Can’t Catch Your Breath?
Some may suggest that the level of pain is the ultimate measure of a patient’s suffering, but the sensation of dyspnea has to be one of the worst symptoms a patient can experience. It may be an anthropomorphic assessment, but 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)
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
- Pulse oximetry
- Arterial blood gas analysis
|A number of techniques exist for supplementing oxygen in our patients. The most common methods include:|
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
Treating the “In-Between” Patients with Degenerative Valve Disease
Degenerative valve disease, or endocardiosis, is a disease that affects many canine patients, particularly small-breed dogs. The vast majority of our patients with degenerative valve disease are at the “in-between” stage, where they have a heart murmur and various levels of left-sided cardiomegaly, but are not yet in congestive heart failure. Many patients stay in this preclinical, in-between stage for their entire lives, but there is still the unlucky handful that do progress to congestive heart failure, typically with pulmonary edema. Studies such as the PREDICT cohort study, along with some common sense, indicate that left atrial enlargement and biomarkers such as NT-proBNP, can signal patients that are at a higher risk of developing congestive heart failure in the near future. However, it is more difficult to predict the clinical course that patients will experience when they are still in the more mild stages of the disease.
As doctors, we want to be able to fix problems for our patients. Sadly, this is one disease that we cannot fix (yet). We have been frustrated alongside our clients with nothing to offer them in this common preclinical stage. One intervention that has gotten a lot of research attention is ACE-inhibitors. We seem to really want them to make a difference in delaying the time to onset of congestive heart failure, maybe because we can make physiological justifications for why ACE-inhibitors should, theoretically, help. Multiple studies have shown “trends” to improvement, but no statistical significance (VETPROOF, SVEP). Many arguments suggest that we simply haven’t performed the right study to find the benefit, but one could also argue that if multiple different studies didn’t show a statistical difference, then the true benefit is likely modest, at best. That said, many of us have prescribed ACE-inhibitors in the preclinical stage just in case it does help. It makes us, and our clients, feel like we are doing something that may possibly help, while we are, in all honesty, in a position where our hands are tied. All of that changed with the release of the EPIC study results at ACVIM in June 2016.
Historically, we have found that pimobendan outperforms ACE-inhibitors after the onset of congestive heart failure by reducing heart size and retention of free water (QUEST study). The EPIC study (Evaluation of Pimobendan in Dogs with Cardiomegaly) was a prospective, double-blind, randomized, placebo-controlled, international, multi-center study that was started in June 2010. Pimobendan (or placebo) was administered chronically to small-breed (4.1-15 kg) canine patients with cardiomegaly due to degenerative valve disease (ACVIM Stage B2) to determine if it could delay the onset of congestive heart failure. For the study, 360 patients were enrolled – 180 dogs in the pimobendan group and 180 dogs in the placebo group. The primary endpoint was the development of left-sided congestive heart failure or death due to a cardiac cause.
A planned interim analysis was conducted, showing a significant benefit in the administration of pimobendan prior to the onset of clinical signs, and no concerns over safety were found. The investigators found that the time to the primary endpoint was increased by over a year. Patients in the pimobendan group did not live as long as the placebo group after the onset of congestive heart failure, but overall survival time (all-cause mortality) was increased. Said another way, patients that receive pimobendan starting in the preclinical stage (ACVIM Stage B2) live longer than those who don’t and spend less of their life battling clinical signs of congestive heart failure. The results were significant enough that the study was prematurely discontinued in March 2015.
One of the major concerns with the EPIC study is that many dogs with only mild enlargement never experience clinical signs of congestive heart failure in the first place, so treating them long-term with pimobendan does not change their clinical outcome. Luckily, it appears to be a very safe medication for the majority of patients, but it is not a cheap medication to give for years when it does not change the outcome. Since we do not have a good way of predicting which dogs with mild disease will progress to clinical signs, it becomes difficult to decide whether or not to recommend pimobendan for some patients.
This is where the art of clinical practice comes into play. Each patient is an individual who deserves personalized thought and attention. If a patient has mild cardiomegaly and is already 16 years old, it is far less likely that the patient will progress to congestive heart failure during his or her lifetime than a different patient with similar disease who is only 5 years old. Also, does the patient have other clinical diseases that otherwise limit its lifetime? Potentially, these patients will not be expected to benefit from chronic pimobendan administration. Since the EPIC study was announced, I have started to recommend giving pimobendan with increased urgency to patients of mine with progressive cardiomegaly. When in doubt, I often take the approach of educating the owners on the potential benefits and the downfalls of starting their dog on pimobendan at any given time, empowering them to make the decision that is best for them and their companion.
Questions still remain about the best way to treat patients at various stages of degenerative valve disease, and questions will probably always remain since each patient is a different case to consider. So, we anxiously await publication of the EPIC study results, but it feels good to have something to offer many of our clients when their patients are “in-between.”
We would like to thank our colleague from BluePearl in Washington, Mikaela Mueller, DVM, DACVIM-Cardiology, for allowing us to use this article for Companion.
Leptospirosis: A Growing Concern for Urban and Suburban Dogs
No longer primarily a concern for country and hunting dogs, leptospirosis is a now a big threat for suburban and urban canine populations as well. Factors such as wildlife adaptability to our urban landscapes and a dog’s uncanny ability to find a puddle of standing water to drink from, have dramatically increased the rate of confirmed cases in the U.S. in recent years. Leptospirosis is a deadly bacterial disease spread via the urine of infected wildlife, and it can persist in standing water or wet grass for long periods of time. If diagnosed early, this bacterial infection is easily treated with a course of antibiotics. Unfortunately, the initial symptoms of leptospirosis can be vague, and by the time the patient is noticeably ill, the bacteria may have already begun to damage the patient’s liver and kidneys. Treatment for the later stages of disease is possible, but can be costly. Leptospirosis is not discriminatory to canine size or breed and is also zoonotic. Any dog that steps outside is at risk for contracting this disease. It can be as simple as sniffing wet grass, licking a puddle or wading in standing water.
The prevalence of leptospirosis in the urban and suburban environments has greatly increased in the past five years. Some risks include:
- Wildlife such as squirrels, skunks and deer are potential vectors of leptospirosis, with raccoons and rats being the main threat to our urban canine population.
- Infected wildlife can appear healthy, though actively shedding the bacteria through their urine, as symptoms are often subclinical.
- Leptospirosis can persist in wet soil and stagnant water for long periods of time.
- Common routes of transmission are mucous membranes, open skin or ingestion.
- Leptospirosis is zoonotic: Increase risk to our canine patients = increased risk to owners
- Increased risk in areas of floods
- There is a greater risk associated with the changing of seasons, such as the beginning and end of winter, when wildlife activity increases.
- Any dog that goes outside is at risk of contracting leptospirosis.
- Once contracted, the leptospirosis bacteria will begin multiplying within ~ 1 day
- Rapid replication occurs within the next few consecutive days
- Symptoms can be vague, and an infected animal can be easily misdiagnosed
- Target organs of the leptospirosis bacteria include (but are not limited to):
- Liver, kidneys, lungs
- Endothelium, central nervous system, reproductive organs
- Clinical symptoms are usually vague and non-specific, such as lethargy, abdominal pain, pu/pd, anorexia, and vomiting
- Other signs to keep leptospirosis on your differential list:
- Azotemia, liver enzyme abnormalities, hyperbilirubinemia
- Coagulation defects, thrombocytopenia, leukocytosis, thrombocytopathy
- Imaging such as thoracic radiographs and abdominal ultrasound
- Supportive care
- Organ specific treatment
- Doxycycline and penicillin derivatives both terminate bacteremic stage and sterilize urine. Doxycyline terminates carrier states.
- Fluid therapy (sometimes in high rates due to polyuric state) with electrolytes
Veterinarians and staff should always wear gloves when handling the suspected or confirmed cases. Infected patients will actively shed live bacteria for up to two days after antibiotic treatment has begun. Place a urinary catheter if urine is contaminating hospital and use bleach for cleaning.
There is an effective vaccination for leptospirosis available. Our specialists at BluePearl Veterinary Partners highly recommend annual vaccination by the primary care clinician. It is the most affordable way to protect your clients’ pets from a disease that can be very costly to treat. Inform clients on the risks of leptospirosis and how to take certain precautions, such as discouraging pets from drinking from or wading in stagnant water.
Negative Pressure Wound Therapy (NPWT):
A Better Solution for Complex Wounds
Wounds are a common cause of morbidity in our patients, and management of complex wounds can be prolonged and debilitating, leading to long hospital stays, painful and labor-intensive bandaging, and significant financial hardship. The most successful wound care plan takes into consideration all of the components of a wound (depth, degree of contamination, size, location, chronicity) as well as the clinical presentation of the patient (systemic health, personality, age). We have come a long way from the time of the wet-to-dry bandage, and today there are a number of moist wound care products to choose from that follow the typical course of healing through inflammation, proliferation, and finally maturation.
Negative pressure wound therapy (NPWT) is a wound healing modality that intervenes at the proliferation stage of healing and has some pretty amazing results. Functionally, NPWT is the application of subatmospheric pressure to a wound bed, open or closed, through foam dressing. This results in decreased interstitial edema, reduced bacterial load, the creation of a closed environment, improved circulation and enhanced granulation bed formation. While there’s never only one way to treat a wound, I have found that in some cases NPWT is the most efficient path to resolution. Faster granulation bed formation means fewer trips to the hospital, fewer bandage changes and often sets the stage for earlier delayed primary closure.
Nuts and bolts of bandage application
NPWT bandages have to be applied at the right time to the right wounds. They have no part in the debridement phase of a dirty, devitalized or infected wound. After adequate debridement (that may take several days), the bandage is applied. This consists of open cell foam covered by adaptic dressing placed within the wound bed. Skin edges can be advanced to the foam edges as determined by the wound configuration. Adhesive drape material covers the entire dressing and tubing that connects the foam to a vacuum pump and collection reservoir. Negative 125 mmHg is an adequate setting for most applications, and the bandage can stay in place for up to 72 hours. Most commonly, NPWT therapy is used for 3 to 6 days, but the bandage is often only changed once under moderate sedation. This results in a hospitalized patient who needs less sedation or anesthesia, gets more consistent nutrition, and is more comfortable and amenable to treatment.
Photo 1: Placement of foam dressing within a septic incisional dehiscence wound
Photo 2: After placement of tubing and adhesive dressing
Photo 3: After 6 days of NPWT
Photo 4: Closure
Photo 1: Multiple wounds, such as these bite wounds, can be treated in one bandage.
Photo 2: Foam bridges connect wound dressings.
Photo 3: After placement of the adhesive
Photo 4: Patients are comfortable with the NPWT bandage in place.
How does it work?
The application of uniform negative pressure to a wound bed removes from the area interstitial fluid that contains high levels of inflammatory cytokines and proteases in chronic wounds. It also helps to decrease the local pressure which can increase perfusion pressure and restore blood flow to previously collapsed capillaries and lymphatics.1 Negative pressure also has a direct effect on blood vessels by increasing vascular diameter and blood velocity and by initiating earlier angiogenesis – within the first hours of the application of negative pressure.2,3 Negative pressure also deforms tissue by deforming the skin edges and limiting the loss of domain that happens when wound edges naturally retract. On a microscopic level, the mechanical force of microdeformation has a fundamental role in regulating tissue growth by placing traction on the extracellular matrix and thereby turning on growth factors that regulate cellular proliferation.4 This is similar to the Ilizarov technique of distraction osteogenesis, which is based on the principal that tissue, in this case bone, responds to mechanical tension. Finally, NPWT stabilizes the wound environment by creating a semipermeable membrane that keeps ongoing contamination out, provides an appropriate electrolyte balance, and maintains body temperature. Under these conditions and through these mechanisms, granulation tissue forms more quickly.
NPWT was developed for humans to treat diabetic ulcers and open fractures. Since its inception over 500 peer-reviewed articles have been published in the human literature reporting its efficacy. Veterinarians have adapted the use of NPWT to our patients over the past 15 or so years, but evidence of efficacy is sporadic. Excellent evidence supports the use of NPWT in early treatment of distal extremity shearing wounds5 and to stabilize full thickness skin grafts.6 It was confirmed to speed the formation of smooth, nonexuberant granulation tissue in acute wounds7 and as an acceptable modality in treating traumatic wounds.8 Veterinarians at the University of Florida have reported its successful use in other applications including skin avulsions, degloving injuries, abdominal and thoracic wounds, surgical dehiscence, chronic nonhealing wounds, to prevent postoperative edema, and myofascial compartment syndrome.9 NPWT is contraindicated in a few cases in which cancer cells or overexposed vessels are present in the wound bed, in the face of active bleeding, or in devitalized tissue beds.
Complications are few and are usually technical issues related to the application or use of the system. Mild skin irritation of surrounding skin can develop from the tissue adhesive and drape. In my experience, as with any wound care tool, NPWT works best in carefully selected wounds. It has proven significantly effective in our patients in many traumatic wounds resulting in more comfortable and earlier wound closure. Let us help you to determine if NPWT may be helpful in your complicated wound cases.
Thanks to Jennifer Weh, DVM, DACVS-SA, from BluePearl in Washington for writing this article for Companion.
Medical Directors’ Column
Welcome to winter and 2017! We hope you had a great holiday season. We would like to take this opportunity to talk about the BluePearl Portal and thank you for your continued feedback on the Portal.
We’re pleased to announce the referral function within your practice’s BluePearl Portal account has been greatly enhanced. A link to a step-by-step illustrated guide is available at the top of the Portal login page on our website and on all screens within the Portal.
PLEASE REMEMBER: Using the referral form within the Portal or on our main website is solely for your convenience. If you prefer, just call us for a consultation or to refer a patient. We love communicating by phone, so please don’t hesitate to call.
Enhancements to the e-referral form include the following:
- The form is separated into different sections for easier viewing and completion.
- The number of required fields has been kept to a minimum.
- You may save your work so that you or another member of your staff can come back to it at any time to complete and submit the information.
- You may update referral information even after the form has been submitted to BluePearl.
- If you choose to attach medical records, lab results or images to the referral, these can be easily loaded – and reviewed – before or after the referral is submitted.
- Review, update and manage your practice’s referrals through a screen that allows you to review what was sent; add information to previous referrals; and sort your practice’s referrals by date, specialty, or location of the BluePearl hospital you referred your patient to.
Once a referral is submitted via the Portal, you will receive immediate email confirmation that the referral has been sent, along with a PDF of the information you provided. That PDF is the same one that is available to view within your Portal account.
Thank you for giving us the opportunity to partner with you on your cases. We hope this enhanced form makes sending us patient information easier and faster for those who choose to use it. As always, feel free to call us for a consultation or to refer a patient. Use of the form is entirely optional, for your convenience.
If you have any questions or suggestions, please contact Dr. David Wohlstadter at firstname.lastname@example.org.
Marc Greenberg, DVM, MS, DACVS-SA
Timothy Rocha, DVM, DACVIM-Oncology