Respiratory distress is one of the most stressful emergencies. Animals often present on a knife edge. The need for rapid recognition and determination of the cause of respiratory distress needs to be balanced with stress-free handling.

The key to successful respiratory distress cases is having a good grasp of normal respiratory anatomy and physiology. The respiratory system can be divided anatomically into six main regions; upper respiratory tract (nasal passages, pharynx, larynx, and trachea), lower airways (bronchi and bronchioles), lung parenchyma, pleural space diaphragm, and chest wall (ribs and intercostal muscles). During each breath, air is inspired and moves via the upper and lower airways to the lungs through an active process involving the diaphragm and intercostal muscles. The diaphragm contracts and flattens and the intercostal muscles contract causing the ribs to move up and outwards. This creates a negative pressure gradient from the nose to the thoracic cavity causing air movement and air expansion of the lungs. Expiration is passive, elastic recoil of the lungs secondary to the relaxation of the diaphragm that expels air from the lungs. The chest wall is not actively involved in expiration, but the abdominal wall muscles may assist when there is increased expiratory effort (Lowewen et al. 2022).

When examining an animal in respiratory distress, it is very important to observe the animal as they breathe. This allows for assessment of the movement of the chest and abdominal wall alongside their breathing rate and effort.

Commonly used terms to describe abnormal breathing patterns include asynchronous breathing, an inverse breathing pattern, and paradoxical breathing (Sigrist et al. 2011). During normal inspiration, the abdominal wall may move synchronously with the chest wall; the contraction of the diagram pushes the abdominal contents down and subsequently forces the abdominal wall out (Robinson et al. 2002).

Asynchronous, inverse, and paradoxical breathing are terms often unused interchangeably to describe the outward movement of the chest and abnormal inward movement of the abdomen during inspiration; however, there are inconsistencies in the definition of inverse and paradoxical breathing in the veterinary literature, and therefore, it is recommended in an attempt to avoid confusion and keep it simple, the term asynchronous is used; the chest and abdominal wall are moving asynchronously.

An asynchronous breathing pattern is a very sensitive indicator of pleural space disease but has lower specificity; in other words, the absence of this breathing pattern can make you less suspicious of pleural space pathology, but it should not be used alone to diagnose pleural space disease. This breathing pattern, alongside the presence of reduced lung sounds on auscultation, can further support a diagnosis of pleural space disease (Sigrist et al. 2011; Le Boedec et al. 2012). An asynchronous breathing pattern has also been associated with chest wall pathology, diaphragm dysfunction, and severe upper respiratory obstruction (De Troyer et al. 1982; Smith et al. 2004; Ludwig et al. 2000; Raillard et al. 2017).

Upper respiratory obstruction can be readily identified due to the presence of loud inspiratory noises without the need for a stethoscope (Sigrist et al. 2011). A stertor, a low-pitched sound, is associated with nasopharyngeal pathology, and stridor, a high-pitched sound, is most commonly associated with laryngeal pathology (Clarke 2015). Early recognition of the upper respiratory tract as a cause of respiratory distress is crucial as this pathology is associated with hyperthermia and may substantially worsen with handling; therefore, these patients usually require cooling interventions and early administration of anxiolytic or mild sedatives before a full physical examination is performed.

Expiratory dyspnoea with noticeable abdominal “push” and elevated respiratory rates are most commonly detected in patients with lower airway disease, and although associated with lower airway disease, wheezes are less consistently auscultated in these patients (Corcoran et al. 1995; Sigrist et al. 2011; Chalifoux et al. 2021).

Tachypnoea, commonly described as a respiratory rate of greater than 40–44 breaths/minute, is commonly encountered in a wide range of respiratory diseases. However, tachypnoea can also occur secondary to non-respiratory disease as well as in healthy animals. In healthy cats, respiratory rates in excess of 100 breaths per minute have been documented in cats on initial examination; therefore, the respiratory rate in isolation is not a reliable indicator of primary respiratory disease (Dijkstra et al. 2018; Sigrist et al. 2011). Respiratory rate should still be assessed and recorded, and it is particularly useful to assess trends in the respiratory rate to monitor the patient’s progression as well as the effect of your interventions. History and other physical examination findings may help in determining the relative significance of the elevated respiratory rate. For example, when you encounter an elevated respiratory rate in Cavalier Kings Charles Spaniel with known mitral valve disease, you should suspect congestive heart failure and, in an emergency setting, can consider trial treatment with diuretics prior to further investigations (Hezzell, et al. 2020).

Point-of-care thoracic ultrasound has become increasingly popular in small animal veterinary practice and can help with respiratory localisation. Alongside history, physical examination findings can rapidly confirm the presence or absence of a pleural effusion, as well as being particularly helpful in expediating the diagnosis of cardiac disease and congestive heart failure and monitoring the effect of treatment (Loughran et al. 2019; Ward et al. 2017, Murphy et al. 2021).

Animals with respiratory distress are on a knife edge. Accurate respiratory localisation is key to successfully managing these cases and involves close attention to not only the animal’s breathing rate and effort but also their chest excursion relative to the abdomen as well as the presence of any respiratory noise. Taking the time to attempt to localise the respiratory pathology can streamline diagnostics minimising stress for both you as the clinician and the patient under your care.

References

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