The flask holding a litre, or other convenient reservoir, is filled with Dakin's solution, coloured to a rose-tint with permanganate of potassium. This coloration distinguishes Dakin's solution from physiological saline solution, and most assuredly prevents mistakes.
1st. Continuous instillation gives better results than intermittent instillation. But it is not so frequently employed. In fact, it is only suited to wounds where the liquid can remain in quantity, or to small wounds for which a single conducting tube sheathed with absorbent fabric will suffice. The flow of the liquid is regulated by means of a screw pinch-cock interposed between the flask and the drop-counter. Five or six drops per minute will usually give sufficient moisture to this type of wound. It should be remembered that the pressure of the liquid at the surface of the wound is represented by the difference in level between the wound and the lower portion of the drop-counter, and not between the wound and the upper portion of the reservoir. If the drop-counter be placed too low, on a level with the wound, it will not work. It is equally necessary to be aware that drop-by-drop instillation should only be used when the end of the irrigating tube is connected up with only one of the little tubes which distribute liquid to the wound. Under these conditions, continuous instillation permits the degree of concentration of the antiseptic liquid on the surface of the wound to be maintained under better conditions than intermittent instillation.
Intermittent instillation is used for the greater number of wounds. As a matter of fact, the great majority of wounds are extensive and irregular and have several openings. To these continuous instillation is not suited.
Intermittent instillation is carried out by releasing for a few seconds, every two hours, the pinch-cock which is placed on the irrigating tube just below the reservoir.
Liquid immediately escapes from the flask (irrigating bottle or reservoir), and spurts out in great abundance from every hole of all the conducting tubes. The duration of flow of the liquid should be very short, lest the patient be flooded out. The quantity thus injected varies, according to the nature of the case, from 20 to 100 c.c.1 and sometimes more. As a general rule, the injections are made every two hours; occasionally, with greater frequency. When the apparatus is installed as we have described, the work of the nurse in charge of the instillations is very light. In fact, as in each case she halts at the foot of the bed, she has only to press for a few seconds the spring "pince de Mohr" fixed on the irrigating tube.
Intermittent instillation is practised every two hours, but it would be of advantage to practise it more frequently, as the hypochlorite decomposes very rapidly when in contact with the tissues. On the other hand, more frequent instillations often make too great a call on the energies of the nurses. In order to diminish the amount of manual work required, and, where desirable, to increase the number of instillations, attempts have been made in the direction of automatic instillation. The automatic devices which have hitherto been employed are based on the principle of the intermittent fountain. As a rule, they work well under experimental conditions, but in the actual conditions of surgical treatment they reveal defects. In the case of small discharges more especially, the siphon fails to prime, and the liquid runs drop by drop into the tube, or the siphon does not discharge itself, and again the liquid flows drop by drop. It has therefore been necessary to abandon apparatus based on this principle, as its working was very irregular, and required almost as much attention as the ordinary apparatus.
1 Say from 3/4 oz. to 3 1/2 oz.
As a result of experiments carried out by Lecomte du Nouy in the Compiegne laboratories, an electromagnetic distributing apparatus for the irrigation of wounds has been invented. It consists of an individual electro-magnetic distributor and a clockwork device for making contact. The electro-magnetic distributor consists of the bobbin of an electric bell, a core, an armature, the latter movable, and a wooden stopper, which contains the whole, and is fixed upon the neck of the ampoule. The current, automatically transmitted, raises a valve which closes the bottom of the ampoule, and the liquid flows until the current ceases. The principle consists in the utilisation of the well-known solenoid coil, through which is sent, for a very short time, a current of sufficient strength to produce a mechanical effect. The bobbin, which could not resist such a current if long continued, can easily carry it for a few seconds. Calculation shows, in fact, that the instantaneous rise of temperature - taking into account the fact that radiation is practically nil- is, for a bobbin of 9 ohms resistance, covered with copper wire 0.4 mm. in diameter, 1.23° C. per second for a current of 2 amperes. This current seems at first sight to be a considerable load for such fine wire, but as it flows through the bobbins for one or two seconds only, it does not overload them, nor does it entail any appreciable expense. In fact, a group of 12 such appliances, served by a current of 220 volts pressure, consumes barely 0.15 kilowatt per month, so that it costs only a shilling or so yearly. Contact is established every half-hour by means of a clock or clockwork train, and the current is sent through all the appliances, mounted in series, the number of the groups in series depending on the tension of the current and the resistance of the bobbins. It is important that the contacts shall be of regular duration, and the contact-making device must be reliable in working. Daufresne has worked out an arrangement of this kind by means of a very simple alteration of a striking clock. One clock suffices to control any number of such appliances - enough, for example, to serve 500 or 1000 beds.
Each time contact is made by the clock the valves of the ampoules are lifted for two seconds, and the liquid flows. The quantity of the liquid reaching the wound may be regulated by reducing as required the calibre of the supply-tube. As the frequency of the irrigations does not increase the work of the staff, and as it is of advantage that the liquid in the wounds should be renewed as often as possible, instillations are now practised every half-hour.
2nd. The total quantity of liquid injected in 24 hours varies from about 250 to 1200 c.c.1 In very extensive wounds, more can be injected without inconvenience. The only fixed rule is, that the wound should be kept constantly moistened by the liquid, without the patient being made uncomfortably damp.
3rd. In intermittent instillation, the pressure varies from forty centimetres to a metre. It should be regulated according to the particular needs of the wound and the sensitiveness of the patient. At the moment of commencing the instillation, he experiences sometimes a slight impression of pain which may last some minutes. Sometimes, again, he has only a sensation of chilliness, or actual cold. The patient should never suffer actual pain from the instillation. Should he complain, it shows that an error of technique has been committed. The pain may be due to excess of pressure, or to the wound-opening being too small. If the pressure be too great, the liquid spurts out violently from the apertures in the tubes against the walls of the wounds and bruises the tissues. That is why the pressure should never be greater than one metre. With sensitive patients, a pressure of 20 to 30 centimetres is sufficient. Another cause of pain is retention of the liquid in the wound under pressure. If the incisions are too limited, and if the conducting tubes are too tightly gripped by the tissues or by compresses, the liquid cannot escape freely from the wound. It accumulates under pressure, and the patient feels it. The wound should be freely opened up, so that the liquid may escape without hindrance.
1 Roughly, eight ounces to two pints.