An important point is to keep the can nula as free as possible from the copious discharges which are formed for a couple of days after the operation. An intelli gent attendant should be carefully in structed to withdraw the inner cannula every two hours, to cleanse it carefully with hot water, then to reintroduce it into the outer tube after having effect ively freed the cavity of the latter of any mucus that might have accumulated there. This may be done by means of a feather, a piece of sponge, or absorbent cotton securely and tightly fastened to a suitably bent piece of thin, brass wire.
The patient should be provided with two complete cannulas so as to occasion ally be able to withdraw the outer tube also and cleanse it thoroughly. This can be done after a couple of days, the wound having had time to assume the shape of the outer cannula, thus enabling it to remain patulous for a short time after the instrument has been withdrawn com plete. The extra cannula, previously warmed to avoid exciting cough, should be introduced immediately upon the withdrawal of the other, using, to assist its entrance, a Cohen pilot. This instru ment, introduced into the outer cannula, presents a blunt-pointed knob which separates what tissues might. impede the progress of the latter. It should, of course, be instantly withdrawn as soon as the tube is in position. The occa sional (once or twice a week after the first few days) withdrawal of the tubes serves also to avoid what danger the cor rosion of a metallic cannula might incur.
Cases have been reported in which pieces of such a cannula, broken off at an eroded point, occasioned alarming symptoms.
Occasionally, granulations are formed at the external tracheal orifice. and in the trachea itself, the latter being espe cially the case when a fenestrated tube is employed. Strong astringent solutions sometimes suffice to destroy them; in some cases, however, surgical measures are necessary.
When the cannula is to be withdrawn permanently, the natural breathing powers of the patient should be tested by closing the aperture of the cannula with a stopper. If this is borne without difficulty, the instrument may be with drawn, but kept within easy reach, with pilot in position, for sudden replacing if necessary. As a rule, however, this is not required, and the wound closes up after a few days to finally heal com pletely a week or two later.
The cannula has occasionally to be worn permanently, the patient, to speak, being obliged to place his finger upon the external opening. In this case. Liter's tracheotomy-tube, the inner can nula of which contains a silver pea. whose object is to arrest the expired cur rent of air, so as to enable it to pass be tween the vocal bands, will be found very useful, rendering the use of the finger to close the tube unnecessary.