458 DANGERS OF TRACHEOTOMY. 



indeed, after the lapse of an hour or two the introduction of the cannula 

 may be difficult, or even impossible. Whilst the horse is in the stable, the 

 opening of the tube may be covered with a metal cap, or stopped with a 

 cork, which will prevent dust, seeds, etc., entering the windpipe. Double 

 tubes have been recommended to obviate the necessity for changing the 

 cannula. They are generally used in man (Fig. 364). Whilst the outer 

 tube lies in the trachea, the inner can be cleaned from time to time. But 

 this form, shown in Fig 364, must be condemned, because the curvature 

 of the upper part is too slight, and that of the lower part too great ; the 

 lower portion, as already stated, should be quite straight. In double 

 tubes this curvature cannot be avoided ; hence they are unsuitable, and 

 can only be used where the trachea is very near the surface. This model 

 also possesses another fault — its opening lies at the side. Injuries from 

 its lower border are certainly thus avoided, but the lateral opening coming 

 in contact with the mucous membrane, hinders passage of air. 



To obviate the necessity for a cannula, Strauss recommends cutting 

 out an oval piece from the trachea, with precautions against injuring 

 the mucous membrane, which is sutured to the skin. But Hering doubts 

 whether this operation can be successfully done, and Holler's experience 

 tends in the same direction. In the absence of a cannula, hooks may be 

 introduced on either side into the tracheal opening, and held apart by 

 tapes passed round the animal's neck. 



As a temporary expedient, a piece of gaspipe, the neck of a bottle, 

 or the spout of a coffee-pot may be inserted. To save animals from 

 threatening suffocation, there is often insufficient time to proceed 

 according to rule. Most practitioners, furnished merely with a 

 bistoury, have on occasion been forced to operate in a dark stable, 

 to find the middle line of the trachea as they best could, and insert 

 a tube. Despite these difficulties, the parts usually heal well. 



Krieshaber has recommended an operation under the title of 

 " tracheotomie sous-cricoidienne," in which an incision is made 

 immediately below the cricoid cartilage ; the crico-traeheal ligament 

 is divided, and a double-limbed cannula introduced. The position 

 of this ligament is easily discovered by palpation, especially in horses, 

 where the muscles of the neck are not greatly developed. With 

 the head extended, the operation is not difficult in quiet animals. 

 This method has the advantage of only slightly impairing the animal's 

 appearance, and facilitates direct examination and treatment of 

 the larynx, while the action of the tube, moreover, widens the larynx, 

 and it is said that, after wearing the cannula for a time, animals 

 sometimes cease roaring. This may perhaps result from the irri- 

 tative process produced by the cannula fixing the arytenoid cartilage 

 on the paralysed side. 



The most frequent complications of tracheotomy are formation 

 of excessive granulations round the wound and thickening of the 

 mucous membrane with narrowing of the lumen of the trachea 



