Acute lung injury and acute respiratory distress syndrome: Two challenging respiratory disorders - Veterinary Medicine
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Acute lung injury and acute respiratory distress syndrome: Two challenging respiratory disorders
These disorders are just starting to become more recognized in veterinary patients. Once established, they carry a heavy mortality rate, but since they result from a variety of primary causes, understanding how and when they might develop may help save a patient's life.


VETERINARY MEDICINE


Ventilator therapy

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.

CONCLUSION

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

REFERENCES

1. Ashbaugh DG, Bigelow DB, Petty TL, et al. Acute respiratory distress in adults. Lancet 1967;2(7511):319-323.

2. Wilkins PA, Otto CM, Baumgardner JE, et al. Acute lung injury and acute respiratory distress syndromes in veterinary medicine: consensus definitions: The Dorothy Russell Havemeyer Working Group on ALI and ARDS in Veterinary Medicine. J Vet Emerg Crit Care 2007;17(4):333-339.

3. Ware LB, Matthay MA. The acute respiratory distress syndrome. N Engl J Med 2000;342(18):1334-1349.

4. Parent C, King LG, Van Winkle TJ, et al. Respiratory function and treatment in dogs with acute respiratory distress syndrome: 19 cases (1985-1993). J Am Vet Med Assoc 1996;208(9):1428-1433.

5. Brady CA, Otto CM, Van Winkle TJ, et al. Severe sepsis in cats: 29 cases (1986-1998). J Am Vet Med Assoc 2000;217(4):531-535.

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7. Chan DL, Rozanski EA. Acute lung injury and acute respiratory distress syndrome. In: Respiratory diseases in dogs and cats. 1st ed. St. Louis, Mo: Saunders, 2004;504-507.

8. Walker T, Tidwell AS, Rozanski EA, et al. Imaging diagnosis: acute lung injury following massive bee envenomation in a dog. Vet Radiol Ultrasound 2005;46(4):300-303.

9. Haskins SC. Interpretation of blood gas measurements. In: Respiratory diseases in dogs and cats. 1st ed. St. Louis, Mo: Saunders, 2004;181-193.

10. Dunphy ED, Mann FA, Dodam JR, et al. Comparison of unilateral versus bilateral nasal catheters for oxygen administration in dogs. J Vet Emerg Crit Care 2002;12(4):245-251.

11. Wiedemann HP, Wheeler AP, Bernard GR, et al. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med 2006;354(24):2564-2575.

12. Hughes D, Boag AK. Fluid therapy with macromolecular plasma volume expanders. In: Fluid, electrolyte, and acid-base disorders in small animal practice. 3rd ed. St. Louis, Mo: Saunders, 2006;621-634.

13. Miao CH, Sun B, Jiang H, et al. Pharmacodynamics and pharmacokinetics of inhaled nitric oxide in dogs with septic acute respiratory distress syndrome. Acta Pharmacol Sin 2002;23(3):278-284.

14. Brower RG, Ware LB, Berthiaume Y, et al. Treatment of ARDS. Chest 2001;120(4):1347-1367.

15. Chan DL, Freeman LM. Nutrition in critical illness. Vet Clin North Am Small Anim Pract 2006;36(6):1225-1241.

16. Mohr AJ, Leisewitz AL, Jacobson LS, et al. Effect of early enteral nutrition on intestinal permeability, intestinal protein loss, and outcome in dogs with severe parvoviral enteritis. J Vet Intern Med 2003;17(6):791-798.

17. The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342(18):1301-1308.


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