Page 413 - Small Animal Internal Medicine, 6th Edition

CHAPTER 25 Emergency Management of Respiratory Distress 385

use in animals with an upper airway obstruction once the Most of these complications were clinically insignificant
obstruction has been bypassed. (e.g., pneumomediastinum, subcutaneous emphysema) or
VetBooks.ir the tracheal lumen and a length of 5 to 10 rings. It is neces- correctable. The most common complications were tube
The tube itself should have a diameter nearly as wide as
obstruction (26%), dislodgment (21%), aspiration pneumo-
sary to use high-volume, low-pressure cuffs to prevent tra-
(81%) had a successfully managed temporary tracheostomy
cheal damage and subsequent stricture. Double-lumen tubes nia (21%), and stoma swelling (21%). Overall, 34 of the dogs
are ideal for this method. The inner tube can be removed for tube.
cleaning and can be replaced easily. Single-lumen tubes also
work and may be necessary in small animals. Oxygen Cages
Tracheal tubes are usually placed with the animal anes- Oxygen cages provide an oxygen-enriched environment
thetized with a short-acting agent. The trachea is exposed with minimal stress to animals. However, the animal is
through a ventral midline incision made just beneath the isolated from direct contact, which can be a disadvantage.
larynx. The trachea is entered through an incision made a Other environmental factors, such as humidity, tempera-
few rings below the cricoid cartilage, parallel to the trachea ture, and carbon dioxide concentration, must be moni-
and perpendicular to the rings, and through just enough tored and controlled, or extreme stress and even death
rings to allow passage of the tube. Either end of the incision can occur. The animal is totally dependent on proper cage
can be widened with a small transverse incision. Stay sutures function. The ability of the cage to maintain the correct
are placed on each side of the incision to facilitate initial environment varies with the specific cage as well as with
placement of the tube as well as later replacement if the tube each animal. Commercial cages are available for veterinary
is accidentally or intentionally removed. The tube is then use. Incubators from human hospitals can be modified for
inserted into the opening. With minimal pressure on the small animals.
airway, it is tied with gauze around the neck of the animal.
Few or no sutures are used to close the incision to prevent VENTILATORY SUPPORT
the collection of air subcutaneously. A gauze sponge with a The purposes of ventilatory support are to decrease the
slit cut in it and coated with antiseptic ointment can be retention of carbon dioxide and to improve oxygenation.
placed over the incision and around the tube. Ventilatory support is labor intensive and associated with
The tube must be monitored for obstruction and complications. It is used when other means of respiratory
cleaned. The inner tube of double-lumen tubes can be easily support are not adequate.
removed for this purpose. The tube is cleaned every 30 to Retention of carbon dioxide, or hypercapnia, occurs in
60 minutes initially, with the interval increased as fewer animals unable to ventilate adequately. Spontaneous ventila-
secretions accumulate. Sterile technique is used when the tion can be impaired by neurologic dysfunction, such as that
tubes are handled, and they must be replaced if they become which occurs with severe head trauma, polyneuropathies,
contaminated. and some toxicities. Ventilatory support is recommended in
Single-lumen tubes are difficult to remove and replace such animals if the PaCO 2 level increases to greater than
safely for the first few days unless stay sutures are left in 60 mm Hg. Hypoventilation caused by a pleural effusion or
place. Periodic cleaning can be performed with the tube pneumothorax is treated by removing the fluid or air, not by
in place. Sterile saline solution is instilled into the tube positive-pressure ventilation. Hypoventilation caused by an
for this purpose. To perform suctioning, a sterile urinary upper airway obstruction is treated by establishing a patent
catheter with several openings at the end is attached to airway.
a suction unit and passed through the tube. The trachea Animals with severe lung disease may be unable to main-
and tracheal tube are then suctioned to remove secre- tain adequate oxygenation without ventilatory support.
tions. Suctioning is performed for short intervals to allow Positive-pressure ventilation is routinely necessary for the
the lungs to reinflate. Cleaning is performed every few management of patients with ARDS (see Pulmonary Edema,
hours initially, then less frequently if secretions are not Chapter 22). As previously noted, long-term administration
accumulating. of air with an oxygen concentration greater than 50% results
A smaller tube can be used once the animal is able to oxy- in serious lung damage. If the PaO 2 cannot be maintained at
genate adequately with room air. The tube can be removed greater than 60 mm Hg without excessive oxygen supple-
when the animal can oxygenate by breathing around a small mentation, ventilatory support is indicated.
tube with the lumen obstructed. The incision is allowed to The delivery of air by positive pressure is different from
heal without suturing. The tip of the tube is cultured for normal inhalation of air by negative pressure. With positive
bacteria. pressure, the distribution of ventilation within the lungs is
Antibiotics are not administered prophylactically. Any altered. The intrathoracic pressure increases each time the
existing infection or infections that occur during therapy are lungs are filled with air, which results in decreased venous
treated on the basis of culture and sensitivity information. return to the heart. Along with other effects, systemic hypo-
Complications of tracheal tubes are common. In a report tension results and can be severe enough to cause acute renal
of temporary tracheostomy tubes by Nicholson and Baines failure. Compliance of the lungs also decreases over time in
(2012), complications occurred in 36 of 42 (86%) patients. animals receiving positive-pressure ventilation. As the lungs