Page 103 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

associated with eating and drinking. Exercise tolerance motion. In patients with signs of chronic upper airway
decreases over time and inspiratory stridor becomes more obstruction, or following a recent dyspnoeic event, the
VetBooks.ir episodes of severe dyspnoea, cyanosis and syncope. varying degree of oedema and erythema due to turbulent
apparent. The most severely affected animals may have
mucosa overlying the laryngeal cartilages may show a
instead of laminar airflow.
Various degrees of dysphagia may also accompany laryn-
geal paralysis, due to pararecurrent laryngeal nerve dys-
function, and this is correlated with an increased likelihood
of aspiration pneumonia. The physical examination find- Emergency treatment
ings for an animal with laryngeal paralysis are typically Animals with laryngeal paralysis can be presented in either
unremarkable with the exception of the respiratory system. a stable or unstable condition, depending on the severity
Inspiratory stridor that does not improve with open-mouth of the dysfunction (paresis versus complete paralysis) and
breathing is often present. Referred upper airway noise prevailing environmental conditions. In an emergency
can be heard on thoracic auscultation. Animals with con- presentation, patients are presented with severe breathing
current pneumonia or non-cardiogenic pulmonary oedema difficulty, cyanosis or collapse, as a result of their upper
may have pulmonary crackles on auscultation. airway obstruction. Excitement, exercise or increased
ambient temperature is usually the catalyst for such an
aborator ndin s event in an animal with laryngeal paralysis. With prompt
medical therapy, most patients recover initially. Excitement
Consistent bloodwork abnormalities are uncommon in and increased ambient temperature lead to an increased
patients with laryngeal paralysis. If concurrent pneumonia respiratory rate and laryngeal oedema. As the speed of
is present, leucocytosis with neutrophilia may be present. air flowing over the arytenoid cartilages increases, the air
Animals with hypothyroidism can have hypercholesterol- pressure decreases. This tends to draw the arytenoids
aemia, hyperlipidaemia and elevated liver enzymes. further towards each other. The upper airway obstruction
Thyroid testing is recommended in these cases. If myas- causes distress to the animal and leads to greater inspir-
thenia gravis is suspected, edrophonium chloride testing atory effort, which exacerbates the turbulent airflow
or acetylcholine receptor antibody titres can be performed. through the rima glottidis, worsening the laryngeal oedema
and paradoxical laryngeal motion.
Initial stabilization should include sedation with anxio-
Radiographic examination lytics (acepromazine at a dose of 0.02–0.1 mg/kg i.v., maxi-
Radiographic examination is typically utilized to evaluate mum dose 3 mg). If the patient’s stress level is increased
the thoracic cavity for evidence of pneumonia, mega- by the restraint needed to facilitate intravenous injection,
oesophagus or any mediastinal mass that could be the intramuscular injection is a reasonable second option.
cause of laryngeal paralysis. Secondary cardiac changes Intravenous corticosteroids may be used to reduce laryn-
(right ventricular hypertrophy) due to chronic upper airway geal oedema. Dexamethasone at a dose of 0.2–1 mg/kg i.v.
obstruction can be seen. Hiatal hernia has been reported q12h or prednisolone sodium succinate at a dose of
in association with laryngeal paralysis and is probably 1 mg/kg i.v. q24h may be used initially. Supplemental
secondary to the extreme subatmospheric intrathoracic oxygen therapy is indicated after the sedation has been
pressure generated in dogs during an upper airway administered. Patients in an acute crisis are often hyper-
obstructive crisis. Cervical radiographs tend to be un- thermic, and active cooling should be instituted using water
remarkable, although caudal retraction of the larynx can baths, ice packs or alcohol applied to the foot pads. Finally,
be seen in animals that are dyspnoeic. for animals with refractory upper airway obstruction, intu-
bation or emergency tracheostomy can be considered.
Laryngeal examination
Medical management
A sedated laryngeal examination is the most definitive
diagnostic tool for laryngeal paralysis. Historically, sodium Medical management is considered conservative manage-
thiopentone was used to induce a light plane of anaes - ment and is reserved for patients with mild clinical signs.
thesia for functional examination of the larynx; more Laryngeal paralysis is a progressive disease and clinical
recently, propofol or alfaxalone has been used. To evaluate signs will worsen with time. The hallmarks of medical
the larynx, the patient must be at a deep enough plane of management are lifestyle changes. This means avoiding
anaesthesia to allow the mouth to be opened, but not so strenuous exercise, maintaining a low ambient tempera-
deep that the pharyngeal and laryngeal reflexes are com- ture, and sedation as needed. Clients need to be coun-
promised. If the anaesthetic plane is thought to be too selled on the fact that clinical signs will progress and
deep, the patient should be given time to recover from the that their pet could have an acute respiratory event at any
anaesthetic event until the pharyngeal gag reflex or cough time. Ultimately, surgery is recommended when medical
reflex returns. management is not sufficient to control clinical signs.
With the animal in sternal recumbency and the mouth
opened at the level of normal head carriage, the arytenoid
cartilages and ventrally located vocal folds should retract Surgical management
laterally during each inhalation and return to a neutral posi- The goal of surgery in the treatment of laryngeal paralysis
tion on exhalation. Subjectively decreased or absent is to palliate the clinical signs associated with inspiratory
movements and/or ‘paradoxical motion’ of the arytenoid failure. This may be achieved by the permanent removal or
cartilages or ‘paradoxical flutter’ signifies paresis or para- repositioning of the laryngeal cartilages to widen the rima
lysis. For animals taking short shallow breaths, doxopram glottidis. According to Poiseuille’s law, the resistance to
can be administered intravenously to increase the tidal fluid flow through a cylinder is proportional to the radius of
volume and respiratory rate. It is also helpful for an assis- the cylinder (at its narrowest point) to the fourth power,
tant to mark each attempt at inhalation so that the laryn- which means that even a modest change in glottic radius
geal observer can focus on the corresponding laryngeal can make a profound difference in resistance to airflow.

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