Figure 14 . A transmylohyoid intubation technique in a cat . Image © Andrew Foster .
Airway humidifiers
Figure 13 . A patient being intubated in lateral recumbency prior to an MRI scan . Image © Simon Goulty .
Other intubation routes
Some patients may require alternative intubation techniques to gain airway access , including tracheostomy or pharyngostomy tube placement . The technique and management of these tubes are not described further in this article , but an overview is provided in Table 3 .
Table 3 . Differences between tracheostomy and pharyngostomy tube placement .
Tracheostomy tube
A tracheostomy tube ( TT ) is placed in the ventral neck , through the third and fourth tracheal rings .
Patients may require emergency placement of a TT before surgery or in recovery , or have this planned in oral surgery .
TT placement in cats has a high incidence of complications ( 87 %) [ 22 ] .
Pharyngostomy tube
The ETT does not extend from the rostral part of the mouth , but instead from caudal to the lower mandible via a surgical incision .
A transmylohyoid approach has been successful in both cats and dogs [ 23 , 24 ] . The ETT extends from a surgical incision that is more rostral than the pharyngotomy approach ( Figure 14 ).
When dry gases are provided to a patient , they can damage the airway mucosa and cilia , and thicken respiratory secretions . During low-flow anaesthesia , the reaction of soda lime and carbon dioxide in a circle breathing system creates heat and moisture , which can preserve the respiratory mucosa . Alternatively , heat and moisture exchanges ( HMEs ) and bubble-through humidifiers can be used in breathing systems with high fresh gas flows .
HMEs have porous hygroscopic material that absorbs heat from the expiratory breath , creating condensation . An HME can be used to maintain a moist respiratory environment but is ineffective for use in the preservation of the patient ' s body temperature [ 25 , 26 ] . It will , however , increase the apparatus dead space and can increase the labour of breathing .
Bubble-through humidifiers are not usually used in anaesthesia but are common in the intensive care setting with supplemental oxygen systems . Although they do not heat the gas as it passes through the distilled water or saline , they do produce large water droplets that condense in the airway .
Considerations for intubation and extubation
Intubation considerations
Before induction , the patient should be preoxygenated with 100 % oxygen . Preoxygenation with a face mask for 3 minutes delays the onset of desaturation ( SpO 2
< 90 %) by creating a high concentration of oxygen within the alveoli ( and FRC ) for gas exchange for 5 minutes if there is a delay in securing the airway [ 27 ] . Using a tight-fitting face mask and providing oxygen at 5 – 6 l / min can produce
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