Differences between panting, dyspnoea and tachypnoea in dogs
Introduction
Owners are often alarmed if they notice that their pet has an increased breathing rate or altered respiratory pattern. When this occurs, a higher respiratory rate is usually presumed to be the result of a respiratory system problem and so the dog requires urgent veterinary assistance. While it is true that most dogs with a severe respiratory disease usually have these clinical signs, this is not always the case. Moreover, what owners sometimes interpret as difficulty breathing is actually just physiological panting or tachypnoea.
How can we differentiate between panting and tachypnoea in dogs?
Panting is defined as a marked increase in respiratory rate and can even reach rates of 200–400 breaths/min. Panting dogs generally breathe with their mouths wide open and tongue hanging out. When a dog is panting, the tidal volume (the amount of air passing through the lungs per breath) decreases, whereas the minute ventilation (the amount of air entering and leaving the lungs in one minute) remains the same or increases.1
Tachypnoea in dogs is also characterised by an increase in respiratory rate, but it is not as marked as when panting, because it generally remains in a range of 40–90 breaths/min. Dogs with tachypnoea have a normal or elevated tidal volume and may breathe through the nose or mouth, but their tongue normally remains in the mouth. Although not always the case, tachypnoea may be accompanied by dyspnoea. Dyspnoea is defined as difficulty or laboured breathing or the conscious perception of breathlessness or a lack of air.2
Causes of panting and tachypnoea in dogs
PANTING
Dogs may pant for various reasons, and they are not all pathological. In fact, in most cases, panting is the body’s physiological response to an increase in ambient temperature, with the aim being to maintain a normal body temperature by increasing evaporation from the upper respiratory tract.1,3 In this scenario panting is alternated with periods of normal breathing.
However, when panting becomes excessive, it could be indicative of a disease that requires veterinary attention.
Causes of excessive panting include anxiety or fear, pain, pyrexia, opiate treatments, heat stroke, intense exercise, hyperadrenocorticism, brachycephalic airway syndrome, hypocalcaemia, vascular compromise and diseases of the central nervous system that affect the respiratory centre.1,3,4
TACHYPNOEA
Tachypnoea increases the rate of gas exchange in the alveoli. That is why it is considered a normal physiological response during exercise in order to compensate for the tissues’ increased oxygen demand. Notwithstanding, the presence of tachypnoea may also be a sign of an underlying disease, although not necessarily a primary respiratory disease.
Diseases that can course with tachypnoea in dogs include:
- Respiratory diseases: laryngeal paralysis, chronic bronchitis, tracheal collapse, pneumonia, pulmonary oedema, infiltrative lung diseases and pulmonary fibrosis
- Pulmonary thromboembolism
- Cardiogenic pulmonary oedema
- Shock
- Pulmonary hypertension
- Pleural diseases: effusions, pneumothorax, diaphragmatic hernia and fractured ribs
- Diseases affecting the respiratory muscles: diaphragmatic hernia, myasthenia gravis or polyradiculoneuritis
- Processes affecting oxygen transport capacity: anaemia and haemoglobin disorders
- Altitude hypoxia
- Compression of the diaphragm: ascites or abdominal masses
- Metabolic acidosis: for example, secondary to chronic kidney disease, diabetes mellitus or diarrhoea
- Severe obesity1,3,4
Diagnostic approach
The diagnostic approach for patients with tachypnoea initially depends on clinical suspicion. For example:
- Tachypnoea in the absence of dyspnoea suggests the primary cause is not respiratory, so other tests should be prioritised.
- On the other hand, the presence of rales and stridor suggests that the problem may involve an upper respiratory tract disease.
- Crackles are usually associated with a pulmonary parenchymal disease.4
So, once the patient is stabilised and depending on the initial suspicion, the first steps in the diagnosis may be imaging (cervical spine and chest X-rays) or laboratory tests (blood count, blood chemistry, urinalysis). Various other tests should then be performed depending on the results, for example, a stool analysis, hormonal determinations, serology, coagulation tests, blood gas analysis, computed tomography, echocardiography, abdominal ultrasound, respiratory endoscopy or cytology of any effusions.4
Conclusions
As veterinary practitioners, we must also learn to quickly decide if a dog is panting or has tachypnoea or dyspnoea. Communicating this information to the owners as soon as possible is also crucial, as these signs often generate quite a lot of anxiety. In any case, given the differential diagnosis is fairly broad, the various diagnostic tests should be structured according to clinical suspicion and the steps to follow explained to those responsible for the animal’s care.
