What causes acute respiratory distress syndrome?
Acute respiratory distress syndrome is a complication of other severe systemic diseases. These diseases may include sepsis (infection), pancreatitis, pneumonia (due to infection or the inhalation of foreign materials), and other severe illnesses. Some cases are caused by severe trauma, near-drowning, snake bite, and other accidents. In each of these conditions, massive body-wide inflammation frequently occurs. Acute respiratory distress syndrome is one known complication of this massive inflammation. In most cases, ARDS occurs one to four days after the onset of the pet’s severe inflammatory disease. In many cases, this is a period when the dog is hospitalized for treatment.
In ARDS, inflammation and the release of various inflammatory chemicals lead to the leaking of capillaries (small blood vessels) within the lungs. These leaky capillaries leak fluid into the lungs; this fluid interferes with the body’s ability to exchange oxygen effectively via the lungs. When the animal can no longer exchange oxygen, tissue damage occurs throughout the body and can lead to death.
How is acute respiratory distress syndrome diagnosed?
The most important test in diagnosing ARDS is a blood test called a blood gas analysis, which provides detailed information on the levels of oxygen and carbon dioxide within the blood. Your veterinarian will also likely perform a complete blood cell count, serum biochemistry profile, and urinalysis to assess your dog’s overall health. Chest radiographs (X-rays) and an echocardiogram (ultrasound of the heart) may also be performed.
In addition to these tests, your veterinarian will also perform tests to determine the underlying cause of your dog’s illness (if it has not already been identified). These tests may include radiographs of the abdomen, ultrasound, exploratory surgery, bacterial cultures, and other diagnostic tests that may vary based on the exam findings.
Diagnostic approach to a patient in respiratory distress should consider the patient’s signalment and history as well as the broad anatomic differential diagnoses of dyspnea (Table 1).
Extensive diagnostics should not be performed until the patient has been stabilized as much as possible, a brief physical examination has been performed, and the practitioner has localized the disease to the most likely anatomic location (Table 1). Diagnostic tests may subsequently involve:
Upper respiratory tract obstruction involves a mechanical or functional obstruction of the upper (large) airways (i.e., the pharynx, larynx, or trachea). Nasal disorders are not considered in this article as the animal should always be able to open its mouth and breathe, preventing the development of dyspnea even if the nasal cavity is obstructed.
Dogs and cats with respiratory distress can be classified into 8 disease categories, some of which are associated with distinct breathing patterns observed during physical examination.1,2 These categories include both primary respiratory diseases and secondary causes of respiratory difficulty. Diagnostic approach is determined by the category of disease causing respiratory distress.
Upper airway examination. Examination is performed after preoxygenation under sedation. At its most basic, examination may involve inspection of the oropharynx and larynx with a laryngoscope; in patients with suspected tracheal disease, it may involve tracheobronchoscopy with a flexible bronchoscope or endoscope.
3 Types of Dog Breathing Problems and What to Do
Managing dogs and cats in respiratory distress is a multifaceted effort that involves stabilizing patients prior to determining a definitive diagnosis. Fortunately, respiratory distress—no matter what the cause—requires somewhat standardized interventions during initial stabilization.
One of the benefits of initial stabilization is that it provides the practitioner time to consider the appropriate diagnostic and subsequent therapeutic approach.
Initial stabilization of a patient in respiratory distress generally involves provision of oxygen supplementation, with or without patient sedation.
Sedation with careful monitoring and, if necessary, intubation and ventilation can be extremely useful in animals that have become anxious due to hypoxemia and/or hypercapnia. In some patients, especially dogs with upper airway obstruction, stabilization may require sedating the animal by administering some form of anesthetic induction agent; then clearing the oral cavity of obstructing material (eg, secretions or foreign material in a choking animal) prior to intubation or tracheostomy.
Animals with upper airway obstruction, such as those with laryngeal paralysis, may become hyperthermic due to the increased work of breathing. Because of the airway obstruction, these animals are unable to effectively pant, resulting in inability to thermoregulate and dissipate heat. As such, cooling hyperthermic patients in respiratory distress is an important component of initial stabilization, and can be accomplished by:
Initial stabilization may also include thoracocentesis, if severe respiratory distress is secondary to pleural space disease, such as pneumothorax or pleural effusion.
Diagnostic approach to a patient in respiratory distress should consider the patient’s signalment and history as well as the broad anatomic differential diagnoses of dyspnea (Table 1).
In general, breathing patterns help narrow the list of differential diagnoses (Table 1). For example, upper airway obstruction is associated with inspiratory dyspnea and an externally audible noise. In contrast, lower airway obstruction tends to be associated with expiratory dyspnea and wheeze, with the wheeze generally just audible on thoracic auscultation with a stethoscope, rather than externally audible.
Extensive diagnostics should not be performed until the patient has been stabilized as much as possible, a brief physical examination has been performed, and the practitioner has localized the disease to the most likely anatomic location (Table 1). Diagnostic tests may subsequently involve:
Dogs and cats with respiratory distress can be classified into 8 disease categories, some of which are associated with distinct breathing patterns observed during physical examination.1,2 These categories include both primary respiratory diseases and secondary causes of respiratory difficulty. Diagnostic approach is determined by the category of disease causing respiratory distress.
Upper respiratory tract obstruction involves a mechanical or functional obstruction of the upper (large) airways (i.e., the pharynx, larynx, or trachea). Nasal disorders are not considered in this article as the animal should always be able to open its mouth and breathe, preventing the development of dyspnea even if the nasal cavity is obstructed.
Characteristic signs in patients with an upper airway obstruction include inspiratory distress and an externally audible noise associated with breathing (eg, stertor, stridor). Tracheal disease is usually associated with a cough.
Upper airway examination. Examination is performed after preoxygenation under sedation. At its most basic, examination may involve inspection of the oropharynx and larynx with a laryngoscope; in patients with suspected tracheal disease, it may involve tracheobronchoscopy with a flexible bronchoscope or endoscope.
Cervical and thoracic radiographs are useful for patients with laryngeal or tracheal disease to detect masses and collapse.
Fluoroscopy is useful for detecting dynamic upper airway collapse that may not be visible on standard radiographs.
Definitive management for upper respiratory tract obstruction is extremely varied, depending on the definitive diagnosis, and beyond the scope of this review.