Three horses with severe respiratory distress like Adult Respiratory Distress Syndrome

The Adult Respiratory Distress Syndrome (ARDS) is a rare fatal disease in humans with a sudden interruption of the respiratory function characterized by non-cardiogenic pulmonary edema, alveolar epithelial injury, decreased surfactant, atelectasis and fibrosis. The objective of this study was to clarify the clinical and clinicopathologic findings of horses with severe respiratory distress such as ARDS, and to find out the optimal therapeutic approaches. In 2002 three horses with signs of acute respiratory failure, similar to those seen in ARDS, were examined at the Department of Large Animal Medicine. The typical clinical findings such as an acute onset of severe dyspnea and tachypnea (50-64 breaths/minute), therapy-resistant hypoxemia (arterial pO(2) 4.6-7.2 kPa) and an oxygen saturation of 53.9-87.9% were the basis for the diagnosis. Based on the definition of the American-European Consensus Conference in 1994 human patients with ARDS require the presence of hypoxemia as manifested by a ratio of the partial arterial pressure of oxygen and the fraction of inspired oxygen (PaO2/FIO2) < 200 mm Hg. In two cases the PaO2/FIO2 ratio was < 200 mm Hg and in one case 200.4 mm Hg. Depending on the severity of the disease, also serum lactate and lactate dehydrogenase (LDH) were increased. Thoracic radiographs of one horse revealed the characteristic interstitial and alveolar infiltrates and pulmonary opacity with a normal cardiac silhouette. Only in one case an allergic small airway inflammation similar to those seen in acute onsets of recurrent airway obstruction could be determined as the basic cause of the disease. The cornerstone of therapy of ARDS in these horses was the continuous supplementation of oxygen. The application of the bronchodilator clenbuterol hydrochloride in a dosage of 2.4 mu g/kg BW IV twice daily was found to be very effective in facilitating respiration in one horse. The administration of corficosteroids (0.1 mg dexamethasone/kg BM IV) deteriorated the dyspnea in two horses. These horses died 26 respectively 72 hours after admission. In conclusion human criteria for identification of ARDS may be helpful in diagnosis of ARDS in horses. Serum lactate and LDH could be of prognostic importance. The oxygen supply is the basis of treatment. Highly dosed bronchodilators appear to have a positive effect on the respiratory effort. The application of corticosteroids in the early stage of ARDS seems to worsen the dyspnea of horses.