Dr Guy, Dean of the Edinburgh Dental School, introduced some years ago a method of giving ethyl chloride in mixture with nitrous oxide. Guy’s objective was to utilise the many excellent features of the drug without incurring the risks which are apparently inherent in it when a dose sufficient in itself to induce full narcosis is used. Given in mixture with gas, a much smaller dose suffices.
Fig. 42.—Guy’s inhaler for N2O and Ethyl Chloride.
His original apparatus is shown in Fig. 42, the details are shown in Fig. 43. The horizontal limb of a 3-way gas tap is prolonged half an inch. In each side of the prolongation is a hole. The bag mount has in its side also one hole, which is connected by a universal ball and socket joint, with the rubber tube to which the ethyl chloride vial is attached. An indicator on the outside of the bag mount and a mark upon the outside of the horizontal limb of the 3-way tap, serve by their apposition or the reverse to show whether the ethyl chloride vial is in direct continuity with the interior of the inhaler. For purposes of description, Dr Guy calls these two positions, “in register” and “out of register.”
To use the instrument, the ethyl chloride vial is removed, and the side pipe attached to a cylinder of nitrous oxide. The indicator of the 3-way tap is put at “air” and the bag mount “in register.” The bag is then filled with gas by opening the head of the cylinder. The bag mount is now put “out of register,” and the side tube disconnected with the cylinder. The bag, being closed, remains full of gas.
Fig. 43.—Guy’s Instrument for Gas and Ethyl Chloride. Details of valve piece and bag mount, showing side tube for attachment of Ethyl Chloride vial.
A suitable dose of ethyl chloride is now squirted into the vial. To an adult, Dr Guy gives 3 c.c.: on no account is this dose exceeded: children take 1½–2 c.c.—even adults often get less than 3 c.c. The vial is now attached to the side tube again, and the inhaler is ready for use.
After application of the mask to the face, the 3-way tap is at once pushed over to “no valve” and the patient rebreathes the gas in and out of the bag for some six or eight respirations. The bag mount is now turned round “into register,” and the ethyl chloride tipped into the bag. In a further twenty-five seconds the mask may be removed and the operation begun.
The available period of anæsthesia is eighty to ninety seconds, counting from the instant of the removal of the inhaler.
This method was in use for some years at the Dental Hospital of Edinburgh; no instance of danger to life was ever seen. With so small a dose of ethyl chloride, the erect position necessary for the purposes of dentistry is perfectly safe.
Fig. 44.—Diagram of the method introduced by Dr Guy and the author for giving Nitrous Oxide and Oxygen, with or without Ethyl Chloride.
This inhaler, of course, will serve admirably for giving ethyl chloride without gas, and the author habitually uses it for giving the drug by the “vapour” method.
In 1911, Dr Guy and the present author modified the method so as to permit the use of oxygen with the nitrous oxide. The inhaler which they then introduced serves also for nitrous oxide and oxygen, unaided by ethyl chloride, and the author has by its means given gas-oxygen to a considerable number of major surgical cases. He now, however, limits its use to short anæsthesias, and uses a sight-feed or a Clarke apparatus for long cases.
Fig. 45.—The Guy-Ross Inhaler for Nitrous Oxide and Oxygen, with or without Ethyl Chloride.
In Fig. 44 will be found a diagram showing the method by which the oxygen is introduced. The 1-gallon oxygen bag is either attached directly to a cylinder, or suspended on an upright as shown in Fig. 45. In either case, the bag is, before the administration, moderately filled with oxygen: one bagful will suffice for a short anæsthesia, and the supply of the oxygen from the cylinder is therefore turned off at once. For long cases, of course, a small trickle of oxygen into the bag is required to replace the gas used.
In the outlet pipe from the oxygen bag is placed a ball syringe of 2 ounces capacity. A valve in the pipe obliges the flow of oxygen to take place in one direction only when the bulb is squeezed, viz. from oxygen bag to inhaler.
The remainder of the apparatus is identical with Guy’s original inhaler, except that the bag is of 2-gallon capacity, and is perforated at its base by a Y-tube, one limb of the fork bringing in the nitrous oxide, the other the oxygen.
A few breaths of pure nitrous oxide gas are usually allowed “on the valve.” Rebreathing is then instituted, and the addition of oxygen begun. The amount required to each type of patient can only be learnt with experience, but the average is one full compression of the bulb every ten seconds. If anæsthesia is not complete at the end of one minute, put the indicator to “valves” again, and allow the patient nearly to empty the bag. Then push back the indicator to “no valves,” and refill the bag with nitrous oxide by opening the cylinder with the foot key. Some four to six compressions of the bulb are made while the nitrous oxide is running in. The time will now have come to add the dose of ethyl chloride if it be judged necessary at all. This will have been placed in the vial before the administration is begun. After emptying the ethyl chloride into the bag of the inhaler, anæsthesia should be complete in twenty-five seconds.
The same small doses of ethyl chloride are used as is the case with Guy’s original method.
After a little practice under supervision, students at the Dental Hospital learn to use this method safely and well. No example of risk to life has arisen after eight years’ daily experience.[11]