Procedures in respiratory medicine (Proceedings)
Treating animals with respiratory distress may be very challenging. It is essential for the practitioner to have a strong knowledge base of available therapeutic and diagnostic techniques. It is also prudent to be prepared for any potential complications that may develop during diagnostic or therapeutic interventions. Respiratory distress may be divided into canine or feline, and upper or lower airway disorders. It is often practical as well to consider distinguishing animals with known causes for distress (eg. Trauma) from those that present with acute difficulties of unknown origin.
Supplemental oxygen is beneficial in all types of respiratory distress. Oxygen may be administered via a face mask, oxygen cage, via a nasal catheter or hood, or with an endotracheal tube and intermittent positive pressure ventilation. Flow-by or face mask oxygen requires and external source of oxygen and connecting tubing. Additionally, unless the pet is very obtunded, a person is required to help hold the oxygen source near the animal. Some animals do not tolerate this very well and may actually increase their work of breathing by struggling to avoid oxygen. Nasal oxygen is well-tolerated in larger non-brachycephalic dogs. Nasal oxygen placement requires a local anesthetic, soft red rubber catheter (5- 8 Fr), suture and an oxygen source (ideally humidified). For placement, the local anesthetic is infused into the selected nostril and permitted time for efficacy. The catheter is inserted to the level of the medial canthus of the ipsilateral eye and sutured in place. Oxygen flow rates of 100 ml/kg/min are recommended. The actual inspired concentration of oxygen will reflect the dog's breathing strategy as panting will result in a lower inspired oxygen concentration than quiet nasal breathing. If the potential need for supplemental oxygen can be predicted for a patient undergoing anesthesia, it is often much easier to place nasal oxygen while the pet is recovering from anesthesia. Some animals require placement of an Elizabethan collar to prevent premature dislodgement of the catheter. An oxygen hood can be easily constructed with an E-collar and cellophane wrap to cover the front. The oxygen can flow in from tubing attached at the collar. A small area can be left open to allow for venting. Dogs that pant excessively may overheat with an oxygen hood, but in the majority of cases it is a well-tolerated and useful technique. In animals with severe respiratory distress or marked upper airway obstruction, the best option may be to anesthetize the animal and provide positive pressure ventilation or perform a tracheostomy. This may be performed short-term to permit adequate time for diagnostic and stabilization such as for a dog with a large volume pleural effusion or may be required for a longer time as part of a therapeutic intervention. It is important to realize that animals with severe respiratory distress are typically not going to rapidly improve without an intervention AND that respiratory distress is very frightening to all animals.
Laryngeal and complete upper airway examination should be a part of the diagnostic evaluation for any dog or cat that presents with signs compatible with upper airway obstruction. Due to the routine nature of endotracheal intubation or the delegation of such a task to support staff, the normal anatomy and function of the upper airway may be underappreciated by some practitioners. Additionally, when given in standard dose to permit endotracheal intubation, laryngeal function is often substantially depressed.Difficult endotracheal intubation should be anticipated in dogs and cats with brachycephalic airway configuration, masses, bleeding (either oral or airway) or anything else that may distort the anatomy. Additionally, in neonates, the size of the tongue may be a particular impediment to intubation due to difficulties in visualization. In preparation for elective intubation, it is prudent to have a variety of sizes of endotracheal tubes and a good light source. Additionally, other equipment may be modified to help provide an airway. An 8 – 14 Fr red rubber catheter may be used to provide supplemental oxygen, although the resistance of the tube is typically too great to permit adequate ventilation. In some dogs with large airway masses, digital intubation is much easier that trying to visualize the larynx. Clearly, general anesthesia is required to prevent either being bitten or triggering a strong gag reflex. It is a good idea to practice digital intubation in a normal dog so the anatomy is easily recognized. If a small bronchoscope is available, an endotracheal tube may be threaded over the scope, and then the scope advanced into the airway and then the tube fed over the scope.
In some cases, an animal with a temporary tracheostomy has a disease process that requires a permanent tracheostomy. (eg. Laryngeal tumor). Surgically, it is much easier to create a permanent tracheostomy with an endotracheal tube already in place. In these cases, after induction of anesthesia, a small endotracheal tube may be advanced through the tracheostomy site into the mouth, then another larger tube passed over the guide tube and directed into the desired location.