Outcome of 45 Dogs With Laryngeal Paralysis Treated by Unilateral Arytenoid Lateralization or Bilateral Ventriculocordectomy
The purpose of this retrospective study was to assess risk factors and complications affecting postoperative outcome of dogs with laryngeal paralysis treated by either unilateral arytenoid lateralization (UAL) or bilateral ventriculocordectomy (VCC). Medical records of all dogs having either UAL or VCC between 2000 and 2011 were analyzed. Twenty-five dogs had VCC and 20 dogs had UAL. The overall postoperative complications rates for VCC and UAL were similar (52% and 60%, respectively; P = .0887). Dogs that had UAL were more likely to have acute postoperative respiratory distress and aspiration pneumonia (P = .0526). Dogs with VCC were more likely to have chronic postoperative respiratory distress and aspiration pneumonia (P = .0079). Revision surgery was required in 6 dogs (24%) following VCC and 2 dogs (10%) following UAL. Sex, breed, presenting complaint, type of service provided, and concurrent diseases were not significantly associated with higher risk of either death or decreased survival time postoperatively with either procedure. Overall postoperative complication rates, required revision surgeries, and episodes of aspiration pneumonia were similar in dogs undergoing UAL and VCC surgeries. Dogs that had VCC appeared to have an increased risk of lifelong complications postoperatively compared with UAL; therefore, VCC may not be the optimal choice for treatment of laryngeal paralysis.
Introduction
Laryngeal paralysis (LP) is a common upper respiratory disease that results in failure of abduction of the arytenoid cartilages. Inherited and acquired forms exist, with acquired LP affecting predominantly older large-breed dogs of which Labrador retrievers and rottweilers may be predisposed. Clinical signs include respiratory stridor, coughing, exercise intolerance, collapse, dyspnea, and dysphonia. Acquired LP is most commonly considered idiopathic, but may also be caused by trauma, infection, neoplasia, may be iatrogenic, or may be associated with systemic disorders such as hypothyroidism, diabetes mellitus, or myasthenia gravis.1–8 The most recent data suggests that the condition known as “idiopathic” LP may be part of a generalized, progressive neuromuscular disorder referred to as “geriatric-onset LP polyneuropathy” syndrome.6–10 Previous studies have demonstrated degeneration of the distal part of the longest peripheral nerve fibers evidenced by electrophysiological changes and decreased motor nerve conduction velocities. Nerve degeneration was present in thoracic and pelvic limbs in addition to recurrent laryngeal nerves, which is consistent with a generalized polyneuropathy. Typically the first obvious clinical sign of geriatric-onset LP polyneuropathy syndrome is LP, which is often accompanied by slowly progressive pelvic limb weakness, esophageal motility disorders, and muscle atrophy.6–10
Although medical treatment options exist for LP, surgical treatment is often required to alleviate clinical signs and decrease the risk of either severe respiratory distress or dyspnea during daily physical activity. The goals of surgical treatment are to allow free air movement through the larynx while preserving its protective function. The ideal surgical procedure would be minimally invasive, low in cost, last the lifetime of the patient, and result in a return to normal activity for the patient. Common treatment options for LP include arytenoid lateralization, bilateral ventriculocordectomy (VCC) performed via a transoral approach, VCC performed via a ventral approach, castellated laryngofissure, partial laryngectomy, permanent tracheostomy, and reinnervation.4,11–18 Unfortunately, none of those surgical procedures are without risk of complication. Currently, the most commonly performed surgery for treatment of LP is unilateral arytenoid lateralization (UAL).12,19
The purpose of UAL is to abduct the entire arytenoid laterally and enlarge the rima glottidis both dorsally and ventrally to allow increased air passage. The UAL surgical procedure has the disadvantage of being more invasive due to dissection through the neck musculature, which increases surgical time and is considered a more advanced procedure that is typically performed by board-certified surgeons. It is commonly performed, however, due to consistently good clinical results with comparative complications to other procedures.20 Complications with UAL include aspiration pneumonia, seroma or hematoma formation at the surgical site, inadequate lateralization, suture failure, and fragmentation of the arytenoid cartilage.3,12,19,21–27 Previous studies have reported postoperative complications rates of 10–28% with UAL, with aspiration pneumonia occurring in 8–19% of patients.4,12,19 Variable definitions of postoperative complications and patient selection criteria, as well as duration of follow-up, likely contribute to differing results.
Although UAL is currently the most common surgical treatment of LP, VCC may offer a less-invasive and more cost-effective alternative. The purpose of VCC is to remove the vocal cords bilaterally to create a larger opening ventrally and allow increased air passage through the rima glottidis. It has been suggested that a ventral opening may decrease the risk for aspiration pneumonia by being physically located further away from the esophageal opening. Because VCC is performed transorally, it has decreased costs and can be performed with ease compared with other surgical procedures. Complications with VCC include scar tissue formation (webbing or cicatrix formation), aspiration pneumonia, and continued respiratory distress. Limited data are available regarding the postoperative outcome following VCC surgery. Scar tissue formation has been reported in 12.5–37.5% of patients, and one study reported aspiration pneumonia in 15% of cases following transoral VCC surgery.22,24,28
To the authors’ knowledge, no study has compared the postoperative outcome between UAL and VCC. The purpose of this study was to assess risk factors and complications affecting postoperative outcome of dogs with LP treated by UAL or VCC. The hypotheses were that aspiration pneumonia occurs as a complication with equal frequency in VCC and UAL and that VCC will have a higher overall complication rate and requires revision surgery more commonly than UAL, resulting in decreased owner satisfaction.
Materials and Methods
Case Selection and Medical Records Review
A retrospective search of the medical databasea was performed at Texas A&M University to identify all dogs having either UAL or VCC surgery performed from 2000 to 2011. Cases were selected for inclusion in the study if they met the following criteria: idiopathic, acquired LP confirmed by laryngoscopy; documentation in the medical record of the surgical procedure performed as determined by surgeon preference; surgical procedure performed for the purpose of treating LP; and a known outcome at the time of follow-up (regardless if the patient was dead or alive). For cases in which postoperative follow-up and outcome information was not available in the medical record, owners were contacted by telephone to complete a client questionnaire (Table 1).
Data Analysis
Patient data extracted from the medical records included signalment, appointment type, history, primary complaint, physical examination data, laboratory test results when available, concurrent diseases, type of surgical procedure, postoperative outcome, and any follow-up appointments. The primary complaint was divided into one of the four following categories: difficulty breathing, dyspnea, voice change, and other. Difficulty breathing was defined as increased respiratory rate and effort that was not life threatening. Dyspnea was defined as struggling to breathe and an inability to oxygenate adequately that could become life threatening. Surgical records were reviewed for all dogs included in the study and did not reveal any variations in the surgical technique for either procedure. Surgical procedures were performed by multiple board-certified surgeons and surgery residents; however, a board-certified surgeon was present at the time of all surgeries.
Concurrent diseases were defined as diseases present on diagnosis of LP. Those concurrent diseases were divided into the categories of hypothyroidism, polyneuropathy, aspiration pneumonia, megaesophagus, and other. A diagnosis of hypothyroidism was made only if a thyroid panel was performed that included both free thyroxine and thyroid-stimulating hormone. A diagnosis of polyneuropathy was made only if electromyography and muscle biopsy were performed. A diagnosis of aspiration pneumonia and megaesophagus was made based on radiographic and clinical findings.
Complications were defined as an event occurring postoperatively that likely would not have occurred had the surgical procedure not been performed or that could be attributed to either the surgical procedure or concurrent disease at the time of diagnosis of LP. Excluded from the complications category were events that occurred as an expected part of recovery from the surgical procedure (i.e., voice change, mild coughing). Events were considered an expected part of recovery if they were either self-limiting or did not clinically affect the patient as determined by examination of the records, which included follow-up evaluations by veterinarians (in most cases) and client questionnaire. Complications were classified as either acute or chronic. An acute complication was one that occurred ≤ 10 days postoperatively and a chronic complication was one that occurred > 10 days postoperatively. Complications were divided into the following categories for comparison: scar tissue formation, aspiration pneumonia, respiratory distress, revision surgery required (permanent tracheostomy, VCC, UAL, ventral laryngotomy), and death. Death was regarded as a complication if it occurred acutely following surgery and when the cause of death was related to the surgery. Scar tissue formation was confirmed by laryngoscopy, and respiratory distress was defined as owner-assessed breathing problems of the same or greater severity than prior to surgery.
Follow-up information was evaluated for complications (as previously defined), if the animal was still living, and cause of death. Owners contacted by telephone provided information on postoperative activity level, appetite, tolerance to exercise, recurrence of clinical signs, revision surgery if one was required, occurrence of aspiration pneumonia, cause of death, time of death in relation to surgery, and overall owner satisfaction.
Surgical Procedures
UAL
All dogs were positioned in right lateral recumbency. A left lateral approach to the larynx was made ventral to the left jugular vein. The thyropharyngeus muscle was incised along the dorsomedial edge of the thyroid cartilage, and the cricoarytenoideus dorsalis was transected. Disarticulation of the cricoarytenoid articulation was performed. Two separate strands of either 0 or 3-0 polypropyleneb, depending on the size of the dog, were passed from the caudodorsal aspect of the cricoid cartilage to the muscular process of the arytenoid cartilage. Closure of the surgical site was routine.
Transoral VCC
All dogs were positioned in sternal recumbency with the maxilla propped open, suspended with gauze. The tongue was extended ventrally to expose the larynx. The vocal folds were grasped with Allis tissue forceps and transected with curved Metzenbaum scissors at the ventral aspect of the cuneiform process, leaving 1–2 mm of mucosa at the ventral aspect of the vocal cord. The same action was performed on the opposite side. Hemostasis was achieved with digital pressure and the wounds left to heal by second intention.
Statistical Analysis
Interactions between variables in different categories were calculated using the Independent χ2 testc. Statistical significance for all analyses was defined as the probability that the null hypothesis was rejected although true was < 5.0% (i.e., P < .05). A comparison was made to test if the study sample (n = 45) was a representative sample of the hospital's breed database over the exact same time period. The hospital's breed values (n = 65,535 as a percent) were used to calculate the χ2 expected values for the breeds found in this study. The complications analysis used a null hypothesis that stated that there was no difference between the surgical techniques, UAL, and VCC, wherein the χ2 expected values were equal (i.e., 50%) between the surgical groups for the observed complications.
Results
A total of 45 dogs met the inclusion criteria. Twenty-five dogs had transoral VCC performed and 20 dogs had UAL performed. Breeds represented included 26 Labrador retrievers (57.7%), 3 mixed-breeds dogs (6.6%), and 1 each of the following breeds: Boston terrier, Weimaraner, giant schnauzer, wheaten terrier, English springer spaniel, Bernese mountain dog, Doberman pinscher, Siberian husky, Australian cattle dog, Chihuahua, Rhodesian ridgeback, Great Dane, German shepherd dog, Pekingese, cocker spaniel, and Yorkshire terrier. Comparison of this study sample to the hospital's breed database over the same time period was not consistent with a random sample (P < .0001) because Labrador retrievers were overrepresented (57.7%). Patient ages at presentation ranged from 3 to 16 yr of age with median and mean ages of 11 and 10.9 yr, respectively (standard deviation, 3.24 yr). Eighty percent of the animals in this study were older than 9 yr. Twenty animals were spayed females, 1 was female, 17 were castrated males, and 7 were intact males.
At Texas A&M University twenty-six dogs (57.7%) presented to the Soft-Tissue Surgery Service, 10 dogs (22.2%) presented to the Emergency Service, 5 dogs (11.1%) presented to the Internal Medicine Service, and of the 4 remaining dogs, 1 dog (2.2%) each presented to Cardiology, Neurology, Oncology, and Orthopedic Services. Thirty-two dogs (71.1%) presented for difficulty breathing, 8 dogs (17.8%) for dyspnea, 2 dogs (4.4%) for voice change, and 3 dogs (6.6%) for other reasons. LP was found to be bilateral in 41 cases (91.1%), left-sided in two cases (4.4%), and was not listed in the medical record in two cases (4.4%).
Eight of 45 cases (17.8%) had no documented concurrent diseases. Subsequently, 37 of 45 dogs (82.2%) had concurrent diseases at the time of diagnosis. Aspiration pneumonia and hypothyroidism were the most common (n = 6 for each), followed by polyneuropathy (n = 3). The number of dogs tested for each concurrent disease consistent with the definitions provided previously is as follows: aspiration pneumonia (n = 40), hypothyroidism (n = 19), and polyneuropathy (n = 4). Twenty-two dogs were placed into the “other” category for a variety of concurrent diseases, including cervical pain, chronic bronchitis with bronchiectasis present on radiographs, bacterial laryngitis, vomiting, lumbosacral disease, cranial nerve five deficits, thyroid adenocarcinoma, heartworm disease, degenerative joint disease, and sinusitis.
Follow-up data were available for 20 dogs with UAL that ranged in age from 8 mo to 10 yr, except in cases that either died or were euthanized immediately postoperatively. Postoperative complications occurred in 12 dogs (60%). Of those, 9 dogs (45%) had acute complications and 3 dogs (15%) had chronic complications. Aspiration pneumonia occurred in 5 dogs (25%) postoperatively, with 3 of those episodes occurring as an acute complication and 2 as a chronic complication. Only 1 dog was suspected of having two episodes of aspiration pneumonia following the initial radiographically documented episode. Those two suspected episodes occurred < 6 mo following surgery; however, aspiration pneumonia was not confirmed by radiography in either episode.
Respiratory distress also occurred in four dogs (20%) postoperatively following UAL. Revision surgery was required in two of those dogs (10%). One dog was a Chihuahua that was noted to have an abnormally narrowed air passage before the initial surgery, which did not widen following UAL. The other dog was a Pekingese that had a permanent tracheostomy performed 14 days postoperatively and was subsequently reoperated on 18 mo postoperatively due to stenosis. That dog was noted to have concurrent laryngeal collapse at the time of the initial UAL. Of the two dogs that did not have revision surgeries, one dog did not have return of clinical signs until 2 yr after the procedure, and the other dog never seemed to improve following surgery.
At the time of follow-up, 16 of 20 dogs (80%) were reported to have died since UAL, and 4 of 20 dogs (20%) were reported alive. Of the 16 dogs that died, the presumed causes of death were listed in all 16 cases (Table 2). Four dogs died < 6 mo following surgery, 5 dogs died between 6 and 12 mo following surgery, and 7 dogs died > 12 mo following surgery. Seventeen dogs (85%) survived to discharge, while 3 dogs (15%) did not survive to discharge. Death occurred as an acute complication in 2 dogs (10%), and 1 dog was euthanized 1 day postoperatively when aspiration pneumonia occurred immediately following surgery. Eleven of the 15 owners (73%) who completed the survey were satisfied with the UAL.
Follow-up data were available for 25 dogs with transoral VCC, ranging in age from 1.5 to 9.5 yr, except in cases that either died or were euthanized immediately following surgery. Postoperative complications occurred in 13 dogs (52%). Only 1 dog (4%) had an acute complication, and 12 dogs (48%) had chronic complications. Respiratory distress was the most common complication that occurred in 9 dogs (36%) postoperatively, with all of those episodes occurring as a chronic complication.
Six dogs (24%) following transoral VCC had revision surgeries performed, ranging from 6 wk to 1 yr after leaving the hospital. Three dogs (12%) required one revision surgery, and three dogs (12%) required two revision surgeries. All cases requiring revision surgery presented for examination of respiratory distress, and five of those dogs (20%) had cicatrix formation. Cicatrix formation was similar in all cases and consisted of complete fibrous scar tissue formation across the rima glottidis from the mucosal surfaces of each vocal fold that had been previously resected bilaterally. Of the three dogs that had only one revision surgery, the revision surgery performed was UAL in two dogs and transoral VCC in one dog. All of those dogs were Labrador retrievers. Of the three dogs that had two revision surgeries, the revision surgeries performed in their respective order were: transoral VCC and permanent tracheostomy in one dog, a ventral laryngotomy for cicatrix resection and permanent tracheostomy in the second dog, and transoral VCC and a ventral laryngotomy for cicatrix resection in the third dog. The first two dogs were Labrador retrievers and the third dog was a Siberian husky. Both dogs had permanent tracheostomies performed due to failure of a second surgery to alleviate clinical signs (i.e., second transoral VCC in the first case, and ventral laryngotomy for cicatrix resection in the second case).
Aspiration pneumonia occurred in four dogs (16%) postoperatively following transoral VCC. All of those episodes occurred as a chronic complication. One dog died of complications of aspiration pneumonia, and one dog was euthanized from severe aspiration pneumonia.
At the time of follow-up, 19 of 25 dogs (76%) were reported to have died since transoral VCC surgery, and 6 of 25 dogs (24%) were reported to be alive. Of the 19 dogs that died, the presumed causes of death are listed in all 19 cases (Table 3). Eight dogs died < 6 mo following surgery, 4 dogs died between 6 and 12 mo following surgery, and 7 dogs died > 12 mo following surgery. Twenty-three dogs (92%) survived to discharge, and 2 dogs (8%) did not survive to discharge. Both dogs that did not survive to discharge were euthanized, one because of progressive respiratory distress and concurrent upper airway disease (brachycephalic syndrome, esophageal dysmotility, esophageal diverticulum, and a hypoplastic trachea), and the other because of severe underlying gastrointestinal disease of unknown cause that was present before surgery. In total, 18 of the 21 owners (86%) that completed the survey were satisfied with the VCC, while 3 owners (14%) were not satisfied.
Sex, breed, appointment type, presenting complaint, and concurrent diseases were not significantly associated with either a higher risk of death or decreased survival time postoperatively with either VCC or UAL. The presence of concurrent diseases did not significantly affect the type of complication that occurred or whether animals presented with difficulty breathing or dyspnea for either procedure.
The number of dogs with episodes of respiratory distress and episodes of aspiration pneumonia was similar between both surgical methods postoperatively and the differences were not significant (P = .0877). Dogs that underwent UAL however, were significantly more likely to have dyspnea on initial presentation (P = .004), have acute complications following surgery (P = .001), and have acute postoperative respiratory distress and aspiration pneumonia (P = .052). Dogs that underwent VCC were significantly more likely to have difficulty breathing on initial presentation (P = .004), have chronic complications following surgery (P = .001), and have chronic postoperative respiratory distress and aspiration pneumonia (P = .0079). Revision surgery was required in six dogs (24%) following VCC and two dogs (10%) following UAL, but that difference was not significant (P = .0877).
There was no difference in the level of client satisfaction between VCC and UAL (P = .418), and there were no breed associations between procedures deemed either satisfactory or unsatisfactory for either procedure.
Discussion
The overall postoperative complication rates, episodes of aspiration pneumonia, and episodes of respiratory distress were similar in dogs undergoing UAL and transoral VCC surgeries. The high rate of postoperative complications found in this study following both procedures may be attributable to both a broad definition of complications and inclusion of cases with preexisting conditions, such as neoplasia, hypothyroidism, polyneuropathy, etc. Only three dogs that were diagnosed with polyneuropathy were included in this study, which may underestimate the true number of dogs with this condition due to lack of specific testing for this condition and neurologic exams on all patients. The aspiration pneumonia rate following VCC surgery in this study was similar to previously reported results; however, limited information was available and case numbers in all studies were small. The UAL aspiration pneumonia rate was higher in this study (25%) than reported studies (8–19%).4,12,19 That difference may be due to either various definitions of aspiration pneumonia among different studies or reflect the small case numbers in the current study. Owner satisfaction for UAL in this study was lower (73%) than previously reported (88–90%) and may be related to the higher incidence of aspiration pneumonia in the study population.3,4,12,19 Owner satisfaction for VCC (86%) in this study was similar to previously reported studies (83%).24
Interestingly, this study found that although both postoperative aspiration pneumonia and respiratory distress occurred with similar frequencies following both procedures, they were both significantly more likely to occur in the acute postoperative period after UAL surgery. Many studies exist that support this study’s finding that there is low risk of long-term complications following UAL surgery. A study by MacPhail et al. assessed 109 cases that had UAL surgery performed. In that series, 15 dogs (13.7%) had acute complications and 16 dogs (14.7%) had chronic complications following UAL. The complications that occurred chronically were not specified in that study. Their definition of a complication was a respiratory tract problem requiring either hospitalization or surgery, which was more specific than the definition provided in the current study. That difference may explain why our overall and acute complication rates were higher.4 Another study by Hammel et al. evaluated the postoperative outcome of 39 dogs with idiopathic LP after UAL surgery. They found no correlation between signalment, pre- and postoperative clinical signs, and development of pneumonia on postoperative survival in their study. Complications in that study were divided into major and minor based on the need for hospitalization. That study did not divide complications into acute or chronic categories; however, only two dogs (5.1%) developed aspiration pneumonia > 6 mo after surgery and only one dog (2.5%) developed a complication > 12 mo after surgery.19 Based on those results, this study suggested that dogs, after an initial adjustment period following UAL, become less likely to suffer from aspiration pneumonia as time increases from surgery.
A study by Snelling et al. examining outcome after UAL in 100 dogs found that 8% of dogs were diagnosed with aspiration pneumonia following surgery. Of those, half occurred as an acute complication (< 7 days) postoperatively and the other half occurred 120–870 days postoperatively. That study did not divide all complications into acute and chronic categories; therefore, speculation about overall complications in this study cannot be inferred.12 A study by White that examined postoperative outcome in 62 dogs with LP following UAL, perioperative complications were found in seven dogs (11.3%). Long-term follow-up was 1 yr in that study and chronic complications occurred in only four dogs (6.2%), and overall owner satisfaction was 91%.3 Based on the results of those studies and the current study, there is supporting evidence that most complications after UAL occur in the acute postoperative period.3,4,12,19
Transoral VCC was significantly more likely to have complications occur chronically, many of which required revision surgery due to respiratory distress and scar tissue formation. In the current study, six cases (24%) required revision surgery postoperatively following VCC and only two cases (10%) required revision surgery following UAL postoperatively; however, that difference was not significant. Interestingly, both cases that had revision surgery following UAL had concurrent airway abnormalities along with LP. It is likely that those abnormalities led to the need for revision surgery following UAL because none of the other dogs that had UAL performed had concurrent airway abnormalities other than LP or required revision surgery following UAL.
Although there is limited data on postoperative outcome following VCC surgery, the studies that exist support this study's finding that complications occur more commonly in the late postoperative period.22,24 In a study by Holt et al. assessing long term postoperative outcome of 40 dogs that had transoral VCC in which the mucosal defect was left to heal by second intention, only 3 dogs (7.5%) had postoperative complications acutely (< 10 days) following surgery. In the chronic postoperative period, 5 dogs (12.5%) had scar tissue formation requiring revision surgery. In addition, 6 dogs (15%) developed aspiration pneumonia, and 5 of those occurred between 2 and 36 mo following surgery. Follow-up in this study ranged from 5 to 52 mo.24 In a retrospective study by Petersen et al. that assessed the outcome following transoral VCC in 24 dogs, 9 dogs (37.5%) had scar tissue formation and required revision surgery and 14 dogs (58%) had complications occurring from 2 wk to 7 mo postoperatively. Complications in that study included aspiration pneumonia, persistent cough, exercise intolerance, and increased respiratory stridor.22
Scar tissue formation following transoral VCC in the current study was comparable to the reported rates in previous studies and was likely due to the use of an oral approach during VCC that leaves the mucosal defect to heal by second intention. That technique was associated with a higher risk of scar tissue formation.28 Cases with cicatrix formation often require revision surgery to alleviate respiratory distress caused by blockage of the airway. In a recent study by Zikes et al., of 88 dogs that had VCC performed via a ventral approach, the mucosal defect was sutured closed and no dogs postoperatively had cicatrix formation. In the short term, complications were divided into major and minor, with a total of 6 dogs (6.8%) affected, which is comparable to the current study. Only 42 dogs included in that study were available for follow-up. Of those, 3 dogs had long-term complications (7.1%). In total, 3 dogs developed documented aspiration pneumonia and 3 dogs had episodes of antibiotic-responsive coughing that occurred as both short- and long-term complications.29 That complication rate was lower than reported in the current study; however, aspiration pneumonia rates postoperatively were similar. There were 9 dogs in the current study that developed respiratory distress, five of which had cicatrix formation postoperatively. It is possible that the postoperative chronic complications identified in the current study would have been more comparable to the study by Zikes et al. if the ventral approach was used to suture the mucosal defect closed thereby preventing cicatrix formation, postoperative respiratory distress, and subsequent revision surgery.29 It seems performing VCC via ventral laryngotomy and suturing the mucosal defect closed may be effective in reducing the frequency of cicatrix formation, but would consequently eliminate the minimally invasive benefit of the transoral approach.29,30
The authors of the current study did not find an association with any of the risk factors included in this study on either death or survival time with either surgical procedure. MacPhail et al. found an association between respiratory tract abnormalities, neurologic disease, and esophageal disease on overall outcome, which was not a finding supported by the current study. It is possible that significant associations may have become apparent had there been more cases in the current study.4
There was an increased likelihood for dogs presenting with dyspnea to be treated with UAL, which may indicate that clinicians are more likely to perform UAL in cases that are perceived as having an increased severity of clinical signs. Labrador retrievers represented 57.8% of the sample population (26 dogs). The overabundance of Labrador retrievers in the study population agrees with previous studies that report the breed as commonly affected, potentially indicating a genetic basis for LP in that breed.1–8
There are several limitations of this study because of its retrospective nature. As with any retrospective study, reliance on the written records and owner assessment for follow-up can influence conclusions drawn about postoperative outcome. Although a majority of cases in the current study had follow-up evaluations performed by a board-certified surgeon, that was not always available, and owner assessment was relied upon. The authors considered a diagnosis of aspiration pneumonia only in cases with clinical signs and documentation, which may underestimate the total number in patients suffering from subclinical aspiration. The authors do not believe that had a significant impact on this study because the definition of a complication would not have included subclinical aspiration pneumonia due to the self-limiting nature and lack of clinically affecting the patient.
Cases in which follow-up was not available beyond discharge after surgery were excluded from the study. It is, therefore, possible that the results of the study would be influenced with a higher number of cases with follow-up information. Another limitation of the study was that multiple surgeons with different levels of experience performed the surgeries over the span of the study, which could affect outcome in specific cases. Conversely, in the study by Hammel et al. that attempted standardization of the surgical procedure, the overall postoperative complication rate was comparable to previous studies in which surgical technique was not standardized.19 It is possible that because cases with UAL performed were more likely to present with dyspnea, the increased severity of clinical signs affected the number of complications that occurred postoperatively. Although that may have increased the number of acute complications postoperatively, the authors do not believe this influenced conclusions drawn about the chronic postoperative period. The decision to perform either UAL or VCC in a particular patient was surgeon preference, and further reasoning for the decision was not available in the medical records. Ideally, a prospective study investigating UAL and VCC performed by the same surgeon, randomizing what patient received either treatment, with follow-up evaluation by the same surgeon, would be beneficial to provide a more complete picture about risk factors, complications, and overall outcome following each procedure.
Conclusion
Based on past and present study results, it is likely that dogs surviving the first 10 days after surgery will have a better overall outcome following UAL. The study authors conclude that dogs that have transoral VCC have an increased risk of life-long complications following surgery compared with UAL; therefore, transoral VCC may not be the optimal choice for treatment of LP in many dogs.
Contributor Notes
