Respiratory distress is a common emergency in veterinary practice and requires rapid recognition, assessment and treatment. Successful emergency management of dyspnoeic patients requires clinicians to remain acutely aware of how fragile dyspnoeic patients can be. Dyspnoeic animals are potentially the most unstable emergency cases we deal with and even brief evaluation may prove fatal, especially in cats. The risks of diagnostic evaluation should always be carefully balanced against potential benefits. Determination of the underlying cause using brief, directed physical examination and noninvasive 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. In the majority of cases oxygen and stress reduction will allow some stabilisation of the patient.

Diseases leading to respiratory distress can be localised to the following anatomical locations:

 Upper respiratory tract

 Lower airways

 Pulmonary parenchyma

 Pleural space

 Supporting structures including diaphragm, thoracic wall

Attempting to categorise the nature of respiratory disease into these discrete anatomical locations is useful because the diagnostic and therapeutic plans are specific for the types of disorders. Emergency interventions may be attempted solely on the basis of the localisation of the problem and therefore this is an important component of the approach to the dyspnoeic patient.

Initial Evaluation

On arrival at the practice it is likely that the animal will have endured a car journey and therefore be stressed at the unfamiliarity of the situation. The patient should be provided with oxygen supplementation whilst a brief examination of the respiratory tract is carried out to rule out easily treatable conditions. The patient should then be left to relax (as much as possible).

In severely dyspnoeic animals actively taking control of the airway (which often only requires very small doses of sedative in severely dyspnoeic animals) is vastly superior to intubating them following a respiratory arrest. This decision, although a big step, may be life saving in conditions such as upper respiratory tract obstruction secondary to brachycephalic obstructive airway syndrome, or laryngeal paralysis. 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.

The first part of the evaluation of the respiratory tract should be to watch and listen without a stethoscope. An enormous amount of information can be gleaned from just observation, before even touching the patient. In normal animals the majority of inspiration is due to diaphragmatic contraction, therefore little chest wall movement is seen. As the diaphragm contracts the abdominal contents are pushed caudally and therefore the abdominal wall moves out. In cats and small dogs slight inward movement of the cranial thorax is a normal finding. Paradoxical abdominal movement, where the abdomen moves in with inspiration, is seen in conditions preventing adequate lung inflation with respect to thoracic wall movement and indicates severe respiratory compromise. Conditions causing this include upper respiratory tract obstruction, diaphragmatic rupture or paralysis, decreased lung compliance and pleural effusion (particularly in cats).

One should also be aware of the postural manifestations of dyspnoea such as an extended neck, abducted elbows, open-mouth breathing, an anxious facial expression, increased abdominal movement and paradoxical abdominal movement. Straightening of the neck and open-mouth breathing occur in both dogs and cats; however, some other postural manifestations of more severe dyspnoea vary between species. Dogs prefer to stand with abducted elbows, while cats tend to sit in sternal recumbency. 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 and it often means impending respiratory arrest in a cat.

The differentiation between inspiratory and expiratory dyspnoea can also aid in the localisation of the disease process. Inspiratory dyspnoea with stridor or stertor is associated with dynamic upper airway obstruction; in cats chronic pleural effusions may be associated with inspiratory dyspnoea without stertor. Expiratory dyspnoea is a feature of feline allergic airway disease. Most other causes of dyspnoea will be associated with mixed respiratory patterns. Short shallow respiration and sometimes panting may be seen in some pneumothoraces.

Methods of Oxygen Supplementation

The simplest way to provide supplemental oxygen is via a facemask; however, the majority of animals do not like having their face covered and so this may prove stressful in many patients. In these cases it is preferable to hold the circuit or tube without the facemask close to the mouth or nose of the patient. This method is easy, cheap and effective and may allow initial assessment to be carried out.

Nasal catheters or nasal prongs provide another simple method. The nasal mucosa should be anaesthetised using proxymetacaine (approximately 2-3 drops) 5-10 minutes prior to placement. The tube should be measured to the medial canthus of the eye before insertion. It should be sutured as close to the nose as possible to prevent displacement. The amount of oxygen administered via this method will depend on the oxygen flow rate and whether the animal is open-mouth breathing but may be up to 60%.

Personal oxygen tents can be constructed using buster collars and cling film. Space must be left to prevent carbon dioxide build up or overheating, although the space around the collar is often sufficient.

The best method of oxygen supplementation is an oxygen cage. These vary from polythene door fronts to temperature-, humidity-and oxygen-controlled environments. The latter, though expensive, allow even large dogs to be kept cool whilst providing up to 100% inspired oxygen concentration.

The ultimate method of oxygen supplementation is intubation and ventilation. This allows full control of ventilation and inspired oxygen concentration but requires general anaesthesia and/or tracheostomy and continuous sedation. It is expensive and extremely labour intensive and in patients with lung disease survival rates are poor. However, as our experience/understanding of mechanical ventilation advances, we may be able to improve our success with such severe cases.

Pulmonary Auscultation

Auscultation is an art that with practice can be learnt and perfected by all. It requires a decent stethoscope and a methodical approach. All lung fields should be auscultated; this is easily accomplished by dividing the thorax into a noughts and crosses board, i.e., nine smaller fields. Left and right lung fields should be assessed and compared for symmetry and there should be cross-referencing at all stages with respect to what you would expect given the degree of dyspnoea. In normal lungs increased noise is expected in the cranioventral lung fields. This is due to increased turbulence in these smaller airways. The lungs should be symmetrical left to right in similar fields.

Abnormal sounds are associated with a number of different disease processes within the airways. Increased respiratory rate and effort should cause increased harshness within the lung fields, so one should cross-reference findings with what would be expected given the degree of respiratory embarrassment. The distribution of the abnormal lung sounds can provide information as to the cause of the disease.

Adventitious lung sounds are associated with parenchymal disease. It is somewhat easier to classify abnormal lung sounds as either:

 Harsh, i.e., louder and coarser than normal

 Crackles, either fine or coarse, associated with lower airway or parenchymal disease

A cranioventral distribution of crackles or harshness in dogs is associated with aspiration pneumonia. Cardiogenic oedema may be associated with sounds loudest over the heart base. Neurogenic oedema is seen most commonly in puppies after cervical trauma or upper respiratory tract obstruction. This usually results in a caudodorsal 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:

 Dorsal dullness--associated with accumulation of air, pneumothorax

 Ventral dullness--fluid or soft tissue

 Gut sounds may be heard with diaphragmatic hernias

Animals that have been hit by cars and have pneumothoraces and pulmonary contusions may complicate auscultation. The contusions cause harshness, whereas the pneumothorax dampens sounds down, resulting in overall normal sounding lungs.

Diagnostic Tests

A risk-benefit analysis for each individual case should be done before considering further diagnostic tests. A thoracic radiograph is of no use if the patient dies during exposure! Thoracocentesis should be performed in any cases where pleural space disease is suspected. Removal of fluid or air from the pleural space will lead to rapid stabilisation of the patient and the potential benefits outweigh the risks in the majority of cases. Thoracocentesis can be performed without sedation and anaesthesia in the majority of cases. It is generally a fairly low-risk procedure, though there is a small risk of cardiac or vena cava puncture and pneumothorax (usually subclinical). Key points include:

 Oxygen should be provided during the procedure

 The thorax should be clipped ventrally for fluid and dorsally for air

 The area should be cleaned with surgical scrub and spirit although surgical asepsis is not necessary

 The choice of needle is dictated by patient size and space occupier; in cats a butterfly needle is usually sufficient whereas in larger dogs it may be easier and quicker to use a longer larger-gauge catheter

 The needle should be inserted at rib space seven to eight, one-third of the way from the bottom for fluid and one-third of the way down from the top for air (or at the point of dullness)

 The needle should be placed cranial to the rib, to avoid blood vessels and nerves

The ability to establish a working diagnosis and treat on the basis of history and physical examination without additional diagnostics, such as chest radiographs, can mean the difference between life and death in some dyspnoeic animals. When empirical treatment must be instituted prior to a definitive diagnosis, good clinical reasoning and maintaining perspective as to the likely differential diagnoses is tantamount. Although there is no replacement for following the problem-orientated approach with a complete problem list and all diagnostic differentials, the emergency clinician must always maintain perspective as to what are the most likely probable diagnoses.

References

1.  Lee JA, Drobatz KJ. Respiratory distress and cyanosis in dogs. In: King, LG. ed. Textbook of Respiratory Disease in Dogs and Cats. St Louis: Elsevier, 2004; 1-12.

2.  Raffe MR. Respiratory Care. In: Wingfield, WE; Raffe, MR. eds. The veterinary ICU book. Jackson Hole: Teton NewMedia, 2002; 147-165.

3.  Rozanski EA, Chan DL. Approach to the patient with respiratory distress. Veterinary Clinics of North America Small Animal Practice 2005; 35(2): 307-317.