365

MINIMUM DOSAGE LOCAL ANAESTHESIA.*

By ADRIAN COWAN~ M.B., B.Ch., B.Dent.Sc. (U. Dubl.), F.D.S.R.C.S. Eng.

I H A V E chosen the subject of local anaesthesia for my Address this evening because since my student days it has fascinated me that we should have in our hands an agent which can relieve pain so efficiently

and allow us time to work deliberately in sensitive tissues without the disconcerting sense of urgency that a suffering patient implies.

Efficient though it is in infiltration, this control is all the more dramatic in nerve blocks, in which, by depositing anaesthetic solution at a specific point, often quite deep in the tissues, a precise area of anaesthesia can be predicted.

]n dent is t ry nerve blocks are used for four main reasons : (i) Where bone is too dense for an infiltration to penetrate to the

nerve required, as in the mandibular molar region ; (if) where a large area of the jaw is involved in a surgical or conserva-

tive procedure ; (iii) where inflammation in the operative area precludes infiltration

locally ; (iv) for the relief of neuralgic pain, or as an aid in the diagnosis of

its origin. William Stewart Halstead was the first known person to block the

mandibular nerve with the aid of the then new anaesthetic, cocaine, at the end of 1884 (Cahnl), but it was in 1905 when Einhorn produced Novocaine synthetically with its admit tedly less potent anaesthesia, but very much lower toxicity, that dental interest became aroused. Later Braun in Leipzig added adrenaline to the mixture, and by 1914 the technique of nerve blocking was beginning to make its presence felt (or perhaps I should say, not felt). F rom that time on, the words which have been wri t ten and spoken about anaesthetic technique are countless.

Unfor tunate ly famil iar i ty may breed, if not contempt, a certain carelessness, and, while interest in local anaesthesia remains high, a degree of hit-and-miss is still apparent . In these days of vastly improved materials failures in anaesthesia should be largely confined to anatomical and physiological abnormalities, and faul ty technique should be at a minimum.

I have seen in my own time in dent is t ry the switch from the potent but highly toxic Locosthetic (which had a cocaine base) to Novocaine and its derivatives such as Monocaine, to the newer rapid acting drugs of which the Swedish Lignocaine, or Lidocaine, or Xylocaine is the one with which I have most experience. I believe that it is all the more important to adhere to strict technique with the better agents, especially in teaching at student level, because their greater efficiency will mask inaccurate positioning.

To this end there are two considerations to be borne in mind. First, the anatomy :

I t is necessary not only to know what nerve is to be anaesthetised, but also the precise anatomy of the tissues which surround the needle from

*Presidential Address to Section of Odontology, March, 1959.

366 IRISH JOURNAL OF MEDICAL SCIENCE

the time of its entry. I t is our good fortune that most of our injections are guided by contact with bone at some stage; this provides reassuring confirmation of position.

Second, and this has a bearing on the first point, sterility. Of all wounds the punctured wound caused by a spike in which impaled bacteria or particles are driven deep into the tissues is the most dangerous, and every injection is potentially such a wound. Hence the importance of a sterile chain in loading syringe, hub and cartridge, and of swabbing with antiseptic, or flaming the rubber diaphragm of the cartridge, which will be penetrated by the needle.

My own practice is to keep the cartridges for the day in a container of surgical spirit, or surgical Dettol. The syringes, however, and the needles are boiled, as I consider spirit inadequate for them. In the United States, autoclaving is advocated because of the possibility that the virus of toxic jaundice may be transmitted in this way.

Used cartridges are discarded even if half empty, because the elastic rebound of the rubber plunger may allow aspiration of infected material into the cartridge, and re-use of that tube on another patient is a false economy which may be dangerous.

Lastly, the site of the injection should be thoroughly swabbed, prefer- ably with a surface anaesthetic which contains antiseptic, so that the

needle is not contaminated during entry, for it is sometimes forgotten how deeply the point may go into the soft tissue especially in the spheno- palatine and mandibular blocks, and since the pterygoid space is the gateway to most of the other faseial spaces about the jaws, deep-seated infection at this level can set up a serious cellulitis.

In Germany much work has been done on the extra-oral approach to the injections and Her-

:FIG. 1.--Pterygoid space mann 2 wrote an account last year in which he (after Tulley). claimed that much maxillo-facial surgery can be

performed under nerve blocks rather than under general anaesthesia. In the technique which he describes, the maxillary nerve is blocked at the foramen rotundum through the space between the zygomatic arch and the sigmoid notch of the mandible, and the mandibular nerve is approached at the foramen ovale from a point above the most prominent part of the zygomatic arch. Personally, I feel that these techniques are needlessly complex for dental and maxillo-facial work and provide no particular advantages over the intra-oral approach.

In the title of this Address I mentioned " minimum dosage ". I became interested in the onset times and side-reactions of anaesthetic agents about ten years ago, and carried out a number of clinical investi- gations then (Cowan 3) and during the ensuing years with various anaesthetic solutions, using Procaine as a standard base from which to make comparisons. I confirmed the opinion then expressed by many other workers that Lignoeaine is more efficient and rapid acting than Procaine, and was able to show in addition that it is effective in very much ,~maller doses (less than half that of Procaine) and that its onset time is predictable in most cases with a considerable degree of precision.

MINIMUM DOSAGE LOCAL ANAESTHESIA 367

Perhaps I should explain the term " onset time " as I use it. I t is the time in minutes and seconds from insertion of the needle until the development of anaesthesia suitable for operative work, and therefore includes the injection time. The operative work includes preparation of sensitive cavities, extraction, pulp extirpation, minor surgery and other procedures involving the raising of a periosteal flap, and the onset of anaesthesia is judged by the only person competent to give an opinion -- the patient. ~Tests were made on sensitive areas after injection, deliberately starting before anaesthesia was fully developed, and repeated at 15-second intervals until the requirements were fulfilled, when the times were noted.

The mean onset time for infiltration is of the order of 1 min. 20 sees., for mental blocks, 1 min. 40 secs. and for mandibular blocks, 4 mins. 30 sees., and although figures much below the last may be recorded, it was shown statistically that anaesthesia with Lignocaine may be confi- dently predicted in these times in 98 per cent. of injections (Cowan').

Many of us have been in the habit of giving a little extra anaesthetic to make sure, and sometimes quite a lot extra where a difficult extrac- tion is contemplated for example. Although this is done with the best intentions it causes a good deal of distortion and stretch- ing of tissues if 2-4 ml. are injected into the rather sparse dental mueosa, and is a frequent cause of after-pain and trismus. In addition, by introducing more anaesthetic and more adrenaline, the chances of side- effects or hypersensitivity reactions are increased, and these can be quite severe, especially if a small vein is inadvertently penetrated.

The advantage of the small dosage of Liguocaine, and its low adrenaline content (1:80,000 as compared with 1:30,000-1:50,000 for other anaesthetics) is that the incidence of these two complications may be reduced to their lowest level if a minimum dosage technique is employed.

To this end ] have suggested 4 the following doses of Lignocaine for everyday dental procedures :

0"25 ml. : Single teeth, or two adjacent upper premolars: Routine restorations.

Routine restorations. 0"5 ml. : Upper' molars, canines, incisors : Routine extractions.

0.75 ml. : Mental blocks. 1.0 ml.: (i) Two or three adjacent

restorations. Pulp extirpation.

(ii) Single rooted teeth : Jacket or ~ crown preparation.

(iii) Infraorbital block (iv) Spheno-palatine block.

1.5 ml. : Surgical extractions, except lower molars. 1.8 ml. : Mandibular blocks. I have used these doses to my own satisfaction during the last three

years, and believe that a number of colleagues in various placea have been converted also.

In the diagnosis of obscure neuralgic pain a knowledge of the onset time altogether with extremely low dosage infiltrations (of the order of 3-4 minims) will, in the presence of pain, help greatly in identifying

upper molars : Routine

368 IRISH JOURNAL OF MEDICAL SCIENCE

the causative tooth in the upper jaw, or lower incisor region by limiting the area of anaesthesia to one or two teeth. If the pain is controlled wi th in the onset t ime des ignated above, the tooth anaesthetised is responsible: a similar procedure with mental and mandibular nerve blocks is used in the lower premolar-molar region.

It is highly probable that before much time has passed a substance will be synthesised which, when injected into the controlling site of an anacsthetised area, will rapidly bring that tissue back to normal again; apart from its use in reducing the discomfort of prolonged anaesthesia after brief dental procedures, the value of such a substance for diag- nostic purposes where pain has been deliberately or accidentally masked would be inestimable.

The film* which you are about to see describes the amounts used and the onset times and extent provided by them, and is an attempt to teach technique with the three main features of anatomy, sterility, and economy of material as its theme, on the grounds that when anaesthesia ~is adequate there is nothing to be gained by exceeding the smaller dosage.

*A s o u n d fi lm m a d e b y t he a u t h o r was t h e n shown to i l lus t ra te a n a e s t h e t i c t e chn ique for all t h e inf i l t ra t ions a n d ne rve blocks used in t he buccal cav i ty , a n d e m p l o y i n g the m i n i m u m dosage t e c hn i que m e n t i o n e d above .

References 1. Cahn , L. (1953). Oral Surg., Oral Med., and Oral Path., 6, 1, 55. 2, I-Iermann, M. (1958). Int. Dent. Journ., 8, 4, 671. 3. Cowan, A. (1952). Irish J. Med. Sci., vi, 160. 4. Cowan, A. (1956). J. Dent. Res., 35, 6, 824.

GASTRO-INTESTINAL LESIONS IN BULBAR POLIOMYELITIS.

N. J. AINL E Y, M.D. Bell., M.R.C.P.I.

St . Luke ' s Hospi ta l , Brad ford .

A CUTE ulceration of the upper gastro-intestinal mucosa sometimes occurs in bulbar poliomyelitis. These ulcers are usually super-

"ficial, but they may give rise to haemorrhage or perforation (Lenarsky et al., 1~ Schlumberger, ~3 Hoxsey, 7 Schaberg et al.12).

Another gastro-intestinal complication is rupture of the oesophagus, cases of which, all of which were fatal, have been reported by Kinsella et al., ~ Erskine, G Cook et al., 3 Brooke William, 2 Maciver et al. 11

Two fatal cases of bulbar poliomyelitis with gastro-intestina 1 com- plications are here presented, the first complicated by haematemesis, the second by rupture of the oesophagus.

Case Repor t s CASE 1 . - - A m a n , aged 31, was a d m i t t e d to Leeds R o a d Hosp i t a l , B rad fo rd on J u n e 14,

1958. D u r i n g t he p rev ious 4 d a y s he h a d compla ined o f ach ing in t h e back a n d in b o t h legs, a n d on t h e d a y before admi s s i on he was unab l e to m o v e h is legs.

On admission. There was pares is of t h e left side of t h e pa l a t e a n d t o n g u e a n d t he e rec tor sp ine musc l e s o f t h e neck a n d back , t h e d i a p h r a g m a n d t he a b d o m i n a l rect i were also affected. B o t h legs were pa ra lysed , wi th t h e excep t ion of t he p l a n t a r f l exors a n d t h e smal l musc le s of t h e feet .

Progress. He h a d a smal l h a e m a t e m e s i s on t h e d a y a f te r admi s s ion ( June 15). Gas t r ic a sp i r a t ion a n d i n t r a v e n o u s D a r r o w ' s so lu t ion were s t a r t ed . B lood- s t a ined f luid was still be ing a sp i r a t ed on J u n e 16, w h e n he became confused . Some i m p r o v e m e n t fol lowed t he ~ransfus ion o f t h r ee p i n t s o f whole blood a n d t he bleeding a p p e a r e d to h a v e s topped . However , on J u n e 17 h is genera l cond i t ion de te r io ra ted , b u t h a e m a t e m e s i s did n o t recur , a n d he d ied on J u n e 18.