Brodbelt reported that 63% of cats that died were intubated compared to 48% of cats that were not.¹ For short procedures (<30 minutes) intubation increased the risks of death. Respiratory obstruction as a cause of death has been reported more frequently in cats than in dogs indicating that close attention to the airway in this species is important. Respiratory problems are most common in the post-operative period suggesting airway trauma and edema may be involved. Tracheal injury related to intubation is well documented in cats^2,3 as is damage to the larynx.⁴ Approximately 70–75% of tracheal rupture reports are related to the cat having undergone a dental procedure, with presenting signs of subcutaneous emphysema, coughing, gagging and varying degrees of dyspnea occurring 4 hours to 12 days after the procedure. These reports indicate that great care should be taken when placing an endotracheal tube in a cat. Intubation should be performed under the correct plane of anesthesia (not too light), under direct vision (laryngoscope). The use of topical local anesthetics (usually lidocaine) applied to the arytenoids and vocal cords, in correctly metered doses (if given by aerosolized spray) can be used if laryngospasm occurs. However, these drugs may cause mucosal damage⁵ and laryngeal function will be inhibited for the duration of action of the local anesthetic making the cat more susceptible to aspiration. Patience is required and the tube should only be advanced when the vocal cords are open. Distal tracheal tears are associated with a poor outcome² therefore the length of the endotracheal tube (ETT) should be measured against the cat prior to insertion and the tip of the tube should not extend beyond the point of the shoulder. Hardie² documented that over-inflation of the cuff is the cause of tears and that they occur directly over the cuff. One theory is that cuffs are overinflated for dental procedures due to a fear of aspiration. Larger tears are more difficult to repair or medically manage therefore the choice of type of endotracheal tube should be made with care. Low volume high pressure (referring to the cuff) and high volume, low pressure tubes are available; the latter have a longer cuff so should be used with caution. The cuff should only be inflated only if necessary; the seal can be tested by closing the pop-off valve and squeezing the reservoir bag - air is added in small increments to the cuff until there is no leak at 15 cm H₂O. A small (3 ml) syringe should be used to prevent over-inflation. The use of water soluble gel on the cuff improves the airway seal, even at low cuff inflation pressures.⁶

Thought should be given to using non-cuffed endotracheal tubes (with or without pharyngeal packs), oxygen masks, laryngeal mask airways (LMAs) or supraglottic airway devices (SGADs) as alternatives to cuffed endotracheal tubes. For short procedures not involving the oral cavity an oxygen mask will usually suffice; however, in brachycephalic cats, establishing an airway is always advisable.

LMAs have not been designed specifically for cats however a supraglottic airway device (the Cat v-gel® (Docsinnovent Ltd, London, United Kingdom) has been designed to conform to the shape of the feline larynx and pharynx and has been evaluated.^7,8 The time to obtain a clinically acceptable capnograph (end tidal carbon dioxide) reading was shorter when a SGAD (median time 44 seconds) was used compared to an ETT tube (median time 109 seconds) suggesting that the airway can be more rapidly secured using the former technique. Compared to placement of an ETT, less propofol is required to secure an airway with a SGAD.⁹ There was also less airway discomfort and stridor and greater food intake after use of a SGAD compared to an ETT.^8,9

SGADs are also available for rabbits, a species that is notoriously difficult to intubate. As in cats, time to secure an airway is faster with these devices than an ETT and are less likely to cause trauma. Another advantage of SGADs is that they do not enter the trachea and therefore do not damage the delicate mucociliary tree. The latter is involved in the movement of particles from the lungs and bronchial tree to the pharynx for expulsion and is an important protective mechanism against infection.

References

1.  Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Risk factors for anaesthetic-related death in cats: results from the confidential enquiry into perioperative small animal fatalities (CEPSAF). Br J Anaesth. 2007;99(5):617–623.

2.  Hardie EM, Spodnick GJ, Gilson SD, Benson JA, Hawkins EC. Tracheal rupture in cats: 16 cases (1983–1998). J Am Vet Med Assoc. 1999;214(4):508–512.

3.  Mitchell SL, McCarthy R, Rudloff E, Pernell RT. Tracheal rupture associated with intubation in cats: 20 cases (1996–1998). J Am Vet Med Assoc. 2000;216(10):1592–1595.

4.  Hofmeister EH, Trim CM, Kley S, Cornell K. Traumatic endotracheal intubation in the cat. Vet Anaesth Analg. 2007;34(3):213–216.

5.  Rex MA, Sutton RH, Reilly JS. The effects of lignocaine spray on the laryngeal mucosa of the cat. Anaesth Intensive Care. 1983;11(1):47–51.

6.  Blunt MC, Young PJ, Patil A, Haddock A. Gel lubrication of the tracheal tube cuff reduces pulmonary aspiration. Anesthesiology. 2001;95(2):377–381.

7.  Crotaz IR. An observational clinical study in cats and rabbits of an anatomically designed supraglottic airway device for use in companion animal veterinary anaesthesia. Vet Rec. 2013;172(23):606.

8.  van Oostrom H, Krauss MW, Sap R. A comparison between the v-gel supraglottic airway device and the cuffed endotracheal tube for airway management in spontaneously breathing cats during isoflurane anaesthesia. Vet Anaesth Analg. 2013;40(3):265–271.

9.  Barletta M, Kleine SA, Quandt JE. Assessment of v-gel supraglottic airway device placement in cats performed by inexperienced veterinary students. Vet Rec. 2015;177(20):523.