qualitative and quantitative The signs of nitrogen narcosis are most con- measurement of mental disaibility of nitrogen veniently observed in a pressure chamber. These under pressure, with that of Bennett and his include delayed responses to sensory stimuli co-workers outstanding. They used both electro- particularly visual, aud'itory and tactile. Mis- encephalographic changes and flicker-fusion takes are made in mental arithmetic that would frequencies in estimating time of onset of nar- not normally 'be made on the surface. A loss cosis. ('Bennett and Glass, 1957; Bennett, 1958, of fine neuro-muscular contrcl and co-ordina- Bennett and Cross, 1960.) tion renders a delicate manipulation impossible. Other workers attempted to ;relate changes Although all individuals are narcotised to some in performance efficiency to pressure of inert extent under pressure, an emotionally stable gases. (S'hilling and Wil'lgrube, 1937; Kiessling person reacts to the stress by increased effort and Maag, 1960; Frankenhaeuser, Graff-Lon- and may carry out his task quite well until nevig and Hesser, 1963; Poulton, Catton and consciousness is 'lost. The unstaJble individual Carpenter, 1964.) These latter workers, in their is incapable of any further purposeful effort. initial experiments, found evidence of perform- As the pressure is increased, the signs and ance impairment in su'bjects at only 2 atmos- symptoms 'become more severe, there is loss pheres absolute but more recent work has not of memory that may last for many 'hours, and by copyright. revealed any abnormality lbelow 4 atmospheres between 10 and 13 atmospheres loss of con- absolute. sciousness occurs. With a helmet diver, this is not so dangerous as wit-h a free diver in Clinical Features 'whom the loss of the mouthpiece would result The signs and symptoms of inert gas narcosis in death 'by drowning. are varialble in 'tiime 'of onset, aind in regard The similarity between the presenting features to the pressure at which it appears, individuals of nitrogen narcosis and acute alcoholic poison- show some effedt 'soon after reaching 4 'atmos- ing is very close and hence the first descrip- pheres absoluite. Sensitivity differs among divers tion of Junod is so apt and observant. The http://pmj.bmj.com/ and some may have demonstralble signs at Jess French name for the condition, "l'Ivresse", is pressure while 'others m'ay inot be affected fti,l that used for -the vice of drunkenness. Another the pressure reaches 5 or 6 atmospheres. Many interesting parallel between nitrogen narcosis factors influence the pressure at which the onset and alcoholic poisoning is the variability and of symp:oms may occur and ;the severilty of individual susceptibility that exist. Resistance the at,ack. Exertion, prevlious faibigue, alcoholic to nitrogen narcosis (and alcohol) can be built excess prior to 'a dive, even apprehension, may and up 'by practice experience, and adaptation on September 26, 2021 by guest. Protected both advance 'onset and increase severilty. It also does occur. appears thait carbon difoxide retention, through either ilneffecltive apparatus or an increased pro- Theories portion of carbon dioxide in ;bhe respired gas, Many theories have'been proposed to explain ailso speeds 'the onset of narcosis. inert gas narcosis. The first, put forward in The symptoms which generaitly, though not 1835 by Junod and later in 1881 by Moxon, i'nevxKJalbly, appear first are lightheadedness, suggested increased pressure alone as the factor dizziness, euphoria, aind apparent mental stimu- involved. J'unod considered that "the increased laltion associaited with great self-confidence. The density of the air lessened the calibre of the completion of a difficult underwater task will venous vessels, resulting in greater blood flow seem easy ..ald straightforward, and safety pre- in the arterial system and towards principal cautior, usualily metlicul'ou'sly observed, appear nerve centres especially the brain, protected 'by to 'become superfluous. The subject shows a its bony case from direct pressure". He thought grea)t itendency to become jovial and 'alkative, that this increased blood 'flow stimulated the a,nd easily amused. Later, mental concentrattion nerve centres and resulted in narcosis. Moxon, Postgrad Med J: first published as 10.1136/pgmj.42.488.378 on 1 June 1966. Downloaded from 380 POSTGRADUATE MEDICAL JOURNAL June, 1966 on the other hand, regarded the increased pres- pressure were not due to oxygen. Recently the sure as driving the blood from the surface of interest in h'igh partial pressures of oxygen as the body into parts not accessible to respiratory a cause of narcosis has been re-aroused by exchange and that this devitalised blood caused Fenn (1965).