Few definitive options exist to manage acute respiratory disease - DVM
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Few definitive options exist to manage acute respiratory disease


DVM360 MAGAZINE


The typical clue to the presence of pneumonia is a moist, productive cough, which can often be elicited on tracheal palpation. Mucous membranes vary in color from normal pink and moist to cyanotic, depending on the degree of compromise of gas exchange. In the hyper-dynamic stage of sepsis, the mucosal membranes might be hyperemic. Rectal temperature may be elevated or low, but in many cases, it is normal. On auscultation, rales or crackles might be detectable, especially in the cranioventral lung fields, although lung sounds might appear deceptively normal, especially in large recumbent dogs. If coughing is present in a susceptible dog, then thoracic radio-graphs can rule out the presence of pneumonia even if auscultation is normal. On radiographs, bacterial pneumonia usually manifests as an alveolar pattern, which can be variable in location and severity. The type of pneumonia often can be inferred by the distribution of alveolar disease on the radiograph — aspiration pneumonia is usually cranioventral whereas septic emboli can appear to be nodular.

Cytologic exam key The definitive diagnosis of bacterial pneumonia resides with cytologic examination and microbiologic culture of samples obtained by transtracheal wash or bronchoalveolar lavage. Cytology of these aspirates often reveals an acute to chronic suppurative process with excessive mucus and proteinaceous material, many neutrophils and some alveolar macrophages. Intracellular bacteria might be evident but are not always seen. Cultures commonly demonstrate gram-negative organisms, but gram-positive and anaerobic bacteria or Mycoplasma also can act as respiratory pathogens.

Therapy for bacterial infection includes antibiotics, which should be given parenterally rather than orally in the critically ill dog, particularly those that are vomiting or regurgitating. Drugs with high activity against gram-negative and gram-positive organisms and are well distributed to the pulmonary parenchyma should be considered. Good choices for intravenous administration in critically ill dogs with pneumonia include fluoroquinolones or ampicillin/aminoglycoside combinations. In severely compromised dogs with hypoxia, oxygen supplementation also is required.

In addition, measures that maximize the host immune response are just as important for elimination of the organism by allowing the animal to clear mucus and secretions from the airway more efficiently. Maximum clearance of secretions from the airway can be achieved when the secretions are maintained in a moist state, rather than allowing them to become thick and viscid. Close attention should be paid to the hydration status of the dog, and provide intravenous fluids if necessary.

Nebulization can help Coughing is one of the most important airway clearance mechanisms and is to be encouraged. Nebulization with an ultrasonic nebulizer also can make a big difference to the dog's ability to clear secretions. The tiny water droplets produced by the nebulizer are inhaled into the lungs, where they shower-out moistening and loosening secretions. If saline nebulization is combined with thoracic wall coupage, bouts of productive coughing can be initiated, which can significantly improve the rate of recovery. Nebulization and coupage for 10 minutes to 15 minutes several times daily are warranted. Similarly, any physical activity, by allowing the mobilization of secretions and by promoting an increased tidal volume per breath, will help the dog to clear the pneumonia. Dogs that are recumbent or have weak cough reflexes are among the most difficult to treat.

Pulmonary thromboembolism The incidence of diagnosed pulmonary thromboembolism has increased dramatically in the last few years. Thrombi can develop as a result of a combination of hypercoagulability, vascular endothelial damage and abnormal blood flow patterns or blood stasis. In sepsis, disseminated intravascular coagulation and other disease states, the dog's coagulation system can become excessively active or the action of the fibrinolytic system can become depressed and result in hypercoagulability. Hyper-coagulability also occurs in animals that have been exposed to high levels of endogenous or exogenous steroids. Some disorders, such as protein-losing nephropathy, can result in low blood levels of antithrombin III, a serine protease that modulates the coagulation system.

Diffuse vascular damage occurs frequently as a consequence of a variety of inflammatory disorders, such as sepsis, pancreatitis or immune-mediated diseases, including immune-mediated hemolytic anemia. In each of these situations, various inflammatory mediators are activated, and all of these mediators can contribute to endothelial damage. Once endothelial damage has occurred, activation of the coagulation cascade follows and contributes to the development of thrombi. Stasis of blood is a feature of many critical illnesses. Any condition that leads to poor perfusion or shock may predispose to pooling of blood in the periphery or in the splanchnic vasculature. Other disorders that can be accompanied by blood stasis include vascular obstructive diseases and heart failure.


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Source: DVM360 MAGAZINE,
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