Treating canine bacterial pneumonia: Beyond antibiotics (Proceedings)
In most patients with pneumonia, antibiotic therapy should be considered part of an overall management scheme, rather than the only treatment. Since resolution of pneumonia largely depends on clearance of secretions from the airway via the cough reflex and the mucociliary escalator, measures must be taken to ensure that the secretions are liquid and easily expectorated. Additionally, chest physiotherapy can play a vital role in promoting the cough reflex. Supportive care should include oxygen therapy if the patient is hypoxic, and other nursing care including nutritional support and routine monitoring and care of the recumbent patient if appropriate. In some situations, all of this may be virtually ineffective if unaccompanied by other therapy. For example, since many antibiotics cannot penetrate abscesses effectively, and are inactivated by the presence of pus, therapy in patients with lung abscesses or pyothorax must be accompanied by other aggressive forms of treatment, for example lung lobectomy or pleural drainage. Additionally, attempts should be made to resolve the cause of pneumonia, if possible, in order to effect complete resolution of the bacterial infection.
Airway hygiene and clearance of secretions
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 dogs and cats with pneumonia, large amounts of viscous secretions are produced, and 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.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. Orally administered expectorants such as ammonium bicarbonate and potassium iodide act by irritating the mucosa of the gastrointestinal tract, thereby stimulating a vagal gastropulmonary reflex that results in increased secretion by the bronchial glands. Phenolic compounds such as guaiacol, and inhaled volatile oils such as Eucalyptus oil, may directly stimulate production of increased amounts of watery mucus.
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. Droplets greater than 10 microns reach only the upper airway and trachea. In the range of 1-10 microns, the smaller the droplet, the deeper it is able to penetrate into the respiratory tract. Droplets less than 0.5 microns reach the alveoli and are exhaled. Most ultrasonic nebulizers create droplets in the 2-5 micron range.
Once the respiratory tract secretions have been moistened and increased in volume, clearance of the material depends on normal function of the other respiratory defense mechanisms. Atelectasis predisposes to pneumonia because bacteria can be trapped and proliferate in collapsed airspaces and cannot effectively be cleared by the mucociliary escalator. In addition, animals with prolonged or recurrent atelectasis are often recumbent, and because they are weak and sometimes painful they may also have a depressed cough reflex, further impairing their ability to clear organisms and material from their airways. In particular, the cough reflex is a vital part of recovery from serious pneumonia. The simplest method of stimulating coughing is simply to stimulate an increased tidal volume during respiration, usually by mild exercise. Dogs with pneumonia should not be allowed to lie in one place for long periods of time. The amount of exercise needed to increase the tidal volume and respiration rate is variable depending on the severity of disease. In some, simply turning the animal from one side to the other in lateral recumbency is enough. The next step may be to stand the patient for brief periods of time, then to take a few steps, gradually building strength and mobility. Mild to moderate exercise often stimulates productive coughing which should be encouraged by coupage.
Coupage is the action of firmly striking the chest wall of the patient with a cupped hand, which helps to stimulate the cough reflex and to "break up" secretions in the airways. Coupage should be performed several times daily, especially in patients that are unable to stand and move around. It is usually well tolerated, except in patients that have experienced thoracic trauma or thoracic surgery.