Airway management and ventilation (Proceedings)
There are many factors that play a role in airway management and ventilation. One should consider reasons for airway support as well as types of materials that are available. Some patients have a need for ventilation support, therefore it is important to understand the terminology as well as equipment available for the veterinary patient.
Endotracheal Tubes and Intubation
The main reason for intubation is administration for administration of inhalation anesthesia, reduced waste gas pollution and protection of the airway. Intubation reduces the risk of saliva or regurgitated stomach contents being inhaled. An endotracheal tube also allows for the administration of oxygen as well as intermittent positive pressure when required. Many designs of endotracheal tube are available and the choice will depend on your patient. A large diameter tube offers the advantage of reducing airway resistance and will therefore facilitate breathing and ventilation. Pre-measure the length of the tube as a short tube might get dislodge during a procedure, while a long tube might increase dead space as well as creating lung trauma and respiratory complications. To increase airway protection, use as often as possible, cuffed tubes. When inflating the cuff, be sure to check the pressure to insure a good seal so to avoid leak, but also to avoid tracheal damage with too much pressure. Always use clean, dry tubes. There are various materials available to aid intubation such as a laryngoscope, mouth gags, lubricating gel, local anesthetic spray, stylets and endoscopes.Intubation Complications
Some complications associated with intubation are damage to the larynx (more common in small species such as cat, ferret and rabbit). This can come from an over-inflated cuff, an oversized diameter or frequent manipulation of the tube. You may also see hematoma formation, edema, and some species will laryngospasm such as the cat, ferret and rabbit if larynx is stimulated frequently. Use local anesthetics to avoid this. Mucosal sloughing may result due to any airway damage. Endobronchial intubation is another concern if tube was not measured properly. Aspiration can also occur if patient extubates pre-maturely, or if there is a leak in the cuff and or endotracheal tube. This fluid/ reflux can derive from the esophagus or stomach. It may also include fluid from the larynx or oral cavity such as blood or excessive saliva. One must make sure there is little resistance in the tube. The inside of the tube should be clean and free of fluid; avoid kinking the tube at all times. Use elbow adapters if angling is necessary or use a wire-reinforced tube for procedures that involve much head and neck manipulation.
Depression of the respiratory centers in the brain can cause inadequate ventilation. This can be drug-induced. If the inadequacy is due to respiratory depression from anesthetic gas, reduce inhalant and consider ventilatory support. There are metabolic disorders that can affect your patient's ventilation such as an acidosis. A metabolic acidosis can alter the respiratory centers as well. Another cause for altered ventilation would be a physical change in your patient such as thoracic pain. Patients who are unable to expand their lungs or thorax to a normal ability may need ventilation support. To provide this, one must perform intermittent positive pressure ventilation (IPPV).
Intermittent positive pressure ventilation consists in opening the airways of a patient by blowing a flow of gas into the lungs. This will create a positive pressure. Exhalation is usually passive. The magnitude, rate & duration of flow are determined by the operator. The flow can be a pre-set volume & pressure variable or pressure limited & volume variable. IPPV can benefit many patients, especially those with respiratory inadequacy