05 Dec From the Proceedings Library: Respiratory Distress
Breathe Easy: Approach to Respiratory Distress
Tekla Lee-Fowler, DVM, MS, DACVIM (SAIM)
Respiratory distress can be an inherently stressful and intimidating situation for all members of the veterinary team. It is essential that all members of the team readily recognize signs of respiratory distress and are trained to respond promptly. This includes preparing front desk staff to recognize the urgency of the situation, preparing technical staff to recognize signs of respiratory distress, and ensuring that we can promptly localize the problem and act to stabilize the patient.
Presenting signs of respiratory distress can include increased respiratory rate or appearance of effort, open-mouth breathing, extension of the neck, abduction of the elbows, anxious facial expression, flared nostrils, pronounced abdominal component to the respiratory pattern, frequent changing of body positions or unwillingness to rest, and cyanosis.
These patients may be extremely fragile, and it may be necessary to begin initial stabilization prior to a thorough physical examination. Often, it is necessary for procedures directed at initial stabilization occur simultaneously with this abbreviated physical examination. Obtaining a detailed and accurate history also provides key information; prior medical history, vaccination status, routine health maintenance and travel histories are important in addition to details regarding the onset, duration, and clinical signs of the specific episode of respiratory distress.
Determining airway patency and gaining control of the airway, if necessary, is the first major step in patient assessment. A physical examination that is targeted to the respiratory system first is recommended, with the remainder of the examination completed once the patient is stabilized. Closely observing respiratory pattern and character in combination with thoracic auscultation can rapidly narrow the differential sufficiently to guide administration of life-saving therapy. Determining the phase of respiration which is most affected (i.e. inspiration vs. expiration) and the respiratory character (e.g. rapid, shallow breathing) can assist in initially narrowing the differential. Respiratory sounds (e.g. stertor, stridor, crackles, and wheezes) are also very useful in this process.
|Respiratory Phase Most Affected
|Other Associated Characteristics
|Wheezes; “Abdominal Push”
|Inspiratory, Expiratory, or Mixed
|Crackles; Increased Bronchovesicular sounds
|Shallow, Rapid Pattern; Dull or Absent Lung Sounds
Sedation and Oxygen Supplementation
Providing supplemental oxygen and easing anxiety via mild sedation are two of the first steps in patient stabilization that are appropriate for nearly all patients in respiratory distress. The aim of sedation is to reduce anxiety associated with respiratory distress. Butorphanol (0.1- 0.4 mg/kg IV or IM) can be used with minimal risk. If additional sedation is necessary, this can be combined with a low dose of a benzodiazepine. Oxygen supplementation can be delivered in various ways; availability, severity of the patient’s condition, and what the patient will tolerate without causing undue stress are factors that determine how supplemental oxygen is delivered. Flow-by oxygen, use of a facemask, nasal cannula, oxygen hoods, and oxygen cages will all be considered here.
Flow-by oxygen is widely available and generally well tolerated. With this method, oxygen tubing is physically held near the patient’s nose and mouth. Due to patient movement and dilution of the supplemental oxygen with room air, this is the least efficient method of increasing the fraction of inspired oxygen (FiO2). However, it can be useful upon initial presentation and during evaluation. A tight fitting facemask can increase the FiO2 being delivered. However, some patients in respiratory distress may not tolerant the use of a facemask. Both flow-by methods and facemasks are short-term oxygen delivery methods for use when initially evaluating and stabilizing patients or for transport to other areas of the hospital for diagnostics.
Nasal cannulas, an oxygen hood, or an oxygen cage are more suited for oxygen supplementation over a longer duration of time. Humidification is necessary when oxygen supplementation is administered over longer periods of time. Commercially available humidifiers which attach to the flow meter are the best method for accomplishing this. Oxygen cages provide the benefit of a less handling leading to a lower stress environment while providing adequate oxygen supplementation and allowing simultaneous monitoring of the patient. Oxygen cages should allow for regulation of oxygen concentration, ambient temperature, and humidity. Humidity should be maintained at 40-50%, and temperature should be kept at approximately 70oF. Oxygen flow should generally be adjusted to provide an FiO2 of 40-60%.
Mechanical ventilation may be required if the patient fails to respond to oxygen supplementation, experiences respiratory fatigue, or has neurological deficits which result in hypoventilation. Maintenance of mechanical ventilation requires intensive monitoring and management, and as a result, is time, resource, and labor intensive. As a result, it is also typically quite expensive. Prognosis for patients with primary pulmonary disease requiring mechanical ventilation is considered guarded to poor; however, this is dependent on the underlying condition.
In many cases, oxygen supplementation and sedation are adequate to stabilize the patient enough for more thorough examination and the initial round of diagnostics (e.g. obtaining a blood sample for analysis and thoracic radiographs). In some cases, the anatomical localization of the disease using the singalment, history, and physical examination finidings (see
table above) can provide guidance on additional treatments that might be required to accomplish stabilization. Once example of this is pleural disease. If pleural disease is strongly suspected, particularly pneumothorax or pleural effusion, thoracocentesis should be performed as part of the stabilization plan. This may need to occur prior to the patient being stable enough to undergo radiographic assessment, and this would result in immediate improvement of the patient and stabilization for further diagnostics.
Once the patient is stabilized, differential diagnoses can be more thoroughly explored and diagnostics pursued in order to establish a diagnosis. As mentioned above, history and physical examination can often assist in anatomical localization at which point differential diagnoses can be considered. Specific treatment thereafter depends upon the underlying disease condition.
Stertor and stridor are respiratory noises that are typically associated with upper airway distress. These are sounds that do not require a stethoscope to appreciate. The inspiratory phase of respiration is most affected and is often prolonged. Differential diagnoses include brachycephalic syndrome, laryngeal paralysis, laryngeal/tracheal trauma, tracheal collapse, and foreign body, mass, or edema of the pharynx, larynx, or trachea.
Lower airway disease tends to produce an exaggerated or prolonged expiratory phase of respiration. Wheezes and an “abdominal push” may be appreciated. Differential diagnoses include feline asthma, foreign body, mass, bronchial collapse, and severe bronchitis which has resulted in bronchomalacia.
Pulmonary parenchymal disease can present as a mixed respiratory pattern with distress in both inspiratory and expiratory phases of respiration. Thoracic auscultation may reveal increased bronchovesicular sounds and crackles. Broad categories of differential diagnoses include pulmonary edema, pneumonia (infectious or non-infectious), neoplasia, pulmonary hemorrhage/contusions, interstitial lung disease (e.g. pulmonary fibrosis), and pulmonary thromboembolism.
Pleural space disease typically manifests as a rapid, shallow breathing pattern.
Decreased bronchovesicular sounds (dorsally for pneumothorax and ventrally for pleural effusion) upon thoracic auscultation are often a feature of pleural space disease. In the case of diaphragmatic hernia, sounds associated with the GI tract (borborygmi) may be appreciated on thoracic auscultation. Differential diagnoses include pneumothorax, pleural effusion of various types, and diaphragmatic hernia.
Patients with thoracic wall disease severe enough to present in respiratory distress are typically afflicted with more obvious disease which may include severe rib fractures, flail chest, open chest wounds, and penetrating wounds. More subtle differentials in this category include neuromuscular and neurologic conditions as well as electrolyte abnormalities (e.g. hypokalemia) that can result in decreased movement of the thoracic wall and hypoventilation.
Conditions in this category either result in decreased respiratory function (abdominal distension) or have characteristics that may mimic respiratory distress (e.g. hyperventilation or panting). Differentials in the latter category include anxiety, pain, hyperthermia, acidosis, anemia, endocrine conditions (e.g. hyperadrenocorticism), and medications (e.g. prednisone), among others.
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