The operator can then lower the mandible and carefully withdraw the tongue to open the mouth wide . Use of a laryngoscope is recommended as it allows for the tongue to be depressed at the base and the opening of the trachea to be clearly seen ; this makes it possible to estimate the tube size ( from the few sizes prepared ) that can be placed , as a larger or smaller tube than anticipated may be needed ( Figure 3 ).

Often the larynx in cats may be closed , so patience is important and the ETT should be advanced in inhalation ; repeatedly trying to insert the tube may cause damage to the tissues and increase the risk of laryngospasm ( Hughes , 2016 ). A small amount of sterile lubricant can be applied to the lower part of the tube and cuff to help it slip into the trachea ( Figure 5 ).

Figure 3 . Using a laryngoscope aids visualisation and depression of the tongue .

The tube should be advanced over the epiglottis , depressing it ventrally and between the arytenoid cartilages into the trachea . Cats are susceptible to laryngospasm , so a lidocaine spray can be applied to desensitise the larynx and , after 90 seconds , intubation can be attempted . Intubeaze ^® ( Dechra Veterinary Products ) is commonly used , which delivers 2 – 4 mg lidocaine in one spray , so care should be taken to avoid overdosing ( Murrell & Ford-Fennah , 2020 ) ( Figure 4 ).

Figure 4 . Example of lidocaine spray .

Figure 5 . Example of sterile lubricant that can be used on the ETT .

Correct positioning of the tube can be confirmed using capnography . If the ETT has been inadvertently placed in the oesophagus , there will be no exhaled carbon dioxide detected . In the absence of capnography , condensation may be detected within the ETT . The ETT should then be secured with a bandage to the upper jaw ( behind the ears in brachycephalic patients and cats ). Care should be taken to not tie the bandage too tightly . Careful loosening and re-tying during long procedures ( without moving the ETT ) will relieve pressure on the lips and gums . The anaesthetic breathing circuit should be connected and oxygen ( O ₂

) provided . The reservoir bag on the breathing system and the thorax will move simultaneously with correct placement and a couple of ‘ sigh ’ breaths may be provided to ensure thoracic movement ( especially if apnoea following induction is noted ).

Inflation of the cuff to prevent gas leakage should be done using a manometer ( maximum pressure 25 mmHg or 34 cmH ₂

O ) or by filling the circuit with O ₂

, closing the pressure relief valve , squeezing the bag and listening for gas leaks while inflating , until no leaks are heard ; the valve should then be re-opened . The volatile anaesthetic agent can be safely turned on and respiration ( along with other parameters ) can be monitored . If turning of the patient is required ( e . g . during dental procedures

54 Veterinary Nursing Journal