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Companion Animal
Pulmonology
THE CLINICAL APPROACH TO A PATIENT WITH
RESPIRATORY DISTRESS
Respiratory distress is a common and often life-threatening clinical presentation in
small animal medicine. These patients are often brittle, so a clinician needs to make
rapid, yet appropriate therapeutic and diagnostic choices. Expertise in the varying
manifestations and pathophysiologic causes of respiratory distress will enable accurate
recognition and management of patients, increasing the likelihood of a successful
patient outcome.
Jason M. Eberhardt, DVM,
MS, DACVIM (SA)
College of Veterinary
Medicine - Glendale
Companion Animal Clinic
323-H
Phone: 623-806-7481
Fax: 623-537-6399
Phoenix, Arizona
[email protected]
INITIAL ASSESSMENT
Once respiratory distress is recognized in a patient, the first therapy (regardless of
the cause) is to provide oxygen supplementation. Once oxygen supplementation is
provided, it is critical that airway patency is confirmed. In a patient with true respiratory
distress, there will likely not be adequate time to wait for a full list of diagnostic
tests prior to initiating stabilization and treatment. Clinicians must resist the urge to
immediately perform a thorough physical exam and/or advanced imaging. The patient’s
respiratory pattern should be carefully observed and categorized (see below). This will
potentially prevent a patient in a precarious status from complete decompensation and
the development of respiratory arrest. It can also allow for evaluation of possible signs
of wall trauma that are related to the distress (i.e. flail chest). Furthermore, respiratory
pattern categorization will provide insight on the most appropriate therapeutic and
diagnostic interventions.
Complete airway occlusion produces a characteristic respiratory pattern that includes
a prolong inspiratory phase with little/no airway movement. If a complete airway
occlusion is present, immediate therapeutic measures (i.e. sedation, airway exam,
intubation/tracheostomy, mechanical ventilation) is indicated. Due to the urgent
nature of such scenarios, it is vital that clinicians and technical staff are able to quickly
recognize and intervene.
A patient’s respiratory pattern should help guide subsequent therapeutic and
diagnostic steps. Again, an attempt to stabilize the patient and intervene with
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
potentially life-saving therapeutics should be the priority before preceding to more
advanced diagnostics that require patient manipulation. For example, a feline
patient should be considered as having pleural space disease if they have no audible
respiratory sounds, no auscultatory respiratory sounds, a prolonged inspiratory phase
and a restrictive respiratory pattern. A patient with suspected pleural space disease
should prompt immediate therapeutic thoracocentsis (possibly with ultrasound
guidance, if available) prior to thoracic radiographs. Alternatively, the feline patient that
presents with an audible and auscultatory wheeze, an expiratory push and obstructive
respiratory pattern should incite concern of bronchial disease. This these patients,
sedation and bronchodilators prior to further diagnostics should be considered.
Ideally, intravenous access should also be obtained prior to advanced diagnostics
since immediate administration of emergency drugs and/or fluids may be necessary.
If possible, blood should be obtained at this time for an emergency database (PCV/TP,
blood glucose, renal status, electrolytes, etc.). These initial values may be valuable not
only in determining the underlying cause, but also in the management of the eventual
diagnosis. For example, a patient in left-sided congestive heart failure receiving
aggressive loop-diuretic therapy may become azotemic and knowing the renal status
prior to therapy provides a more complete evaluation.
RESPIRATORY PATTERN CATEGORIZATION
It is important to acknowledge that it can often be a significant challenge to
completely categorize an individual patient’s respiratory pattern. However, through
careful observation, clues to the underlying cause of respiratory distress can often be
distinguished. By asking and attempting to answer the following questions, significant
insight on the underlying cause can be elicited:
1)Does the patient make an audible noise while breathing such as stridor, stertor or a
wheeze?
2)Does the patient have sounds on thoracic auscultation such as wheezes or crackles?
3)Does the patient seem to have more effort and prolonged phase of respiration on
inspiration, expiration or both?
4)Does the patient have an obstructive or a restrictive respiratory pattern?
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Audible noise changes
A stertor is a respiratory noise secondary to partial obstruction of the nasopharynx,
pharynx or soft palate. It primarily corresponds with the inspiratory phase and is
typically lower-pitched then stridor. A stertor is the classic snoring sound noted in many
brachycephalic breeds. A stridor is a high-pitched sound resulting from turbulent air
flow in the larynx or the bronchial tree. A stridorous sound originates from a narrowed
or obstructed airway. It can be inspiratory, expiratory or biphasic, although it is usually
heard during inspiration. A wheeze is a continuous, coarse, whistling sound produced in
the lower airways during breathing. Most commonly wheezes are more pronounced on
expiration from bronchi narrowing or collapse. However, wheezes can be biphasic if a
fixed obstruction is present.
Auscultatory respiratory sounds
An auscultatory wheeze has the same characteristics and pathogenesis as an audible
wheeze and also indicates lower airway narrowing and/or collapse. However,
depending on the underlying cause and severity of disease, only an auscultatory
wheeze may be present. Auscultatory crackles are discontinuous, “popping” sounds that
originate from the airways and alveoli. Crackles occur as collapsed or obstructed alveoli
suddenly “pop” open. This sudden opening will cause a very distinct sound that is most
commonly heard on inspiration, but expiratory crackles can also be present in severe
disease. Crackles are a key diagnostic auscultatory sound as they signify pulmonary
parenchymal disease that involves the presence of fluid accumulations within the
alveoli secondary from either inflammation or edema.
Effort and prolonged phase of respiration
Careful attention to which phase of respiration that requires the most effort and seems
prolonged gives insight on which phase requires the most work. When combined with
the identification of an obstructive respiratory pattern, recognizing which phase is
prolonged can help discern the location of the obstruction. It should be appreciated
that identification of a prolonged phase of respiration can be incredibly challenging
for even the most experienced clinician. However, when noted it can be a vital part of
obtaining an accurate diagnosis.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Restrictive and obstructive respiratory patterns
Restrictive respiratory patterns occur when lung expansion is restricted. In restrictive
disease, expiration efforts occur without impediment. A restrictive pattern is
characterized by a rapid and shallow effort. Presence of a restrictive pattern should
prompt close evaluation of the presence or absence of auscultatory respiratory sounds
and possible pleural space disease must be quickly ruled out. Obstructive respiratory
patterns occur when airflow is hindered from airway obstruction. This pattern is
typically slower (in comparison to restrictive patterns) and often “deeper”. Obstructive
respiratory disease is usually classified based upon the location of the obstruction;
extra-thoracic versus intrathoracic. Extra-thoracic lesions are typically characterized
by increased inspiratory effort, while intra-thoracic lesions typically have increased
expiratory effort. Mixed respiratory patterns occur in disease processes that have
both restrictive and obstructive components to the pathophysiology and are most
commonly seen in pulmonary parenchymal diseases that reduce compliance (such as
pneumonia). Patients with mixed respiratory patterns have exam characteristics of both
patterns. ADDITIONAL DIAGNOSTIC AND THERAPY CONSIDERATIONS
Once a patient has had oxygen therapy administered and has been carefully evaluated,
the clinician should attempt to classify whether the patient most likely has an airway
obstruction, bronchial disease, pulmonary parenchymal disease or pleural space
disease (see chart below). Depending on suspicions, further therapy prior to advance
imaging may still be recommended to further stabilize the patient.
Airway obstruction
Patient’s with a partial airway obstruction may be hyperthermic due to inadequate heat
dissipation. Intravenous fluids along with external cooling techniques are critical for
reducing core body temperature in these patients. Caution should be taken however,
to not allow hypothermia to occur, leading to peripheral vasoconstriction. Sedation
and anxiolytic therapy should also be strongly considered in these patients. Decreasing
the respiratory rate can improve the airflow and/or reduce the amount of airway
collapse depending on the cause of obstruction. Careful usage of anti-inflammatory
dosages of steroid should also be considered to reduce edema/inflammation of the
larynx, pharynx, trachea, etc. It should be noted that while prudent usage of steroids
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Companion Animal
Pulmonology
is important to prevent masking diseases such as lymphoma, withholding steroids in
patients with severe airway inflammation may pose an even higher risk. In patients that
do not respond to therapy or a complete airway obstruction is suspected, obtaining
airway control must be done first.
Bronchial disease
Respiratory distress caused by bronchial disease is most commonly seen in the cat,
particularly with the presentation of an “asthmatic crisis”. In patients with suspected
bronchial disease, it is important to notice that a major cause of their signs are likely
due to airway narrowing secondary to bronchoconstriction. Therefore, beta-2 agonist
bronchodilators are crucial medications that can relieve constriction within minutes
of administration and are likely more effective in providing immediate relief over
other medications such as steroids. However, anti-inflammatory dosages of steroids
are considered a mainstay in the therapy of many bronchial diseases and prudent
administration must be considered in many patients. Finally, similar to patient’s with
airway obstruction, usage of sedation and anxiolytic therapy can reduce the respiratory
drive and improve airflow through narrowed airways.
with one notable exception. If a hemothorax is present, only enough blood should be
removed that will improve oxygenation.
Further diagnostics
Thoracic radiographs are a key diagnostic test to perform once a patient is stabilized.
Thoracic radiographs in combination with clinical findings and clinical response to
therapy will then drive a complete diagnostic plan (i.e. echocardiogram, lower airway
imaging/sampling, CT, etc.) if a diagnosis is still not completely elucidated. Likewise,
a specific therapy plan will be based upon the patient’s status, findings and final
diagnosis.
Pulmonary parenchymal disease
Pulmonary parenchymal diseases include some of the most diverse causes of
respiratory distress in small animals. Some of these causes can have significant
differences in therapy recommendations. For example, diuretic therapy is clearly a
mainstay in the therapy of cardiogenic pulmonary edema, but is contraindicated
in patients with pneumonia. For this reason, it can often be challenging to provide
specific therapy recommendations without further insight on the specific cause of the
pulmonary disease.
Pleural space disease
It is crucial that pleural space disease be ruled out early into a patients’ presentation
so appropriate intercessions can be made. If pleural space disease is suspected and
access to ultrasound is available, a quick thoracic scan assessing for effusion should be
performed. If ultrasound is unavailable, a diagnostic and therapeutic thoracocentesis
should be performed based upon the presumptive diagnosis. When removing either
fluid or air from the pleural space, as much drainage should be performed as possible
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
References
1.King, LA. (2004). Textbook of Respiratory Disease in Dogs and Cats. Philadelphia, PA: Elsevier.
2.Barrs, VRD. (2006). Respiratory Patterns – A Diagnostic Aid to Feline Respiratory Disease. Australian College of
Veterinary Scientists.
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