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Introduction

Respiratory distress is a common presenting complaint for veterinary emergency patients. The patient with a respiratory problem needs careful initial assessment, sensitive diagnostic procedures, and treatment while at the same time the clinician needs to minimize stress to a patient that has minimal respiratory reserves. Diagnostic tests are needed for initiation of a specific therapy, however, the goal is to achieve as much information about the cause and extent of the respiratory problem with as less stress as possible. It is very common for patients to significantly worsen at the time of presentation, so further stress through diagnostic procedures should be minimized.

Physical Examination

Initial evaluation should be performed in a stress free manner. Oxygen should be provided by mask, bag, or flow-by at high flow rates (5-15 L/min). The initial evaluation includes identification of the respiratory breathing pattern, presence and type of dyspnea and auscultation results. Heart rate, pulse rate and character, mucous membrane color, capillary refill time, and temperature will help identifying concurrent problems such as cardiovascular shock, and other life-threatening situations.

Localization of Respiratory Distress and Differential Diagnoses

The initial physical evaluation provides enough information to localize the respiratory distress to a specific localization of the respiratory tract (upper airways, lower airways, lung parenchyma and pleural space).

Inspiratory dyspnea and/or respiratory noises refer to the upper respiratory tract including the nasal cavity, pharynx, larynx, trachea and main bronchi. Extrathoracic lesions of the upper respiratory tract are manifested by a loud stridor or stertor, which makes them distinguishable from intrathoracic upper respiratory tract lesions. Causes of upper respiratory lesions include swelling, masses, hemorrhage or foreign bodies in the mouth, larynx or trachea; laryngeal paralysis, tracheal collapse or brachycephalic airway syndrome.

Expiratory dyspnea can be seen with lower airway disease, mainly affecting the bronchi and bronchioli. Auscultation reveals increased lung sounds on expiration and expiratory wheezes, advanced disease and additional alveolar disease may reveal inspiratory crackles as well. The main differential diagnosis of expiratory dyspnea is asthma (cats) or bronchitis/bronchopneumonia of various causes.

Mixed respiratory patterns involving both inspiration and expiration may be seen with parenchymal disease, but are less specific for localization. Prolonged inspiration and expiration suggest diseases such as pneumonia, infiltrative disease (neoplasia), alveolar flooding with cardiogenic or noncardiogenic edema, and pulmonary contusions. Auscultation will reveal harsh lung sounds, crackles and wheezes.

Superficial shallow breathing can occur due to various causes such as pain, stress, thoracic wall injuries or parenchymal disease. Auscultation may reveal decreased or increased lung sounds.

Asynchronous breathing (inward movement of the abdomen during inspiration) is typically seen with pleural space disease and is very specific in combination with decreased breath sounds on auscultation. Auscultation will further help to differentiate between pneumothorax (decreased or absent lung sounds in the upper lung fields), pleural effusion (decreased or absent lung sounds in the lower lung fields), or diaphragmatic hernia (gut sounds in the thorax, shift of heart sounds). Severe upper airway obstruction may lead to inverse breathing (abnormal inward movement of the chest during inspiration) and is usually accompanied by a loud stridor.

Tachypnea: Other causes of increased respiratory rates include cardiovascular shock, pain, excitement, hyperthermia, pulmonary thromboembolism and metabolic acidosis. Auscultation in these patients should reveal no abnormalities.

Emergency Stabilization

Supportive Therapy

Oxygen supplementation and minimizing stress are the main principles in stabilizing animals with respiratory distress. The animal should be allowed to choose its own comfortable position and restraint should be minimized.

Oxygen supplementation can be provided using various methods. Flow-by or mask oxygen should be provided with high flow rates (5-15 L/min). Alternatively, an e-collar with saran wrap covering can be used to supply oxygen (200 ml/kg/min), or nasal oxygen (50-100 ml/kg/min) through a nasal cannula can be used to supply oxygen. After the initial primary survey, especially cats should be left alone in an oxygen-enriched environment. Any stressful situation should be avoided.

A careful attempt at placing an IV catheter can then be performed. This allows IV access in case of patient deterioration and a non-stressful route of administrating repeated or additional medications. Butorphanol (0.1-0.2 mg/kg iv/im) or diazepam (0.2 mg/kg iv) might be helpful in relieving distress associated with many respiratory emergencies, however, sedation might also be dangerous and careful monitoring is necessary.

If the animal is showing severe respiratory distress or cyanosis despite oxygen supplementation, respiratory arrest is imminent and the animal should be intubated and ventilated with 100% oxygen. Intubation and ventilation give control over respiratory function, allow administration of 100% oxygen and the ability to provide mechanical ventilation and administration of PEEP, and should therefore not be postponed if they are indicated. Intubation should be achieved in a rapid fashion, which requires an iv line in order to anesthetize the patient. If not already on board, an analgesic such as methadone, fentanyl or hydromorphone is given, followed by rapid sequence induction with etomidate or propofol together with a benzodiazepine. IM sedation with ketamine/diazepam/opioids can be attempted if an iv line cannot be placed, however, with sedation, patients with severe respiratory distress often lose their "reserve" and may arrest.

If airway access cannot be obtained, an emergency tracheostomy may be required. This is performed with a longitudinal slash incision at the ventral cervical midline region, a quick dissection along the midline of the ventral trachea, followed by an incision between two tracheal rings (max 50%). An appropriately sized endotracheal tube or tracheotomy tube is then inserted and the animal is ventilated if necessary. Stay sutures should be immediately applied so that the airway can be re-secured if accidental extubation occurs. Administration of humidified oxygen at 1-2 L/min should be instituted in any case.

Suction may be required in animals with oral injuries, salivation, or parenchymal disease. Suction is essential to assist in removing fluid from the oral cavity or endotracheal tube, although sometimes it is more effective to carefully tip the patient upside down while gently squeezing on the chest.

Pain may be the cause of respiratory distress or may aggravate symptoms. Analgesia should therefore be initiated in all patients that are potentially painful. A fast-acting, potentially reversible opioid such as methadone (0.1-0.2 mg/kg IM or IV), fentanyl (2-5 ug/kg IV) or hydromorphone (0.1-0.2 mg/kg IV or IM) should be chosen. Butorphanol (0.1-0.2 mg/kg IV or IM) will only provide short-term analgesia with additional (desired or nondesired) sedative, anxiolytic and antitussive effects.

Specific Therapy

Depending on the localization of respiratory distress, specific treatment for the suspected differential diagnoses can be instituted in order to stabilize the patient for further diagnostic procedures and definite diagnosis (Table 1).

If pleural space disease is suspected, thoracocentesis should be performed immediately, prior to taking radiographs. The area between the 7th and 11th rib is clipped and aseptically prepared bilaterally. A butterfly catheter or a needle with an extension set are connected to a 3-way stopcock. Thoracocentesis is performed aseptically in the 8th or 9th intercostal space for air evacuation. For fluid, it might be helpful to use an ultrasound probe to determine the best site for puncture (usually ventrally, cranial or caudal to the heart). Thoracocentesis is both diagnostic and therapeutic and may be life-saving.

Animals with expiratory dyspnea suggestive of small airway disease may benefit from a bronchodilator. Terbutaline (0.01 mg/kg) can be administered sc every 30-60 minutes in the beginning. In cats with suspect asthma, a fast-acting corticosteroid may also be indicated. Administration of bronchodilators and steroids by inhalation provides local therapy and can be administered without the necessity of an iv line.

In animals with moist lung sounds, especially when cardiac edema cannot be ruled out, a dose of furosemide (1-2mg/kg IV or IM) should be considered. Trauma patients with increased lung sounds suggestive of lung contusions are treated with oxygen and rest. Antibiotics should only be instituted if there is high suspicion of bacterial infection and samples for culture have been obtained.

Table 1. Emergency drugs for patients with respiratory distress.

Diagnostic Procedures

Diagnostic procedures should be instituted after stabilization of the patient. Thoracic radiographs will provide information about lung disease (bronchial, interstitial, alveolar, vascular or mixed pattern), heart disease, signs of trauma, and pleural or mediastinal disease. However, proper chest radiographs require restraint of the animal and forcing an animal to lie on the side may actually induce respiratory arrest.

Oxygenation should be assessed by arterial blood gas analysis. Hypoxemia can be seen with hypoventilation, low FiO₂, V/Q mismatch, diffusion problems or right-to-left cardiac shunts. Arterial blood gas analysis will provide information about hypoventilation, V/Q mismatch or diffusion problems. Pulse oximetry is an alternate technique to assess oxygenation. Values less than 90% correlate with a PaO₂ of less than 60% which means severe hypoxia. Pulse oximetry is not accurate in animals with anemia, methemoglobinemia, shock, or hypothermia. Ventilation problems are assessed by arterial or venous PCO₂ values. Values higher than 60 mmHg describe severe hypoventilation and require mechanical ventilation.

CBC, chemistry, coagulation profile, and urine analysis as well as echocardiography, endotracheal wash, or lung aspirates should be considered in order to obtain a diagnosis and institute appropriate treatment.

References

References are available upon request.