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Risk of anesthesia-related complications in brachycephalic dogs | VETgirl Veterinary Continuing Education Podcasts

In this VETgirl online veterinary CE podcast, we review the risk of anesthesia-related complications in brachycephalic dogs – just how worried should we be when it comes to anesthetizing them?

We all have a healthy respect for the troubled airways of our brachycephalic breeds. We see them in our emergency rooms for airway related crises, we see them in our OR for prophylactic and emergent airway surgeries. Anesthesia is risky for any pet. It’s part of our hospital’s practice to warn owners about their pet’s anesthetic risk, which may be increased in these special smush-faced breeds, though we haven’t had any strong veterinary studies to officially document this for us. So, Gruenheid et al out of the Ohio State University wanted to evaluate this in a study called Risk of anesthesia-related complications in brachycephalic dogs. The authors sought to review medical records from brachycephalic dogs that underwent various surgeries in their hospital to determine if these brachycephalic dogs are in fact at a higher risk for perianesthetic complications than non-brachycephalic breeds. The authors retrospectively reviewed anesthetic medical records from 2012. The authors were careful to select medical records from only those brachycephalic and nonbrachycephalic dogs that were relatively healthy as supported by an ASA designation of I, II, or III, and they excluded all emergency surgeries. (As our VETgirl anesthesiologist, Dr. Jane Quandt, DACVAA, DACVECC, always says, the ASA score matches the number of fluid pumps you typically need with the patient). To limit any surgical procedure bias, once a brachycephalic dog’s record was selected for inclusion into the study, the authors matched it with a nonbrachycephalic dog’s record that underwent the same surgical procedure (or at least a surgery of similar degree of invasiveness). The authors tried to match age, weight, and sex between the two groups, but this was not consistent throughout the study. In total, 223 dogs were included in each group. Brachycephalic breeds that were investigated included Boxers, English bulldogs, Shih Tzus, Pugs, Boston Terriers, Mastiffs, French Bulldogs, American Bulldogs, Shar-Peis, Lhasa Apsos, Brussels Griffons, Pekingese, and Dogue de Bordeaux.

So, what’d they find in this study? Brachycephalic dogs were 1.57X more likely than nonbrachycephalic dogs to experience an INTRA-anesthetic complication and that each additional 30-minute increment of anesthesia carried with it an increased odds of developing an intra-anesthetic complication by 0.6%. Unfortunately, the authors don’t clearly describe what they categorized as intra-anesthetic complications, but they reference that they looked at factors that we globally know to be intra-anesthetic complications such as hypotension (described in this paper as systolic BP < 80 mm Hg), hypothermia (described in this paper as rectal or esophageal temperature <96.1˚F) and bradycardia (described in this paper as heart rate < 60 beats/min, though the authors don’t mention whether they considered breed variations in their “normal” heart rate ranges). The authors found that intact females seemed to have an increased risk of intra-anesthetic complications, but this finding would need to be investigated more closely to determine if any other factors such as surgical procedure for these females played any bias. Factors associated with a decreased risk of intra-anesthetic complications included neutering, the surgical service performing the surgery (although this likely was related more to the invasiveness and/or complication of the actual surgery being performed), and increased body weight (although the authors acknowledge that they can’t conclude whether this factor is related to breed variation in size or to body condition index).

When looking at the post-anesthetic complications, brachycephalic dogs were found to be 4.33 times as likely to experience a complication and this risk increased by 18% for each additional 30-minute increment of anesthesia. Orthopedic surgeries were less likely to produce post-anesthetic complications as compared to soft tissue surgeries, but again this finding is likely multifactorial. Invasive procedures were 5 times more likely to produce post-anesthetic complications than non-invasive procedures. The most common post-anesthetic complication was aspiration pneumonia. None of the nonbrachycephalic dogs experienced aspiration pneumonia. Other post-anesthetic complications identified in brachycephalic dogs included regurgitation, dysphoria, prolonged recovery, stertorous breathing, death, vomiting, anemia, facial edema, problems of the urinary tract, and inappetence.

The authors mention that they looked at induction agents and maintenance anesthesia agents, and found that the use of ketamine plus a benzodiazepine for anesthetic induction lead to brachycephalics developing more post-anesthetic complications than if propofol was used instead. This finding is a bit shocking as this combination is regarded as being cardio- and respiratory-protective. However, they do not explain what specific post-anesthetic complications were associated with this combination, and the authors did not provide a suggested theory as to why this relationship might occur, so it’s difficult to put at lot of weight on this finding at this time. That being said, we should always be careful in selection of anesthetic and sedative agents and strongly consider their known protective and potentially harmful effects. Since regurgitation and aspiration pneumonia are a big risk for our brachycephalics, some of us may recommend withholding food for 24 hours prior to surgery for brachycephalic breeds, but study results are conflicting as to whether there’s a benefit to this measure.1,2 We can take away one small positive benefit to being a brachycephalic – they were less likely to develop VPC’s during anesthesia. The authors suggest this is likely due to elevated vagal tone in brachycephalics, which causes sinus bradycardia and may put them at a lower risk for development of VPC’s.

So, what can we take away from this VETgirl podcast? We can now tell our clients that brachycephalic dogs are 1.57 times as likely to experience intra-anesthetic complications than nonbrachycephalic dogs. And their increased risk for post-anesthetic complications merits careful consideration of their anesthetic plan. Measures we can take to potentially minimize these risks are to ensure pre-anesthetic lab work looks clear of any metabolic or organ function troubles, pre-anesthetic radiographs to ensure no smoldering pneumonia or compromise of the airway is present, pre-oxygenation before intubation can help to minimize risks of apnea and hypoxia in the pre-anesthetic period, slow recovery with prolonged intubation until the patient is fully awake can protect against airway obstruction after extubation, gastroprotectant medications can help to minimize post-anesthetic regurgitation, and doing everything possible to minimize anesthesia times will be protective against post-operative complications.

Abbreviations:
VPC: ventricular premature contraction
BP: blood pressure

References:
1. Hendricks JC. Brachycephalic airway syndrome. Vet Clin North Am Small Anim Pract 1992;22:1145-1153.
2. Poncet CM, Dupre GP, Freiche VG, et al. Long-term results of upper respiratory syndrome surgery and gastrointestinal tract medical management in 51 brachycephalic dogs. J Small Anim Pract 2006;47:137-142.
3. Gruenheid M, Aarnes TK, McLoughlin MA, et al. Risk of anesthesia-related complications in brachycephalic dogs. J Am Vet Med Assoc 2018;253(3):301-306.

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