Can’t Catch your Breath?
Jeff Dennis, DVM, DACVIM
Some may suggest that the level of pain is the ultimate measure of a patient’s suffering. I disagree. The sensation of dyspnea has to be one of the worst symptoms a patient can experience. It may be my anthropomorphic assessment, but I believe patients with dyspnea look a lot more ‘scared’ then patients with pain. Effective treatments exist to relieve most pain, but relieving dyspnea is much more difficult. The lives of dyspneic patients are at risk. The options available to treat respiratory compromise are more limited than pain relief, yet pretty straightforward. Dyspneic patients need oxygen delivered to their alveoli.
The first purpose of oxygen supplementation is to restore oxygenation in animals with illnesses that increase oxygen demand or decrease oxygen delivery. Without adequate oxygenation of the tissues, energy production pathways in the body change from aerobic to anaerobic resulting in less energy (ATP) production for the cells to utilize and increased acid byproduct (lactic acid) production. Both the lack of ATP and the low pH of the environment cause dysfunction of cellular metabolic pathways leading to cell death. Organ function within the body becomes compromised.
The second purpose of oxygen supplementation is to decrease the ventilator and myocardial work necessary to maintain adequate oxygen delivery to the tissues. The body will recognize when oxygen concentrations needed to maintain cell health are low and trigger the respiratory and cardiac centers in the brain to stimulate deeper and more rapid respirations and cardiac contractions. The additional work induces energy stores to be used up faster, thereby weakening the body further.
What are some indications for oxygen therapy?
- Pulmonary disease (pneumonia, pulmonary contusions, thromboembolism)
- Airway disease (tracheal collapse, laryngeal paralysis, feline asthma)
- Pleural disease (pleural effusion, pneumothorax, diaphragmatic hernia)
- Heart and vascular compromise (congestive heart failure, pulmonary edema, shock)
- Cerebral injury (trauma)
- Hypoventilation (anesthetic recovery, chest wall compromise, neurologic or mental depression)
- Increased oxygen demand by the tissues due to high metabolic demands (hypothermia, hyperthermia, sepsis)
A number of techniques exist for supplementing oxygen in our patients. The most common methods include:
- Blow-by: An oxygen source is held free flowing in front of the patient’s face. This is most useful for immediate administration. It can achieve oxygen concentrations in the immediate region of 35% using 5 L/min flow.
- Elizabethan collar (e-collar) oxygen canopy: An oxygen source is taped to the inside of an e-collar that has been partially covered with cellophane wrap. This technique allows the patient some mobility and you have continued access to the patient for exams and treatments. It can achieve oxygen concentrations of 70% using 5 L/min flow. The upper 25% of the e-collar opening should be left uncovered to allow heat, moisture and CO2 to escape. The e-collar has to be big enough that the wrap does not contact the nose.
- Conventional cage with plastic wrap covering the door: An oxygen source is taped to the inside of the cage. The top of the cage door should be left uncovered to allow heat, moisture and CO2 to escape. The cage allows the patient some mobility; however, access to the patient is limited because the oxygen within the cage dissipates as soon as the door is opened. It can achieve oxygen concentrations of 50% using 5 L/min.
- Manufactured oxygen cage: Many of these cages have the ability to regulate not only the oxygen concentration within the cage but also the temperature and humidity. The cage allows the patient some mobility; however, access to the patient is limited because the oxygen within the cage dissipates as soon as the door is opened. Newer cages can achieve oxygen concentrations of 50% or higher.
- Intranasal oxygen catheters: Catheters are placed into the patient’s nasal openings through which oxygen is delivered. This is the most effective and efficient means of delivering oxygen to the patient. This technique allows the patient some mobility, and you have access to the patient for exams and treatments. You can increase the concentration of oxygen inhaled by the patient by increasing the oxygen flow rate or utilizing two catheters, one for each nasal planum. The oxygen should be humidified.
- Intra- or trans-tracheal catheters: A catheter or tube to deliver oxygen is passed into the trachea. This technique will provide the highest oxygen concentration in the inspired air; however, it can cause irritation and coughing. It is useful in patients with laryngeal dysfunction, and typically requires some degree of sedation. The oxygen should be humidified.
Did you know? Some oxygen facts
- Ambient room air has an oxygen concentration of 20%.
- Oxygen concentrations exceeding 50% for more than 24 hours can damage the lungs.
- Therapeutic oxygen should be humidified when supplementation is required for more than a few hours or if nasal or tracheal catheterization is used.
- Oxygen concentrations delivered by anesthetic machines approach 100%.
- The larger the chamber to be filled with oxygen, the longer it takes to displace the ambient air contained within the chamber with oxygen.
Methods of assessing patient oxygenation
- Clinical signs
- Open mouth breathing
- Extended head and neck
- Restlessness or unwillingness to lie down
- Dark mucus membranes
- Mental dullness
- Rapid and deep respirations
- General weakness
- Pulse oximetry
- Arterial blood gas analysis
How to create an Elizabethan collar oxygen canopy
An e-collar oxygen canopy is a quick, easy, economical, low stress technique for delivering oxygen to a patient. High oxygen concentrations can be achieved within the canopy very quickly. The patient is not ‘trapped within a cage’ providing you easy access to the patient for evaluation and treatment. To create an e-collar canopy:
- Choose an e-collar big enough that the patient’s nose won’t reach the outside edge.
- Cover the front of the e-collar with cellophane wrap leaving 25% open at the top for heated expired air to rise and escape.
- Tape the oxygen tube inside the bottom of the e-collar. The oxygen source should not be humidified.
- Place the e-collar on the patient fixing it so it won’t spin.
How to place intranasal oxygen catheters
Intranasal catheters are easy to place, economical, and they don’t inhibit access to the patient for evaluation and treatment. By delivering oxygen directly to the larynx where it is inhaled, it is one of the best techniques available to oxygenate a patient. You can double the oxygen concentration that is inhaled by doubling the oxygen flow rate or utilizing two nasal catheters at the same time. To place an intranasal catheter:
- Use the largest red rubber catheter that you feel you can comfortably place into the nose. The larger the catheter, the less the resistance to oxygen flow.
- Pre-measure the red rubber catheter from the corner of the eye to the tip of the nose and mark with a pen.
- You can pre-bend the catheter by gently heating it with a match or lighter at the mark which helps to prevent the catheter from backing out. Be careful not to melt the catheter.
- Drip topical anesthetic into the nasal opening.
- Feed the catheter tip through the nares opening and then ventro-medially.
- Advance the catheter to the mark or bend.
- Fix the outside of the catheter in place with a skin staple placed just lateral to the nasal planum. Suturing or stapling the catheter through butterflied tape applied to the catheter is a convenient method for securing the catheter to the nose and face and preventing it from sliding.
- Apply an e-collar to prevent the patient from removing the catheter.
- Attach the catheter end to a humidified oxygen source.
BluePearl Veterinary Partners provides oxygen therapy 24/7 to patients in need of such support in our ICU ward. Patients are continually monitored under the watchful eyes of our technicians and clinicians providing vital time for their underlying conditions to be diagnosed and treated. If you feel your patient might benefit from oxygen therapy, please give us a call.