Respiratory Therapeutics

The goal of physical therapy is to facilitate the mobilization and removal of secretions from the respiratory tract and to improve ventilation and oxygenating efficiency of the lungs. Premature and term foals dramatically improve the efficiency of their respiratory function by merely moving from lateral recumbency to sternal or standing position. Blood oxygen levels may increase by as much as 40 mmHg with this body position change.

I. Postural Drainage

1. The foals should be positioned so that secretions may gravitate from the involved peripheral airways to the larger central airways where they can be coughed or aspirated out of the respiratory tract. The foal's position should be alternated frequently (at least every 2 hours) to facilitate drainage.
2. Recumbent patients without lung disease should be kept sternal. If in lateral position rotate the foal every 1-2 hours to minimize secretion accumulation and small airway and alveolar collapse in dependent regions of the lung. Every attempt should be made to keep the foal in sternal position.

II. Deep Breathing and Early Ambulation

1. Deep breathing maximizes alveolar inflation and minimizes small airway and alveolar collapse.
2. Encourage early ambulation which may improve deep breathing and postural drainage.
3. Deep breathing may be inhibited by narcotic drugs and heavy sedation, restrictive thoracic or abdominal bandages, pleural or peritoneal space-occupying lesions, or neuromuscular weakness.

III. Chest Percussion and Vibration (Coupage)

1. Percussion and vibration are used to mechanically dislodge secretions from the smaller airways.
2. Percussion is a rapid series (200 or more per minute) of sharp thumps to the chest wall made with cupped hands with the fingers closed.

1. Do not slap the skin with the flat of the hand since this maximizes skin trauma and minimizes chest wall and lung vibration.
2. The air compression between the cupped hand and the chest wall generates the desirable vibrational energy which is transmitted to the underlying lung parenchyma.

IV. Systemic Hydration

1. A well hydrated foal is of paramount importance in the liquefaction of airway secretions. Airway nebulization therapy has minimal beneficial effect in a dehydrated patient.

V. Airway Hydration

1. Mucosal drying predisposes to decreased mucous clearance, tracheal inflammation and infection, and epithelial damage.
2. The airways may be hydrated by either increasing the humidity of the inspired air or by the introduction of particulate water droplets into the inhaled air stream.
3. The water content of air produced by unheated humidifiers is between 10 and 20 mg/L and should be sufficient to prevent mucosal drying in endotracheally intubated patients with a normal respiratory tract.
4. The water content of air produced by direct installation of water into the respiratory tract (5 ml every 1-2 hours) and by unheated nebulizers varies between 15 and 30 mg/L and should be sufficient to prevent mucosal drying in endotracheally intubated foals with normal respiratory tracts or nonexudative diseases.
5. Heated humidifiers and nebulizers generate mist densities of 25-45 and 40-50 mg/L, respectively, and should be very effective in preventing mucosal drying in endotracheally intubated or tracheotomized foals and in providing some liquefaction of airway exudates.
6. If exudate liquefaction is the primary goal of the nebulization therapy, the very high mist densities associated with ultrasonic nebulizers should be used.
7. Large bore tubing with few angled joints should conduct air from the nebulizer to the foal to minimize impaction of water droplets on the walls of the conducting tubing.
8. When heated humidifiers and nebulizers are used, excess water will condense on the walls of the conducting tubing as the air cools on the way to the foal. Water which has accumulated in the conducting tubing may occlude airflow if not periodically drained.
9. Distilled water should be used if the primary objective is the prevention of surface drying. Saline should be used if liquefaction of thick airway secretions and the stimulation of coughing is the primary objective.
10. The heavier the mist density and the smaller the particulate size, the further into the respiratory tract the aerosol will be deposited.
11. Humidification therapy, when utilized, should be applied continuously. Nebulization therapy, particularly those forms associated with higher mist and water densities, should be administered at intervals throughout the day, but not continuously in order to avoid the deleterious effects of excess airway water; 10 to 30 minutes every 2 to 4 hours.
12. Water reservoirs and nebulization equipment support growth of microorganisms and aerosolized water droplets are capable of carrying these microorganisms into the depth of the lung.

1. Nebulization equipment and delivery systems should be sterilized prior to each use and should be completely changed every 24-48 hours.
2. Only sterile solutions should be used in the nebulization reservoirs.
3. Water accumulating in the conducting tubing should not be drained back into the reservoir in case it has become contaminated.
4. Prophylactic antibiotics in the nebulizer reservoir are not indicated.

VI. Nebulized Medicants

1. The most useful nebulized medicant is water. It prevents surface drying, soothes inflamed tissue, and liquifies thickened secretions. Few medicants liquify respiratory secretions more effectively than saline alone.
2. N-acetylcysteine (Mucomyst®, Mead Johnson) is effective in liquefying thickened mucus and also has some effect on purulent exudates.

1. The agent has an unpleasant sulfur odor, is a local tissue irritant, especially in high concentrations, and has been associated with stomatitis, nausea, and bronchospasm in humans.
2. It inactivates penicillin-type antibiotics.
3. Acetylcysteine is not deleteriously affected by nebulization, with either plastic or glass jet, or ultrasonic nebulizers, but should not be placed in heated nebulizers, or in contact with iron, copper, or rubber.
4. Nebulize 3-10 ml of a 10% solution 3-4 times daily; or instill 0.25-2.0 ml directly into the airway as often as hourly.

3. Aerosolized proteolytic enzymes (Varidase®, Lederle; Varizyme®, Cyanamid; Elase®, Parke-Davis) (combinations of streptokinase, streptodornase and fibrinolysin) may be beneficial in the treatment of viscous infectious exudates which contain large amounts of DNA, protein, and calcium.

1. Deoxyribonuclease depolymerizes DNA protein present in degenerating leukocytes and tissue cells.
2. Streptokinase activates intrinsic plasminogen within fibrin deposits.
3. Proteolytic enzymes are associated with a high incidence of pyrogenic and hypersensitivity reactions in humans and are irritating to normal tissues.
4. Their usefulness is limited to less than one week due to the development of inhibiting antibodies.
5. For persistent thick exudates, for which saline alone has been ineffective, nebulize 50,000–100,000 units of deoxyribonuclease in 2.5 ml of water 1-4 times daily.

4. Mucus is less viscous in an alkaline medium and a 1-2% solution of sodium bicarbonate in combination with another carrier may have some beneficial effects.
5. A 25-50% solution of ethyl alcohol decreases the surface tension of airway froth and may have some usefulness in frothy pulmonary edema.
6. Oral potassium iodide (Fleming®; Eli Lilly) 4-10 mg/kg 3-4 times daily) and some volatile oils (camphor, anise, lemon, and nutmeg) may increase bronchial gland secretory activity and decrease secretion viscosity.
7. Beta2 receptor stimulating sympathomimetics cause bronchial and arterial relaxation.

1. Traditional sympathomimetics are often associated with the development of tolerance to the bronchodilating activity (epinephrine, isoproterenol, phenylephrine, ephedrine); an occasionally severe bronchoconstrictive rebound (epinephrine, isoproterenol, phenylephrine); exhibit a short duration of action and are ineffective by the oral route (epinephrine, isoproterenol); and may cause hypoxemia due to increased pulmonary ventilation/perfusion and maldistribution (isoproterenol), and tachycardia.
2. There is little reason to use the more generally acting sympathomimetics now that more selective beta2 receptor stimulants have been developed.
3. The beta2 receptor stimulants (terbutaline, isoetharine, albuterol, metaproterenol) are very potent bronchodilators when administered orally, subcutaneously, intravenously, or by aerosol. Minimal tolerance develops to the bronchodilating activity but good tolerance develops to the induced skeletal muscle tremors.

1. Compared to the traditional sympathomimetics, these agents are longer lasting, are not usually associated with palpitations, marked tachycardia or hypertension.
2. Suggested nebulization doses of bronchodilator drugs:
   Albuterol                0.001-0.01 mg/kg q 6-8 hrs
   Terbutaline            0.001-0.007 mg/kg q 4-6 hrs
   Metaproterenol     0.10-0.30 mg/kg q 3-4 hrs

8. Inhalational glucocorticoids
9. Diuretics
10. Antibiotics