Hyperbaric Oxygen Therapy in Pets: A Life-Saving Treatment
Oxygen therapy is the act of supplementing the air the dog breathes with extra oxygen. This is needed in many situations when the dog has breathing difficulties and struggles to absorb oxygen or transporting that oxygen around the body. Increasing the amount of oxygen the dog breathes in helps counteract the decreased availability of oxygen to the body tissue due to sickness or injury.
Oxygen is vital to life and, depending on the severity of oxygen depletion, the patient may suffer cell death, organ failure, or death. Giving a patient struggling for breath an oxygen supplement can make the difference between life and death. In the critically ill, it is a vital life-saving therapy used to stabilize the dog and make them strong enough to undergo diagnostic tests.
Oxygen is one of the most essential and indispensable components for every living entity on earth. It is a necessary element for proper functioning of the body. Oxygen is vital to life and depending on the severity of oxygen depletion, the patient may suffer organ failure, or death (1). Oxygen therapy is the life-saving treatment for patient struggling for breathing and also for cardiopulmonary resuscitation. It is one of the most emergency procedures for various cardiopulmonary disorders like dyspnoea, shock, sepsis, head trauma and toxicity. With the advancement in veterinary medicine, oxygen therapy is becoming easily available for more and more veterinarians to treat patients suffering from respiratory insufficiencies. Oxygen therapy is the act of supplementing the air in the dog’s breathe with extra oxygen. This is needed in many situations when the dog has breathing difficulties and struggles to absorb oxygen or transporting the oxygen around the body (2). The purpose is to increase oxygen saturation in tissues where the saturation levels are too low due to illness or injury. Oxygen supplementation aims to increase the fraction of inspired oxygen (FiO2) and consequently the partial pressure of arterial oxygen (PaO2) and it is a key component in respiratory care. (3). The body constantly takes oxygen and releases carbon dioxide and when this process is inadequate, oxygen levels in the blood falls and the patient may need supplemental oxygen.
Indication of Oxygen Therapy
In the triage setting, several clues may prompt the clinician to provide oxygen, including tachypnea, shortness of breath, abnormal respiratory noises, nasal flaring, pallor of mucus membrane, cyanosis, panting, irregular chest wall movements (3, 4). Hypoxia, hypoxemia, toxicosis, central nervous system weakness, neuromuscular weakness, and diseases of the thorax like pneumothorax / hydrothorax primarily require oxygen therapy (5). Patients without cardiopulmonary disease, that breathe rapidly or with effort, such as animals with large-volume abdominal effusion, pain, or metabolic acidosis or those that have received certain medications (e.g., opioids or corticosteroids) also require supplementation of oxygen at some point of time. Quantification of pulmonary function can provide more objective data to support the decision to supplement oxygen. Potential tools include measurement of pulse oximetry or arterial blood gas analysis. Oxygen saturation below 93 percent and arterial partial pressure of oxygen below 70 mm Hg should prompt oxygen supplementation (6).
Methods of Oxygen Supplementation
Several options exist for providing supplemental oxygen. Whenever possible, the least stressful method should be considered, but this should be balanced with the ability to provide as much oxygen as needed with each method. For short-term oxygen supplementation, it is generally unnecessary to humidify the oxygen; however, long-term exposure of the respiratory epithelium to dry air may promote the development of respiratory infections. Humidification can be easily achieved by bubbling oxygen through sterile saline or water. The technique by which oxygen therapy is instituted to the patient may be invasive or non-invasive.
Oxygen Therapy Procedure in Dogs
Although there are several different ways of providing oxygen therapy, they all have one thing in common, which is that it’s crucial not to stress the patient. A dog that is fighting for breath could be pushed into a crisis if he struggles during administration of oxygen. With this in mind, the clinician may choose one delivery form over another in order to minimize stress. At all times, the aim is to use the least level of restraint possible.
Options for delivery include:
- Flow by oxygen: This is simply allowing oxygen to flow from the delivery pipe into the airspace close to the dog’s nose. This may be all that’s possible in an extremely stressed patient.
- Nasal catheter: A fine tube is passed into the dog’s nose and oxygen delivered directly into the respiratory system
- Oxygen mask: This means holding a close fitting mask over the dog’s face or muzzle.
- Oxygen chamber: The clinician may improvise a delivery chamber by fitting the dog with a cone with the wide open diameter sealed over with cling film. A tube feeds into the base of the cone, for higher oxygen concentration within the ‘chamber’.
- Oxygen tent: This is a sealed chamber in which the whole dog rests and breathes in an oxygen-rich atmosphere
Non-invasive
Methods Flow-by Oxygen
It is an easy method to provide supplemental oxygen by holding the oxygen tubing close to an animal face. A flow rate of 2L to 3L/minute is maintained, which provides a FiO2 of 25 to 40 percent (7). This approach is impractical for any protracted period and is best suited before the induction of anesthesia or while procedures are being performed.
Face Mask
It is observed that oxygen supplementation delivered using a face mask is more effective than flow-by oxygen supplementation in raising PaO2 (8). Increased FiO2 and PaO2 are reflection of increase in the amount of oxygen flow delivered to the animal. It is due to an increasing concentration of oxygen in the oropharynx and nasopharynx which act as reservoirs for inspired air (9). During normal breathing, airflow is intermittent, but during oxygen supplementation, the airflow is continuous. During the interval between exhalation and the following inspiration, this anatomical space fills with supplemented oxygen and has a fixed volume, which acts as an oxygen reservoir and hence increases the FiO2.
Oxygen Hood
Another non-invasive method is the use of oxygen hoods, in which the hood is covered in the cellophane wrap and secured in place with tape, with a small portion left open for ventilation. The hurdles with this technique involve excessive humidification and poor ventilation if too small of a gap is left in the cellophane wrap(10).
Invasive Methods
Nasal Prongs and Nasal Lines
For larger dogs, oxygen cages may be too confining to be comfortable. The placement of nasal lines can be convenient in such dogs. Nasal prongs can be used but reasonably are relevant only in non brachycephalic breeds. The FiO2 achieved via nasal prongs is not well established so nasal lines can be placed easily by using 5 to 8 French red rubber catheters. Local analgesia should be instilled in the nose before insertion of catheters. The flow rates of 50ml / kg / minute to 150ml / kg / minute should be maintained to provide a FiO2 of 30 to 70 percent(9).
Transtracheal Oxygenation
This technique is used, in patients, intolerant to nasal oxygen delivery like patients suffering from upper airway obstruction. In these cases, a red rubber catheter can be placed extending from the external nares and directed into the trachea, before removal of their endotracheal tube. The flow rate is 50 ml / kg / minute, which provides 40 to 60 percent FiO2 (11).
Hyperbaric Oxygen Therapy(HBOT) in Veterinary Medicine
Hyperbaric Oxygen Therapy (HBOT) is the noninvasive and advanced therapy that uses 100 percent oxygen under pressure delivered in a specialized chamber built to withstand high internal pressure. HBOT has been tested on animals for many years. The earliest documentation of therapeutic use was in 1998. Since then, sporadic treatment reports have appeared in the veterinary literature(12). Hyperbaric oxygen therapy (HBOT) chambers work on the principle that high oxygen concentration, combined with increased air pressure in the chamber, raises plasma-oxygen concentration, allowing oxygen to diffuse into tissues three to four times further than usual to promote healing(13). At normal atmospheric pressure (measured at sea level as 1 atmosphere absolute or 1 ATA), arterial oxygen tension is 100 mm Hg, and tissue oxygenation is 55 mm Hg. In 100 percent oxygen at 3 times atmospheric pressure (3 ATA) arterial oxygen tension is 2000 mm Hg and tissue oxygenation is 500 mm Hg (14, 15). Oxygen under pressure increases the density of oxygen within the alveoli and increases the amount of dissolved oxygen into all of the body’s fluids including plasma, lymph, cerebral spinal fluid, and bone marrow. This allows almost fifteen times increase in oxygen levels in the body. Total treatment time may vary but a standard time of approximately 1.25 hours (inclusive of a gradual pressurization and depressurization period)(16). It is more efficient than other methods in cases of severe smoke inhalation, stroke, anemia, osteomyelitis acute laminitis (17) and in anaerobic conditions like Clostridial infection, Rhodococcus pneumonia, and Lyme’s disease (18). Many researchers have observed that enteritis, ileus, endotoxemia, compressive cord lesions post-op, cerebral trauma, peripheral neuropathies, and vascular diseases show better recovery when treated by HBOT.
Supplementing oxygen reliably and safely is a vital and potentially life-saving intervention in small animal medicine. The success of oxygen therapy varies from patient to patient and depends mostly on the severity of the disease. High-flow oxygen therapy improves oxygenation in dyspneic dogs and is an effective means to deliver oxygen with comfort and minimal complications. Excessive oxygen therapy over a prolonged period may cause oxygen toxicity. To avoid pulmonary oxygen toxicity, small animals should not receive a FiO2 of more than 60 percent for longer than 24 to 72 hours. Choosing a suitable method along with the flow rate of oxygen and careful observation of the patient is the key to successful oxygen therapy.
COMPILED & SHARED BY-DR UDAY, CANINE SPECIALIST,PATNA
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