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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? www.voorjaarsdagen.eu Companion Animal Pulmonology 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 www.voorjaarsdagen.eu 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. www.voorjaarsdagen.eu