Assessment of Dyspnoea

Respiratory distress is a common emergency in veterinary practice and requires quick recognition, assessment and treatment. Dyspnoeic animals are incredibly fragile and even brief evaluation of the patient may prove fatal, especially in cats. The risks of diagnostic evaluation should be carefully balanced against potential benefits.

First Approach

Determination of the underlying cause using brief, directed physical examination and non-invasive diagnostic tests should be attempted concurrently with stabilisation. Oxygen therapy is indicated in all but the most severe upper respiratory obstruction and should be provided as soon as possible by the least stressful method. It is important to gain a capsule history with particular reference to pre-existing disease, concurrent medication, history of trauma and onset and progression of the condition. This may be obtained while the patient is given oxygen. The first part of the evaluation of the respiratory tract should be to watch and listen. An enormous amount of information can be gleaned from just observation, before even touching the patient.
Constantly changing body position in cats implies a much worse degree of dyspnoea than it does in dogs. Lateral recumbency due to dyspnoea is a serious sign in a dog; however, it often means impending respiratory arrest in a cat.

Inspiratory vs expiratory dyspnoea

The differentiation between inspiratory and expiratory dyspnoea can aid in the localisation of the disease process. Inspiratory dyspnoea with stridor or stertor is associated with dynamic upper airway obstruction, although in cats chronic pleural effusions may be associated with inspiratory dyspnoea without stertor. Expiratory dyspnoea is a feature of feline allergic airway disease. Short shallow respiration and sometimes panting may be seen in some pneumothoraces. Most other causes of dyspnoea will be associated with mixed respiratory patterns. Accurate auscultation requires a methodical approach and a decent stethoscope. All lung fields should be auscultated; left and right lung fields should be assessed and compared for symmetry and should be cross referenced at all stages with respect to what you would expect given the degree of dyspnoea. Abnormal sounds are associated with a number of different disease processes within the airways. Adventitious lung sounds are associated with parenchymal disease.
The distribution of the abnormal lung sounds can provide information as to the cause of the disease. A cranioventral distribution of crackles or harshness in dogs is typically associated with aspiration pneumonia, being the most dependant area of lung. Cardiogenic oedema may be associated with sounds loudest over the heart base. Neurogenic oedema (seen most commonly in puppies after cervical trauma or upper respiratory tract obstruction) usually results in a caudo-dorsal distribution of crackles.
Pleural space disease is associated with the absence of lung sounds. The pattern of dullness provides information as to the possible cause. Animals that have been hit by cars and have pneumothoraces and pulmonary contusions make for complicated auscultations. The contusions cause harshness, whereas the pneumothorax dampens sounds down, resulting in overall normal sounding lungs. However the severe dyspnoea such patients experience should raise suspicion.
Examination of the heart may be warranted for arrhythmia, murmur or gallops. Mucous membrane colour may provide additional information, however it should be remembered that cyanosis is associated with life threatening hypoxaemia. [...]