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\begin{document}

\title{Complications of orotracheal intubation in the horse}



\author[1]{Patrick Burns}%
\affil[1]{Atlantic Veterinary College}%


\vspace{-1em}



  
  \date{June 06, 2024}


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\begin{abstract}
Difficulty to extubate any patient is not a problem commonly thought of
during general anaesthesia. This case report describes some of the
factors that lead to this predicament and the successful surgical
removal of the endotracheal tube via a tracheostomy. This case report
also highlights some of the deficiencies in the clinical practice of
veterinary anaesthesia. Further research is required for the selection
size criteria of endotracheal tubes in all species and the monitoring of
cuff pressures during general anaesthesia.%
\end{abstract}%



\sloppy


Main Document

\textbf{Introduction}

This clinical case study describes the highly unusual situation where a
horse was not able to be extubated without the aid of a tracheostomy
assisted extubation. A similar case study has been described in the dog
where extubation was assisted via a tracheostomy (Grzywa \& Barker,
2022). It is interesting to note that the majority of similar case
reports describe the use of either silicone (Romano \& Portela, 2020;
Sanchis Mora \& Seymour, 2011) or red rubber tubes (Grzywa \& Barker,
2022). There was one report in a cat where a reused polyvinyl chloride
tube was difficult to remove and required the instillation of extra
lubrication around the ET cuff (Norgate \& Jimenez, 2017). The cuff in
this instance was bunched-up thus increasing the effective outer
diameter of the ET tube. Could the wider cuff profile of high-volume,
low-pressure polyvinyl chloride endotracheal tubes encourage people to
use smaller tubes? This is something I have observed in several
university clinical practices however it is hard to estimate how it
influences general veterinary practice.

This clinical case study not only describes the situation associated
with the ET tube becoming lodged in the trachea but also how the authors
achieved the successful removal of the ET tube. Both aspects have
clinical relevance to practitioners of anaesthesia. Some of the
clinically pertinent aspects of this case study will be discussed in
further detail below, followed by clinical recommendations.

\textbf{Endotracheal tube size selection}

Investigators have tried to use anatomical predictors for endotracheal
tube selection in the dog however none of these methods have been found
to be accurate (Tong \& Pang, 2019). There are recommendations for
endotracheal tube selection in adult humans as well as for paediatric
patients (Karmali \& Rose, 2020; Miller et al., 2014). It is interesting
to note that the recommended inner diameter endotracheal tube size for
human adults is approximately 50 to 60\% of the tracheal at the level of
the cricoid assuming the average tracheal diameter at this point
(Karmali \& Rose, 2020). There are differences in outer diameter
dimensions based upon the different manufacturers of endotracheal tubes
and this may come into play when selecting an appropriate size of
endotracheal tube. (Karmali \& Rose, 2020).

There are currently no recommended endotracheal tube selection criteria
for horses. The large variety of horse breeds and chondrodysplastic
breeds make this difficult. The large tidal volumes required for horses,
encourage the use of the largest endotracheal tube possible to
facilitate the use of mechanical ventilation. Using relatively small
endotracheal tubes (c.f. human recommendations) may result in increases
in airway resistance and reductions in the alveolar minute ventilation
and subsequently cause elevations in PaCO\textsubscript{2}. Another
issue is the higher cuff pressures in these relatively smaller silicone
endotracheal tubes could result in higher tracheal-cuff interface
pressure, especially with overinflation (Richardson \& McMillan, 2017).
This needs further research into what is the idea endotracheal tube size
that does not injure the respiratory tract and can still facilitate
ventilation.

\textbf{How to assess the adequate amount of air in an ET tube cuff}

The authors of this clinical case report describe palpating the pilot
balloon to assess the pressure within the endotracheal tube cuff. This
technique has been reported elsewhere and the limitations of this
technique has been described (Briganti, Portela, Barsotti, Romano, \&
Breghi, 2012; Veen \& Grauw, 2022). Perhaps more sensitive techniques
such as auscultation over the larynx (Burns, 2020) or the use of
mechanical ventilation (Ferreira, Allen, De Gasperi, Buhr, \& Morello,
2021) would be a better alternative. The latter is based on the fact a
mechanical ventilator will not cycle properly until there is an adequate
seal around the endotracheal tube cuff. Spirometry is another modality
that could be used for this purposed based upon this author's clinical
experience in both small and large animal practice. In small animals, I
have detected differences between an unsealed and sealed endotracheal
tube cuff using as little as 0.2mL of air injected into the cuff based
upon the pressure-volume loop. Unfortunately, there is only one large
animal anaesthetic machine that has this capability11Tafonius, Hallowell
EMC, Pittsfield, MA 01201, USA. There is no current consensus on the
verification of the adequacy of a seal between the ET tube cuff and
tracheal wall.

\textbf{The importance of lubrication}

The use of lubrication gel is commonly applied to endotracheal tube to
both help facilitate the passage of the tube through the glottal opening
and to aid with the formation of a seal around the endotracheal tube
cuff and the tracheal wall (Nishioka, Usuda, Hirabayashi, Maruyama, \&
Andoh, 2017). The instillation of lubrication gel has also been
instilled to help remove endotracheal tubes that were stuck in the
trachea (Romano \& Portela, 2020) as was the case in this report.
Lubrication gel also helps minimize the risk of the endotracheal tube
`sticking' to the tracheal mucosa. I have observed this during my
clinical practice, especially with nasotracheal tube placement. In this
case, the authors speculate that the tight fit of the endotracheal tube
resulting in oedema formation at the location of the cuff. Dorsal
recumbency would have contributed to this risk due to the increase in
hydrostatic pressures (Binetti et al., 2018). Once these changes occur,
it can very difficult to remove an endotracheal tube as evident by the
efforts of the authors of this case study and other techniques used to
help minimize this tracheal swelling, including the instillation of
adrenaline (Grzywa \& Barker, 2022). It is interesting to note that the
use of benzodiazepines and neuromuscular blockers (Grzywa \& Barker,
2022) have also failed to induce tracheal relaxation in other reported
clinical situations.

\textbf{Effect of body position}

As mentioned above, placing a horse in dorsal recumbency will lead to
increases in hydrostatic pressure within the tracheal mucosa. This is
especially true for the Trendelenburg position. This effect could
contribute to the formation of tracheal oedema thus increasing the
tracheal-cuff interface pressure. Another effect of body position is the
degree of neck flexion and how it impacts endotracheal cuff pressures
(J. H. Park, Lee, Lee, \& Kim, 2021; S. Park, Kwon, \& Kim, 2023; Seol,
Jin, Oh, Byun, \& Jeon, 2022). Changes in neck position will change the
cuff pressure. This effect was greater in tapered cuffs as compared to
cylindrical shaped cuffs (J. H. Park et al., 2021; Seol et al., 2022).
It is interesting to speculate what would have been the effect of neck
flexion on the ``tight' fit of the endotracheal tube in this clinical
case since theoretically this should lead to longitudinal shortening of
the tracheal and a slight increase in diameter of the tracheal.

\textbf{Clinical recommendations to minimise problems with associated
with the use of endotracheal tubes.}

\begin{itemize}
\tightlist
\item
  Pressure-check the endotracheal tube prior to use to assess for leaks
  and problems with the pilot balloon (Merlin \& Mileham, 2020). This is
  especially true for reused endotracheal tubes.
\item
  Use auscultation to aid in the detect of the minimal occlusive
  pressure of the endotracheal tube cuff.
\item
  Check the intracuff pressure after the first ten minutes of
  anaesthesia to avoid reductions in the cuff pressure and potential
  micro-leaks (Shin et al., 2018).
\item
  Monitor the cuff pressure whenever the position of the neck has been
  changed.
\item
  Appreciate that it is possible to have a problem with the pilot
  balloon or the inflation channel (Merlin \& Mileham, 2020).
\item
  Consider using a manometer to assist in monitoring cuff pressures.
\item
  Consider replacing any ET tube that feels `snug' during an initial
  intubation.
\end{itemize}

Further recommendations can be reviewed at a previous clinical
commentary (Burns, 2020).

The clinical case reports such as this one, are important to disseminate
to the rest of the veterinary community. Not only have these authors
described the successful treatment of an anaesthesia associated
complication; this report also highlights some deficiencies that are
present in our anaesthetic management of tracheal intubation. Further
research into endotracheal tube selection and verification of cuff seal
are required.

Declarations

The author has no conflicts of interests to declare.

Acknowledgements

References

Binetti, A., Mosing, M., Sacks, M., Duchateau, L., Gasthuys, F., \&
Schauvliege, S. (2018). Impact of Trendelenburg (head down) and reverse
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Briganti, A., Portela, D. A., Barsotti, G., Romano, M., \& Breghi, G.
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