Brachycephalic airway syndrome results from a variety of underlying anatomic abnormalities, including stenotic nares, elongated and thickened soft palate, aberrant nasal conchae, and tracheal hypoplasia.1–3 These features cause upper airway obstruction and increased negative inspiratory pressure that can subsequently lead to laryngeal saccule eversion, laryngeal collapse, and bronchial collapse.4–6 Breeds most commonly affected include the English Bulldog, French Bulldog, Pug, and Boston Terrier, but brachycephalic breeds such as the Cavalier King Charles Spaniel, Shih Tzu, Pekingese, and others can also be affected.7,8 Clinical signs include increased respiratory noise, snoring, stridor, dyspnea, exercise intolerance, collapse, vomiting, regurgitation, and sleep-disordered breathing.9,10
Dogs with anatomic abnormalities and clinical signs of brachycephalic airway syndrome are twice as likely to have perianesthetic complications when compared with nonbrachycephalic dogs, most notably in the postanesthetic period.11 Brachycephalic dogs are 1.57 times as likely to have intra-anesthetic complications and 4.33 times as likely to have postanesthetic complications, such as regurgitation, vomiting, aspiration pneumonia, prolonged recovery, and stertorous breathing, with aspiration pneumonia as the most common complication.11
Numerous surgical interventions are described to improve clinical signs associated with brachycephalic airway syndrome and decrease development of secondary airway abnormalities. Clinical improvement following surgery is noted in > 85% of patients.11–13 Described techniques to correct stenotic nares include amputation of the ventral segment of the dorsal lateral nasal cartilage; lateral, vertical, or horizontal wedge alaplasty; and punch alaplasty and alapexy.14–18 These techniques can be completed by use of a scalpel blade, electrosurgery, or CO2 laser. Laser-assisted turbinectomy creates a patent nasal airway in dogs with aberrant nasal conchae.19 Staphylectomy to shorten the caudal aspect of the soft palate is described with the use of a variety of devices, including a scalpel blade, scissors, bipolar sealing devices, electrosurgery, or CO2 laser.20–23 A folded flap palatoplasty can both shorten and decrease the thickness of the soft palate.24 Everted laryngeal saccules can be resected by use of a variety of surgical instruments, and the sites are left to heal by secondary intention.1,4,25
To the authors’ knowledge, no published studies have established an association between the aforementioned surgical interventions and the occurrence of perianesthetic complications for brachycephalic patients undergoing future anesthetic events. Thus, we sought to determine whether such an association exists. We hypothesized that brachycephalic dogs that have received previous upper airway surgery have a decreased risk of perianesthetic complications when undergoing subsequent anesthetic events.
Materials and Methods
Animals
All medical records of client-owned dogs that underwent surgical procedures to treat clinical signs of brachycephalic airway disease (ie, any combination of staphylectomy, nasal alaplasty, and laryngeal sacculectomy) and subsequently underwent general anesthesia at a later date for additional surgical procedures or diagnostic imaging between August 2, 2007, and February 8, 2019, at 3 teaching hospitals (ie, The Ohio State University Veterinary Medical Center, University of Minnesota Veterinary Medical Center, and University of Wisconsin Veterinary Care) were reviewed.
Data collection
Information retrospectively retrieved from the medical records included breed, age, sex, and body weight; the ASA status26; the procedure performed; any drugs administered in the perianesthetic period (ie, sedation drugs and opioids, induction and maintenance agents, and any additional medications administered throughout the procedure); and anesthetic and surgical duration as well as any intervals of positive-pressure ventilation. Lengths of hypotensive (ie, systolic arterial blood pressure < 80 mm Hg or mean arterial blood pressure < 60 mm Hg, measured by invasive or noninvasive means) or bradycardic (heart rate, < 60 beats/min) events were documented, along with any interventions performed, any instances of hypothermia (body temperature, < 35.5°C [95.9°F]), and any other perianesthetic complications such as hypertension, vomiting or regurgitation, cardiac arrhythmias, dysphoria, respiratory distress, hypoxemia, reintubation, and prolonged recovery periods.11,27 The perianesthetic period was separated into 2 periods for purposes of this study. The intra-anesthetic period was defined as the time from induction to termination of inhalant anesthetic, and the postanesthetic period was defined as the time from the termination of inhalant anesthetic to discharge from the facility.
Procedure invasiveness was grouped into 3 categories on the basis of previous publications.11 Non-invasive procedures included endoscopy, dental hygiene procedures, wound management, and CT or MRI. Minimally invasive procedures consisted of orthopedic surgeries, mass removals, ophthalmic surgeries, ovariohysterectomy and orchiectomy, digit or tail amputation, and cardiovascular coil placement or valvular balloon dilatation. Invasive procedures included any other intra-abdominal procedures (eg, cystotomy, gastrotomy, or exploratory celiotomy), neurologic surgeries (eg, hemilaminectomy), and upper airway surgeries.
Statistical analysis
Marginal logistic regression with generalized estimating equations was performed with statistical softwarea to compare the odds of anesthetic complications during the 2 anesthetic periods (ie, intra-anesthetic and postanesthetic complications) among brachycephalic dogs that underwent subsequent anesthetic procedures after surgical intervention for clinical signs of brachycephalic airway syndrome. A forward selection model was used to select from the independent variables of postsurgical correction of brachycephalic airway syndrome: procedure invasiveness; breed, age, sex, and body weight; ASA status (1, 2, 3, or > 3); administration of preanesthetic medications (ie, sedative or opioid); induction agent (ie, alfaxalone, propofol, or other); maintenance agent; duration of anesthesia; the use of positive-pressure ventilation during anesthesia; administration of any additional drugs during the intra-anesthetic period; and presence of hypothermia, bradycardia, hypotension, or other intra-anesthetic complications. Hypotension, bradycardia, hypothermia, and other intra-anesthetic complications were classified as anesthetic complications in the intra-anesthetic model but were considered independent variables in the postanesthetic complications model so that any intra-anesthetic complication would not increase the odds of having a postanesthetic complication.
Variables with values of P < 0.20 in the univariate analysis were considered for inclusion in the multivariate analysis. All variables excluded from the final model were evaluated for confounding by adding them back to the model and observing for substantial alterations in risk factor coefficients (> 20% change). Continuous variables included in the final models were tested for linearity in the logit scale via fractional polynomial analysis. All model-building approaches were constructed by use of robust SEs estimated by the Huber-White sandwich method. Clustering resulting from repeated measures among individual patients was accounted for by including patient identification as a random effect. Independent variable coefficients in the final 2 models were exponentiated to generate ORs and were considered significant if their 95% CI did not include the value 1.
Results
Animals
Forty-five brachycephalic dogs were included in the study. All dogs received an initial corrective surgery for clinical signs of brachycephalic airway syndrome (45 anesthetic events) followed by a second anesthetic procedure at a future date (45 anesthetic events). Nine of 45 (20%) dogs were anesthetized for a third anesthetic event, and these events were also included in the analysis, totaling 99 anesthetic events. There were 27 (60%) males and 18 (40%) females. Seven brachycephalic breeds were represented, including English Bulldog (n = 21), French Bulldog (11), Pug (9), Shih Tzu (1), Boston Terrier (1), Japanese Chin (1), and Cavalier King Charles Spaniel (1).
Mean ± SD age and weight at the time of corrective surgery was 3.7 ± 3.1 years (range, 0.33 to 11 years) and 16.3 ± 8.6 kg (35.9 ± 19.0 lb; range, 3.5 to 35.7 kg [7.7 to 78.7 lb]). The mean ± SD age and weight at the second anesthetic event was 4.8 ± 3.3 years (range, 0.4 to 11 years) and 16.8 ± 8.6 kg (37.0 ± 19.0 lb; range, 3.2 to 35.6 kg [7.1 to 78.3 lb]). At the third anesthetic event, these values were 5.8 ± 2 years (range, 2 to 8 years) and 15.0 ± 8.5 kg (33.0 ± 18.7 lb; range, 3.0 to 26.3 kg [6.6 to 58.0 lb]).
Outcomes
At the time of initial corrective upper airway surgery, postanesthetic complications (including respiratory distress, prolonged time to extubation, hypoxemia, and regurgitation) were recorded for 23 of 45 (51.1%) dogs. Ten of these 23 dogs required airway support (oxygen supplementation or reintubation), but only 3 of the 10 dogs had a serious complication requiring surgical intervention to be performed during the recovery period (2 dogs required tracheotomy and 1 dog required a soft palate revision because of hemorrhage). When evaluating all subsequent anesthetic events following the initial corrective airway surgery, postanesthetic complications were recorded during 14 of 54 (26%) anesthetic events. Only 3 dogs included in these 14 anesthetic events had complications that required additional oxygen supplementation during the recovery period, and no dogs required reintubation or tracheotomy.
When determining the rate of intra-anesthetic complications as defined by this study, hypotension was noted in 55 of 99 (55.6%) anesthetic events, hypothermia in 13 of 99 (13.1%) anesthetic events, and bradycardia in 20 of 99 (20.2%) anesthetic events. Other intra-anesthetic complications, including cardiac arrhythmias, hypertension, regurgitation, tachycardia, laryngeal edema, and hemorrhage, were noted in 15 of 99 (15.2%) anesthetic events (Table 1).
Summary of intra-anesthetic complications recorded for 45 brachycephalic dogs, with a breakdown by each anesthetic event.
| Intra-anesthetic complications | First anesthetic event (45 events) | Second anesthetic event (45 events) | Third anesthetic event (9 events) |
|---|---|---|---|
| Hypotension | 21 | 29 | 5 |
| Hypothermia | 6 | 7 | 0 |
| Bradycardia | 7 | 11 | 2 |
| Cardiac arrhythmias | 1 | 4 | 2 |
| Hypertension | 1 | 1 | 0 |
| Regurgitation | 2 | 0 | 0 |
| Tachycardia | 1 | 0 | 0 |
| Laryngeal edema | 0 | 1 | 0 |
| Hemorrhage | 1 | 1 | 0 |
Factors associated with outcome
As the full multivariate model was built, no significant associations were found with any evaluated outcomes during the subsequent anesthetic events for breed, sex, age, weight, invasiveness of procedure, ASA status, induction or maintenance agent used for anesthesia, hypotensive events, or periods of hypothermia.
Factors identified through multivariate modeling as significantly associated with postanesthetic complications included periods of intra-anesthetic bradycardia and the overall anesthetic duration (Table 2). For dogs that had an intra-anesthetic bradycardic event, the odds of developing postanesthetic complications were 4.56 times those of dogs that did not have a bradycardic event during anesthesia (P = 0.021). For every 15-minute increase in anesthetic duration, dogs had 12% greater odds (OR = 1.12) of developing a postanesthetic complication (P = 0.013). During the modeling for postanesthetic complications, 1 dog was removed from analysis regarding anesthetic duration because the duration was not recorded in the medical record. When controlling for the effects of bradycardia and anesthetic duration, dogs having surgical intervention to correct clinical signs of brachycephalic airway syndrome were determined to have 79% decreased odds of having a postanesthetic complication during subsequent anesthetic events (OR = 0.21; P < 0.001).
Results of multivariate logistic regression modeling to identify factors associated with intra- and postanesthetic complications in 45 brachycephalic dogs undergoing subsequent anesthetic events following corrective airway surgery.
| Variables | ||
|---|---|---|
| Postanesthetic complications | ||
| Prior airway surgery | 0.21 (0.10–0.47) | < 0.001 |
| Bradycardia | 4.56 (1.26–16.52) | 0.021 |
| Anesthetic duration (1 min) | 1.01 (1.00–1.01) | 0.013 |
| Anesthetic duration (5 min) | 1.04 (1.01–1.07) | 0.013 |
| Anesthetic duration (10 min) | 1.08 (1.02–1.14) | 0.013 |
| Anesthetic duration (15 min) | 1.12 (1.02–1.22) | 0.013 |
| Anesthetic duration (30 min) | 1.25 (1.05–1.49) | 0.013 |
| Intra-anesthetic complications | ||
| Anesthetic duration (1 min) | 1.01 (1.00–1.01) | 0.016 |
| Anesthetic duration (5 min) | 1.03 (1.01–1.06) | 0.016 |
| Anesthetic duration (10 min) | 1.07 (1.01–1.13) | 0.016 |
| Anesthetic duration (15 min) | 1.11 (1.02–1.20) | 0.016 |
| Anesthetic duration (30 min) | 1.23 (1.04–1.45) | 0.016 |
Only 1 factor, anesthetic duration, was identified through multivariate modeling as significantly associated with intra-anesthetic complications (Table 2). For every additional 15 minutes that dogs were under anesthesia, there were 11% greater odds of developing an intra-anesthetic complication (P = 0.016).
Discussion
In the present study, we evaluated the odds of anesthetic complications in brachycephalic dogs undergoing subsequent anesthetic events following a previous corrective upper airway surgery. We hypothesized that brachycephalic dogs that had undergone previous upper airway surgery would have decreased odds of perianesthetic complications during subsequent anesthetic events. This study found that dogs having previous surgical intervention to correct their brachycephalic airway syndrome had 79% decreased odds of having complications during subsequent anesthetic events, specifically in the postanesthetic period.
Although the odds of having an anesthetic complication in brachycephalic patients undergoing subsequent anesthetic events did not decrease during the intra-anesthetic period in the present study, the decreased odds of having a complication during the postanesthetic period may be most clinically important. The postoperative period has been identified as the most common period for dogs to die. Approximately 50% of patient deaths occur during this period, with the majority occurring within 3 hours of the procedure conclusion.28 By decreasing postanesthetic complications following subsequent anesthetic events in brachycephalic patients that have received corrective upper airway surgery, the overall associated risk of anesthetic morbidity and death is lowered.
The incidence of intra-anesthetic bradycardia and prolonged anesthetic duration both accounted for, at least in part, the increase in odds for postanesthetic complications in the present study. Effects of these variables were controlled when the effect of previous brachycephalic airway surgery during subsequent events was calculated. Bradycardia may be caused by drugs that increase vagal tone or vagally mediated reflexes or that cause hypothermia, cardiac disease, or excess anesthetic depth.29 Bradycardia can decrease both cardiac output and blood pressure, which may contribute to postanesthetic complications. Brachycephalic dogs have been shown to have increased vagal tone, compared with nonbrachycephalic dogs.30 This may contribute to the development of bradycardia in these dogs during general anesthesia. Treatment of bradycardia with either atropine or glycopyrrolate was performed during 9 of 20 anesthetic events. It is unknown if the increased risk of post-anesthetic complications was truly the result of the development of bradycardia in these brachycephalic patients or was from the treatment of the bradycardia with these medications. Future investigation is warranted to determine whether a link exists between treatment of bradycardia with these medications and increased postanesthetic complications.
Increasing anesthetic duration was consistently a significant predictor of anesthetic complications in both models of the present study. Anesthetic duration is associated with an increase in perianesthetic complications, including prolonged recoveries, in both humans and domestic species.11,31–33 Longer durations of anesthesia result in prolonged exposure to volatile inhalants used as maintenance agents. In general, inhalant maintenance agents promote vasodilation and reduced tissue perfusion that cause 2 intra-anesthetic complications frequently observed in our study, hypotension and hypothermia.34,35 Other perianesthetic complications such as cardiac dysrhythmias frequently occur in healthy individuals. Dogs undergoing general anesthesia with inhaled anesthetics can also have altered cardiac impulse conduction.36–38
Prolonged anesthesia has also been associated with postanesthetic complications observed in the present study, such as protracted recovery times and increased risk of regurgitation, vomiting, and aspiration.33,39 Prolonged recovery and increased chance of regurgitation and vomiting are especially concerning in brachycephalic dogs, as their upper airway conformation already predisposes them to reflux, regurgitation, and vomiting episodes, thus increasing their likelihood of developing aspiration pneumonia.40 In our study, anesthetic duration was chosen for statistical analysis instead of duration of surgical procedure, as not all anesthetic events had a related surgery (patients requiring diagnostic imaging such as CT and MRI). It is unknown whether a longer duration of surgery would increase the likelihood of complications in the same manner.
By decreasing the odds of postanesthetic complications associated with subsequent surgeries, patients may recover faster and have a shorter time to extubation. Future studies may quantify this anticipated benefit by measuring time to extubation and other vital parameters. By decreasing the odds of significant complications that require interventions such as placement in oxygen cages, nasal oxygen supplementation, or tracheotomies, costs to the client will be decreased by limiting these interventions and likely limiting the overall length of hospital stay.
Study limitations included the retrospective nature and the relatively small sample size. Some medical records were missing detailed patient information. The preanesthetic drugs varied widely between patients, which may affect the development of different perianesthetic complications. Information gathered from different institutions may introduce variability in the matter of which exact variables in the medical record were considered complications versus which were not recorded as complications by the primary anesthetist. Blood pressure measurements recorded in the medical record were obtained by both invasive (direct) and noninvasive (indirect) methods. Measurements taken by noninvasive means may have introduced inaccurate readings, compared with measurements taken by invasive means. This study also did not contain a control group. Including a control group of brachycephalic dogs that had not received previous corrective upper airway surgery undergoing subsequent anesthetic events may have further highlighted the proposed protective effect of previous upper airway surgery.
In conclusion, dogs undergoing previous corrective surgery for clinical signs of brachycephalic airway syndrome had 79% decreased odds of postanesthetic complications during subsequent anesthetic procedures. A large number of brachycephalic dogs will likely undergo multiple anesthetic procedures in their lifetime and can benefit from these corrective upper airway surgical procedures. It is unknown whether the type of corrective airway surgery will influence outcome, and additional studies should be performed to identify any differences between various procedures.
Acknowledgments
No external funding was used in this study. The authors declare that there were no conflicts of interest.
The authors thank Brittney A. Carson for help with data collection for this study.
Footnote
Stata/IC, version 15.1, StataCorp LLC, College Station, Tex.
ABBREVIATIONS
| ASA | American Society of Anesthesiologists |
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