Tracheal Resection and Anastomosis After Traumatic Tracheal Stenosis in a Horse Timothy P. Barnett1, BSc (Hons), BVM&S, Claire S. Hawkes2, BVSc, Diplomate ECVS, and Padraic M. Dixon3, MVB, PhD 1
Rossdale and Partners, Rossdales Equine Hospital and Diagnostic Centre, Exning, United Kingdom ,2 Sycamore Lodge Equine Hospital, The Curragh, Ireland and 3 Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, University of Edinburgh, Roslin, Scotland, United Kingdom
Corresponding Author Timothy P. Barnett, BSc (Hons), Rossdale and Partners, Rossdales Equine Hospital and Diagnostic Centre, Cotton End Road, Exning, Suffolk, CB8 7NN, United Kingdom. E‐mail: [email protected] Submitted May 2013 Accepted January 2014 DOI:10.1111/j.1532-950X.2014.12270.x
Objectives: To report a resection and anastomosis technique to treat trauma‐induced tracheal stenosis. Study Design: Case report. Animals: A 9‐year‐old Warmblood gelding. Methods: Endoscopy, radiography, and ultrasonography were used to diagnose a single ring tracheal stenosis; the stenotic region was resected and adjacent tracheal rings anastomosed with an end‐to‐end technique. Results: The anastomosis healed completely despite formation of a unilateral partial mucosal stenosis “web,” which was subsequently removed by transendoscopic laser surgery. During tracheal anastomosis, the left recurrent laryngeal nerve was damaged, causing laryngeal hemiplegia, later treated successfully by laryngoplasty. The horse returned to its previous level of work. Conclusions: This tracheal resection and anastomosis technique successfully provided the horse with a large tracheal lumen, and despite major complications, allowed a return to full athletic work.
Tracheal obstruction, other than tracheal collapse, is uncommonly described in horses. Focal tracheal stenosis after tracheostomy,1,2 tracheal trauma, and neoplasia3,4 have been reported. Tracheal stenosis in adult people can occur after external trauma or prolonged endotracheal intubation, but can also occur after tracheostomy.5–7 Congenital tracheal stenosis is well described in infants5 but rarely recorded in animals.8 A surgical technique for equine tracheal resection and end‐to‐ end anastomosis has been reported in experimental and clinical cases of tracheal stenosis.1,4,9 Tracheal resection techniques are the treatment of choice in people with tracheal stenosis.6 We report our experience with successful treatment using an alternative surgical technique of tracheal stenosis involving a single ring in a horse caused by external trauma.
CLINICAL REPORT A 9‐year‐old Warmblood gelding successfully used for competitive driving at national level that had been rested for some months was heard to make abnormal inspiratory and expiratory noises at rest. The horse was otherwise normal, but these abnormal sounds increased in intensity over the next The work was performed at the Royal (Dick) School of Veterinary Studies.
2 weeks. On admission, there were no abnormal clinical findings except slightly increased abnormal resting inspiratory and expiratory sounds, audible a few meters from the horse. On resting endoscopy, marked stenosis (20% of normal cross‐sectional area) of the cervical tracheal lumen was present 60 cm caudal to the larynx. Endoscope passage through the strictured area showed that it was 2–3 cm long, and demonstrated that the more distal trachea and the main stem bronchi were normal in appearance. A 5–6 cm long linear scar was identified on left ventral aspect of the neck, at the level of the tracheal stenosis, suggesting external trauma caused the tracheal damage, but no history of neck trauma was reported. No other abnormal findings were identified in the upper airways. Ultrasonography of the caudoventral cervical area in a sagittal plane confirmed the presence of a 3 cm‐long, distinct hypoechoic defect in the ventral tracheal lumen, as indicated by the loss of the hyperechoic air‐tissue interface of the trachea. Moderate enlargement of 1 tracheal cartilage ring was evident, in addition to increased heterogeneity and slight enlargement of the adjacent sternothyrohyoideus muscles. Lateral radiographs revealed marked focal narrowing of the tracheal lumen ventral to 6th cervical vertebrae (Fig 1A). A well‐demarcated ventral protuberance of soft tissue opacity extended from the ventral tracheal surface into the tracheal lumen at this site, and there was poor definition of the caudal aspect of the tracheal ring immediately rostral to this lesion.
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
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Tracheal Resection and Anastomosis in a Horse
Barnett, Hawkes, and Dixon
Figure 1 (A) Preoperative laterolateral radiograph of the distal cervical trachea showing the tracheal defect with a localized soft tissue opacity protruding into the tracheal lumen. (B) Resected deformed tracheal ring with intraluminal cicatrix.
Surgical Procedures Because of the limited length of tracheal damage but marked airway compromise, complete resection of the stenotic area with end‐to‐end anastomosis of adjacent tracheal rings was performed. Neomycin (5 mg/kg) with procaine benzylpenicillin (10 mg/kg) was administered intramuscularly and flunixin meglumine 1.1 mg/kg intravenously (IV) preoperatively. After premedication with xylazine (1.1 mg/kg IV), general anesthesia was induced with ketamine (2.2 mg/kg IV) and diazepam (1 mg/kg IV) and maintained with isoflurane in oxygen. When extubation was required during surgery, anesthesia was maintained using combined 5% guaifenesin (1 L) with xylazine (500 mg) and ketamine (2 g) as a constant rate infusion (CRI; 2 mL/kg/h). The horse was positioned in dorsal recumbency with the neck extended and a temporary tracheostomy was created in the mid cervical region to allow an endotracheal tube to be temporarily inserted through the stricture into the distal trachea. Through an 16 cm long, ventral median incision directly over the affected trachea, dissection between the sternothyrohyoideus and use of hand held retractors revealed a depression in the annular ligament between 2 tracheal rings, and extensive scar tissue on the ventral aspect of this ligament, especially on the left side. The esophagus, locally adherent to the trachea, was dissected free. Identification of other structures including the recurrent laryngeal nerves and carotid sheaths were impaired by this fibrous tissue. The trachea was dissected free from the fibrous tissue on the left side. A 2nd tracheotomy
266
performed immediately cranial to the stricture to allow digital palpation of the stricture determined there was single tracheal ring involvement (Fig 1B). The affected ring was sharply dissected free from its proximal (using the 2nd tracheostomy site) and distal annular ligaments, preserving as much annular ligament and mucosa as possible. The proximal and distal tracheal ends were not secured and when the damaged tracheal ring was freed, the tracheal ends suddenly retracted >10 cm apart. Four, size 3 (6‐metric) stainless steel cerclage wires were loosely placed submucosally around the proximal and distal tracheal rings (1 ventral, 1 dorsal, 2 lateral—each side) to partially appose them. Simple interrupted 0 polyglactin 910 sutures were placed intraluminally, starting at the dorsal hemi‐ circumference of the trachea, to appose the tracheal mucosa that had focal areas of scarring to the adjacent tracheal rings. After closure of the dorsolateral mucosa, the 2 lateral cerclage wires were tightened with Axel wire twisters into the final position. The lateral and ventral tracheal mucosal sutures were then placed before tightening of the ventral stainless steel cerclage wire. Another temporary tracheotomy was created, 3 tracheal rings cranial to the anastomosis to allow a temporary tracheostomy tube to be positioned through the anastomosis site. A Penrose drain was placed in the skin incision, which was closed in 2 layers with 0 polyglactin 910. The more proximal tracheostomy was left to heal by second intention. Unassisted recovery from general anesthesia was uneventful. Neomycin/penicillin and metronidazole (15 mg/kg orally every 8 hours) was administered for 5 days, followed by trimethoprim‐potentiated sulphonamides (30 mg/kg orally twice daily) and metronidazole for a further 8 days. Flunixin meglumine (1.1 mg/kg IV twice daily) was administered for 3 days followed by phenylbutazone (2.2 mg/kg orally twice daily) for 4 weeks. All postoperative feeding was performed from shoulder height. Endoscopic assessment of laryngeal function the day after surgery showed left laryngeal hemiplegia (Havemeyer grade 4)10 in contrast to normal preoperative function, likely because of iatrogenic recurrent laryngeal nerve damage during surgery. The tracheostomy tube was removed at 13 days and the (distal) tracheostomy wound allowed to heal by second intention. Endoscopy on day 13 revealed a healing, but moderately inflamed, tracheal anastomosis with intraluminal penetration of the right lateral cerclage wire. The horse was discharged at day 19 and confined to a box stall for 3 weeks. At 6 weeks, all external surgical wounds had healed. On endoscopy, left laryngeal hemiplegia was still present and the tracheal anastomosis had healed further; however, a mucosal‐ covered web, 10 mm deep on the left lateral aspect of the anastomosis obstructed 1/3 of the tracheal cross sectional area (Fig 2A). Focal areas of granulation tissue surrounded the remnants of the mucosal polyglactin sutures, which were removed using transendoscopic biopsy forceps (Olympus biopsy forceps, 0.8 mm). The 2 tracheostomy sites were healing well with some mucosal thickening evident at the more distal site. Radiography showed that all steel sutures were intact (Fig 2B). Under general anesthesia, left laryngoplasty (using 2 stainless steel wire prostheses) and ventriculocordectomy and right ventriculectomy were performed.11 Hyperabduction of
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
Barnett, Hawkes, and Dixon
Tracheal Resection and Anastomosis in a Horse
Figure 2 (A) Endoscopic view of the tracheal anastomosis at 6 weeks postoperatively showing a membranous cicatrix on the left side. One stainless steel suture is penetrating the right ventral aspect of the tracheal lumen. (B) Laterolateral radiograph of the tracheal anastomosis at 6 weeks showing the 4 stainless steel wires in situ. (C) Endoscopic view at 12 weeks, after laser transection of the cicatrix, and (D) at 27 weeks showing slight narrowing of the tracheal lumen with complete mucosal healing present.
the left arytenoid (grade 1 post laryngoplasty)11 was performed to counteract the anticipated loss in abduction because of sutures cutting into the left cricoarytenoideus dorsalis muscle. Endoscopy 7 days later surgery showed grade 3 arytenoid abduction11 and the focal tracheal inflammation at the anastomosis site had improved after suture removal. In addition to routine perioperative medication and management,11 the horse was discharged on a 4 week course of phenylbutazone (2.2 mg/kg orally once daily). Examination 5 weeks later showed the laryngoplasty incision to have healed well and on endoscopy, there was no further loss in abduction. The membranous tracheal web at the anastomosis site was transected with the horse sedated and using topical local anesthesia (20 mL 2% lidocaine) and a transendoscopic contact diode laser (15 W for 30 seconds) (Fig 2C). The horse was confined to a stall for 2 weeks before gradual return to exercise. The horse was back in full work and competing 13 weeks later when a repeat examination was requested because of a single episode of increased respiratory noise at exercise. Endoscopy showed laryngoplasty abduction to be unchanged (grade 3)11 and a well healed tracheal anastomosis (Fig 2D) with very mild luminal narrowing because of a small circumferential rim of everted mucosa.
Increased tracheal mucopurulent respiratory secretions (grade 3/5) were observed. The horse was discharged with instructions to increase the level of fitness and monitor the respiratory noise. The horse competed successfully; however, increased respiratory noise and effort was reported toward the end of the season. Nine months after initial surgery, during exercise, there was increased respiratory noise that was most obvious on inspiration. Endoscopy revealed further loss (grade 4) of abduction. The tracheal anastomosis was unchanged, and radiography confirmed intact, correctly placed tracheal sutures. A slight (grade 1/5) accumulation of tracheal secretions was identified caudal to the anastomosis. After training, high‐speed treadmill video‐endoscopy, initially of the larynx, and then for a short period of the trachea just cranial to the anastomosis, was performed. The left arytenoid remained in a fixed position during exercise. Some vibration of the left sided rim of tracheal mucosa at the anastomosis was observed. Whereas this was not thought to be causing an airway obstruction, tissue vibration could have been attributing to the noise. The mucosal fold was transected using transendoscopic contact diode laser (1 W for 20 seconds) after local anesthesia, with the horse standing sedated. Postexercise tracheal wash revealed increased
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
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Tracheal Resection and Anastomosis in a Horse
Barnett, Hawkes, and Dixon
neutrophils and on bronchoalveolar lavage cytology there were 12% mast cells, indicating the likely presence of immune‐ mediated inflammatory airway disease. The horse was discharged with a course of oral prednisolone (initial dose 1 mg/kg orally once daily for 2 weeks then tapering over 4 weeks to discontinue). The horse then returned to full work and has competed well, winning national level driving championship competitions. Exercising endoscopic examination of the upper airway 16 months after laryngoplasty, using over‐ground endoscopy, revealed continued grade 4 laryngoplasty abduction with stability of the arytenoid cartilage and no other upper airway problems.
DISCUSSION External trauma can cause tracheal cartilage and mucosal disruption with hematoma formation. In addition to permanent cartilage deformation, subsequent organization of the traumatized area with scar tissue formation can result in increased intraluminal tissue and tracheal stenosis.5 The presence of a cervical scar overlying the region of tracheal stenosis in this horse and the severe and localized nature of the tracheal injury in a previously normal horse indicate that external trauma likely caused the tracheal stenosis. The timescale between likely injury and the relatively acute onset of signs is unknown, but was probably some months’ duration, given the degree of fibrosis at the tracheal stricture. In sedentary dogs and cats, tracheal stenosis causing up to 80% reduction of luminal diameter may be well tolerated8 but this horse even had some stridor at rest. Stenosis of the cervical trachea can cause abnormal inspiratory effort and stridor with affected tracheal sites subject to higher velocity, and potentially more turbulent airflow8 that can potentially cause additional inflammation at the stenotic site. Continued circumferential fibrosis and stricture development is the likely reason for the progression of clinical signs in this horse. Various surgical techniques for tracheal resection and end‐ to‐end anastomosis have been described in human surgery including incising the adjacent annular ligaments and splitting of cartilage rings. Suture techniques include full thickness or submucosal sutures with continuous or interrupted patterns, with or without use of tension sutures.12 A comparison of suture material and suture pattern techniques (polypropylene, simple continuous; polyglactin 910 and polydioxanone, simple interrupted) using full thickness bites found comparable tracheal cross sectional areas and inflammatory reactions (mild) at the anastomosis sites in all groups.12 Tate et al.1 described a tracheal resection technique in experimental horses using annular ligament transection with mucosal eversion before partial thickness anastomosis of the tracheal segments using stainless steel sutures through the cartilage, everted mucosa, and adventitia. They proposed that this technique would reduce mucosal granulation tissue because of the absence of intraluminal sutures. Behrand and Klempnauer12 suggested that the suture material and technique used to achieve tracheal anastomosis are of secondary importance, but other technical
268
details such as accurate approximation of the tracheal ends, creation of an airtight seal, ensuring overlap of the membranous part of the trachea, whilst preventing overlap of the cartilaginous rings are of greater importance. In this horse, localized inflammation was present around some of the tracheal mucosal sutures 4 weeks after surgery, and resolved when these sutures were removed. The use of intraluminal sutures risks allowing microbial infection from the trachea to access the cartilage and perianastomotic tissues, and the tracheal lumen should be monitored postoperatively for this sequela. Excessive tension at the tracheal anastomosis site can cause acute dehiscence of the repair,1,4 and can also cause delayed postanastomotic stenosis.8 The latter occurs because excessive wound tension can be a stimulus for collagen formation and later circumferential contraction of this excessive collagen can cause formation of a circular cicatrix at the tracheal anastomosis.6,8 Consequently, minimizing tension at the site of tracheal anastomosis is important.4,7 Tracheal mobilization can be performed to varying degrees in people depending on the length of trachea resected and residual tracheal mobility.6 Tracheal mobilization by blunt dissection of the peritracheal tissues in a cranial and caudal direction can be performed to reduce anastomotic tension. In people, this can be complemented by release of the suprahyoid muscular attachments (i.e. “laryngeal release” or “laryngeal drop” techniques).5,6 Minimal tracheal mobilization was required for anastomosis in this horse, as only a single tracheal ring was resected and after dissection, the trachea was mobile at the surgical site. The use of stainless steel cerclage sutures around the tracheal cartilages immediately proximal, and distal, to the anastomosis greatly reduced tension on the tracheal mucosal sutures. In people, use of a Grillo suture, between the manubrium and chin, prevents the patient from extending their neck during the postoperative period5–7 and replication of this effect by use of a martingale has been described in horses.1,9 However, the use of a martingale in the immediate postoperative period has been associated with difficulty in standing1 and was not used in our horse. Feeding from shoulder height was performed postoperatively to minimize tension on the anastomosis. Tracheal tension increases with the number of tracheal cartilages resected. Successful anastomosis after resection of up to 5 tracheal cartilages has been experimentally performed in horses. Appositional forces approximately double with removal of 5 compared to 3 tracheal rings.1 Cryopreserved, irradiated, tracheal allografts have been used successfully in a limited number of human patients with severe subglottic tracheal stenosis13,14 and also experimentally in sheep; however, this technique does not appear to have been used in horses. Moderate tracheal stenosis developed at the anastomosis site in this horse because of the formation of a thin membranous intraluminal web (cicatrix). This may have been because of excessive granulation tissue at the anastomosis or suture sites, and/or by irritation from the tracheostomy tube placement. Laser ablation of early intratracheal stenotic lesions (composed mostly of granulation tissue) or of mature stenotic lesions that are
Rossdale and Partners, Rossdales Equine Hospital and Diagnostic Centre, Exning, United Kingdom ,2 Sycamore Lodge Equine Hospital, The Curragh, Ireland and 3 Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, University of Edinburgh, Roslin, Scotland, United Kingdom
Corresponding Author Timothy P. Barnett, BSc (Hons), Rossdale and Partners, Rossdales Equine Hospital and Diagnostic Centre, Cotton End Road, Exning, Suffolk, CB8 7NN, United Kingdom. E‐mail: [email protected] Submitted May 2013 Accepted January 2014 DOI:10.1111/j.1532-950X.2014.12270.x
Objectives: To report a resection and anastomosis technique to treat trauma‐induced tracheal stenosis. Study Design: Case report. Animals: A 9‐year‐old Warmblood gelding. Methods: Endoscopy, radiography, and ultrasonography were used to diagnose a single ring tracheal stenosis; the stenotic region was resected and adjacent tracheal rings anastomosed with an end‐to‐end technique. Results: The anastomosis healed completely despite formation of a unilateral partial mucosal stenosis “web,” which was subsequently removed by transendoscopic laser surgery. During tracheal anastomosis, the left recurrent laryngeal nerve was damaged, causing laryngeal hemiplegia, later treated successfully by laryngoplasty. The horse returned to its previous level of work. Conclusions: This tracheal resection and anastomosis technique successfully provided the horse with a large tracheal lumen, and despite major complications, allowed a return to full athletic work.
Tracheal obstruction, other than tracheal collapse, is uncommonly described in horses. Focal tracheal stenosis after tracheostomy,1,2 tracheal trauma, and neoplasia3,4 have been reported. Tracheal stenosis in adult people can occur after external trauma or prolonged endotracheal intubation, but can also occur after tracheostomy.5–7 Congenital tracheal stenosis is well described in infants5 but rarely recorded in animals.8 A surgical technique for equine tracheal resection and end‐to‐ end anastomosis has been reported in experimental and clinical cases of tracheal stenosis.1,4,9 Tracheal resection techniques are the treatment of choice in people with tracheal stenosis.6 We report our experience with successful treatment using an alternative surgical technique of tracheal stenosis involving a single ring in a horse caused by external trauma.
CLINICAL REPORT A 9‐year‐old Warmblood gelding successfully used for competitive driving at national level that had been rested for some months was heard to make abnormal inspiratory and expiratory noises at rest. The horse was otherwise normal, but these abnormal sounds increased in intensity over the next The work was performed at the Royal (Dick) School of Veterinary Studies.
2 weeks. On admission, there were no abnormal clinical findings except slightly increased abnormal resting inspiratory and expiratory sounds, audible a few meters from the horse. On resting endoscopy, marked stenosis (20% of normal cross‐sectional area) of the cervical tracheal lumen was present 60 cm caudal to the larynx. Endoscope passage through the strictured area showed that it was 2–3 cm long, and demonstrated that the more distal trachea and the main stem bronchi were normal in appearance. A 5–6 cm long linear scar was identified on left ventral aspect of the neck, at the level of the tracheal stenosis, suggesting external trauma caused the tracheal damage, but no history of neck trauma was reported. No other abnormal findings were identified in the upper airways. Ultrasonography of the caudoventral cervical area in a sagittal plane confirmed the presence of a 3 cm‐long, distinct hypoechoic defect in the ventral tracheal lumen, as indicated by the loss of the hyperechoic air‐tissue interface of the trachea. Moderate enlargement of 1 tracheal cartilage ring was evident, in addition to increased heterogeneity and slight enlargement of the adjacent sternothyrohyoideus muscles. Lateral radiographs revealed marked focal narrowing of the tracheal lumen ventral to 6th cervical vertebrae (Fig 1A). A well‐demarcated ventral protuberance of soft tissue opacity extended from the ventral tracheal surface into the tracheal lumen at this site, and there was poor definition of the caudal aspect of the tracheal ring immediately rostral to this lesion.
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
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Tracheal Resection and Anastomosis in a Horse
Barnett, Hawkes, and Dixon
Figure 1 (A) Preoperative laterolateral radiograph of the distal cervical trachea showing the tracheal defect with a localized soft tissue opacity protruding into the tracheal lumen. (B) Resected deformed tracheal ring with intraluminal cicatrix.
Surgical Procedures Because of the limited length of tracheal damage but marked airway compromise, complete resection of the stenotic area with end‐to‐end anastomosis of adjacent tracheal rings was performed. Neomycin (5 mg/kg) with procaine benzylpenicillin (10 mg/kg) was administered intramuscularly and flunixin meglumine 1.1 mg/kg intravenously (IV) preoperatively. After premedication with xylazine (1.1 mg/kg IV), general anesthesia was induced with ketamine (2.2 mg/kg IV) and diazepam (1 mg/kg IV) and maintained with isoflurane in oxygen. When extubation was required during surgery, anesthesia was maintained using combined 5% guaifenesin (1 L) with xylazine (500 mg) and ketamine (2 g) as a constant rate infusion (CRI; 2 mL/kg/h). The horse was positioned in dorsal recumbency with the neck extended and a temporary tracheostomy was created in the mid cervical region to allow an endotracheal tube to be temporarily inserted through the stricture into the distal trachea. Through an 16 cm long, ventral median incision directly over the affected trachea, dissection between the sternothyrohyoideus and use of hand held retractors revealed a depression in the annular ligament between 2 tracheal rings, and extensive scar tissue on the ventral aspect of this ligament, especially on the left side. The esophagus, locally adherent to the trachea, was dissected free. Identification of other structures including the recurrent laryngeal nerves and carotid sheaths were impaired by this fibrous tissue. The trachea was dissected free from the fibrous tissue on the left side. A 2nd tracheotomy
266
performed immediately cranial to the stricture to allow digital palpation of the stricture determined there was single tracheal ring involvement (Fig 1B). The affected ring was sharply dissected free from its proximal (using the 2nd tracheostomy site) and distal annular ligaments, preserving as much annular ligament and mucosa as possible. The proximal and distal tracheal ends were not secured and when the damaged tracheal ring was freed, the tracheal ends suddenly retracted >10 cm apart. Four, size 3 (6‐metric) stainless steel cerclage wires were loosely placed submucosally around the proximal and distal tracheal rings (1 ventral, 1 dorsal, 2 lateral—each side) to partially appose them. Simple interrupted 0 polyglactin 910 sutures were placed intraluminally, starting at the dorsal hemi‐ circumference of the trachea, to appose the tracheal mucosa that had focal areas of scarring to the adjacent tracheal rings. After closure of the dorsolateral mucosa, the 2 lateral cerclage wires were tightened with Axel wire twisters into the final position. The lateral and ventral tracheal mucosal sutures were then placed before tightening of the ventral stainless steel cerclage wire. Another temporary tracheotomy was created, 3 tracheal rings cranial to the anastomosis to allow a temporary tracheostomy tube to be positioned through the anastomosis site. A Penrose drain was placed in the skin incision, which was closed in 2 layers with 0 polyglactin 910. The more proximal tracheostomy was left to heal by second intention. Unassisted recovery from general anesthesia was uneventful. Neomycin/penicillin and metronidazole (15 mg/kg orally every 8 hours) was administered for 5 days, followed by trimethoprim‐potentiated sulphonamides (30 mg/kg orally twice daily) and metronidazole for a further 8 days. Flunixin meglumine (1.1 mg/kg IV twice daily) was administered for 3 days followed by phenylbutazone (2.2 mg/kg orally twice daily) for 4 weeks. All postoperative feeding was performed from shoulder height. Endoscopic assessment of laryngeal function the day after surgery showed left laryngeal hemiplegia (Havemeyer grade 4)10 in contrast to normal preoperative function, likely because of iatrogenic recurrent laryngeal nerve damage during surgery. The tracheostomy tube was removed at 13 days and the (distal) tracheostomy wound allowed to heal by second intention. Endoscopy on day 13 revealed a healing, but moderately inflamed, tracheal anastomosis with intraluminal penetration of the right lateral cerclage wire. The horse was discharged at day 19 and confined to a box stall for 3 weeks. At 6 weeks, all external surgical wounds had healed. On endoscopy, left laryngeal hemiplegia was still present and the tracheal anastomosis had healed further; however, a mucosal‐ covered web, 10 mm deep on the left lateral aspect of the anastomosis obstructed 1/3 of the tracheal cross sectional area (Fig 2A). Focal areas of granulation tissue surrounded the remnants of the mucosal polyglactin sutures, which were removed using transendoscopic biopsy forceps (Olympus biopsy forceps, 0.8 mm). The 2 tracheostomy sites were healing well with some mucosal thickening evident at the more distal site. Radiography showed that all steel sutures were intact (Fig 2B). Under general anesthesia, left laryngoplasty (using 2 stainless steel wire prostheses) and ventriculocordectomy and right ventriculectomy were performed.11 Hyperabduction of
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
Barnett, Hawkes, and Dixon
Tracheal Resection and Anastomosis in a Horse
Figure 2 (A) Endoscopic view of the tracheal anastomosis at 6 weeks postoperatively showing a membranous cicatrix on the left side. One stainless steel suture is penetrating the right ventral aspect of the tracheal lumen. (B) Laterolateral radiograph of the tracheal anastomosis at 6 weeks showing the 4 stainless steel wires in situ. (C) Endoscopic view at 12 weeks, after laser transection of the cicatrix, and (D) at 27 weeks showing slight narrowing of the tracheal lumen with complete mucosal healing present.
the left arytenoid (grade 1 post laryngoplasty)11 was performed to counteract the anticipated loss in abduction because of sutures cutting into the left cricoarytenoideus dorsalis muscle. Endoscopy 7 days later surgery showed grade 3 arytenoid abduction11 and the focal tracheal inflammation at the anastomosis site had improved after suture removal. In addition to routine perioperative medication and management,11 the horse was discharged on a 4 week course of phenylbutazone (2.2 mg/kg orally once daily). Examination 5 weeks later showed the laryngoplasty incision to have healed well and on endoscopy, there was no further loss in abduction. The membranous tracheal web at the anastomosis site was transected with the horse sedated and using topical local anesthesia (20 mL 2% lidocaine) and a transendoscopic contact diode laser (15 W for 30 seconds) (Fig 2C). The horse was confined to a stall for 2 weeks before gradual return to exercise. The horse was back in full work and competing 13 weeks later when a repeat examination was requested because of a single episode of increased respiratory noise at exercise. Endoscopy showed laryngoplasty abduction to be unchanged (grade 3)11 and a well healed tracheal anastomosis (Fig 2D) with very mild luminal narrowing because of a small circumferential rim of everted mucosa.
Increased tracheal mucopurulent respiratory secretions (grade 3/5) were observed. The horse was discharged with instructions to increase the level of fitness and monitor the respiratory noise. The horse competed successfully; however, increased respiratory noise and effort was reported toward the end of the season. Nine months after initial surgery, during exercise, there was increased respiratory noise that was most obvious on inspiration. Endoscopy revealed further loss (grade 4) of abduction. The tracheal anastomosis was unchanged, and radiography confirmed intact, correctly placed tracheal sutures. A slight (grade 1/5) accumulation of tracheal secretions was identified caudal to the anastomosis. After training, high‐speed treadmill video‐endoscopy, initially of the larynx, and then for a short period of the trachea just cranial to the anastomosis, was performed. The left arytenoid remained in a fixed position during exercise. Some vibration of the left sided rim of tracheal mucosa at the anastomosis was observed. Whereas this was not thought to be causing an airway obstruction, tissue vibration could have been attributing to the noise. The mucosal fold was transected using transendoscopic contact diode laser (1 W for 20 seconds) after local anesthesia, with the horse standing sedated. Postexercise tracheal wash revealed increased
Veterinary Surgery 44 (2015) 265–269 © Copyright 2014 by The American College of Veterinary Surgeons
267
Tracheal Resection and Anastomosis in a Horse
Barnett, Hawkes, and Dixon
neutrophils and on bronchoalveolar lavage cytology there were 12% mast cells, indicating the likely presence of immune‐ mediated inflammatory airway disease. The horse was discharged with a course of oral prednisolone (initial dose 1 mg/kg orally once daily for 2 weeks then tapering over 4 weeks to discontinue). The horse then returned to full work and has competed well, winning national level driving championship competitions. Exercising endoscopic examination of the upper airway 16 months after laryngoplasty, using over‐ground endoscopy, revealed continued grade 4 laryngoplasty abduction with stability of the arytenoid cartilage and no other upper airway problems.
DISCUSSION External trauma can cause tracheal cartilage and mucosal disruption with hematoma formation. In addition to permanent cartilage deformation, subsequent organization of the traumatized area with scar tissue formation can result in increased intraluminal tissue and tracheal stenosis.5 The presence of a cervical scar overlying the region of tracheal stenosis in this horse and the severe and localized nature of the tracheal injury in a previously normal horse indicate that external trauma likely caused the tracheal stenosis. The timescale between likely injury and the relatively acute onset of signs is unknown, but was probably some months’ duration, given the degree of fibrosis at the tracheal stricture. In sedentary dogs and cats, tracheal stenosis causing up to 80% reduction of luminal diameter may be well tolerated8 but this horse even had some stridor at rest. Stenosis of the cervical trachea can cause abnormal inspiratory effort and stridor with affected tracheal sites subject to higher velocity, and potentially more turbulent airflow8 that can potentially cause additional inflammation at the stenotic site. Continued circumferential fibrosis and stricture development is the likely reason for the progression of clinical signs in this horse. Various surgical techniques for tracheal resection and end‐ to‐end anastomosis have been described in human surgery including incising the adjacent annular ligaments and splitting of cartilage rings. Suture techniques include full thickness or submucosal sutures with continuous or interrupted patterns, with or without use of tension sutures.12 A comparison of suture material and suture pattern techniques (polypropylene, simple continuous; polyglactin 910 and polydioxanone, simple interrupted) using full thickness bites found comparable tracheal cross sectional areas and inflammatory reactions (mild) at the anastomosis sites in all groups.12 Tate et al.1 described a tracheal resection technique in experimental horses using annular ligament transection with mucosal eversion before partial thickness anastomosis of the tracheal segments using stainless steel sutures through the cartilage, everted mucosa, and adventitia. They proposed that this technique would reduce mucosal granulation tissue because of the absence of intraluminal sutures. Behrand and Klempnauer12 suggested that the suture material and technique used to achieve tracheal anastomosis are of secondary importance, but other technical
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details such as accurate approximation of the tracheal ends, creation of an airtight seal, ensuring overlap of the membranous part of the trachea, whilst preventing overlap of the cartilaginous rings are of greater importance. In this horse, localized inflammation was present around some of the tracheal mucosal sutures 4 weeks after surgery, and resolved when these sutures were removed. The use of intraluminal sutures risks allowing microbial infection from the trachea to access the cartilage and perianastomotic tissues, and the tracheal lumen should be monitored postoperatively for this sequela. Excessive tension at the tracheal anastomosis site can cause acute dehiscence of the repair,1,4 and can also cause delayed postanastomotic stenosis.8 The latter occurs because excessive wound tension can be a stimulus for collagen formation and later circumferential contraction of this excessive collagen can cause formation of a circular cicatrix at the tracheal anastomosis.6,8 Consequently, minimizing tension at the site of tracheal anastomosis is important.4,7 Tracheal mobilization can be performed to varying degrees in people depending on the length of trachea resected and residual tracheal mobility.6 Tracheal mobilization by blunt dissection of the peritracheal tissues in a cranial and caudal direction can be performed to reduce anastomotic tension. In people, this can be complemented by release of the suprahyoid muscular attachments (i.e. “laryngeal release” or “laryngeal drop” techniques).5,6 Minimal tracheal mobilization was required for anastomosis in this horse, as only a single tracheal ring was resected and after dissection, the trachea was mobile at the surgical site. The use of stainless steel cerclage sutures around the tracheal cartilages immediately proximal, and distal, to the anastomosis greatly reduced tension on the tracheal mucosal sutures. In people, use of a Grillo suture, between the manubrium and chin, prevents the patient from extending their neck during the postoperative period5–7 and replication of this effect by use of a martingale has been described in horses.1,9 However, the use of a martingale in the immediate postoperative period has been associated with difficulty in standing1 and was not used in our horse. Feeding from shoulder height was performed postoperatively to minimize tension on the anastomosis. Tracheal tension increases with the number of tracheal cartilages resected. Successful anastomosis after resection of up to 5 tracheal cartilages has been experimentally performed in horses. Appositional forces approximately double with removal of 5 compared to 3 tracheal rings.1 Cryopreserved, irradiated, tracheal allografts have been used successfully in a limited number of human patients with severe subglottic tracheal stenosis13,14 and also experimentally in sheep; however, this technique does not appear to have been used in horses. Moderate tracheal stenosis developed at the anastomosis site in this horse because of the formation of a thin membranous intraluminal web (cicatrix). This may have been because of excessive granulation tissue at the anastomosis or suture sites, and/or by irritation from the tracheostomy tube placement. Laser ablation of early intratracheal stenotic lesions (composed mostly of granulation tissue) or of mature stenotic lesions that are
