JUNE, 1973 P H Y S I O T H E R A P Y Page 7 d o s a g e s Expressed in W a tts /c m 2 o f tre a tm e n t h e a d X tim e. T rea tm e n t h e a d u su a lly 5cm 2 a n d to ta l o u tp u t o f m ac h in e 1 5 w atts, th e re fo re m a x im u m a v ailab le is 3 W /c m 2. f o r c h onic c o n d itio n s s ta rt a t 0,5 m in s a n d w o rk up to 1 5 W /c m 2 o r 2 W /c m 2 d e p e n d in g o n p a tie n t’s tole ran c e a nd m achine. A cute c o n d itio n s, low d o sa g e and. s h o rt tim e to s ta rt, 0,25 \V/cma fo r 3 m ins. T ry in c h ro n ic c o n d itio n s to re a c h o p tim u m d o sa g e fo r W atts in th re e tre a tm e n ts th e n increase th e tim e by 1 o r 2 m ins p e r tre a tm e n t. L im it t o 12 — 15 tre a tm e n ts . L atest re a d in g — d isa p p o in tin g , n o th in g new . b i b l i o g r a p h y Bass, A . L . 1966 R o y . Soc. M e d . 59: 653-6. B ie r man, W. 1954 A rch. P hys. M e d . 35, 209. Brown & Gordon 1967 U ltrasound techniques in B iology & M edicine. B uchan, J . F. 1970 P ractitioner 205: 319-26. D yson, M . and Pond, J. B . 1970 P hysiotherapy, April. G oodm an, C. R . 1971 W y S ta te S M e d . 71: 559-62. Gordon, 1964 Ultrasound a s a diagnostic and surgical tool. L ic h t, S . 1959 Therapeutic H eat. N elson, P . A . 1950 A rch. P hys. M ed. 31-6. P hys. Ther. Jan 1971 P 51: S3. Proc. R . Soc. M e d . 1971 64: 996-7. Soren, A . 1969 M e d . Tim es 971219-25. S u m m er a n d P a tric k 1964 Ultrasonic Therapy. Van N ostrand, 1962 Physics, a basic Science. W right, E . T. et a l 1971 Arch. P hys. M ed. a n d Rehab. 52 280-1. A C K N O W LED G EM EN TS B uchow iecki, D r. J. 1972 D ept, o f Physics. U .C .T . G uyton, Prof. A . C. 1968 L ecture to M edical Students. S loan, P rof. A . W . 1972 D ept, o f P hysiology U.C.T. PREMIXED NITROUS OXIDE AN D OXYGEN - A REVIEW J. F . C O E T Z E E , B .S c ., M .B ., C h .B ., (U niv. Stell.), D e partm ent o f A naesthesia, K arl B rem er H ospital, B elh ille . A p h y sio th e ra p ist is o ften c o n fro n te d w ith th e p ro b lem o f having to tre a t a p a tie n t w h o is in p a in . I f a d e q u a te p a in relief is n o t o b ta in e d , th e n n o t o nly is th e tre a tm e n t less effective, b u t it is alw ays disa g ree ab le fo r th e p a tie n t. T h e use o f p o te n t n a rc o tic analgesics d oes n o t solve th is pro b lem . I f given in a d e q u a te d o sa g e to p ro v id e effective p a in relief, the p a tie n t o fte n h a s re sp ira to ry d ep ressio n a n d is d row sy a n d u n c o -o p era tiv e . T h e ideal analgesic a d ju v a n t fo r use d u rin g p h y sio th e ra p y sh o u ld h a v e th e fo llo w in g p ro p e rtie s : I t sh o u ld p ro v id e p ro fo u n d a n alg esia w ith m inim al h y p n o sis — i.e. a co n sc io u s, c o -o p era tiv e p a tie n t free o f p ain. 1 . 2. 4 ' y 4. 5. A d m in is tra tio n sh o u ld involve a sim ple tec h n iq u e. I t sh o u ld b e sufficiently free o f d a n g e ro u s side effects, to e n a b le a d m in is tra tio n to be p e rfo rm e d by tra in e d p h y sio th e ra p ists w hile n o t u n d e r d irec t m edical supervision. I t sh o u ld n o t be h a b it fo rm in g . I t sh o u ld n o t in te rfere w ith o r w o rsen diseases th a t th e p a tie n t m a y have. S u ch a n a g e n t m a y p ro v e to be n itro u s oxide. History, Physical and Pharmacological Properties o f Nitrous Oxide N itro u s O xide (Syn., N itro g e n m o n o x id e ; F o rm u la , N 20 ) js a c o lourless g a s w ith a fa in t sw eetish o d o u r. I t is su p p lied in b lu e cy lin d ers in to w hich it h a s b een c o m p re ssed to a pressure o f 650 lb /s q . in. A t th is p re ssu re , N 20 is in a liquid form . A s it is re le ased fro m th e cy lin d e r it re tu rn s to th e gaseous sta te . I t is n o n flam m able. N 20 is th e o ld est o f th e gaseo u s a n ae sth etic a g en ts. I t was first p re p a re d by P rie stle y in 1776. I n 1779 H u m p h re y D a v y afte r e x p erim e n ts o n him self, 1 a n n o u n c e d th a t it h a d a n a e s­ th etic p ro p e rties, a n d suggested th a t it be used to relieve p ain. H is su g gestion w ent u n h e ed e d u n til 1844 w hen C o lto n a d m in istere d N aO to W ells w hile a d e n tist e x tra c te d o n e o f W ells’ tee th . W ells’ la te r a tte m p t to in tro d u c e N 20 a s a n a n a e sth e tic ag en t m et w ith ridicule w hen d u rin g th e d e m o n s tra tio n th e p a tie n t cried o u t. In 1868 A nd rew s in tro d u c e d oxygen a d m in istra tio n w ith n itro u s oxide in th e m a n n e r o f its p re se n t-d a y use. T h e e a rly tec h n iq u es o f a d m in isterin g n itro u s oxide were by giving th e p u re gas. M a n y o f th e effects a n d accidents w hich w ere a sc rib e d to N 20 were th e resu lts o f hypoxia. P ro v id e d sufficient oxygen (21% o r above) is given, th e effects o n b o d y system s a re slight. O n th e c entral n e rv o u s system , th e effect d e p en d s o n th e c o n c e n tra tio n in h ale d . N itro u s o xide h a s g o o d analgesic p ro p e rtie s w hile it is a w eak a n ae sth etic a gent. G . D . P a r b r o o k 1 , 2 show ed th a t a m ix tu re o f 2 5 % n itro u s oxide w ith 7 5 % oxygen p rovides b e tte r a n algesia th a n 15 m g o f m o rp h in e . H e show ed th a t a fte r ceasing to in h ale 2 5 % n itro u s oxide, significant a n algesia p ersisted fo r five m inutes, a n d d isa p p e a re d a fte r 15 m inutes. I f c o n c e n tra tio n s o f 5 0% a n d a b o v e a re in h ale d , consciousness is usually lost. W ith su b a n a e sth e tic c o n c e n tra tio n s, a feeling o f e u p h o ria is o ften experienced — h ence th e n a m e “ lau g h in g g as” . S e n so ry effects in clu d e tingling, n u m b n ess, dizziness as well as a u d ito ry a n d visual d istu rb an c es. A t th e hig h er c o n c e n tra tio n s n a u se a a n d co n fu sio n m ay a p p e a r. N a u se a is p a rtic u la rly likely if h y p o x ia is p re sen t. D e p ressio n o f th e re s p ira to ry c en tre does n o t occur. H a b itu a tio n is a possible h a z a rd w ith re p ea te d use, especially in p e rso n s w ho te n d to becom e e u p h o ric . T h e re is n o effect o n b ro n c h ia l secretions. P u lse a n d b lo o d p re ssu re re m a in u n c h an g e d , th e re b e in g n o d irect a c tio n on . th e h e a rt. S om e im p ro v e m e n t o f p e rip h e ra l b lo o d flow does occur. K id n e y a n d liver fu n c tio n s a re unaffected. D e p ressio n o f sk eletal m u sc u la r to n e is m in im al. S m o o th m uscle is unaffected. D e p ressio n o f b o n e m a rro w fu n c tio n in leu k o - p a e n ia o nly o ccu rs if n itro u s oxide is in h ale d c o n tin u o u sly fo r m o re th a n 24-48 h o u rs . 8 , 4 N itro u s oxide is re a so n a b ly in so lu b le in th e b lo o d . U p ta k e a n d ex cre tio n via th e lungs is ra p id . I ts effects a re th e re fo re ra p id ly a c tin g a n d q u ick ly w ear off a fte r te rm in a tin g a d m in is tra tio n . 5 T o d a y n itro u s o xide is used in th e m a jo rity R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Page 8 P H Y S I O T H E R A P Y JUNE, 1973 MAKE YOUR DAY A UTTLE EASIER! Y ou physios are a hard-worked group, we know. In the day’s work, environment and c o m f o r t b e c o m e m o r e a n d m o r e important — and while there’s not much we can do to help fix the background in which you work, y o u ’ll find a comfy, practical working rig in the new special- purpose uniform w e’ve designed with you in mind. It’s a continental style dress, with Bermuda-type shorts to match. A side vent in the skirt and the generous cut, mean that you ’ll work more easily, and feel comfortable right through the hard day. Y ou r option o f short or long sleeves, in drip-dry, hard-wearing fabric . . . white or saxe blue. Sizes 3 2 to 4 2 . Elegance and efficiency . . . what more could you ask ? M W * 4th Floor, Pritchard House, 83 Pritchard Street, JOHANNESBURG. Telephone 2 3-4 4 0 5 . 87 M arion Avenue, Glenashley, DURBAN. Telephone 8 3 -7 2 2 6 . Fully illustrated catalogues and price lists o f our full range are available free to you. Just drop us a postcard (P.O. Box 7 5 2 , Johannesburg) or telephone 2 3 -4 4 0 5 ' any time, including nights, weekends and holidays. W e ’re also happy to execute phone orders, o f course. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) f opneral an ae sth etics, e ith e r as a vehicle fo r c arry in g m o re 0 a n ae sth etic a g en ts o r as p a rt o f th e te c h n iq u e o f g l a n c e d a n a e sth e s ia ” . rise o f Subanaesthetic C oncentrations o f N itro u s O x ide The u s* t 0 p rovide A nalgesia M in n itt6 in 1931 d e v eloped a n d p o p u la riz e d th e em ploy- nt o f n itro u s o xide a n d a ir m ixtures d u rin g c h ild b irth . S frm u s oxide a n a lg e s ia has b een em p lo y e d in d e n ta l .irperv fo r at lea st 100 y e a rs.’, 8 I t has b e en u sed to relieve thp n ain o f m yo ca rd ia l ischaem ia since 1881 by K lik o v ic h nri th is usage h a s b e en re -investigated m o re re c e n tly .9, 10. in shocked sta te s follow ing tra u m a , 5 0 % n itro u s o x ide/ nvveen has been u sed to relieve p a in a n d h y p o x ia . 1 1 O th e r situations in w h ich n itro u s o xide is used fo r p a in relief include p a in an d -isch a em ic lim b p a in . 10 P a rb ro o k et a lia inv estig a te d th e u se o f 25 % n itro u s oxide in oxygen in th e re lief o f p o st-o p e ra tiv e p a in . T h e best results w ere o b ta in e d w hen a c o m b in a tio n o f a n a rc o tic analgesic e.g. m e th a d o n e a n d 2 5 % N aO w as used. T h is c o m bination w as suggested as a n a id to p o st-o p e ra tiv e chest p h y sio th e ra p y . 1 , 2 P rem ixed N itro u s O x id e a nd O xy g en — E ntonox T he M in n itt a p p a ra tu s fo r use in ob ste tric s w as designed to provide a 50-50 % m ix tu re o f a ir a n d n itro u s oxide. It h as been show n th a t th is is n o t safe, as 5 0 % n itro u s o xide in air provides only 1 0 % oxygen. F u rth e rm o re , th e m achines som etim es deliver m o re th a n 5 0% n itro u s oxide. T h e re is therefore a s tro n g lik e lih o o d th a t a p a tie n t w o u ld be re n ­ dered hypoxic w hile b re a th in g fro m o n e o f these m achines. 1 2 , 1 3 T h is d a n g e r is a v o id e d in th e L u cy B aldw in a p p ara tu s w hich p rovides a c o n tin u o u s flow o f n itro u s oxide and oxygen fro m se p a ra te cylinders. T h is m ac h in e is u n ­ fortunately very in a c c u ra te as th e m ixing m ec h an ism has not b een perfected. B a rac h a n d R o v e n stin e 11, (1945) w ere th e first to use nitrous oxide a n d oxygen in o n e cylinder. T h e ir in te n tio n was to elim in a te th e d a n g ers in h ere n t in th e use o f hypoxic m ixtures o f n itro u s oxide. T u n s ta l2’ in 1961, w o rk in g w ith the B ritish O xygen C o m p a n y , in tro d u c e d prem ix ed n itro u s oxide a n d oxygen fo r use as a n analgesic in ob ste tric s. T h e premixed gas a t p resent a v ailab le is a 5 0 :5 0 % m ix tu re o f nitrous oxide a n d oxygen, a n d is called “ E N T O N O X ” . It is sold in a specially c o lo u re d c y linder (blue w ith a w hite top). T he cylinder is filled to a pressure o f l 386 K g /s q cm (1 980 lb/sq in.) a t 19,8°C. I t has b een fo u n d th a t u n d e r these conditions, in spite o f th e p a rtia l pressure o f n itro u s oxide exceeding th a t a t w h ich it sh o u ld liquefy, it re m a in s in th e ■aaseous phase. /H o w e v er, w h en th e te m p e ra tu re o f th e c ylinder d ro p s to below — 7°C th e s itu a tio n is differe n t. 16 T h e n itro u s oxide then liquefies a n d settles to th e b o tto m o f th e cylinder. O n being o p e n ed , such a cylinder will a t first su p p ly a high c o n ce n tra tio n o f oxygen, w ith little N 20 . A s th e cylinder em pties, so th e 0 2 c o n c e n tra tio n falls a n d th e N aO c o n ce n ­ tra tio n rises u n til a lm o st p u re N 20 is being released. A p e r­ son b re ath in g such a m ix tu re w o u ld quickly becom e hypoxic. W arm ing th e c y linder does n o t necessarily reverse th is state, unless th e c ylinder is sh a k e n . JUNE' 1973 P H Y S I O T H E R A P Y Page 9 T h e “ E n to n o x ” “ d e m a n d ” -valve- fits d irectly o n to th e 500 litre p in-index cylinder. T h is valve o pens o n ly w hen th e p a tie n t b re a th s fro m it. A five fo o t length o f c o rru g a te d ru b b e r tu b in g , h a ndpiece, e x p ira to ry valve a n d face m ask a re a tta c h e d to th e valve. T h e u n it b e ars a pressure gauge in d i­ c a tin g th e c y linder c o n te n ts. T h e “ d e m a n d ” valve re sp o n d s to in sp ira to ry effort by th e user, a n d a u to m a tic a lly sh u ts itself o ff a t th e e n d o f in sp ira tio n . I t can deliver a flow in excess o f 275 litre s/m in , w hich easily a cc o m m o d a te s th e larg e st in sp ira to ry effort. T h e in te rm itte n t “ d e m a n d ” flow econom izes o n th e use o f gas. In o rd e r to o b ta in gas fro m th e a p p a ra tu s , it is necessary to effect a n air-tig h t seal betw een th e m a s k a n d face. T h e m a s k m ay be rep laced by a m o u th ­ piece a n d nose-clip. T h e se item s sh o u ld , o f course, be Sterilized in betw een use w ith different p atients. In review o n th e th e ra p e u tic uses o f n itro u s oxide G . D . P a r b r o o k 1’ has d ivided its analgesic effects in to fo u r zones, d e p e n d a n t o n c o n c e n tra tio n (see table). M a n y p e rso n s, o n in h alin g 5 0% N 20 fo r sufficient tim e to achieve sa tu ra tio n (e.g. 2 0 m in u te s), w o uld becom e c o n ­ fused a n d excited, a n d a few w o uld lose consciousness. T h e te c h n iq u e o f E n to n o x a d m in istra tio n is to give a sufficient n u m b e r o f b re ath s to achieve a n alg esia w ith o u t p ro d u c in g a n a e sth e s ia (Z o n e 1). R e sp o n se is n o rm ally very ra p id , b e ing th e tim e ta k e n fo r b lo o d to c irc u la te betw een th e lungs a n d th e b ra in . E ven o n e deep b re a th c a n have a p p rec ia tiv e effects. T h e n u m b e r o f b re a th s necessary, d e p en d s o n v a rio u s fa c to rs w h ich in clu d e th e p a tie n ts in d iv id u a l susceptibility, th e presence o f p u lm o n a ry disease, p revious m e d ic atio n , tid a l v o lu m e a n d re sp ira to ry ra te . P a rb ro o k h a s, how ever, sta te d th a t te n d eep b re a th s o f E n to n o x is eq u iv a len t to s a tu ra tio n w ith 2 5 % n itro u s oxide. A n a lte rn a tiv e m e th o d is to p ro d u c e d ilu tio n o f th e E n to n o x by air. T h is m ay b e d o n e by a c o n tin u o u s flow o f E n to n o x in to a n a ir-e n tra in in g oxygen m ask. T he U se o f E nto n o x in O b s te tric s: F ifty p e r cent N 20 / 0 2 is em p lo y e d extensively in m o d e rn o b ste tric al units. It is u su ally a d m in istere d in te rm itten tly , beg in n in g w ith th e s ta rt o f e ach l a b o u r p ain a n d c o n tin u in g u n til th e c o n tra c tio n h a s passed. B ein g ra p id ly a cting, it pro v id es p a in relief d u rin g e ach u te rin e c o n tra c tio n . N o t on ly is c o -o p e ra tio n re ta in e d , b u t m o th e r a n d fo e tu s a re e n su re d w ith m o re th a n a d e q u a te o x y g e n atio n . T h e C e n tra l M idw ives B o a rd o f G re a t B rita in h a s a p p ro v e d th a t m id ­ wives w h o h a v e b een tra in e d in th e use o f th e E n to n o x a p p a ra tu s , m ay a d m in iste r it w hile n o t u n d e r d irect su p e r­ vision. P hillips, a n d M a c D o n a ld (1971)18 co n clu d ed th a t E n to n o x w as safer th a n b o th tric h lo reth y le n e a n d pethidine. U ses o f E nto n o x in P h y sio th erap y : T h e in cidence o f p o st-o p e ra tiv e chest c o m p lica tio n s is highest a fte r u p p e r a b d o m in a l o p e ra tio n s . P a in leads to “ sp lin tin g ” o f th e d ia p h ra g m , sh allo w re sp ira tio n a n d unw illingness to c o u g h . It is possible th a t E n to n o x m ay p ro v id e th e p a tie n t w ith sufficient p a in relief to e n ab le him to ta k e a few deep b re a th s a n d c o u g h . I n th is situ a tio n a d m in is tra tio n w o u ld h a v e to be re p e a te d a t freq u e n t in te rv als as deep b re a th in g a n d co u g h in g w o u ld lead to ra p id e x c re tio n via th e lungs. Its use m ay o f c o u rse be e x te n d ed to o th e r situ a tio n s in w h ic h deep b re a th in g a n d P la n e Z o n e P a tie n t C o n tac t A nalgesia A m nesia Psychological Effects A p p ro x . n 2o % “ A nalgesia” 1 2 P re se n t P re se n t M o d e ra te M a rk e d N o n e Slight Slight S e d a tio n In e b ria tio n 5-25 26-45 “ A m nalgesia” 3 P re se n t A lm o st to ta l A lm o st c o m plete Som nolence 46-65 4 L ost P a tie n t fully u n c onscious 66-85 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Page 10 P H Y S I O T H E R A P Y JUNE, 1973 and they all1 add up to VERSATILITY 1. A D A P T A B LE TO E X IS T IN G E Q U IP M E N T Horizontal cervical traction on existing x-ray tables, treatm ent tables, hospital b eds and beds in the home. 2. V E R T IC A L C E R V IC A L T R AC TIO N W IT H T H E FTC-20 “ T R U -T R A C " F L E X IO N T R A C T IO N C H A IR Five a ng le adjustm ents c om pensate fo r the forward a ng le of the neck, p o sitioning the cervical sp ine in a straight line with the traction pull, providing in­ creased flexion and greatly a d d in g to patient c o m ­ fort. 3. L U M B A R T R A C T IO N W IT H T H E R T -9 9 "T R U -T R A C '’ T R A C T IO N & TH E R A P Y T A B L E Roller bea ring s in the lum b ar section o f the table elim inates friction w hich provides effective treat­ ment at lower poundage resu lting in added patient tolerance. , H O R IZ O N T A L C E R V IC A L T R A C T IO N W IT H T H E R T -99 "T R U -T R A C ” T R A C T IO N & TH E R A P Y T A B L E N ine vary in g a ng le c h a n g e s (horizontal to 4 5 de­ grees) p osition s traction pull in direct line with the cervical spine, and a s su re s selective flexion angle for the patient. T h e s e are ju s t f o u r a d a p ta tio n s o f th e “T R U - T R A C ” p o rta b le in te r m itte n t tra c tio n m a c h in e . T h is v ersatile m a c h in e m a y a lso be m o u n te d o n a w a ll f o r v ertica l c e r v ic a l tra c tio n use. If you have another application in mind write for descriptive brochure illustrating many additional accessories. Exclusive Distributors for Southern Africa ® PROTEA ELECTRO-MEDICAL SERVICES (PTY.) LTD. A Subsidiary for Protea Holdings Limited Tel. Address: "M an lu " Tel. 838-8351 (10 Lines) P.O. Box 7793, JO H A N N ESB U RG and CA PE TO W N — D U R B A N — E A ST LONDON — PRETORIA PORT ELIZABETH — S A L IS B U R Y — W E L K O M — W IN D H O EKR ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) coughing is painful, e.g. after thoractomy, rib fracture and lam inectom y. It has been used for pain relief during vibration therapy in crushed chests19. Dale Mitchell reported favour­ able results with chest physiotherapy after thoractomy especially when it was combined with a narcotic20. Parbrook has also reported best results when a narcotic analgesic was used in addition to nitrous oxide. The value of the use o f Entonox in burned patients is reported in this journal. Here the danger of bone-marrow depression may safely be ignored as the actual duration of administration each day is short. The remote possibility of development of tolerance and habituation must, however, be borne in mind. C ontra-indications: T here a re a few situ a tio n s in w hich n itro u s o xide sh o u ld be avoided. 1 N20 tends to increase pre-existing nausea. K N20 diffuses rapidly into air containing body spaces, increasing their volume. Gaseous abdominal distension, closed pneumothorax, after air-encephalography, and after tympanoplasty are relative contra-indications, but not necessarily for short-term intermittent admini­ stration. 3. Continuous administration for periods longer than 24-48 hours leads to leukopaenia. J U N E , 1973 P H Y S I O R E F E R E N C E S 1 P arbrook, G. D ., R ees, G. A . D ., R obertson, G. S . “R e lie f o f Post-operative P ain: C omparison o f a 2 5 % N itro u s O xide and O x yg e n M ix tu r e with M o r p h i n e (1964) B rit. M e d . J. 2, 480. 2 P arbrook, G. D . (1966) “P ost-operative P ain R elief: Comparison o f M e th a d o n e a n d M orphine when used con­ currently with N itro u s O xide A nalgesia” . B rit. M e d . J. 2, 616. 3 P arbrook, G. D . (1967). “The Leucopaenic effects o f pro - ~ ^ longed nitrous o x id e tre a tm e n t" . B rit. J. A nnesth. 39, 119. ‘ E astw ood e t a l (1963) “E ffe c t o f nitrous o x id e on the white cell count in leukaem ia”. N e w E ngland J . M e d . 268, 297. 5 Eger, E d m o n d I. (1964) U ptake distribution a n d elim ination o f N itro u s O xide — C linical Anaesthesia 1, 46. 6 M in itt, R . J. (1934) “N e w technique f o r self-adm inistration o f gas-air analgesia in labour”. L a n c e t 1, 1 278. 7 Persson, P. A . (1951) “N itro u s O xide H ypalgesia in M a n ”. A cta . O dont. Scand. 9, Suppl. 7. 8 R uben, H . (1966) “N itro u s O x id e Analgesia f o r D ental P a tie n ts”. A c ta A naesth. Scand. Suppl. 25, 419. 9 P etrovsky, B . V., Yefuni, S . N . (1962) “ Therapeutic A n a l­ gesic A naesthesia”. K hirugiya (M o s k .) 38, 7. H E R A P Y Page 11 1 0 P etro v sk y, B . V., Yefuni, S . N . (1965) “ Therapeutic Inhalational A naesthesia”. B rit. J . A naesth. 37, 42. 1 1 S m o lin a ki, K . I. (1961) “N itrous O x id e A naesthesia as a m eans o f P revention a n d early treatm ent o f Traum atic S h o c k ” . K hirurgiya (M o s k .) 37, 16. 1 2 Cole, P. V., N ainby-L uxm oore, R . C. (1962) “ The hazards o f ga s a n d air in o b stetrics” A n aesthesia 17, 505. 1 3 N a in b y-L u xm o o re , R . C. 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(1970) “A Clinical stu d y o f the value o f N itro u s O x id e a n d o x yg e n a s an analgesic in r e lie f o fp a in follo w in g thoracic surgery a n d its usage physiotherapeutically”. A u st. J. P hysiother. 16, 4. 2 1 Goodm an, L . S ., Gilman, A . (1970) “The Pharm acological basis o f Therapeutics” (4th E dition) M acm illan, p . 71. 2 2 E astw ood, D . W. (1964) Clinical Anaesthesia. 2 3 Gale, C. W ., Tunstall, M . E ., W ilton, D aries, C. C., Cheuler C. Thom as (1964) “P re m ix e d g a s a n d o x yg e n f o r M id w iv e s”. B rit. M . 1, 732. 2 1 P arbrook, G. D . (1967) “ C omparison o f Trichlorethylene a n d nitrous o xide as analgesics”. B r it. J. A naesth. 39, 86. 2 5 M e d ic a l Research C ouncil C o m m ittee on N itro u s O xide a n d O x yg e n A nalgesia in M id w ife (1970) B rit. M e d . J. 1, 709. 2 6 H u siend, R . F. (1964). Clin. A naesth. 1, 98. 2 7 Tunstal, M . E . (1961) “Obsteric analgesia: The use o f a f ix e d nitrous o xid e a n d o x yg e n m ix tu re fr o m one cylinder”. L a n c e t 2, 964. 2 8 Crawford, J. S . (1965) Principles a n d P ractice o f O bstetric A naesthesia. 2 n d Ed. P. 98. O x fo rd : B lackw ell. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )