Plus-Hex CLINICAL
There are several techniques used to inflate an ETT cuff :
• A manometer – this accurately measures the pressure within the cuff against the mucosal wall , where the pressure should not exceed 25 mmHg , or 34 cmH 2
O [ 16 ] . If the cuff is inflated to a pressure above 35 mmHg ( 47 cmH 2
O ), capillary perfusion may become compromised and injury can occur , including tracheal mucosal irritation , ischaemia or necrosis [ 16 ] ( Figure 11 ). Taking this into account , a conservative range of inflation pressures would be 20 – 30 cmH 2
O . The manometer may be attached to a manual pump ( similar to a sphygmomanometer ) or be a syringe-based manometer such as the AG Cuffill and Tru-Cuff devices . In a study , use of the AG Cuffill achieved a higher rate of properly inflated cuffs ( 86.7 %) compared with the Tru-Cuff ( 50 %) [ 17 ] . Two airway manometers are shown in Figures 12a and 12b .
• Minimal occlusion volume ( MOV ) – this is the most popular technique in practice . The technique involves one person delivering a positive-pressure breath to the patient by inflating the lungs to 16 – 18 cmH 2
O and a second person inflating the cuff until no audible leak is heard [ 18 ] . A leak may be heard around the cuff when a positive-pressure breath of 25 cmH 2
O is applied [ 16 ] . Only 3.3 % of cuffs inflated with the MOV technique have been reported as being at a satisfactory pressure [ 17 ] .
Figure 11 . Tracheal mucosa irritation from an overinflated ETT cuff .
Figure 12a . An AG Cuffill .
• Palpation of the pilot balloon and MOV – when used for cuff inflation , optimal intra-cuff pressures are rarely reached , despite no leaks being heard around the cuff when providing PPV . As experience does not affect this skill , a cuff manometer is recommended [ 19 ] .
It is important to note that the cuff of the ETT may increase in size when nitrous oxide is being used [ 2 ] .
An overinflated cuff can be just as dangerous to the patient as an underinflated cuff , which puts the patient at risk of aspirating foreign material and exposes theatre personnel to anaesthetic gases .
Overinflated cuffs can cause tears , from the movement of the ETT during patient positioning or during manipulation of the head during dental procedures . In cats , longitudinal tears form along the length of the trachealis muscle due to trauma when using ETTs . Most tears are approximately 2 – 5 cm in length [ 20 ] . There is no difference in the incidence of tracheal tears between ETT types or when using either HP / LV or LP / HV cuffs ; it is only the length of the injury that differs [ 20 , 21 ] . It may be a personal preference to use larger-sized cuffless ETTs in cats , but unless the diameter is sufficient , the airway may not be fully sealed . Regardless of the species intubated , a patient should always be disconnected from the breathing system while changing recumbency .
Figure 12b . A sphygmomanometer device . Image © Kate Tidey .
Intubation in sternal recumbancy should be practised and mastered by VNs . Patients may also require intubation in lateral recumbency – for example , patients with cervical neck injuries or during cardiopulmonary resuscitation . This technique should be practised by both VNs and veterinary surgeons ( VSs ).
Occasionally , a patient may need to be intubated while in dorsal recumbency ( e . g . if accidental extubation has occurred during abdominal surgery ). During laryngeal tieback or BOAS surgery , the ETT may need to be removed , putting the patient at risk of a respiratory emergency if the airway cannot be confidently secured by someone other than the operating VS . Intubation in lateral recumbency is shown in Figure 13 [ 22 ] ( overleaf ).
Volume 38 ( 3 ) • June 2023
51