33rd Annual Scientific Meeting proceedings

Evidence between HH/ GERD and upper airway obstruction?
Brachycephalic obstructed airway syndrome (BOAS) is strongly linked to digestive disease with studies documenting clinical signs of gastro-oesophageal reflux disease (GERD), oesophagitis, gastritis or intestinal disease in the majority of BOAS cases^1-5. The proposed mechanism of action is negative intrathoracic pressure generated by upper airway obstruction overcoming the barrier of the lower gastroesophageal sphincter leading to gastro-esophageal reflux (GER) and hiatal hernia^6,7.

Oesophageal dysmotility has also been recorded in brachycephalic breeds which may compound the issue⁸. The reflux can, in turn, inflame the larynx, nasopharynx and pharyngeal wall, thus resulting in an escalating cycle of aerodigestive disease. Other airway disease in the dogs and cats has been reported with reflux, presumably causative as the GER resolved after treatment^9,10,11.

The evidence for a link between BOAS and digestive disease in dogs (and cats though to a much lesser degree) is mainly dependent on case series, though we do have some experimental studies. In children, there is an association between GER and asthma, wheezing, hoarseness and croup, which is bidirectional. 

Boesch et al developed an animal experimental study where he placed cuffed and fenestrated tracheostomy tubes in 5 dogs which were then capped. None of the dogs had evidence of GER prior to obstruction, with mean negative inspiratory pressures of 12 cm H20. This increased to 18cm H20 after one week and 3/5 dogs had evidence of GER on oesophageal pH monitoring, with the regurgitation index at 21%. All dogs had food avoidance and vomiting with signs of respiratory obstruction (prolonged inspiratory traces)².  A study in rats found similar results¹².

Results with BOAS treatment
Poncet in 2005 reported 98% cases (out of 73 dogs) had chronic gastritis, 90% had lymphoplasmocytic duodenitis, and there was a positive statistical correlation between severity of respiratory and GI signs.  In 80% of these cases, GI signs resolved after BOAS surgery, with and without GI medication, although immediate post op vomiting and regurgitation were reduced if the dogs were given 0.7mg/kg omeprazole, 0.2mg/kg cisapride and 1g sucralfate¹³.  The authors also believed that concurrent medical management of GI tract pathology may have helped reduce the progression of the respiratory disease (laryngeal collapse).

Mayhew had a case series of 16 dogs with BOAS surgery that had a videofluoroscopic swallowing study (VFSS) pre-operatively (12 post-operatively) and endoscopy (6 post-operatively). 70% of owners reported an improvement in regurgitation after eating, 77% reported an improvement in regurgitation during activity. On VFSS there was no significant differences in GER frequency or severity or oesophageal motility though there was improvement. There was no difference in SHH frequency or severity¹⁴.

In 2016, Pohl et al reported the results of Oechtering’s multilevel upper airway surgery (ala-vestibuloplasty, tonsillotomy, modified folding flap, laser assisted turbinectomy (LATE) and ventriculectomy/ cuneiformectomy if indicated)¹⁵. Of the 102 dogs in the study, they had 62 dogs where owners completed a pre and post operative questionnaire. Of the 18 dogs with daily vomiting pre surgery, only 2 had daily vomiting post-surgery. A modest improvement was reported for eating. The authors concluded though the dogs had, according to their owners, improved, they were still clinically affected.

In human medicine, surgery treatment for obstructive sleep apnoea improved reflux symptomatic index in several studies, as did the use of continuous positive airway pressure (CPAP)^16,17,18,19.

Results with Surgery for Hiatal Hernia
In children, laparoscopic fundoplication has been shown to reduce reflux symptoms, total acid exposure time, increase lower oesophageal resting pressure and increase quality of life scores^19,20. Oesophageal function and gastric emptying are not usually altered.

In dogs, Mayhew et al looked at 18 dogs pre and post laparoscopic treatment for SHH and GER. They were evaluated with a standardised questionnaire pre and post-surgery and 12 of the dogs had VFSS pre and post-operatively. The regurgitation after eating and during activity/exercise decreased in most dogs and HH and GER severity scores improved though SHH and GER scores did not. 8 of the dogs had additional BOAS surgery when under anaesthetic. The conclusion was that there was clinical improvement in most but still residual clinical signs in some dogs²².  He found similar results in a mixed group of dogs which underwent open surgery for hiatal hernia and GER, with about an 80% improvement²³. Mayhew concluded that there was 20-30% of non-responders to surgery - be that hiatal hernia or airway surgery.

Hosgood performed circumferential hiatal rim reconstruction on a case series of 29 dogs with good results (7/29 had short term regurgitation post-operatively which resolved, on telephone long term follow up 16/19 had resolution of regurgitation, with the other three much improved) but 20 of these dogs had upper airway surgery at the time of surgery, 9 had had previous BOAS surgery and all had laryngeal collapse²⁴.

Our Results
When we assessed our surgical results objectively with whole body barometric plethysmography, 32% of our dogs had a BOAS index that we would consider as not affected with BOAS. The remainder of the dogs, although improved, had a BOAS index that we would consider consistent with clinical BOAS. We were better when we used Professor Oechtering’s multilevel BOAS surgical technique (MMS bar LATE) of versus our traditional technique of wedge resection alaplasty, staphylectomy, tonsillectomy and ventriculectomy if required. Of the 32% of dogs that were considered improved to an acceptable level post-surgery, 62% had MMS²⁵. When we re-evaluated the dogs 8-12 weeks post-surgery, if dogs had a BOAS index of over 50%, CT findings consistent with nasal obstruction and clinical signs associated with nasal airway obstruction (regurgitation, heat intolerance, sleep disordered breathing and nasal breathing on exercise) we recommended LATE. Of 57 dogs re-evaluated, 29 had a LATE and the median BOAS index dropped from 67% to 42% (clinically unaffected). 18 questionnaires were returned and 6 dogs were frequent regurgitators prior to surgery, 5 completely resolved and one was much improved²⁶.

Similarly, improvements in the reflux symptom score have been documented in patients treated surgically for obstructive sleep apnoea that had GER^27,28.

References
Available on request