Intubating a tiger
Positioning an endotracheal tube correctly in the trachea of a tiger (“intubation”) is a procedure best taught practically rather than just described in text. For this purpose learning from an experienced zoo vet in the controlled circumstances of a captive environment is thoroughly recommended.
A basic knowledge of the anatomy of the tiger’s mouth, larynx (entrance to the trachea) and trachea is essential – see illustrations here.
Endotracheal tubes (“ET’s”):
Straight endotracheal tubes are the most appropriate design, and those made of silicone will generally cause less damage to the upper respiratory tract than those made from harder red rubber. For tigers endotracheal tubes should be fitted with cuffs to enable the airway to be sealed after placement. Adult tigers require tubes of internal diameter ranging from 14 to 22 mm, although a very large cat may need a tube of up to 26mm internal diameter. Endotracheal tubes should be long enough to pass well beyond the larynx but not so long that they will enter the main bronchus. The correct length is assessed as being the distance between the nostrils and the point of the shoulder.
Position of tiger:
Intubation is only possible in a tiger that is well anaesthetised and relaxed, with negligible jaw tone.
With the tiger in a prone position (i.e. lying on its front), an assistant stands over the shoulders and lifts the head up while keeping it in line with the spine. In other words the head is lifted into a position as if the tiger were looking up at the sky. This is easiest to do by holding each side of the upper jaw with fingers placed behind the upper canines. Twisting the head to one side or the other will make intubation more difficult.
(NB: Some anaesthetists prefer to intubate tigers in the supine position – i.e. lying on their backs – or even on their sides. Both are possible, but in the supine position it is more difficult to position the head correctly unless the back of the neck is laid over the edge of a table, a rolled up blanket, sandbag etc., allowing the head to be extended fully on the neck. This technique is perhaps more suitable for captive animals where facilities are more convenient. Intubating larger tigers lying on their side can be complicated by the larynx falling to the lower side of the mid-line. This requires the anaesthetist to elevate the larynx back into a central position by applying upwards pressure from the outside of the neck, thus facilitating adequate visualisation and ease of intubation.)
Visualising the larynx & intubation:
The mouth is then opened to its full extent by the anaesthetist pulling the lower jaw downwards without moving the head. The assistant needs to keep the head up. The tongue is pulled as far forward as possible and then held over the lower incisors. It can be held in this position by the person intubating or another assistant. At all times the head must be kept straight – i.e. in line with the animal’s spine.
To ensure operator safety it is wise at this point to apply a mouth prop or gag. The simplest design is a length of thick-walled plastic tubing of appropriate length placed between the upper and lower canine teeth of one side, with the tips of the canines lodged in the ends of the tube. As the canines of a tiger are curved and tapered, it is possible to fit a prop without damaging the gums. Polypropylene water pipe is a suitable material from which to make mouth props. NB: Such tube props are only intended for use in fully anaesthetised cats. They may be crushed or split by a semi-conscious tiger.
All areas of the mouth and pharynx (i.e that part of the throat behind the mouth and in front of the esophagus and larynx), should be cleared of any debris, mucous, regurgitated material etc. This may require suction devices or a tube attached to a 50ml syringe.
A long-bladed straight or gently curved laryngoscope is introduced into the mouth over the upper surface of the tongue with the blade tip resting just in front of the epiglottis. The back of the tongue is then depressed by pushing the laryngoscope blade downwards which lowers the epiglottis and allows the entrance to the larynx to be seen. The laryngoscope blade should not touch the epiglottis or used to pull the epiglottis forward and down as that may cause trauma and resultant oedema. Intubation is then performed under direct vision. Passing the tube through the larynx, past the vocal cords and into the trachea is best attempted during inspiration (when the tiger is breathing in), and is facilitated by applying a thin film of a lubricant sch as “KY gel” to the end of the tube. After insertion the cuff should be inflated. Unlike in domestic cats, laryngeal spasm is rarely a problem in tigers unless attempts at intubation are excessively clumsy. NEVER FORCE A TUBE THROUGH A NON-RELAXED LARYNX as this may cause injury.
After placing the endotracheal tube a tape tied around the free end can be secured behind the tiger’s ears or behind the upper or lower canines to prevent the tube moving within the trachea or even working its way out. The tape can also be tied to a mouth prop if still in place. Rather than use cotton bandage tape strips of bicycle inner tube can be used which will tend to slip less when wet.
Removing an endotracheal tube:Removing the tube is best done while the tiger is still quite deeply anaesthetised. It should not be left in until the cat is coughing or gagging on the tube. The cuff is deflated, and then the tube is removed gently immediately after an inspiration – i.e. when the lungs are full of air.