Respiratory distress in cats and dogs (Proceedings)

Respiratory distress is common and challenging. Cats often compensate well for pulmonary diseases, and some conditions can rapidly fulminate. Dogs are often more "honest" although they can decompensate rapidly as well. It is crucial to balance the equal goals of limiting stress on the patient with respiratory distress, and to work to identify the specific cause of the distress so that appropriate therapy can be provided.

Phone triage

Home care of the pet with respiratory distress is not advised. Pets with respiratory distress should be evaluated by a veterinarian as soon as possible. Pets with known pre-existing therapy may receive additional therapy at home immediately before leaving to come to the hospital, such as an additional dose of furosemide to a known heart failure patient, or albuterol/terbutaline and prednisone to a known lower airway disease cat.

Initial examination and stabilization

Initial physical examination should focus on the major body systems (heart, brain and lungs) and include an assessment of respiratory rate and effort, with a specific focus on evaluation increased airway sounds, or dull/absent sounds with increased effort. Auscultation of the heart may document a murmur or gallop, although it should be recalled that that murmurs may be hard to hear in the ER at times. Rectal temperature should be recorded, as hypothermia is common in cats with congestive heart failure. Temperature is much less commonly low in dogs with heart failure. Following rapid assessment, supplemental oxygen should be provided, and a history obtained from the cat's family. Care should be taken to inquire about past diagnosis (including auscultation of a heart murmur), possible trauma/exposure to the outdoors, and any other changes, such as decreased appetite, cough (or suspected "hairballs"), current heartworm status or PU/PD. Following a brief physical examination and assessment of the pet's medical history, an initial attempt at therapy should be provided, including continuing oxygen therapy, diuretics, glucocorticoids, or thoracocentesis. In a growing number of hospitals, ultrasonography (US) is readily available. Used of US is vital for rapid assessment of pleural effusion with minimal training, with more advanced training and practice, other assessments, such as left atrial size, evidence of LV hypertrophy, or mediastinal masses may also be provided. In my experience, the use of ultrasound has largely negated the need to perform a "diagnostic" thoracocentesis, and limits unnecessary discomfort and eliminates the possibility of iatrogenic pneumothorax.

Thoracic radiographs are ultimately required to (well at least HELP..) determine the cause of respiratory distress in most animals. Ideal positioning is NOT required when pets are in respiratory distress. It may be wise to start with a single view, and then to allow the patientt to recover for a few minutes before taking a second view.

A standard approach to interpretation of the thoracic radiograph includes evaluation of the pulmonary parenchyma, the pleural space, the cardiac silhouette, ribs and diaphragm. Tips for evaluation of chest film include

     1) When looking for pleural effusion, small volumes will obscure the lung/diaphragm interface on a DV or VD projection.

     2) Cardiomegaly may be subtle, even in fulminate heart failure in cats.

     3) Patchy infiltrates are most often heart failure in cats,; dogs tend to have cardiomegaly with perihilar edema.

     4) Bronchial disease can look like metastatic disease in cats

     5) Rib fractures can accompany coughing/respiratory distress in all species

     6) If films look normal, consider upper airway disease.

Other diagnostic testing may include echocardiography, pleural effusion cytology, transoral tracheal wash, and/or computed tomography. Common differentials include consideration of a)upper airway disease b) lower airway disease c)Parenchymal disease d) pleural space disease or e) trickery. Hypoventilation may cause hypoxemia or hypercarbia, but these will not be easily appreciated on physical examination.

Initial therapy

Pets that have respiratory distress should be promptly treated with supplemental oxygen. An oxygen cage is very appealing to the cat, although it may be challenging to evaluate a cat in a closed cage. Recall that oxygen does not "rush" out of the cage if opened, but does equilibrate quickly with room air. Supplemental oxygen in dogs reflects the pet's size and temperament. I typically try to determine if there is any pleural effusion present, because if it is, and may be removed, if can provide immediate clinical improvement. Pleural effusion may be appreciated on FAST ultrasound, or by radiographs. If no effusion is present, then it is important to try to determine if there is pulmonary edema (eg. Left sided -heart failure). Important clues include hypothermia in cats, and the presence of a gallop. Dogs will often have a loud murmur with mitral disease, or atrial fibrillation and a gallop with dilated cardiomyopathy. A single dose of furosemide is warranted if heart failure is not able to be excluded. In the normothermic cat, particularly with a history of cough, lower airway disease is highly likely and 2-4 mg of dexamethasone should be administered, perhaps coupled with injectable or inhaled Beta-2 agonists. In dogs with a history of vomiting, antimicrobials for potential aspiration should be administered.

Disorders to be familiar with

Upper airway:

CATS Nasopharyngeal polyps- Young cats, with loud stridor/stertor, occasionally dysphagia. Direct visualization on oral examination, removal with traction or ventral bulla osteotomy. Nasopharyngeal stenosis- narrowing of NP, treat with balloon or stent. Laryngeal paralysis- cats may be clinical with unilateral paresis, maybe idiopathic or due to tumor/infection etc. May be managed medically or surgically (avoid if possible!) Laryngeal masses- usually squamous cell carcinoma, may be benign. Specific therapy dependent on underlying condition.

The prognosis for nasopharyngeal polyps is excellent. NP stenosis is more challenging but may have an acceptable outcome. Laryngeal paralysis is recognized with increasing frequency, and is different from the dog form Laryngeal tumors carry a very guarded prognosis, with survival times of typically weeks at best.

Lower airway

Feline asthma, which implies reversible bronchoconstriction and chronic bronchitis are common disorders. Infection, such as M ycoplasma may also result in respiratory disease. Therapy is currently directed towards addressing the underlying irritant and then long-term prednisone. Some clinicians and clients report good success with inhaled steroids (eg. Fluticosone). Recall that in order for inhaled steroids to be effective, there needs to have been a good response to parenteral steroids. The web site www.fritzthebrave.com, provides helpful client-oriented information on inhaled medication.

Parenchymal disease

Congestive heart failure, typically from cardiomyopathy may result in pulmonary edema. This may appear patchy in distribution. Pro-NT BNP testing has been recently introduced and may be helpful in identifying cats at risk of CHF or in CHF. Heart failure is NOT a death sentence in cats; many cats, even those with a bout of heart failure may live for years after diagnosis with committed owners. Infection is rare in adult cats, but may occasionally occur in kittens or due to atypical organisms (eg. Toxoplasmosis), and finally neoplasia (metastatic or primary) may occur in cats as well. Pulmonary contusions may also result parenchymal infiltrates. Recall that severe bronchial disease may look like metastatic disease.

Pleural effusion

May represent congestive heart failure, pyothorax, chylothorax or neoplasia (specifically lymphoma). Pleural effusion is a sign, not a final diagnosis. See abstract by Anastasio et al in the oral sessions here at IVECCS 2010 for more details on feline pyothorax. Other pleural space diseases ("parasites") include pneumothorax (spontaneous or traumatic), diaphragmatic hernia, or neoplasia.

Trickery

Occasionally cats with metabolic disease (such as acidosis) with have an increased respiratory rate and effort, this may be mistaken for pulmonary disease in some individuals. Painful cats tend to hide, but increased respiratory rate may be observed.

Therapeutic approach to respiratory distress in best directed at the "best guess" of the underlying disease process. Specific tips that are important to consider for evaluating cats with respiratory distress are:

     • Iatrogenic pneumothorax is very common following thoracocentesis in cats with long-standing effusions. Pleural effusion leads to the thickening of the pleura, and this if nicked, will continue to leak air. Recall that normal lung seals quickly.

     • Old cats don't get new onset asthma. Airway disease in cats is a young to middle age cat disease. Cats may cough their entire lives, but barring lifestyle changes(eg moving to a different climate or with a smoker) they should not develop cough as geriatric cats.

     • Cold cats have heart failure. While admitably, cats may be hard to "temp" if they are stressed, cats that are hypothermic are very commonly in heart failure.

     • Cats that eat well in oxygen are hyperthyroid or have neoplastic disease. Anorexia is common in the stressed/short of breath cat, and finding a cat who is truly devouring the offered food, makes the likelihood of cancer or hyperthyroidism higher.

     • Pro terminal BNP, a biomarker of atrial stress, may prove useful in cats.

     • Bronchial disease may appear similar to mets.

     • Rounded lung lobes, suggest chronic effusion, and increase the risk for pneumothorax.

References available upon request (Please contact me if I may be of help- Elizabeth.rozanski@tufts.edu)