Medical Management of the BOAS Patient for Sleep and Gastrointestinal Disorders
Dr Stefanie Mitze
RCVS Internal Medicine Specialist
Brachycephalic obstructive airway syndrome (BOAS) is a chronic conformation-related respiratory disorder. Affected dogs show mainly noisy and laboured breathing to varying degrees, which is linked to the severity of the chronic upper airway resistance present. So-called ‘primary lesions’ in BOAS include an elongated and thickened soft palate, nostril stenosis and tracheal hypoplasia. ‘Secondary lesions’ can also develop in these patients, such as laryngeal collapse and eversion of the laryngeal saccules, leading to a more guarded prognosis.
BOAS is therefore a serious welfare issue. The average life span of a BOAS patient is 3 years less than that of breeds of a similar body shape which are not brachycephalic.
The paradox of these breeds is that despite owners being increasingly aware of the health issues faced by brachycephalic breeds, their popularity is increasing in the face of increased evidence and knowledge. In publications it has been established that the majority of dog owners want a healthy dog, which sounds reasonable. However, owners continue to prioritise the physical appearance of brachycephalic dogs, and they will therefore readily accept all these health challenges for the sake of outer appearances. This has an effect on the owners’ likelihood to seek veterinary care, and their expectation of what is normal. It is important to be mindful of this when engaging with the client as nurses and vets.
It is even more tricky to ask ourselves as professionals, what do we expect as normal in these breeds? If a border collie walked into your practice with the same respiratory effort as a pug, how would you react?
The sad truth is that BOAS patients are not only suffering from the obvious respiratory issues the general public are aware of. We now increasingly understand just how many systemic health issues are associated with a state of chronic hypoxemia, as experienced by BOAS patients. Brachycephalic breeds are strongly predisposed to disorders intrinsically linked to their conformation, including dystocia, spinal disease, eye and skin diseases, and more.
Gastrointestinal signs, such as vomiting, regurgitation, ptyalism or drooling, dysphagia or difficulty swallowing, gastroesophageal reflux and flatulence are highly prevalent in brachycephalic patients. These signs occur in almost 100% of male, obese French Bulldogs with BOAS. However, these misleading signs are only the tip of the iceberg.
In BOAS patients these GI signs have been linked to, amongst other things, a profoundly negative inspiratory intrathoracic pressure. This results in an increased breathing effort, aerophagia, esophageal dysmotility, and other congenital or acquired abnormalities, such as hiatal hernias and esophageal anomalies. We also know that the severity of respiratory signs seen in BOAS patients is closely linked to severity of the gastrointestinal signs, and that these signs improve after surgical correction of the upper airway in 91.4% of patients (Poncet et al, 2006).
A major concern in these breeds are pathologies of the upper gastrointestinal tract, particularly those affecting the oesophagus. Gastroesophageal reflux disease (GERD) is the main cause of oesophagitis and oesophageal strictures in dogs. The clinical presentation is highly variable and can be easily missed, since the diagnosis is not straight forward. A tailored and individual approach is therefore needed. Therapy involves treatment of the underlying cause, a strict long-term feeding management plan and a combination of medications which lower the acidity of the stomach, as well as increasing the tone of the oesophageal sphincter.
The parallel occurrence of gastrointestinal signs, biopsy-confirmed gastrointestinal lymphocytic/lymphoplasmacytic inflammation, and upper respiratory signs has been repeatedly reported. Studies including a full medical gastrointestinal work-up for these breeds are, however, lacking. The diagnosis of chronic IBD is one of exclusion. Careful elimination of extraintestinal factors and step-by-step therapeutic trials are required to understand the underlying pathology of this umbrella group of heterogeneous diseases. As a final diagnostic step, gastrointestinal biopsies are indicated. It must be remembered that the gastrointestinal tract can only respond in a limited number of ways to insult. The mere presence of a lymphoplasmacytic infiltrate within the lamina propria is not definitively diagnostic for IBD, and can only be used as an indicator for the presence of chronic gastrointestinal disease. Additionally, clinical disease severity varies among individuals and the severity of histology findings is not robustly linked to the clinical severity. Hence gastrointestinal therapy cannot be standardized and must be individualised at all times, even in brachycephalic breeds.
Sadly, abnormalities of sleep are very common among brachycephalic breeds and might have a greater systemic effect than previously thought. Obstructive sleep apnea (OSA) has been well studied in the English Bulldog, which seems to be so similar to humans that these breeds are used as models for the human disease. OSA means intermittent total and/or partial upper airway collapse whilst sleeping or when awake, leading to hypoxia, sleep fragmentation, arousal from sleep and oxygen desaturation. A pre-stage of sleep apnea is snoring.
OSA leads to a state of intermittent chronic hypoxemia and this has been proven to lead to systemic inflammatory and metabolic dysfunctions in humans and dogs (Hoareau et al, 2012; Facin et al, 2020). The associated liver hypoxia leads to cell injury and eventually to fibrosis, which can culminate in the development of portal hypertension and splenic changes. Patients with BOAS have been shown to have higher liver and spleen stiffness than healthy dogs. This means BOAS has a confirmed systemic effect and these breeds are predisposed to hepatic disorders, similarly to OSA in humans. Brachycephalic breeds with confirmed OSA developed a hypercoagulable state, which seemed to be worsened with increased severity of BOAS.
This situation might be aggravated by the presence of chronic hypomagnesaemia which has been associated with OSA and the occurrence of arterial hypertension in selected brachycephalic breeds (Mellema & Hoareau, 2014). It should be noted that the long-term usage of proton pump inhibitors is known to enhance/induce hypomagnesaemia due to malabsorption, a medication often prescribed to brachycephalic breed dogs due to the chronic gastrointestinal problems.
The pathogenesis of sleep-disordered breathing is rather complex and includes neurochemical changes within upper airway dilator muscles, as well as other respiratory muscles (Veasey et al., 2001). Ondansetron, a serotonin antagonist, has been suggested for medical management of central apneas and recent reports show promising efficacy for OSA. More prospective studies are needed and suggested dosage regimes are empirical.
Medical therapy of non-respiratory syndromes in BOAS patients cannot be curative, and can only be of temporary benefit if the respiratory problems are not addressed. Long term medication is also not without side effects and may even worsen BOAS, so should be used cautiously. Therapy must always include thorough weight management and an optimised lifestyle, since obesity negatively impacts respiratory function and contributes to the severity of many upper airway diseases. Concurrent treatment of gastrointestinal disease improves outcomes in patients with BOAS, however gastrointestinal work up and treatment must be individualised, and treatment is considered only palliative and inferior to surgical correction of the respiratory abnormalities.
In summary, brachycephalic breeds with BOAS suffer from systemic consequences directly or indirectly linked to their chronic hypoxemia. All these variables negatively affect animal welfare. Without doubt the leading problem to prioritise must be the respiratory tract. To improve the long-term quality-of-life, owners and breeders, as well as veterinarians, must change the perception that these abnormalities are “normal”, and shift the popularity actively towards a healthier anatomical formation.
Catch up on the VVS Webinar on BOAS Patients delivered by Dr Stefanie Mitze
Internal Medicine cases can feel overwhelming to deal with in general practice, but VVS’ friendly world-class medicine specialists are on hand to support you and to enable you to bring outstanding clinical care to your patients and reassurance to their owners. Bring the specialist to you and your patient with the help of the VVS service. Get in touch to speak to us further about trying this unique service in your practice!
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