Gaining intravenous access allows administration of drugs, fluids and, if necessary, allows intravenous anaesthesia to be rapidly administered; this may be necessary if the patient decompensates and endotracheal intubation to gain control of the airway is required. But if the animal is too stressed by restraint to allow a catheter to be placed, then supplement oxygen and try again later.
Initially observing the patient prior to a physical examination is invaluable in recognising dyspnoea.
Changes in Posture
The patient will adopt positions to minimise any restriction to air flow, restraining the patient prevents these adaptations and can lead to decompensation (see Figure 9.2). Postural changes include the following:
- Flared nostrils, open mouth breathing
- Extension of the neck, and lifting the head
- Abduction of elbows to minimise chest wall compression
- Sitting or lying in sternal recumbancy, and shifting positions.
Changes in Breathing Pattern
Normal respiration is at 15–30 breaths per minute; little chest movement is seen as the diaphragm does most of the work. Inspiration is usually equal in length to expiration. Abnormalities include the following:
- Abdominal effort – contraction of abdominal muscles to help with expiration.
- Paradoxical breathing – severe dyspnoea, intercostal muscle contraction draws the diaphragm forward and the abdomen is sucked in.
- Inspiratory phase longer than expiratory phase, or vice versa.
Mucous membrane colour and capillary refill time provide useful information about the respiratory system. Cyanosis gives a blue coloration to the mucous membranes; this is typically what students are told to look out for as an indication of low blood oxygen levels. Cyanosis will only be present in severe hypoxaemia (<80% arterial blood saturation), so while it is definitely a sign supplementary oxygenation is required, the absence of cyanosis does not mean all is well. The moderately hypoxic animal will still have pink mucous membranes. Pulse oximetry can be useful in confirming the presence of hypoxaemia.
Auscultation of the respiratory system as part of a rapid physical examination provides vital information to help localise the cause of respiratory distress. The cervical trachea, lung fields and heart should be auscultated. Abnormal sounds, or asymmetry in sounds from one lung compared with the other are relevant (see Figure 9.3). Abnormalities may include the following:
- Wheezes: narrowing on the airways likely (e.g. inflammation, masses). If heard on inspiration, upper airway pathology is suspected. If wheeze occurs on expiration, suspect lower airway disease (e.g. feline asthma).
- Crackles: air bubbling through fluid, or opening and closing of small airways. Often indicate pulmonary oedema, haemorrhage or exudates in the alveoli.
- Muffled sounds: suspect pleural space disease, liquid, air, or diaphragm rupture.
- Heart sounds: in dogs the absence of a murmur or dysrhythmia means heart failure as a cause of dyspnoea is unlikely. This is more difficult in cats, as they usually develop myocardial disease rather than valvular disease.
History, observation and physical examination should help to localise the cause of dyspnoea to one of four areas: upper airway, lower airway, lung parenchyma or the pleural space. Having localised the source of the problem, specific stabilisation techniques can be applied where suitable.
The upper airway consists of the nose, mouth, pharynx, larynx and trachea. Causes of respiratory distress at this level are related to partial or complete obstruction. This may be due to a number of factors:
- Brachycephalic obstructive airway syndrome (BOAS)
- Foreign body
- Space occupying lesions (abscess, neoplasia)
- Laryngeal paralysis
- Laryngeal or pharyngeal oedema
Patients with upper respiratory tract obstruction tend to present with audible inspiratory noise (stridor) with a long drawn out inspiratory phase. In cases with an acute onset, such as a foreign body, the patient is often very stressed and panicked.
Stabilisation relies on oxygen supplementation, which helps to calm the patient; gentle technique is required as patients often resent handling of the face or neck. Cases of laryngeal paralysis will often respond to cooling, anti-inflammatories to combat oedema and low doses of sedative as an anxiolytic.
In cases where there is no response to medical management, or where a foreign body is suspected, then urgent control over the airway needs to be gained (see Figure 9.4). Following pre-oxygenation, general anaesthesia is induced and the patient intubated with an endotracheal tube (see Practical techniques in Chapter 8). If intubation is not possible, the clinical team should be ready to immediately place a tracheostomy tube (see Practical techniques at the end of the chapter).
Lower Airway Disease
Disease of the lower airway usually refers to problems with the small bronchi, and coughing is common (non-productive). Dyspnoea, with expiratory effort, and wheezes audible on auscultation are common findings. Common disorders include the following:
- Feline asthma
- Bronchial irritation
- Foreign body
- Smoke inhalation.
These animals usually present due to crises or flare ups of existing problems, or when the disease becomes end stage.
If lower airway disease is suspected, radiography is helpful, and should show a ‘bronchial pattern’ with minimal signs of alveolar disease (see Figure 9.5). As well as oxygen supplementation, treatment may include bronchodilators, corticosteroids and antibiotics.
Lung Parenchymal Disease
The alveoli are concerned with gas exchange. Interference with the ability to expel carbon dioxide and absorb oxygen in the alveoli will give rise to dyspnoea. Interference in the process may be caused by filling or collapse of alveoli, or an increase in the thickness of the diffusion barrier due to infiltration. Common disorders include the following:
- Pulmonary oedema
- Neurogenic pulmonary oedema (choking, strangulation, seizures)
- Pulmonary contusions
- Pulmonary haemorrhage
- Pulmonary inflammatory diseases.
Patients often present with hypoxaemia, harsh lung sounds and crackles, and a productive cough and nasal discharge may be present. Careful auscultation of the heart should be carried out to try to ensure congestive heart disease is not present (e.g. mitral valve murmur in dogs, gallop rhythm in cats).
Thoracic radiographs are useful; the distribution of pathology can be an aid to identifying the underlying cause. If radiographs cannot be obtained due to severe respiratory distress, then treatment should be initiated based on the likely diagnosis given both history and physical findings. Pneumonia may be due to respiratory tract pathogens, or secondary to aspiration of foreign material or gastric contents. Broad spectrum antibiotics with nebulisation and coupage are indicated where bacterial pneumonia is suspected; diuretics are indicated in suspected cases of pulmonary oedema.
Pleural Space Disease
The pleural space is the potential space that exists between the pleura of the lungs and the pleura of the chest wall. Accumulation of air, fluid or soft tissue within the pleural space leads to reduced ventilation and so poor respiratory function (see Table 9.1). The most important physical finding with these patients is the presence of dull or diminished lung and heart sounds.
Common presenting signs in pleural space disease are as follow:
- Increased respiratory rate and effort
- Dull or muffled lung and heart sounds.
Stabilisation relies on oxygen supplementation, minimal stress and vascular access followed by thoracocentesis. It is important that in all cases of suspected pleural space disease thoracocentesis is performed before any attempts at radiography. Thoracocentesis is both diagnostic and therapeutic, and will rapidly improve the condition of patients with pleural effusion or pneumothorax (see Practical techniques at the end of the chapter). Thoracic radiographs can then follow thoracocentesis; removal of effusion will also now make underlying pathology easier to visualise. The results of thoracocentesis coupled with radiography should allow a diagnosis to be made (see Figure 9.6).