Managing pneumonia in puppies (Proceedings)
Puppies are predisposed to acute infectious tracheobronchitis, which can progress to pneumonia, because they are often physiologically stressed by changes in ownership and new environments. In addition, poor nutrition, overcrowding, poor hygiene, and concurrent diseases such as parasitism all predispose them to development of contagious respiratory tract infections. A variety of organisms are implicated, including viruses such as parainfluenza, adenovirus and canine distemper virus; and bacteria such as Bordetella, Streptococci, and Mycoplasma sp. Puppies that have infections confined to the upper respiratory tract are usually clinically healthy, eating and afebrile. Most of these puppies will respond favorably to time, good husbandry, and antibiotic therapy. The youngest, most immunosuppressed puppies, or those of breeds such as English bulldogs with congenital abnormalities including brachycephalic airway syndrome or hypoplastic trachea, have a decreased ability to resolve respiratory tract infections. In these patients, pneumonia is a real and life-threatening risk. Puppies with infectious bronchopneumonia can be recognized because they are usually systemically sick, often febrile, and they may have significant respiratory distress.
Representative cultures should be obtained from the respiratory tract prior to initiation of antibiotic therapy. In most puppies, cultures are best obtained by endotracheal lavage. Once samples have been obtained for culture, antibiotic therapy should be instituted immediately. The initial antibiotic should provide broad-spectrum coverage for the most likely organisms, bearing in mind the possibility of polymicrobial infection. Cytologic results may assist in choice of the best antibiotic, by documenting whether the bacterial organisms are gram positive or gram negative, rods or cocci. As a general rule, oral antibiotics can be used if the pneumonia puppy is systemically healthy and is not dyspneic. Antibiotics should be administered by parenteral routes (ideally intravenously) in puppies that are dyspneic, febrile, debilitated, or depressed. Intravenous antibiotics are the best way of ensuring that adequate plasma concentrations are achieved, because there is no guarantee of adequate absorption of drugs from the gut in such sick animals. Our experience suggests that the best initial antibiotic choice in puppies with severe pneumonia is a combination of ampicillin and an aminoglycoside (once dehydration has been corrected). When ampicillin is combined with an aminoglycoside, a synergistic effect provides excellent broad spectrum coverage in serious respiratory infections. Other options such as enrofloxacin or tetracyclines must be avoided because of their respective adverse effects on joints and teeth. Interestingly, the beta lactams such as amoxicillin, ampicillin and ticarcillin do not penetrate well into the mucus lining the bronchi, and therefore are often ineffective in puppies with Bordetella pneumonia. Once culture and sensitivity results are available, a specific and narrow spectrum antibiotic can then be chosen for ongoing care.
Clearance of secretions from the airways occurs via the mucociliary escalator and cough reflex, and is delayed if the secretions are extremely viscous and tenacious. In puppies with pneumonia, large amounts of viscous secretions are produced, and must be moved up through a very narrow airway. Attempts to resolve the infection must include attention to the character of the respiratory secretions. Productive coughing must be actively encouraged, and the secretions must be maintained as liquid as possible. More than 90% of the mucus in the respiratory tract is water, so even a mild degree of dehydration leads to drying of the secretions. The most important means by which this is achieved is by parenteral fluid therapy. Unless extreme respiratory distress is present, these patients should not be allowed to become dehydrated, and diuretic use should be avoided. Nebulization is a technique in which tiny spherical droplets of water are generated and inhaled by the patient. The droplets then "shower out" at various levels of the respiratory tract, depending on their size, due to changes in direction of air flow, brownian motion, and gravity.The tenacity of mucus also depends on the structure of the mucopolysaccharides that it contains. N-acetylcysteine can be administered orally, and acts as a mucolytic by opening disulfide bonds, thereby decreasing the viscosity of the mucus. It can also be administered by nebulization, but it can cause bronchospasm by this route, which is usually manifested by coughing. If coughing or dyspnea occurs, the patient may be pre-treated with bronchodilators prior to nebulization. N-acetylcysteine can also be given intravenously or orally. Drug therapy can also include a bronchodilator such as aminophylline or terbutaline, ideally administered parenterally.