Stabilization of respiratory emergencies (Proceedings)
Animals with acute respiratory distress are often some of the most challenging emergency patients seen by veterinarians. The initial approach to these animals is of utmost importance as it can determine whether these critical patients live or die.
Clinical signs of respiratory distress may be obvious or subtle. Obvious signs of "oxygen hunger" include tachypnea, extended head and neck, abducted elbows, flaring of the nares, cyanosis, open-mouth breathing, anxiety, and inability to rest or lie down. Paradoxical movement of the chest and abdomen also occurs with severe respiratory distress. Signs of respiratory distress are more commonly seen in dogs than cats. Cats often mask the severity of their disease, and commonly the only evidences of respiratory dysfunction are tachypnea and prominent respiratory motions while maintaining a posture of sternal recumbency. Even if these patients appear to be relatively stable, they are often very fragile and have the potential to rapidly decompensate if stressed.
The first step in dealing with a respiratory emergency is to ensure a patent airway. If the airway is not patent, it should be cleared of secretions, foreign body, or other obstruction and immediate intubation performed. The animal should then be ventilated with 100% oxygen at a rate of 20-30 breaths per minute. If an upper airway obstruction prevents tracheal intubation, an emergency tracheostomy should be performed.Clinicians often have difficulty making the decision to sedate or anesthetize an animal in respiratory distress. If possible, supplemental oxygen should be provided by face mask or "flow by" while assessing the patency of the airway. If there is no improvement and airway examination and intubation are deemed necessary, rapid induction with minimal cardiopulmonary depression can be achieved with Ketamine (5 mg/kg) and Midazolam (0.25 mg/kg) IV or etomadate (0.5 - 2.0 mg/kg IV). Propofol (3-8 mg/kg IV) or thiopental (5-10 mg/kg IV) could also be used but are associated with more severe cardiopulmonary depression in critical patients. Sedation with immediate intubation allows the clinician to take control of the airway and hopefully avoid the prospect of intubating the animal following cardiopulmonary arrest.
There are several methods of supplying oxygen to critical patients, and each has advantages and disadvantages.
"Flow-by" oxygen is convenient, inexpensive, and easily administered to critical patients during the initial examination. Oxygen can also be delivered by face mask, but some animals fight against the mask and become even more stressed. High flow rates of 3-15 L/min are used.
An oxygen cage is useful for cats or dogs in such severe respiratory distress that they may decompensate with even minimal handling. The oxygen cage provides an oxygen rich environment where the patient can "chill out" while the clinician observes the breathing pattern. The disadvantage of oxygen cages is that they are expensive and require large volumes of oxygen to fill the cage. Whenever the cage door is opened, the oxygen level drops substantially, thereby hindering the clinician from making frequent patient evaluations. In addition, animals can easily become overheated in a sealed oxygen cage. Cages that provide temperature and humidity control are safer but are very expensive. If these features are not provided, an oxygen cage should only be used for short term management of dyspneic patients. A bowl of melting ice placed in the cage with the animal may help provide some humidification and temperature control.
Nasal oxygen is an inexpensive and effective alternative to providing oxygen supplementation to animals with respiratory distress. The major advantage is that it allows for continuous delivery of oxygen to the patient while physical examination, radiographs, ultrasound, etc. are performed. This is the preferred method of oxygen support in our hospital for animals that need ongoing support. At flow rates of 50-100 ml/kg (1 liter per 20 lbs), the inspired oxygen concentration is approximately 40%. If the patient remains dyspneic, a second nasal line may increase the inspired oxygen concentration to 60%.