Endotracheal intubation is used to secure the patient's airway allowing delivery of inhalational anaesthesia and supplementation of inspired oxygen to an anesthetised patient. Additionally, the endotracheal (ET) tube protects the airway from aspiration of harmful material should regurgitation occur. The ET tube may be connected to a ventilator to support breathing in a compromised patient, for example one with traumatic brain injury.
Previously, there has been a tendency to use uncuffed rather than cutted ET tubes in small patients such as cats. However, the use of cuffed tubes has advantages even in patients of this size. In human medicine, research over the past several years for paediatric patients has indicated either that cuffed ET tubes are not disadvantageous compared to uncuffed tubes (Chen et al, 2018; de Wit et al, 2018), or that they are advantageous (Mukhopadhyay et al, 2016; Chambers et al, 2018), and their use has increased, although more data are needed (De Orange et al, 2017; Chen et al, 2018).
This short article discusses some of the risks and benefits of using a cuffed ET tube in cats.
Practical aspects
Laryngoscopy is invaluable when performing endotracheal intubation in the cat, whether using a cuffed or uncuffed tube. A cuffed ET tube may be more difficult to pass into the trachea than an uncuffed tube, because of the difficulty of seeing beyond the size and shape of the cuff. Consequently, the internal diameter size of the selected cuffed ET tube may be slightly smaller than the corresponding non-cuffed tube.
After passing the ET tube into the trachea, the cuff should be inflated as necessary to seal the airway. There is a risk of over-inflation of the cuff and potential damage to the tracheal mucosa from this. A cuff manometer is essential to ensure correct filling of the cuff without over-inflation. It is important to note that palpation of the minimum occlusive volume to fill the cuff is unreliable even in experienced hands (White et al, 2017).
The use of a cuff manometer is shown in Figure 1. With an intracuff pressure of 30 cm H2O, the vast majority of cats do not have an audible leak around the cuff (Bird et al, 2018). The American Association of Feline Practitioners Anaesthesia Guidelines (Robertson et al, 2018) recommend an inflation pressure range of 20–30 cm H2O as being safe for use in cats.
Comparing three methods of cuff inflation
In addition to the cuff manometer method, other methods by which appropriate cuff inflation may be determined are the pilot baloon palpation method and the minimal occlusive volume method. While these methds have been in use traditionally, the cuff manometer method is preferable because of its improved consistency, as shown in Table 1.
Table 1. Comparing three methods of cuff inflation
| Method | Pilot balloon palpation | Minimum occlusive volume | Cuff manometer |
|---|---|---|---|
| Technique | Digital palpation of the pilot balloon until the anaesthetist feels that the endotracheal tube is safely sealed | Rebreathing bag is set to 50% of full volume. Adjustable pressure limiting valve is closed. Normal breath(s) given. Cuff inflated until no leak audible at mouth | Cuff inflated to 20–30 cm H2O using a manometer |
| Consistency | Highly variable | Reasonable | Precise |
| Additional equipment needed | No additional equipment required | No additional equipment required | Single-use or multi-use syringe device(s) must be purchased |
Implications of use of cuffed ET tubes
There are benefits of using cuffed ET tubes; there are also potential drawbacks. Both must be considered when deciding what type of ET tube to use:
- The airway seal of a cuffed ET tube is superior to that of the non-cuffed tube. This is beneficial because it reduces exposure of personnel to volatile agent leakage
- The disadvantage of a superior seal is the increased risk of barotrauma when combined with factors such as high fresh gas flow rates and assisted ventilation
- A small, uncuffed tube may fail to produce an adequate capnography trace (Figure 2)
- Appropriate inflation of a cuffed tube ensures adequate sampling for capnography.
- Care is needed to deflate the cuff before removing the ET tube.
- Partial deflation may be used with caution to assist in removal of debris, for example following dental procedures
- The risk of iatrogenic damage to the tracheal mucosa if withdrawing a cuffed tube while still partially inflated must be weighed against the advantage of removing aspirated foreign material
- Endotracheal intubation is a risk factor for anaesthetic safety. High-volume, low-pressure cuffs should be used rather than traditional red rubber high-pressure, low-volume cuffs. A safe inflation pressure in cats (unlikely to cause tracheal mucosal damage) is 20 cm water (Bird et al, 2019).
- Intubation is likely to take a few seconds longer for a cuffed tube: the time required for initial placement of the tube and the need to inflate the cuff
- Cuffed ET tubes are approximately 20% more expensive than non-cuffed tubes
- If the tubes are used repeatedly, it may be more difficult to clean a cuffed tube than a non-cuffed tube.
- The cuff should be inspected for damage before use.
- An effective check is to leave the cuff inflated after cleaning and check that it has not deflated before use.
Conclusions
Securing the patient airway is an essential part of safe general anaesthesia. In the UK, most feline practitioners will be aware of the simplicity and limitations of a non-cuffed ET tube. A cuffed ET tube may improve the airway ‘seal’, which is advantageous for both patient and (via reduced leakage of volatile anaesthetic agents) for personnel. However, a cuff manometer is essential to minimise the risk of iatrogenic tracheal damage.
KEY POINTS
- Currently uncuffed ET tubes are widely used in feline practice.
- Cuffed ET tubes may offer patient and practitioner benefits such as reliable capnography traces.
- Care should be taken to avoid cuff overinflation and the risk of iatrogenic tracheal damage.
- Use of a cuff manometer is highly recommended to ensure correct cuff inflation.