Page 411 - Small Animal Internal Medicine, 6th Edition

CHAPTER 25 Emergency Management of Respiratory Distress 383

OXYGEN SUPPLEMENTATION AND TABLE 25.3
VENTILATION
VetBooks.ir OXYGEN SUPPLEMENTATION Maximum Achievable Oxygen Concentrations and
Associated Flow Rates for Various Methods of
Oxygen supplementation is generally indicated to maintain
arterial blood oxygen pressures (PaO 2 ) at greater than 60 mm Supplementation
Hg. Oxygen supplementation is indicated in every dog or MAXIMUM
cat with signs of respiratory distress or labored breathing. OXYGEN
Cyanosis is another clear indication. Whenever possible, METHOD OF CONCENTRATION FLOW RATE
ADMINISTRATION
(%)
the cause of hypoxemia should be identified and specific
treatment initiated as well. Assisted ventilation is indicated Mask 50-60 8-12 L/min
for animals with an inadequate arterial oxygen concentra- Nasal catheter 50 6-8 L/min or
tion despite supplementation, and for animals with arte- 50-150 mL/
rial carbon dioxide pressures exceeding 60 mm Hg (see kg/min
Chapter 20). Transtracheal 30-40 1-2 L/min
The inhaled concentration of oxygen can be supple- catheter
mented by the administration of 100% oxygen by mask,
hood, nasal catheter, transtracheal catheter, endotracheal Endotracheal tube 100 0.2 L/kg/min
tube, tracheal tube, or oxygen cage. Administration of oxygen Tracheal tube 100 0.2 L/kg/min
by nasal catheter is very well suited to most practices. Oxygen cage 60 2-3*
When administering 100% oxygen to an animal, the clini-
cian must consider the anhydrous nature of pure oxygen and *After cage is filled, flow is adjusted on the basis of oxygen
the toxic effects of oxygen in a high concentration. Because concentration as measured by oxygen sensor.
From Court MH et al.: Inhalation therapy: oxygen administration,
oxygen from tanks contains no water, drying of the airways humidification, and aerosol therapy, Vet Clin North Am Small Anim
can occur quickly, particularly if the nasal cavity has been Pract 15:1041, 1985.
completely bypassed by catheters or tubes. All animals with
respiratory tract diseases should be systemically hydrated.
Moisture must be added to the airways of animals who Oxygen Hoods
have been receiving oxygen by catheter or tube for longer Oxygen hoods that can be placed over the animal’s head are
than a few hours. Ventilators designed for long-term use available. With some, the animals must be laterally recum-
have a heated humidifier incorporated into their design. bent and still, limiting the use of hoods to animals recovering
Humidity exchange filters, which can also be attached to from anesthesia, those that are severely depressed, and those
tracheal and endotracheal tubes, function by retaining mois- that are heavily sedated (Fig. 25.2). Others are designed to
ture from exhaled air and adding it to inhaled air. These completely surround the animal’s head and are attached
filters can support bacterial growth and must be replaced around the neck. One design is an adaptation of an Elizabe-
daily. Nebulization can also be used to add moisture to than collar (OxyHood, JorVet). In some situations, oxygen
the airways. Less effective methods of hydration, such as hoods may be better tolerated than oxygen masks, and it may
instillation of sterile 0.9% sodium chloride solution directly take less manpower to care for an animal for which one is
into tubes or catheters, can be used if other options are being used than an animal with an oxygen mask. A means
not available. Some water vapor can also be added to the for escape of exhaled air must always be provided to prevent
oxygen by incorporating pass-over or bubble humidifiers in the buildup of CO 2 within the hood.
the system.
Inhalation of air with greater than 50% oxygen is toxic to Nasal Catheters
the pulmonary epithelium. Pulmonary function deterio- Nasal catheters can be used for long-term oxygen supple-
rates, and death can result. Air with greater than 50% oxygen mentation (Fig. 25.3). The animal is relatively free to move
is therefore not provided for longer than 12 hours. If higher and is accessible for evaluation and treatment. Most animals
concentrations are necessary to maintain adequate arterial tolerate the catheter well. Catheters can become obstructed
oxygen concentrations, ventilatory support is initiated. with nasal secretions, however. Soft red rubber or infant
feeding tubes or polyurethane catheters can be used. Tube
Oxygen Masks size is based on patient size. In general, a 3.5 to 5F tube is
Oxygen masks are useful for short-term supplementation. used for cats, and a 5 to 8F tube is used for dogs.
The animal experiences minimal stress, and manipulations Sedation is rarely necessary for catheter placement. First,
such as venous catheter placement and thoracocentesis can the length of tubing to be inserted into the nasal cavity is
be performed. A snug fit is desirable to decrease the volume measured against the head of the animal. The tubing should
of dead space, and a relatively high flow rate is necessary reach the level of the carnassial tooth. A water-soluble lubri-
(Table 25.3). Sterile eye ointment is applied to prevent desic- cant or 0.2% lidocaine jelly is applied to the length of the
cation of the corneas. catheter that will be within the nasal cavity. Next, 0.2%