Hewitt, Frederic William

English

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TE-IE  JOURNAL OF THE: ORIGINAL  COMMUNICATIONS. Further  observations  on  the  Use of Oxygen with Nltrous  Oxide." BY FREDERIC HEWITT,  M.A.,  M.D.CANTAB. ANIESTHBTIST  AT THE LONDON  HOSPITAL,  ETC. G~NTLEMEN,---~~~C~  1 ,bad  the honoiir  of  addressing the lilember~  of tl~is  Association  at the Annual Meeting at Man- chester, in 1892, I have been steadily endeavouriilg to simplify arid render nlore universally applicable the method of produc- ing nitrous  oxide  an~sthesia  to  whicli  I  then referrcd-a rnethod with which  you  are all  now familiar, and one which has for many years occupied a considerable share of iny atten- ti~n.  I use the word method in a wide sense, applying it not to any particular  line of  procedure  depeildent  upon the em- ployrnent of  any particular apparat~is,  but to the adiilinistra- tion of oxygen with nitrous oxide, witli. the  ol3ject of preventing certain asphyxial symptoms ~vhich  ai-ise when that anzsthetic ic administered in the customary manner,  iss.,  free froni oxygen. Before I proceecl  I  should  like to dispose of  an argument ~vliich  is not infrequently brouglit  against any attempt to iim- prove the customary method of  nitrous oxide administration. It is urged that this method is so satisfactory aild so free from risk, even in  comparatively iinsl<illed hancls, thal: ihere is no necessity for improvement, no need  for  advance.  But such an argument, even though advanced, as I regret  to say it has been advanced by men of  experience, inust completely fall to pieces  when  seriously  examined.  I  readily  grant tBat  un- satisfactory  symptoms  under  nitrous  oxide,  as ordinarily given,  are  extremely  rare,  and  that  fatalities  are so  e,x- ceptional that when one does occur it creates the ~nost  wide- spread sensation amongst those who, lilre  ourselves, take no little interest in the best means of  preventing paiii.  I3ut even if  accidents and  deaths occurred less frequently than is  the case ; even if tl~ere  were but one recorcled faiality from nitrous oxide as ordinarily given ; I siibiiiit that it woulcl  still be oiir duty to attempt to find soine safer method of  administration, in order  to  minimise  the alreacly small risk, and reduce it, if possible, to 9ziZ. * A paper read at the Ana~ial  Meeting nt Newcastle-on-Tyne. The asphyxiating properties  of  nitrous  oxide,  when  ad- ministered  free from  oxygen,  appear to  constitute its sole objection and danger as an an~sthetic. The lividity  of  the features,  the stertorous  snorting  and obstructed  breathing, the muscular twitchings, and the congested and swollen  state of the tongue and other parts, are one and all due to Want  of oxygen.  A  study  of  the  fatal  cases which  have  already arisen under nitrous oxide reveals the fact that in most, if not in  all of  thern,  death toolr  place  with  asphyxial  symptoms brought  about  by  oxygen  deprivation,  so  that  it is  in the higliest  degree  probable  tl-iat ,had a  suitabIe  proportion  of oxygen  been mixed  with the nitrous  oxide,  tl-iese  fatalities would  either  have  been  less  numerous,  or  more  probably would not l-iave talcen place at all.  The presence  OE  oxygen robs nitrous oxide of its one disadvantage, and of  its one rislr. Let us carry the matter  one step f~irtl-ier,  so  that we  may fully  realise  the  importance and  perl-iaps  the necessity  of oxygen in the aclministration.  In order to obtain sufficient anzstl-iesia  froii-i  piire  nitrous  oxide  it  is  necessary,  as  a general rule,  to push  the inl-ialation to the point  at wl-iicl-i either deep stertor or  "jactitation " manifests itsclf.  Now, tliis  point  inay be safely reaclied, in fact the administration may  even  be  carried  on  for  a  second or  two beyond it, in, let  us say, ggg  cases  out of  1,000 without  risk, but  in the ~,oooth  case rislc will be incurred.  Patients cannot be placed in  the  asphyxiated  condition  with  whicli  all  of  you  are familiar  without  some risk  of  suspended  respiratioii.  The deprivation of  oxygen, which, necessarily occurs in the cus- tomary n-iethod ~if~administration,  may, in  fact, bring  breath- ing to a standstill, in at least two and possibly in tl-iree ways. (I) The air-way may become  mecl-ianically obstructed from spasrn  or  swelling  of  parts  within  it ;  (2)  the  respiratory muscles  inay  be  thrown  into  a  state  of  tonic  spasm ; or possibly (3) the respiratory centre inay  simply become para- lysed,  breathing  gradually  ceasing  witllout  obstruction  or spasnl. Mechanical occlusion of  the air-tract-a  condition to which~ I have elsewherel drawn special attention, and one which may arise in various ways-is  the chief  danger to be apprehended Ft'i-mts.  XOJJ.  Afeed  Chif-.  Sor., vol. lxxiv.,  p.  107. -82  2  THE JOURNAL  OF TI-IE in administering  nitrous oxide  free frorn  oxygen.  It is an irlteresting and  sigiiificant  fact that in  WO  of  the recorded iiitrous Oxide deatlis tl-ie patients had enlarged tonsils.  Wheli oxygen is withl~eld  in  acltninistering  nitrous oxide the vez-ious System becomes lnore and more engorged, and vascular struc- tures, such as the tonsils,  may increase in size to such an ex- tent as to obstruct  breathing.  When oxygen is  mixed  with tl1e nitrous oxide the venous  engorgement  and consequentl~ tlie  swelling  of  vascular  structures  is  far  less,  so  that obstructed breatl-iing from enlarged  tonsils does not occur.  1 do not mean to say tl-iat enlargenlent of  the tonsils is a con- dition  wl-iich  contra-indicates  the  use  of  nitrous oxide, but such a condition sliould niake one cautious.  I refer to it here because it serves to exeiilplify  what I  arn  wishing to convey, viz., that tlie possibility  of  danger from such a  source is re- moved by adopiing the metl-iod I ain advocating. There is yet  another advantage in the use  of  oxygen  to wliich I should lilre to refer.  Those of  you whose experience with  nitrous oxide  has extended  over  lnany years will  find tl-iat, almost  unconsciously,  you  have acquired  tlie l~abit  of selecting yoiir  cases  for  anzsthesia.  Experience has nlade you  familiar  with  patients  wholn  you  regard  as  bad sub- jects."  Now  ihe great  majority  of  patients  who  are  bad subjects for nitrous oxide  se will  be  found to do remark- ably  well  with  nitrous  oxide  mixed  with  oxygen.  The hysterical subject who remains but a brief  time under nitrous oxidc as ordinarily  given  and recovers with excitement and screaming, behaves in a totally different way when  oxygen is employed.  The Same,  too,  is  true  of  anzmic and  feeble persons.  Very  obese  siibjects  and tl-iose wlio have lleart or lung  affections  pass  through  non-asphyxial  iiitrous  oxide anzsthesia with remarkably little disturbance.  Aild,  lastly, the very young and the very old rnay be far more satisfactorily aiizsthetised by this than by tlie custornary method. I am glad  to find that much  rnore  interest is being talren in tliis matter tllan was tlie  case a few years ago.  The new ilietliod  is  gaining  ground,  not  only  in  England,  but  in Gerinany, France, Sweden, and other countries.  It is true that it is a trifle more  difficult and that it requires somewhat inore attention to detail than that customarily employed; but by rneans of  an improved  and  siinplified apparatus which  I BRITISH  DENTAL ASSOCIATION.  38.3 have  brouglit with nie for your  inspection, aild which I shall have  tlie  pleasure  of using before you,  I thinlr  you  will see that  the  diflerences  between  administering  nitrous oxide  in the  usi~al  iilanner  and  giving it witli  oxygen  are in  reality very  slight.  The gain is great, not  only  from  the point  of view of  tlie  acliilinistrator, who is able to produce a  longer, better, and safer form of  anzsthesia than has hitherto been foiind possible, but fi-orn the point of  view of the patient, wlio is not  subjected  to  the  often  distressing sensations  which ncco~n~an~  iinperfectly established an~esthesia  during dental operations. T11e  ltind of  apparatus einployed is of  tlle'greatest possible iinportance  in  snccessfully  inducing  non-asphyxial  nitrous oxide  anssthesia.  In  niy  atternpts  to  obtain  an efiicient apparatus I  have  over  and  over  again met with  difficulties dependent upon  apparently trivial  details in construction.  I should weary you  were I to eniimerate  the numerous  points I have liad to consider in bringing  the apparatus, whic1-i  I ilow show you, to its preseilt  state.  In admiilistering these two gases as they slio~~ld  be administered we- are einploying a  delicateiy  acljusted  process,  and  the  apparatus  must  be delicately acljusted  also,  or we  shaIl not succeed as' well  as we  could  wisli.  The apparatus wliich  I  described  at Man- chester- in  1892 leaves little if  anything to be desired in tlie results wl-iicli it produces.  But with the object of  sendering the  method  more  universally  applicable  I  have  been  en- deavouring to simplify this apparatus, and thus to render the iiiechanicaI process  of  administration  easier  of  performance, aiid  to reduce tlie cost  of  manuIacture.  In atteiilpting this simplification I  liad  before  nie  two problenis.  One was  to malre  an apparatus wliicli would  be as  portable  as, and in outward  appearances  siinilar  to  an  ordinary  nitrous  oxide apparatus ; the otlier was to devise a  stopcoclr which would, by one contii~uoiis  i~iovement  of  a single handle, allow in the first  place air, in the second  place  nitrous oxide, and in  the third place nitrous oxide mixed  with  oxygen  to be inhaled. You may reinember tliat in tlie previous apparatus there were two handles to tlie stopcocl<,  two separate bags  for the two gases, and two  separate tubes fro~i~  the gas cylinders to the Bags.  The present apparatiis has one handle to its stopcoclr, one bag dividecl by a septum into ;wo  parts, and one apparent tube (in reality two) between the cylinders and bag. 3 84  THE JOURNAL OF THE Fig.  I  shows  the  complete  apparatus.  There  are  two cylinders  for nitsous  oxide, and  one  for oxygen.  The rubber  supply tubes  from the cylinders  are attached to two arms of  a specially  constructed  meta1 Y  piece.  '  The third arm of  this Y piece consists in reality of two concentric brass tubec with a space between  them, the inner tube being con- tinuous  with  the  arm  receiving  the rubber tube from  the oxygen  cylinder, the outer  being  continuous  1vitl-i  the arm receiving  the rubber tube from the nitrous oxide cylinders. To this third arm of  the Y piece two rubber tubes, one inside the  other,  are  attached,  the  small  inner  one  transmitting oxygen to the oxygen division  of  the double bag, the larger outer  one  transmitting  nitrous  oxide  to  tlie nitrous  oxide BliITISH  DENTAL  ASSOCIATION.  385 division of the double bag.  Just before the two rubber tubes, one inside the other, reach the double bag,  tl-iey are, as it were,  split up again into two separate tubes by  another Y piece, so that the two gases may be delivered to the respective divisions  of  the large bag.  It will be  Seen  that the large double bag has two neclcs to it, which  fit over the two  wide nletal tubes colning from the combined stopcoclr and rnixina cllan~ber. The wide  meta1 tube througl-i which  the nitrouc oxide is delivered to tliis stopcoclr  and mixing cylinder (here called  stopcoclr  for  brevity)  coiilrnunicates  by  means  of  a large cii-cular orifice with tl-ie interior of  the stopcock, so tbat a wide Passage is always Open for the supply of  nitrous oxide from the bag during tlle administration.  But tl-ie wide meta1 tube through  w11icl.i  t11e  oxygen passes on  its way from  the oxygen division of  the bag to the stopcoclr does not communi- cate thus freely witl-i the interior of  the stopcoclr.  The outer part of  the stopcock to which this oxygen tabe is soldered is pierced by ten small l-ioles, so  tliat  the oxygen  tube may be -86  .  3  THE  JOURNAL  OE'  TL-CE looked  upon  as bcing  subdivided  into ten sinall tubes.  An inner druin which  revolves in the stopcocli: when the handle is turned deterinines  what shall be breathed  by the patient. JVheil the indicator points to "  AIR," as in both drawings, the air-hole is open and the inner drum Covers not only the  nitrous Oxide inlet to tl-ie stopcock, but all the oxygen  holes, so that only air is breathed.  When the indicator points to  N,O," the air-hole is closed, tlie ilitrous oxide inlet  is freely Open, the oxygeil holes are closed, and hence  only nitrous oxicle is breathed.  When the indicator is turned still further, so that it points  to "  I,"  one  smalI oxygen hole  is  opened up,  one smail stream of  oxygen being thus permitted to mix with the large  and continuous stream  of  nitrous  oxide.  When  the indicator  points  to  '' 10,"  ten  sinall  oxygen  streams  are adinitted  with  the  large  nitrous  oxide  stream.  There are two r~~bber  valves (inspiratory and expiratory) at the part of the stopcoclr to which the face-piece is  fitted,  and there are also  two  smaller ones  in  the large nletal  delivery  tubes  to dich  tlie double bag is attacl-red, the last-nained valves being r~ecessary  to prevent  the  contents  of  the two  bags mixing. An audible cliclr talres place each time the indicator is moved to a fresh point.  The apparatus can be taken to pieces in a rnoment,  without  any  screw-driver, by simply turning  and reinoving tlle milled head screws shown. To iise the apparatus the folIowing directions should be fol- lowed.  All air or gas should first be pressed out of  the double bag, the indicator  turned  to  AIR,"  and tlie two divisions of  the bag nearly, but not  quite, filled with  their respective gases,  by  rotating  the  foot  keys.  No  further  addition  of oxygen will  be  needed.  The face-piece should  then be very accurately  applied.  Air  will  be breathed  freely through the apparatus.  The valves should be heard to act, other~vise  the face-picce  is  not  fitting, or the patient is not  brenthing as freely as he should.  The  indicator is now  turned  to  I, I  b wl-iich  means that nitrous oxide witli a  small quantity, pos- sibly I or 2 per cent.,  of  oxygen will be inhaled.  It is most in~portant  that the two divisions  of the double bag should be lrept  ep2mEly  mzd  Pavtly  IZ~SEC~Z~GCI,  as shown  in  fig.  I.  The anresthetist  must  therefore keep his  foot  almost constantly turning the nitrous oxide foot lrey in order that the two parts of the bag tnay remain equal in size throughor~t. After two or  three breaths at  I,"  the indicator should  be  turned  to 2,"  and progressively,  after every two or  three breaths,  to 14 3,"  6'  4, 93 C< ,-,'Y  C6  6,3>  f  ,  i  8,  19 0r 'C  99  I o, " according to tha type of  patient.  In cl-iildren and very an~mic  persons the indicator may be placed at  2,"  <L 3,"  01:  even  4,"  to start ~ith,  and turned to a fresh number every breath or two.  But in adults in good  health less oxygen must  be  given.  I  need not  here refer to the Symptoms which tl-ie patient will exhibit -tl-iese  I  liave fully described  on  previous  occasions.  The ~ymptonis  produced will  be the saine as those met witli when employiiig the previously described  apparatus.  I  may, how- ever, briefly mention two practical  points.  Tlle first of  these is that I find tlie abseilce of conjunctival reflex an ever available and usually reliable test of  proper anaesthesia.  The second is that I have found it better  to give ratl-ier less oxygen than  I origiiially  administered, at all  events  in the  case of  adultc, you inay reinember that I pointed out that when nitrous oxide is  givei-i witli  oxygen tliere is a soinewhat  greater  chance  of after-sicliness tlian  witl-i  nitrous  oxide  alone.  I  have found that wlien such a  percentage  of  oxygen is  given  tllat  a very tranquil form of  respiration  results,  and especially when  the  . administration is a'prolonged one, after-vomiting is inore liable to arise than if  less oxygen is given, the breathing lrept  softly siioring,' and tlie aclininistration  terminated  after  about  one and a-half or two ininutes. In coi~clusion,  I cannot too stroiigly recoiilmend  every one \vho acliiiinisters nitrous oxide to inalte himself and his patients fc~rniliar  with  the non-aspliyxial method  of  producing  anEs- thesia.  I do not contend that it is  possible in every case to obtain the almost ideal and sleep-lilie condition which  is  met with  in wl-iat  we inay call typical cases.  Rut in  the great majority it is possible ; and it is witli the majority that Jve  are conceraed.  In those  cases in  wliich  the use  of  oxygen,  for some reason  or  anotlier, does not  produce such  satisfactory efiects as one could desire, we must, of  Course, fall back on the pure gas and  terminate tl-ie administration witli the custoii~ary syinptoins.  But  sucl-i cases are so highly  exceptional  that they  need not be talren into consideration. I cannot close these remarks without expressing my thanlts to  Messrs.  EartIi  &  Co.,  the inalrers  of  the apparatus,  for their patience in carrying out the worlr which has been placed in their hands. 

Further observations on the use of oxygen with nitrous oxide

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