Chapter 17 Endotracheal Intubation
Endotracheal intubation describes the procedure of inserting a tube into the trachea. The three main indications for tracheal intubation are: (1) provision of a patent airway in a patient with upper airway obstruction, (2) protection against aspiration in a patient without normal airway protection reflexes, and (3) administration of oxygen, gaseous anesthetics, or positive-pressure ventilation.1-3 Intubation is a frequently performed and often lifesaving procedure in critically ill patients. Recognizing the need to intubate and understanding procedures to aid difficult intubation are essential skills for the critical care veterinarian.
Airway assessment is the first priority in the evaluation of a critically ill or emergency patient. Both airway patency and protection must be ascertained. When upper airway disease is severe, rapid induction of anesthesia and tracheal intubation is indicated. If orotracheal intubation is unsuccessful, a temporary tracheostomy is required (see Chapter 18, Tracheostomy).
Any patient lacking an adequate gag reflex, as may occur with neurologic disease, sedative or anesthetic drug administration, or cardiopulmonary arrest, requires immediate intubation for airway protection, oxygen therapy, and positive-pressure ventilation as needed. The gag or swallow reflex can be assessed by inserting a tongue depressor into the pharynx.
Intubation of animals with normal upper airway anatomy is commonly performed using laryngeal visualization and insertion of an appropriate sized, cuffed endotracheal tube. An adequate level of anesthesia is required. After correct placement is confirmed, the tube is secured by tying it around the maxilla or mandible, being sure that the tie lies caudal to both canine teeth. Alternatively, a tube can be tied around the back of the head. The tube usually is connected to an oxygen source such as a Bain circuit or an anesthetic machine circuit. Finally, the cuff is inflated until it gently occludes the airway exterior to the tube. To determine how much cuff inflation is required, a manual breath is delivered while simultaneously inflating the cuff and listening for resolution of the air leak around the endotracheal tube.3
For routine intubation of the dog, a laryngoscope with a blade long enough to allow adequate visualization of the larynx is required. Intubation commonly is performed with the dog in sternal recumbency. An assistant holds the animal’s upper jaw by grasping either side of the maxilla with one hand, keeping the head raised and extended. Either the assistant or the operator opens the mouth by pulling the tongue out and down, and the endotracheal tube is passed between the arytenoids.3 Alternatively, many dogs can be intubated in lateral or dorsal recumbency without the aid of an assistant.
Routine intubation of cats is performed in a manner similar to that used for dogs, except application of lidocaine to the larynx is recommended before attempting intubation in an effort to prevent laryngospasm. Some operators favor the use of a stylet to stiffen the endotracheal tube for feline intubation.3
The possibility of a difficult intubation should be considered in animals with evidence of upper airway obstruction, trauma, or abnormal anatomy (e.g., brachycephalic breeds). Preplanning for intubation of cases such as these is essential to maximize the likelihood of success.
Any delay in intubation of a patient places the animal at risk of hypoxemia. When breathing room air, complete upper airway obstruction or apnea will lead to hypoxemia within approximately 3 minutes. Preoxygenation of a patient with 100% oxygen via a tight-fitting face mask can prevent hypoxemia for up to 10 minutes of airway obstruction or apnea. Although a study in human patients found preoxygenation not as effective as previously thought, it still is recommended before attempting intubation of any critically ill patient or any patient at risk of a difficult intubation or apnea.4
If a difficult intubation is anticipated, all equipment that may be required should be set up before the procedure. Endotracheal tubes of the size appropriate for the patient, in addition to several smaller sizes, should be selected. Stylets or a guide tube, such as a polyethylene urinary catheter, should also be available. Large-bore catheters for transtracheal gas insufflation and a surgical kit for an emergency tracheotomy in case intubation is unsuccessful should also be on hand.