Almost all people with ARDS require ventilation for respiratory support.3 ARDS reduces lung compliance, so, over time, respiration effort increases, which eventually causes respiratory muscle fatigue.
Ventilator therapy helps decrease fatigue by performing the work required for breathing. Therefore, any animal with excessively
labored respirations may be a candidate for mechanical ventilation. Additionally, ventilator therapy allows the delivery of
higher oxygen concentrations than can be obtained through routine methods. If an animal cannot maintain a PaO2 of at least 60 mm Hg with oxygen therapy, mechanical ventilation should be considered.
Ventilators use positive pressure ventilation, often with positive end-expiratory pressure (PEEP), which keeps airway pressure
above atmospheric pressures during exhalation. This helps to keep small airways and alveoli open even during exhalation, facilitates
a more uniform distribution of tidal volume, recruits collapsed lung units, and may help reduce lung inflammation from repeated
opening and closing of small airways and alveoli.3,14,17 In people, ventilator therapy with lower tidal volumes than traditional ventilator therapy also reduces lung inflammation,
resulting in a lower mortality rate and an increased number of ventilator-free days.17
The benefits of ventilator therapy for ARDS are tremendous and often necessary for survival, but there can be serious side
effects. Ventilator therapy can result in decreased venous return or ventilator-associated pneumonia or pneumothorax, which
may cause more respiratory compromise. Another downside in small-animal patients is the requirement for anesthesia to allow
constant intubation of the patient or the need for a tracheostomy. Anesthesia and the critical care monitoring to properly
manage these cases necessitate 24-hour patient care. Thus, ventilator therapy is extremely labor- and time-intensive and can
only be performed at 24-hour clinics with ventilator equipment, proper monitors, and trained staff. This level of care results
in substantial cost for the client that may be financially impossible in many cases. Regardless of these downsides, the ventilator
can be a life-saving device in patients with acute lung injury or ARDS.
Acute lung injury and ARDS are secondary disorders caused by a severe primary respiratory or systemic disease. To properly
make a diagnosis, four criteria must be met. The most important and practical diagnostic tests include a thorough history,
thoracic radiography, echocardiography, and arterial blood gas analysis. Treatment usually involves addressing the primary
disease and providing supportive therapy and, possibly, mechanical ventilation.
Acute lung injury and ARDS are important disorders for all small-animal practitioners to understand and to be able to diagnose
so treatment can be instituted early and aggressively, with referral to a critical care facility if necessary. However, by
the time acute lung injury or ARDS is diagnosed, safe referral may be difficult unless a critical care facility is only a
short distance away or veterinary care can be provided during transport. Diagnosing acute lung injury or ARDS provides important
prognostic information for clients. Much remains to be learned about these disorders, but for now they continue to carry an
extremely high mortality rate and a grave prognosis.
Katherine Snyder, DVM, DACVIM
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
Texas A&M University
College Station, TX 77843
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