Carla Molina DVM, ECVECC Resident and Luís Bosch LV, MSc, Dipl. ACVECC, Dipl. ECVECC
Oxygen therapy is indicated for any patient with laboured breathing, respiratory fatigue, overt cyanosis, or hypoxemia that is defined as partial pressure of oxygen (PaO2) less than 70 mmHg or oxygen saturation (SaO2) less than 93% on room air.1,2
Techniques and sources
Techniques can be divided into noninvasive, partially invasive, and invasive (table 100.1). The selected technique depends on patient’s tolerance to manipulation, degree of hypoxemia, and FiO2 needed and equipment available (fig. 100.1).1,2,3
Oxygen can be supplied by oxygen concentrators, individual portable oxygen tanks, and a centralized in-house source.3 All methods require some degree of humidification, especially invasive techniques or if long-term oxygen therapy is required.1,2,7,8 Non-humidified oxygen causes airway irritation, impairs mucociliary clearance, and increases the risk of infection.
Non-invasive techniques are a useful method as a first emergency approach for any patient with respiratory distress. Oxygen cages are likely the best technique (figs. 100.2 and 100.3) for severely dyspneic patients since they don’t require manipulation;1 they do limit access to the patient. Flow-by oxygen allows convenient patient manipulation and involves an oxygen source that flows 2 to 4 cm close to the patient’s nose or mouth (figs. 100.4 and 100.5).1,2,3,4 It is less effective than face mask oxygen (fig. 100.6) but may be better tolerated by dyspneic animals. Face mask delivery involves administration of oxygen using a face mask that covers the patient’s muzzle. Loose-fitting face masks or tight-fitting face masks may be used. If a tight fit is achieved, FiO2 can increase up to 60%. It is especially useful as a long-term oxygen administration for patients with suspected increased intraocular or intracranial pressure, for which more invasive techniques are often contraindicated due to potential to induce sneezing.1,2,3 If long-term oxygen administration is required, the oxygen collar technique is a viable option; it does not require specialized equipment and consists of an oxygen tube connected to an oversized Elizabethan collar covered with a piece of clear plastic wrap. A portion must be left open to allow for carbon dioxide and heat to escape.1,4,5
Partially invasive techniques
Pediatric nasal prongs can be placed and secured with mild modifications (fig. 100.7). They are usually well-tolerated by sick patients but can be easily dislodged in awake patients. In that case, nasal catheters (NC) (figs. 100.8 and 100.9) are simple to place and usually well tolerated (video 100.1). Unilateral NC can provide an FiO2 up to 40% and bilateral NC can reach a FiO2 greater than 60%.2,3,6
When conventional oxygen therapy methods do not adequately relieve respiratory distress or hypoxemia or in case of upper airway obstruction, intratracheal oxygen administration can be provided through a transtracheal catheter, as well as via endotracheal intubation or tracheostomy tube.
Transtracheal catheter is a short-term technique indicated in upper airway obstruction. An over-the-needle catheter is percutaneously placed between two tracheal rings caudal to the larynx and attached to an oxygen source. This technique is contraindicated in patients with tracheal collapse or coagulopathies.1,3 Endotracheal intubation (fig. 100.10) is indicated in patients with severe respiratory distress, cyanosis, upper airway obstruction, or in a comatose state. Main advantages include airway control, administration of 100% oxygen, and ability to ventilate. General anesthesia and a high level of care are always required.3,4
Tracheostomy tubes are indicated to bypass upper airway obstructions. The main advantage is to bypass the obstruction and allow the patient to be awake after placement. Disadvantages include a requirement of general anesthesia, high level of care, and multiple potential complications.3,9
A FiO2 greater than 60% administered for a prolonged period can induce pulmonary epithelial damage, absorption atelectasis, suppression of erythropoiesis, pulmonary vasodilation, and systemic arteriolar vasoconstriction.1,2,3 It can also lead to severe hypoventilation, inhibiting the respiratory drive in patients with chronic lung disease.
1. Tseng LW, Drobatz KJ. Oxygen supplementation and humidification. In King LG (editor). Textbook of respiratory disease in dogs and cats, St Louis, 2004, Elsevier, pp 205-213.
2. Mazzaferro E. Oxygen therapy. In Silverstein DC, Hopper K (editors). Small animal critical care medicine, St Louis, 2015, Elsevier, pp 77-80.
3. Boyle J. Oxygen therapy. In Burkitt Creedon JM, Davis H (editors). Advanced monitoring and procedures for small animal emergency and critical care, UK, 2012, Wiley-Blackwell, pp 263-273.
4. Guenther CL. Oxygen therapy. In Drobatz KJ, Hopper K, Rozanski E (editors). Textbook of small animal emergency medicine, Hoboke, 2019, Wiley-Blackwell, pp 1177-1182.
5. Loukopoulos P, Reynolds W. Comparative evaluation of oxygen therapy techniques in anaesthetized dogs: intranasal catheter and Elizabethan collar canopy. Aust Vet Pract 26:199, 1996.
6. Dunphy ED, Mann FA, Dodam JR, et al. Comparison of unilateral versus bilateral nasal catheters for oxygen administration in dogs. J Vet Emerg Crit Care 12:245-251, 2002.
7. Fitzpatrick Robert K, Crowe DT. Nasal oxygen administration in dogs and cats: experimental and clinical investigations. J Am Anim Hosp Assoc 22:293-300, 1986.
8. Camps-Palau MA, Marks SL, Cornick JL. Small animal oxygen therapy. Comp Cont Educ Pract Vet 21:587, 2000.
9. Guenther-Yenke CL, Rozanski EA. Tracheostomy in cats: 23 cases (1998-2006). J Feline Med Surg 9:451-457, 2007.
Video 100.1 Placement of nasal cannula in a cat