Localization of the pulmonary problem (Proceedings)

Evaluation of the pet with respiratory disease may be challenging. The best approach to problem solving usually reflects first an assessment for immediate intervention, and then careful evaluation to localize the problem, and then finally determination of the specific problem and the available options for controlling or curing it. Immediate intervention is warranted in any pet that is having difficulty breathing. Respiratory distress may be appreciated by observing loud or noisy breathing, labored breathing, discolored (pale pink, grey or bluish) mucous membranes or by difficulty laying down or on one's side (orthopnea). Respiratory distress may be a life-threatening emergency and should be treated promptly. The appropriate immediate therapy will reflect the underlying cause, and may include supplemental oxygen, thoracocentesis, or sedation and intubation.

Localizing the problem

All causes of true pulmonary problems may be traced to abnormalities in the upper airway, the lower airway, the pulmonary parenchyma or the pleural space. Occasionally, pets with either marked metabolic acidosis or pain may have tachypnea which may be misinterpreted as respiratory distress.

Most effective localization relays on pattern recognition, which is an appreciation of a conglomerate of historical and physical findings which are linked with a specific condition. Most successful clinicians incorporate pattern recognition as a method of problem solving in most day to day clinical challenges.

Upper airway obstruction

Causes of upper airway obstructions include brachycephalic airway syndrome (specifically elongated soft palate, laryngeal collapse and everted laryngeal saccules), laryngeal paralysis, pharyngeal foreign bodies, and neoplasia. Recently nasopharyngeal turbinate have also been described as a component of upper airway obstruction in brachycephalic airway syndrome. All upper airway obstructions are magnified in heat, humidity and with exertion. Clinically, upper airway obstruction may be suspected with loud or noisy breathing and longer inspiratory times.

Clinicians should be familiar with normal upper airway anatomy and function and be prepared to deal with any number of crises, including the ability to deal with challenging intubations and the potential for urgent tracheostomies.

Table 1: Common characteristics of upper airway disease

Management of upper airway obstruction may include surgical or medical therapy. Surgical therapy includes soft palate resection, stenotic nares resection, arytenoids lateralization and in rare cases permanent tracheostomies. Medical therapy includes sedation, anti-inflammatory agents (steroids), harnesses and weight loss. Dogs that have laryngeal paralysis may have concurrent neuromuscular disease or esophageal motility disorders, including megaesophagus.

Lower airway disease

Lower airway disease is common in cats and smaller breed dogs (particularly Cocker spaniels). Intra-thoracic tracheal collapse can be a specific form of lower airway disease, while cervical collapse will result in signs of upper airway collapse. Signs of lower airway disease include cough, wheeze and occasionally shortness of breath. Some affected dog have a marked expiratory push, similar to heavey horses. Lower airway disease may be either acute, such as infectious tracheobronchitis or chronic. Chronic bronchitis is defined as cough most days of the previous two months without other underlying cause. Thoracic radiographs from dogs with chronic bronchitis may be relatively normal or may reveal a heavy broncho-interstitial pattern and/or evidence of bronchiectasis. Bronchoscopy is considered the gold standard to evaluate airways. Appropriate therapy involves addressing inflammation, attempting to limit airway remodeling and controlling cough. This might include glucocorticoids, antibiotics (for secondary infections), bronchodilators, and cough suppressants.

Table 2: Common characteristics of lower airway diseases

Pulmonary parenchymal disease

Parenchymal pulmonary disease will cause respiratory distress on both inspiration and expiration. Patients will commonly seem very distressed. Thoracic radiographs will document interstitial to alveolar infiltrates. Common sources of parenchymal disease include pulmonary edema (cardiogenic and non-cargiogenic), pneumonia, pulmonary contusion, pulmonary fibrosis and neoplasia. Treatment is directed at the underlying cause. In some cases, multiple sources may co-exist.

Figure 3.Lateral thoracic radiograph from a Westie with pulmonary fibrosis.

Table 3: Common characteristics of parenchymal lung disease

Pleural space disease

Pleural space disease is characterized by a short and shallow ventilatory pattern, often with increase abdomen effort. Auscultation may document a quiet thoracic cavity with louder sounds dorsally. Small volume pleural effusions may be helpful as diagnostic aids, but less so therapeutically. Treatment of pleural effusion is directed at removal of the effusion and specific therapy directed at the underlying cause.

Table 4: Common characteristics of pleural effusion