References
Laryngeal assessment in dogs: a clinical review
Abstract
This article reviews the literature describing the anaesthetic and ancillary drugs used during the assessment of laryngeal function in dogs, and summarises the evidence for their use in clinical practice. A review of the literature was conducted using PubMed and Google Scholar, with the search terms ‘laryngeal assessment dogs’, ‘laryngeal collapse’, ‘laryngeal paralysis’, ‘premedication laryngeal assessment’, ‘induction agent laryngeal assessment’ and ‘dogs’. Further studies and reports were obtained from the reference lists of the retrieved papers. Related anaesthesia textbooks were also reviewed. Drugs used to induce anaesthesia affect laryngeal function by diminishing the laryngeal reflex. Based on the current literature, premedication using acepromazine and an opioid allows for the assessment of laryngeal examination without impairing laryngeal motion. Dexmedetomidine in combination with an opioid may offer an alternative, but there are no studies comparing these sedative drugs directly. Examination times were shorter with propofol compared to alfaxalone, while ketamine was not recommended as an anaesthetic induction agent for this purpose. The use of doxapram hydrochloride may be helpful, particularly when airway assessment remains equivocal. At low doses, doxapram causes minimal increases in arterial blood pressure and heart rate.
The larynx regulates air flow to the ventilatory tract, protects the lower airway from aspiration during swallowing, and controls phonation. Diseases commonly affecting the larynx include paralysis, collapse, stenosis and neoplasia. Each condition results in an alteration in air flow that can increase the work of breathing. If air flow is completely occluded, collapse may occur. Dogs with conditions affecting the larynx present to their veterinarian with respiratory stridor, a change in phonation, coughing or gagging (Greenfield, 1987; Burbidge, 1995). The presentation and progression of clinical signs can be highly variable. Diagnosis of pathology affecting the larynx is initially based on the animal's clinical history and physical examination. A definitive diagnosis is obtained with a functional and structural laryngeal examination using either sedation or a light plane of general anaesthesia preceding intubation.
Laryngeal assessment can be challenging because the plane of anaesthesia should relax the jaw muscles to allow examination without inhibiting laryngeal reflexes and inspiratory efforts. As the level of anaesthesia increases, breathing may become shallow, or apnoea may occur alongside cessation of active laryngeal movements (Burbidge, 1995). Drugs used to induce anaesthesia reduce laryngeal reflexes (Burbidge, 1995). The effect of different sedative and anaesthetic drug combinations, assessment methods and complementary diagnostic aids for examining the larynx has been investigated.
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