Approach to the dyspneic cat (Proceedings)

Assessment and emergent treatment of the dyspneic cat is often considered one of the most difficult tasks of the emergency clinician. Underlying causes of shortness of breath can vary considerably, and must often be decided with only a history and a brief physical examination. Understanding the diseases that can lead to shortness of breath and application of a few helpful guidelines can help the clinician rule out certain common disease processes and initiate prompt life saving treatment. In general management of the dyspneic cat consists of emergent treatment, followed by diagnostics when the clinical state has stabilized.

The dyspneic cat that presents to the emergency clinic must be handled very carefully, as it likely has a very low tolerance for stress. Not only is shortness of breath itself a source of great stress, but these cats may have been on multiple car rides to several clinics. While it is often tempting to conduct a physical examination and place an intravenous catheter on arrival, such seemingly benign interventions may lead to decompensation and death, even with oxygen supplementation. The key components of emergent care consist simply of oxygen supplementation and a low stress environment with minimal handling. Oxygen supplementation can be provided in several ways, listed below in order of increasing efficacy.

"Flow by" oxygen

Generally provides inconsistent supplemental oxygen but may be enough to prevent a crisis while a cage is prepared or until a mask is available.

Supplementation by mask

In theory may provide 50-60% oxygen. However, placement of a tight fitting mask over the head of a dyspneic cat may cause more stress than the cat can tolerate, and is generally not the approach of choice. Tight fitting masks are often not tolerated in conscious cats for any significant period of time.

Placement into an oxygen rich environment (i.e., an oxygen cage)

Oxygen cages can vary from a regular cage with a plexiglass door, an incubator, or a specialized cage that can deliver humidified air and supplemental oxygen at a specific concentration. While ideal in many respects including digital readout of the concentration of oxygen provided and the ability to provide heat, disadvantages include rapid loss of the oxygen rich environment when the door is opened which restricts access to the pet. If available, an oxygen cage allows a cat to move about, provides some insulation from the noise and stress of the emergency room, and is the treatment of choice. A member of the emergency team should continue to observe a cat that has been placed in an oxygen cage to make sure that further decompensation does not occur.

Sedation, intubation, and administration of 100% oxygen

If the dyspneic cat continues to show signs of distress despite the methods mentioned above then sedation and control of the airway may be necessary. Signs of impending crisis include excessive vocalization, restlessness or thrashing, and expectoration of pulmonary edema fluid. While this intervention may seem extreme, it is often very effective not only because 100% oxygen can be administered, but also because interference with respiration due to anxiety and panic is eliminated.

The last component of the emergent plan consists of the decision of whether further intervention is required. A decision of whether medication needs to be administered emergently is based on an index of suspicion as to the cause of dyspnea, as well as the response to oxygen supplementation. The cat that is resting comfortably in oxygen may be able to wait until diagnostics are performed before therapy. On the other hand, the cat that continues to show signs of distress despite oxygen supplementation may require more emergent therapy. Observation of respiratory pattern and a very brief physical examination will provide valuable clues as to the nature of the respiratory distress.

Observation of the respiratory pattern can be helpful in raising an index of suspicion for upper airway obstruction, pleural disease and parenchymal space disease. Upper airway obstruction is often characterized by a prolonged and exaggerated inspiratory phase. Loud striderous breathing may be heard, and nasal discharge may be present in some cases. Causes for upper airway obstruction in cats include nasopharyngeal polyps, laryngeal masses, laryngeal paralysis, and upper airway swelling of other causes. Cats with parenchymal disease have a mixed inspiratory and expiratory effort, and crackles and wheezes are often heard on auscultation. Causes of parenchymal disease include congestive heart failure, asthma, neoplasia, and rarely infection. Pleural space disease is characterized by rapid breathing with marked abdominal effort.

Additional information can be obtained both from a history and a very brief physical examination. Information relating to previous medical conditions and duration of respiratory signs are helpful. Knowledge of a previous history of cough would support the possibility of asthma, while prior identification of a heart murmur or treatment for heart disease would suggest congestive heart failure. A history of pronounced effort while swallowing would support a chronic process and possible upper airway obstruction. The development of respiratory distress during hospitalization rather than as a presenting sign would suggest that a disease such a congestive heart failure may be more likely. Other than observation of respiratory pattern, the two most important components of a physical examination include the temperature and auscultation. These can often be performed in less than one minute and with minimal restraint. Cats with congestive heart failure are typically hypothermic, sometimes profoundly so. A quick assessment of lung sounds can be helpful but is non-specific, and most importantly the cat should be auscultated for the presence of a heart murmur or a gallop rhythm. The finding of hypothermia, and a heart murmur in the presence of dyspnea should prompt emergent treatment for congestive heart failure. Furosemide should be withheld if possible if the cat is normothermic and no cardiac murmur is identified.

Once stabilized, additional diagnostics can be performed to determine the cause of respiratory distress. These include laboratory testing, chest radiographs, an endotracheal wash, and in some case an echocardiogram, thoracic ultrasound, or CT scan. Laboratory testing should include a complete blood count, chemistry profile, and a T4. Cats with allergic bronchitis or asthma as well as heartworm disease may have a circulating eosinophilia. A leukocytosis along with the presence of excessive immature neutrophils (bands) and toxic changes to the neutrophils are more suggestive of an inflammatory or infectious process. Thoracic radiographs are key in determining the cause of respiratory distress, but may not be tolerated by the dyspneic cat. The thoracic radiograph should be examined for heart and vessel size, parenchymal changes, and evidence of pleural effusion. In general radiographs should only be taken once the cat has stabilized. However in cases where respiratory distress continues to be severe, radiographs may be necessary to provide additional options for treatment. In these cases the radiology suite should be prepared ahead of time (technique should be set) and oxygen should be available. Immediately following the radiograph the cat should be returned to the oxygen cage, and then the radiograph can be processed. While 2 views are ideal, one view may be sufficient for the formation of a treatment plan. Echocardiography can be helpful in examining heart function, for the diagnosis of pulmonary hypertension and possibly heartworm disease. Thoracic ultrasound can be used when a pulmonary mass is identified on radiographs to further characterize the lesion and to obtain an ultrasound guided biopsy. Other forms of imaging that may be helpful if the underlying cause of respiratory distress is difficult to identify is computed tomography (CT) and more subtle evidence of diffuse disease may be more easily recognized.

The tracheal wash can be very helpful in supporting a diagnosis of allergic lung disease, and in rare cases, infection. However the procedure carries significant risk and should not be performed if respiratory distress is present. In cats an endotracheal wash is typically performed, which requires a period of brief anesthesia. A period of pre-oxygenation is recommended, followed by a short action induction agent such as propofol. Following placement of a sterile endotracheal tube, a red rubber tube is passed as far into the airway as possible and sterile saline in 3ml aliquots is instilled and then removed. This can be repeated 3 times. The recovered fluid should be submitted for cytology as well as aerobic culture and sensitivity. Following the tracheal wash 100% oxygen should be administered as long as the endotracheal tube is tolerated. Following extubation, cats should be carefully monitored for signs of respiratory failure or decompensation.

Upper airway obstruction

Causes of upper airway obstruction include nasopharyngeal polyps, laryngeal masses, laryngeal paralysis, and upper airway swelling of other causes. As stated previously, cats with upper airway obstruction frequently have a pronounced inspiratory effort, and may have striderous breathing. Nasal discharge may or may not be present, and chest radiographs are typically normal. As with all cats in respiratory distress, a low stress environment and minimal handling are a must. Emergent treatment including sedation and capture of the airway (intubation or tracheostomy) may be required. Following sedation a quick upper airway examination can be performed, and oral intubation can be attempted. In the presence of a foreign body or a laryngeal mass, oral intubation can be difficult to perform and a tracheostomy may be necessary. If emergent treatment is not required, sedation and an oral examination should be performed in a controlled setting, with all materials needed for intubation and tracheostomy tube placement available. In general tracheostomy tubes are challenging to manage in cats due to the production of secretions and a small tracheal lumen leading to increased airway resistance. However, it can be a life saving procedure, and should absolutely be performed if indicated.

Nasopharyngeal polyps should be considered as a differential diagnosis in any young cat presenting with signs of upper airway obstruction. These non-neoplastic masses originate in middle ear, and extend into the nasopharynx, obstructing the flow of air as well as drainage of secretions into the nasopharynx. The history often includes a chronic history of respiratory effort, noisy breathing and possibly nasal discharge. Other common complaints may include difficulty swallowing, and in some cases a head tilt. Many of these cats are treated for possible upper respiratory infection, and are not responsive to antibiotic therapy. A diagnosis of nasopharyngeal polyp is typically made following sedation and oral examination, where a smooth mass is visualized dorsal to the soft palate. Removal of the polyp consists of grasping the stalk and applying gentle traction until the polyp is released. A ventral bulla osteotomy on the side of origin of the polyp is generally recommended for further removal of polyp material.

Upper airway swelling secondary to foreign material (grasses) or insects can also lead to upper airway obstruction. Laryngeal swelling can also occur secondary to head trauma, and allergic reactions. In these cases the foreign object should be removed if possible, and short acting glucocorticoids can be administered to reduce inflammation. If these interventions are unsuccessful, then a tracheostomy may be required. Laryngeal masses are also common, and occur more frequently in the older cat. Tumors that commonly affect the larynx include squamous cell carcinoma, lymphoma, and adenocarcinoma. In some cases, laryngeal masses can consist of granulomatous changes. While benign, these changes can have devastating consequences. A history of noisy breathing is common, as well as loss of the ability to vocalize normally (loss of meow). Debridement of the mass as well as partial laryngectomy can restore airflow, although a permanent tracheostomy may be required for long-term management of these cases.

Common causes of parenchymal disease include congestive heart failure, allergic bronchitis (asthma), and neoplasia, and rarely infection. Congestive heart failure should be the leading differential diagnosis the dyspneic cat with a cardiac murmur or gallop that is hypothermic. Pulmonary crackles can often be heard on auscultation, and jugular venous distension may be recognized on physical examination. Radiographic signs consistent with congestive heart failure include cardiomegaly with enlarged pulmonary vessels. Alveolar and interstitial infiltrates are also common, although the distribution of these infiltrates is inconsistent and less helpful than in the dog. Hypertrophic cardiomyopathy is the most common cause of congestive heart failure, and causes radiographic signs of cardiomegaly due to secondary left atrial enlargement. Dilated and intermediate cardiomyopathy are less common. Although congestive heart failure is more common in the older cat, young cats with occult cardiomyopathy may present with congestive heart failure, especially following any stressful event. Echocardiography is used to confirm or exclude the presence of heart disease, and can also be used to define the severity of the cardiac changes. Diuretics (Furosemide) are the mainstay of emergent treatment of congestive heart failure along with oxygen and a low stress environment. Furosemide can be administered intramuscularly if placement of an intravenous catheter cannot be tolerated, but should not be administered subcutaneously as it is unlikely to be absorbed in such a state of poor perfusion. Other vasodilators such as nitroglycerin or nitroprusside should be used if Furosemide alone is unable to provide relief.

Allergic bronchitis is most commonly accompanied by a history of cough. Pulmonary wheezes are described as classic findings in cats with asthma, although pulmonary crackles can also be auscultated. Generally the factor that differentiates these cats from those with congestive heart failure is the finding of normothermia on physical examination (as well as the lack of a cardiac murmur or gallop rhythm). Radiographs typically show a normal cardiac silhouette, along with bronchial and interstitial changes. Treatment consists of a combination of glucocorticoids and bronchodilators, with a rapid response typically seen. Laboratory testing as well as a tracheal wash can be used to support the diagnosis of allergic bronchitis. An important component of long-term management of these cats includes reducing the exposure to allergens, including smoke if the cat comes from a smoking household.

Neoplasia is typically suspected when congestive heart failure has been excluded using echocardiography, and when empirical treatment for allergic bronchitis fails to lead to resolution of signs. Respiratory signs are generally slow in onset, and are often accompanied by either a mass lesion on radiographs or atypical pulmonary infiltrates. A tracheal wash can be performed in hopes of obtaining neoplastic cells (and excluding asthma), but is often a low yield procedure. In these cases, a CT scan of the chest and in some cases a fine needle aspirate of the lung (or of any solid masses) may be necessary to determine the underlying disease process.

Pleural space disease is common, and can result from cardiac disease, infection (pyothorax), neoplasia (lymphosarcoma), or an idiopathic process. Cats with pleural disease typically have marked abdominal effort both inspiratory and expiratory effort. Thoracocentesis and drainage of the pleural space is the treatment of choice. Thoracocentesis in cats can be performed by placing a butterfly catheter in the 7-9th intercostal space (sedation is generally not required but may be in the fractious cat). Any fluid retrieved should be submitted for fluid analysis and cytology (as well as culture if purulent).

The dyspneic cat can be difficult to manage due to the low tolerance for stress and diagnostics. However signalment, careful observation of respiratory pattern and a thorough history can provide valuable clues, and a few simple tests such as temperature and heart auscultation may be all that is required to provide prompt life saving treatment.