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Approach to Respiratory Distress
Laura A. Nafe, DVM, MS, DACVIM (SAIM)
Assistant Professor, Small Animal Internal Medicine
Oklahoma State University
Introduction
Respiratory distress is a common reason for dogs and cats to present on an emergency basis to a
veterinary clinic. The general approach to the veterinary patient in respiratory distress is dependent on
signalment of the patient, localization of the respiratory pattern, evaluation of vital parameters, and
cardiothoracic auscultation.
The goals of this presentation include: 1) Understanding of respiratory terminology 2) Localization of the
respiratory pattern 3) Immediate stabilization of the respiratory distress patient 4) Recognition of
physical exam abnormalities that may help guide specific treatments.
Respiratory terminology
When a dog or cat presents with increased respiratory effort, it is important to understand proper
terminology when describing the patient’s respiratory abnormalities. Common terms used to describe
respiratory distress or difficulty in dogs and cats include:
Tachypnea – Increase in rate of respiration.
Hyperpnea – Increase in depth and rate of respiration.
Orthopnea – Dyspnea that can be improved with alterations in position.
Dyspnea – The sensation of difficult or distressed breathing; “air hunger.”
Dyspnea is a term that is used often over-used clinically, as it should be reserved for patients that are
truly in respiratory distress. These are dogs and cats that are truly “oxygen hungry” and therefore
unable to interact with their environment normally. This is in contrast to a patient that has an increase
in respiratory effort, but is not truly distressed. It is also important to note that not all patients in
respiratory distress are tachypneic. A classic example is a dog with severe laryngeal paralysis may have a
normal respiratory rate with severe inspiratory dyspnea.
Localization of the respiratory pattern
Approach to managing the dog and cat in respiratory distress is dependent on which area of the
respiratory tract is affected. The following scheme is helpful when localizing the respiratory pattern:
1.
2.
3.
4.
5.
6.
Respiratory localization
Upper airway
Lower airway
Abdominal distension
Pulmonary parenchyma
Pleural space disease
“Look-a-like” diseases
Respiratory pattern
Increased effort on inspiration; stridor or stertor
Increased effort on expiration; wheezes
Severe abdominal enlargement
Mixed inspiratory and expiratory effort; pulmonary crackles
Shallow breathing with mixed respiratory effort; decreased lung sounds
Mixed inspiratory and expiratory pattern with normal oxygenation
The first 3 should be evident simply by watching the patient breath. Upper airway disease results in a
prolonged inspiratory phase of respiration and generally results in loud upper airway noise (stridor
and/or stertor) during inspiration. Stridor localizes the problem to the larynx or pharyngeal region,
whereas stertor localizes to the nasal or nasopharynx. Lower airway disease results in a prolonged
expiratory phase and often an “abdominal push” can be observed. Wheezes (musical airway sounds)
may be heard with or without a stethoscope. Although uncommon, patients can present for respiratory
distress secondary to severe abdominal enlargement (eg; ascites, GDV, abdominal mass) and this should
be obvious when initially evaluating the patient. Patient’s with increased respiratory effort secondary to
abdominal distension/enlargement should really never be truly dyspneic.
In contrast, further investigation is needed to help differentiate between pulmonary parenchymal,
pleural space, and “look-a-like” diseases. Pulmonary parenchymal diseases include pulmonary edema
(cardiogenic or non-cardiogenic), pneumonia, pulmonary thromboembolism, and pulmonary fibrosis.
These patients often have a mixed inspiratory and expiratory respiratory pattern and may have
pulmonary crackles on auscultation of the lungs. Patients with pleural space disease also may have a
mixed respiratory pattern with most cases having slightly more effort on inspiration. One consistent
feature of pleural space disease is a shallow breathing pattern. Dogs and cats with pleural effusion will
often have decreased ventral lung sounds and may have muffled heart sounds (remember that
pericardial effusion or a thoracic/mediastinal mass could also cause muffled heart sounds) on
cardiothoracic auscultation. Patients with pneumothorax will have decreased lung sound dorsally. Most
patients that present for a “look-a-like” disease may have tachypnea, but should not have an
appreciable increase in respiratory effort. These patients should NOT have decreased oxygenation
based on SpO2 or arterial blood gas evaluation. In addition, thoracic radiographs in these patients should
be normal.
Immediate stabilization
One of the first and most important steps in stabilization is providing oxygen therapy. Cats presenting
in respiratory distress are best provided oxygen via an oxygen cage, because flow-by oxygen via mask
often adds additional stress and anxiety. Many dogs can be provided oxygen flow-by via mask or nasal
prongs while the patient is being assessed. Initial assessment of the patient’s respiratory pattern and
brief cardiothoracic physical exam with vital parameters is extremely important, as this information
determine the best stabilization management strategy.
Efforts should be made to place an intravenous (IV) catheter as soon as possible if the patient will
tolerate flow-by oxygen and it does not place additional stress on the patient. Placing an IV catheter
allows intravenous medications, including additional sedatives and potentially propofol if the patient
requires intubation. The best way to manage most cats initially is to administer intramuscular sedation
(butorphanol is the author’s preference) and minimize stress by allowing them to calm down in an
oxygen cage without the need for restraint. After the cat has been mildly sedated, attempts can be
made to then place a catheter quickly with flow-by oxygen and minimal stress and restraint.
Utilizing the localization scheme may help to determine if this is an upper airway or lower airway
respiratory condition. Patients with upper airway obstruction are going to benefit the most from
sedation (butorphanol +/- acepromazine) and possibly intubation in severe cases. For example, the
laryngeal paralysis Labrador Retriever or brachycephalic airway syndrome English Bulldog may need to
be intubated on initial presentation to capture and bypass their upper airway if sedatives and oxygen
does not improve their respiratory status. Both dogs and cats with severe upper airway disease
resulting in respiratory distress benefit from anti-inflammatory glucocorticoids to help reduce
inflammation and associated edema, although remember that these effects will not be immediate.
Alternatively, lower airway disease may be responsive to bronchodilator agents. The best example being
the cat in status asthmaticus that presents with increased expiratory effort, an abdominal push, and
expiratory wheezes (audible with or without a stethoscope). This patient may benefit greatly from
inhaled albuterol or injectable terbutaline (IM or SQ). Dogs have not been documented to have true
bronchoconstriction like cats and humans do, and therefore, do not benefit from bronchodilator therapy
in most cases. Anti-inflammatory therapy (eg; glucocorticoids) is an important aspect of chronic
management of canine and feline airway disease, and is often beneficial in the acute management of
airway disease as well. Unless the abdominal distension is due to severe ascites or gastric dilatation
volvulus, there is little that can be performed initially to stabilize the patient with abdominal distension.
Sedatives and proper positioning may be helpful in these patients.
Other than oxygen, patients with pulmonary parenchymal disease can be difficult to stabilize initially
without further diagnostics. If congestive heart failure is suspected, a bolus dose of furosemide (2
mg/kg IV or IM in dogs; 1-2 mg/kg IV or IM in cats) can be administered to help reduce pulmonary
edema. Ideally, thoracic radiographs should be performed prior to furosemide administration to avoid
situations where the diagnosis is clouded by previous furosemide administration. Remember that often
a single dorsoventral thoracic radiograph may be enough to diagnose congestive heart failure and/or
pleural effusion and minimizes stress to the patient.
If pleural space disease is strongly suspected, a thoracocentesis can be performed to help stabilize the
patient prior to additional diagnostics (even thoracic radiographs). With the addition of portable
ultrasound available in many veterinary clinics, this technique may be useful to quickly evaluate for
pleural effusion. Alternatively, a single lateral or dorsoventral radiograph is diagnostic for effusion or
pneumothorax if the patient is stable to perform this test.
Treatment
Butorphanol
Acepromazine
Furosemide
Terbutaline
Albuterol
Glucocorticoids
Dose
0.2-0.4 mg/kg IV, IM, SQ
0.01-0.04 mg/kg IV, IM, SQ
2-4 mg/kg IV or IM bolus (Dogs)
1-2 mg/kg IV or IM bolus (Cats)
Consider CRI following bolus
0.01-0.04 mg/kg IM or SQ
Metered dose inhaler: 1-2 puffs
- Spacer and facemask required
Nebulization: 1.25 mg in 2 mL of 0.9%
NaCl over 10-20 minutes
Dexamethasone: 0.1-0.3 mg/kg IV, IM, SQ
Prednisolone: 1-2 mg/kg IV, IM, SQ
Indication
Sedation
Sedation
Congestive heart failure
Bronchoconstriction secondary
to lower airway disease (cats)
Bronchoconstriction secondary
to lower airway disease (cats)
Upper airway inflammation
Tracheal collapse
Lower airway disease
Recognition of physical exam abnormalities
Dogs and cats presenting in respiratory distress are challenging cases, because we are often forced to
make therapeutic decisions with minimal diagnostic information (due to the need to reduce stress to the
patient). That being said, there are specific aspects of a case that can help localize the cause of the
respiratory distress anatomically without invasive diagnostic testing.
Signalment of the patient: Although any species, breed, or age of animal is capable of acquiring any
respiratory disease, this information can be helpful when thinking about the “likely” differential
diagnoses. For example, the Yorkshire Terrier is more likely have tracheal collapse and the Labrador
Retriever is more likely to have laryngeal paralysis. Additionally, the Cavalier King Charles Spaniel and
Doberman Pincher are more likely to have congestive heart failure. In general, cats are less likely to
acquire aspiration pneumonia and more likely to have a true lower airway obstruction secondary to
bronchoconstriction from asthma. Cats also commonly develop pleural effusion associated with
congestive heart failure. Age and environment may be helpful in patients in which a viral or bacterial
infectious disease is suspected, as these tend to be young animals with a history of exposure to other
animals (eg; shelter, pet shop, boarding). In addition, given our geographic location of Oklahoma,
histoplasmosis is also a consideration in patient’s the respiratory disease (especially cats).
Vital parameters: With the exception of upper airway obstruction, most patients with respiratory
distress have an increase in respiratory rate. In addition, patients that are hypoxic will often have
concurrent tachycardia in an effort to improve oxygenation and/or secondary to the stress and anxiety
associated with respiratory distress. In my opinion, temperature is perhaps the most important vital
parameter, as hypothermia is often observed in patients with congestive heart failure (especially cats).
In contrast, an increase in temperature associated with fever may be observed in patients with
pneumonia (eg; fungal, bacterial), pyothorax , or neoplastic disease. Hyperthermia is often documented
in patients with airway obstruction (upper airway more often than lower airway).
Cardiothoracic auscultation: In addition to observing the respiratory pattern, pulmonary and tracheal
auscultation can be useful when differentiating upper airway, lower airway, pulmonary parenchymal,
and pleural space diseases. Most dogs that are congestive heart failure have a heart murmur heard on
auscultation (exception might be a dog with dilated cardiomyopathy). However, many cats (up to 50%)
do not have a heart murmur or gallop auscultated at the time of congestive heart failure diagnosis. If
pulmonary crackles are heard, determining if they are diffuse or focal may help narrow the differential
diagnoses list, as aspiration pneumonia may be focal whereas diffuse crackles could indicate pulmonary
edema or other causes of pneumonia (viral, fungal). Decreased lung sounds ventrally would support
pleural effusion, whereas decreased lung sounds dorsally indicates pneumothorax.
References
Ettinger SJ, Feldman EC. Textbook of Veterinary Internal Medicine. 7th ed. St. Louis: Saunders, 2010.
Rozanski EA, Rondeau MP. Respiratory pharmacotherapy in emergency and critical care medicine. Vet
Clin North Am Small Anim Pract 2002 ;32: 1073-1086.
Sumner C, Rozanski E. Management of respiratory emergencies in small animals. Vet Clin North Am
Small Anim Pract 2013; 43: 799-815.