Tubeless Tracheotomy for Survival Airway Surgery in the Leporine Model

Transcription

1 The Laryngoscope VC 2014 The American Laryngological, Rhinological and Otological Society, Inc. Tubeless Tracheotomy for Survival Airway Surgery in the Leporine Model Maurits S. Boon, MD; James J. Daniero, MD; Shivam Saxena, BS; Mark Balceniuk, BS Objectives/Hypothesis: The ideal animal experimental tracheostomy technique is one that is 1) safe and easy to perform, 2) requires no tracheostomy tube, and 3) requires minimal cleaning or suctioning to maintain patency. The leporine model for airway injury has been well established and offers an inexpensive and practical animal model for experimental evaluation. However, previous research has demonstrated a high mortality rate with survival airway surgery in rabbits. This study demonstrates the feasibility of airway management in the leporine model using a simple maturing suture tracheostomy that avoids a tracheostomy tube. Study Design: Tracheostomy was performed in six New Zealand white rabbits in the setting of survival surgery over a 2-week study period. Methods: A vertical tracheal incision was made from the second to the sixth tracheal ring. The anterior portion of the tracheal rings was removed and the skin surrounding the stoma was sutured down to the tracheal wall. The lateral tracheal wall was then suspended to the soft tissue in the lateral neck. Results: All six rabbits survived the study period with minimal care and maintained stoma patency until sacrifice. Granulation tissue and edema were noted during the first week and largely resolved by the second week. An average of 5-mmdiameter stoma was measured 14 days after surgery without intraluminal stenosis or laryngeal edema. Conclusions: This method meets the defined criteria for the ideal experimental tracheostomy, demonstrating potential benefit in a laryngotracheal stenosis model and a rabbit model of evoked phonation. Key Words: Tracheostomy, laryngeal stenosis, tracheal stenosis, rabbit model, survival surgery. Level of Evidence: NA Laryngoscope, 125: , 2015 INTRODUCTION Laryngeal and tracheal research in animals involving survival surgery often requires a permanent tracheostomy to develop the model and for airway protection. Three key factors were identified by Dahm and Paniello in creating the ideal experimental tracheostomy technique in animals; one that is safe and easy to perform, requires no tracheostomy tube, and is low maintenance, requiring minimal cleaning or suctioning. 1 The leporine model for airway injury has been well established and offers an inexpensive and less cumbersome animal model for experimental evaluation than the canine model. However, previous research (unpublished data) and the published studies of others have demonstrated a high mortality rate with survival airway surgery in rabbits. 2 4 This can present difficulty with Institutional From the Department of Otolaryngology Head & Neck Surgery (M.S.B., J.J.D.), Thomas Jefferson University, Philadelphia, Pennsylvania; Thomas Jefferson University, Jefferson Medical College (S.S., M.B.), Philadelphia, Pennsylvania, U.S.A. Editor s Note: This Manuscript was accepted for publication September 16, The authors have no funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Maurits S. Boon, MD, Department of Otolaryngology Head and Neck Surgery, Thomas Jefferson University Hospital, 925 Chestnut Street, 7th Floor, Philadelphia, PA maurits.boon@jefferson.edu DOI: /lary Animal Care and Use Committee (IACUC) approval and study design. The tubeless canine tracheostomy was introduced in 1963 by Thilenius and Vial and further improved by Miles in More recently, in 1998 this technique was modified by Dahm and Paniello to create a canine induced phonation model. 6 However, to our knowledge, no study has described a technique to create a sustainable tubeless tracheostomy in the leporine model. In 1981, Natvig and Olving compared different tracheostomy techniques and their associated development of tracheal stenosis in New Zealand white rabbits. 7 The New Zealand rabbit is considered the animal of choice for similar airway studies because it has been used in prior airway research, is inexpensive, and serves as a model for the human neonate. 2,3,8,9 The rabbit and the human neonatal trachea have a comparable average tracheal lumen diameter of 6 mm. 10 This study aimed to demonstrate the feasibility of airway management in the rabbit model using a maturing suture tracheostomy technique to create a permanent, low maintenance, and sustainable tubeless stoma for the study of laryngotracheal pathology. The animals themselves maintain airway patency with a tubeless stoma. Moreover, with a patent bare stoma, obstructive postsurgical complications are reduced and minimal postoperative care is required. This method meets the previously defined criteria for the ideal experimental tracheostomy and also demonstrates potential for

2 Fig. 1. Humidified air delivered directly to rabbits to reduce airway crusting. [Color figure can be viewed in the online issue, which is available at laryngotracheal stenosis model as well as an induced phonation model. 6,11 MATERIALS AND METHODS Six New Zealand white rabbits were obtained and housed at Thomas Jefferson University Animal Laboratory. Approval for this study was granted by the IACUC, which monitored all of the described procedures. The decision to use six rabbits was made upon recommendation of the biostatistics department based on the senior author s previous research in rabbit tracheostomy and based on the pilot nature of the study. After an initial 1-week quarantine period, each animal underwent an additional week of acclimation that included daily handling of the rabbits, introducing humidifiers, and the intermittent sound of a portable suction machine. Room humidifiers were modified with corrugated aerosol tubing to directly deliver humidified air to each animal (Fig. 1). This was utilized to help reduce postoperative crusting resulting from dry air bypassing the moisture rich mucous membranes of the upper airway. After this acclimation period, the procedures were performed in sets of two rabbits to minimize the postoperative care and maximize monitoring due to limited personnel. Each procedure took approximately 15 minutes to complete, and 3 operative days were sufficient to perform tracheotomies in all of the animals. The rabbits were administered general anesthesia with intramuscular ketamine hydrochloride (40 mg/kg) and intramuscular xylazine (4.0 mg/kg) to enhance analgesia. Spontaneous respiration was maintained throughout the procedure with continuous pulse oximetry to monitor the heart rate and oxygen saturation. The rabbit was placed supine, and the anterior cervical area was shaved and prepped with povidone-iodine solution. After prepping and draping in the usual sterile fashion, a 2-cm-horizontal incision was made in the midline of the neck below the level of the cricoid cartilage. The underlying strap muscles were dissected bluntly to expose the trachea below the level of the cricoid cartilage. A vertical tracheal incision was then made from the second tracheal ring inferiorly to the sixth tracheal ring. The anterior quarter of the tracheal rings were removed, preserving as much mucosa as possible. The skin surrounding the stoma was sutured down to the tracheal wall with 4-0 polyglycolic acid suture to mature the stoma in a similar technique to the one described by Miles. 5 The lateral tracheal wall was then sutured more laterally in the neck skin to secure the trachea in a superficial position. Of note, the technique employed in rabbit 6 used 4-0 polydiaxanone rather than the 4-0 polyglycolic acid suture used in the preceding procedures due to granulation noted with the prior suture. This technique was chosen to avoid obstruction and reapproximation of the stoma edges given redundant soft tissue and flexed position of the rabbit neck. A fentanyl patch applied for the first 72 hours provided postoperative analgesia. A single dose of 0.1 mg/kg buprenorphine was administered during the procedure to cover the first 12 hours while fentanyl levels were subtherapeutic. Postoperative care involved hourly wound and airway checks by medical professionals including veterinary technicians, physicians, and medical students for the first 24 hours. The airway and wound checks proceeded with decreasing frequency over the first week until maintained at every six hours. During airway checks, rabbits were evaluated for any signs of respiratory distress and suctioned of any potentially obstructing sputum and blood clots using an 8-French catheter. The data points recorded for each rabbit included: initial and final stoma diameter, patency of stoma at 1 and 2 weeks, degree of peristomal edema and granulation at 1 and 2 weeks, and degree of intraluminal tracheal stenosis in the excised trachea (Table I). Edema and granulation were graded as follows: minimal, with 0% to 10% of the circumference involved; mild, with 10% to 25% involvement; moderate, with 25% to 50% involvement; and severe, with >50% involvement in stoma circumference. Luminal stenosis was graded with a modification of the Cotton-Meyer scoring system for subglottic stenosis, adding the designation of none when no appreciable stenosis was noted (I 5 0% 50%, II 5 51% 70%, III 5 71% 99%, and IV 5 no identifiable lumen). 12 After 2 weeks of successful maturation, the stoma healed to a satisfactory condition, and the animals were sacrificed. Euthanasia was performed with sodium pentobarbital overdose in a concentration of 150 mg/kg. Laryngotracheotomy was performed to examine the laryngotracheal complex ex vivo and allowed for detailed evaluation of the larynx, tracheal wall integrity, and tracheal lumen. Photo documentation was performed 1 week postoperatively and at time of sacrifice to help standardize subjective assessments of the stoma. Upon completion of the study, a cost analysis was performed comparing the leporine to the canine model. The data for this assessment were obtained from the institutional veterinary department and took into consideration: purchase costs, routine daily care, anesthetic care, and postoperative monitoring (Table II). All standard sterile technique and universal precautions were maintained during surgical procedures and the handling of animals. IACUC research veterinarian faculty and veterinary technician staff attended all procedures and provided anesthesia, analgesia, and euthanasia services. RESULTS All six rabbits survived the 2-week study period with minimal care and maintained stoma patency until sacrifice. Despite the intensive monitoring protocol established, one rabbit experienced a respiratory event. Rabbit 6 required airway suctioning on postoperative day 2 due to mild respiratory distress resulting from blood-tinged mucus in the distal trachea. This was presumed to be due to aspiration of blood during the procedure. The respiratory difficulties resolved after this intervention and this rabbit did not require any further intervention. Granulation tissue and edema was noted in all rabbits during the first week, but had largely 681

3 TABLE I. Rabbit Trachea Evaluation Data. Rabbit Initial Length, mm Initial Width, mm Final Length, mm Final Width, mm Patency Patency Granulation, Granulation, Edema Edema Luminal Stenosis % 75% Moderate Minimal Moderate Mild None % 50% Minimal Minimal Moderate Mild None % 50% Moderate Moderate Severe Moderate None % 25% Moderate Moderate Moderate Mild I % 75% Minimal Moderate Minimal None None 6* % 75% Minimal None Moderate None None The stoma was sized at completion of initial tracheotomy (initial length) and immediately prior to sacrifice (final length). Edema and granulation were graded as: minimal, with 0% to 10% of the circumference involved; mild, with 10% to 25% involvement; moderate, with 25% to 50% involvement; and severe, with >50% involvement in stoma circumference. Luminal stenosis was graded with a modification of Cotton-Meyer scoring system for subglottic stenosis adding the designation of none when no appreciable stenosis was noted (I 5 0% 50%, II 5 51% 70%, III 5 71% 99%, and IV 5 no identifiable lumen). *Rabbit 6: 4-0 polydiaxanone suture was used for maturing and lateral support. TABLE II. Comparison of Costs of the Rabbit Versus Canine Model. Item Cost Multiplier Usage Cost Rabbit model Rabbit purchase $ rabbits $ Rabbit per diem $ Average 30 days alive $ OR time $35.00/hour 6 3 procedures for 1 hour $ Scalpel $ procedures/rabbit $18.00 Suture $ box for all procedures $ Sterile processing $ procedures/rabbit $ Humidifiers $ per cage $ OR disposable costs $ procedures/rabbit $1, Fentanyl patches $ per rabbit $90.00 Buprenex $7.50/mL 6 1 ml/rabbit with two procedures $90.00 Ketamine $1.50/mL ml/rabbit with two procedures $27.00 Postoperative care $35.00/hour 6 4 hours postoperative care $ Total cost $4, Cost per rabbit $ Dog model Dog purchase $ dogs $5, Dog delivery fee $ dogs $ Dog per diem $ Average 30 days alive $1, OR time $35.00/hour 6 3 procedures for 1 hour $ Scalpel $ procedures/dog $18.00 Suture $ box for all procedures $ Sterile processing $ procedures/dog $ Humidifiers $ per cage $ OR disposable costs $ procedures/dog $1, Fentanyl patches $ per dog $90.00 Buprenex $7.50/mL 6 10 ml/dog with two procedures $ Ketamine $1.50/mL 6 15 ml/dog with two procedures $ Postoperative care $35.00/hour 6 4 hours postoperative care $ Total cost 12, Cost per dog $2, Difference per animal $1, Cost data were obtained from the institutional veterinary department. OR 5 operating room. 682

4 Fig. 2. Rabbit 6 with edema and erythema at 1 week postoperatively (left) and resolution at 2 weeks (right). [Color figure can be viewed in the online issue, which is available at com.] resolved by the second week. An average stoma diameter of 5 mm, maintaining an average of 70% of the initial diameter, was measured 14 days after surgery (Table I). Rabbit 6, sutured with 4-0 polydiaxanone suture, showed limited granulation tissue and inflammation at both 7 and 14 days (Fig. 2). Upon ex vivo examination, minimal to no intraluminal stenosis was observed in any of the rabbits despite varying levels of granulation tissue at the level of the stoma (Fig. 3). Cost analysis of the leporine versus canine model yielded a difference of $1, per animal. Total costs of identical studies were $4, and $12, for the rabbit and dogs study, respectively (Table II). Charges for operative instruments, sutures, and postoperative care were identical. DISCUSSION The New Zealand white rabbit provides a suitable and inexpensive animal model for airway research due to the similarity of its trachea to the human neonate. 8 Developing a method of permanent tracheostomy is essential to creating an animal model for laryngeal and tracheal research. However, successful maintenance of a long-term, stable tracheostomy in animals can pose significant difficulty due to the airway anatomy and intensive postoperative care that is required. The canine trachea is the most commonly used animal model previously described in studies. Although it still has a role in airway research, costs can pose a significant impediment to routine use. In contrast, the leporine model is relatively inexpensive. This is formally analyzed in Table II, in which a cost breakdown comparison is made between rabbits and dogs if an identical study were to be performed in each animal. The relative cost difference per animal was $1, This variance was attributable primarily to purchase and daily care, with less significant factors related to cost of intraoperative medications. The increased cost reflects heavily in the choice of an animal for research and is an additional reason to optimize the leporine model for airway research. Although published data on performance of rabbit tracheostomy exist, mortality rates vary from 10% to 33%, and previous studies describe placement of an indwelling tube. 2 4 Utilization of a tubeless tracheostomy technique has previously been described in the canine model. 1,5 However, no such published data exist for the leporine model. In this study, a method of creating a sustainable tubeless tracheostomy is described for the leporine model. The technique requires little time, is technically uncomplicated, and is replicable. The technique is similar to previous reports creating a vertical incision in the trachea between the second and sixth tracheal ring. Once a stoma is created, an indwelling tracheostomy tube is not placed. Instead, the trachea is sutured to the surrounding skin of the neck, and additional sutures are placed between the lateral wall of the trachea and the more lateral neck skin to maintain a more superficial position of the trachea. The result was a sustainable stoma with no mortality in any of the animals and only one respiratory event that was addressed with limited intervention. Fig. 3. Ex vivo examination of the laryngotracheal complex in rabbit 5 revealed a patent stoma (left) and no evidence of laryngeal edema or tracheal stenosis (right). [Color figure can be viewed in the online issue, which is available at 683

5 The method of a vertical incision in the trachea was chosen, because it parallels a technique described and utilized in previous rabbit research, as well as neonatal tracheostomy, and is straightforward to apply. 1,2 The authors acknowledge that other tracheostomy techniques exist and might have utility and even advantages for this model. Further study would be warranted to identify the optimal technique. Initially, all rabbit stomas developed some degree of granulation tissue and edema with impact on the size of the stoma (Table I). However, despite some narrowing, all animals maintained airway patency, and by week 2 nearly all rabbit stomas had improved toward their original operative size. Of note, in the final animal, a polydiaxanone suture was utilized as compared to the polyglycolic acid sutures used in previous animals. Although less edema and granulation tissue occurred in this animal, it is not known whether this finding was a result of the use of different suture material. As mandated by the IACUC, the initial postoperative monitoring was intensive, requiring hourly checks for each of the animals. This level of monitoring places a burden on the research team and can increase costs if dedicated animal personnel are employed. With the development of a large and stable stoma, the placement of a tracheostomy tube can be avoided, limiting the direct irritation secondary to the tube and reducing the mucusinducing properties of a foreign body in the airway. Only one airway event occurred during this monitoring period in the six rabbits, so it may be possible that less intensive monitoring would be acceptable to an IACUC. The major limitation of the study was a small number of study subjects. However, based on previous studies describing use of an indwelling tracheostomy tube, as well as experience in the senior author s laboratory with an indwelling tracheotomy tube (unpublished research), the data would suggest that this technique is still valid. 2,7 CONCLUSION This study demonstrated the feasibility of airway management in the rabbit model using a using a maturing suture tracheostomy technique to create a permanent and sustainable tubeless stoma for the study of laryngotracheal pathology in the setting of survival surgery. This method meets the previously defined criteria for the ideal experimental tracheostomy and also demonstrates potential for a laryngotracheal stenosis model and an induced leporine phonation model. 6,11 Furthermore, the model s ease of use and substantial cost savings in comparison to the prevalent canine model should make study of laryngotracheal pathology more accessible to a larger number of research institutions. Acknowledgments The authors thank Elizabeth Duddy, RN, for her assistance with coordinating the study logistics and IACUC application. We would also like to thank the medical students who volunteered time to care for the rabbits postoperatively: Ryan McSpadden, MD, Sriharsha Gummadi, BS, and Fahim Hashmi, BS. BIBLIOGRAPHY 1. Dahm JD, Paniello RC. Tracheostomy for long-term laryngeal experimentation. Otolaryngol Head Neck Surg 1998;118(3 pt 1): Nakagishi Y, Morimoto Y, Fujita M, Ozeki Y, Maehara T, Kikuchi M. Rabbit model of airway stenosis induced by scraping of the tracheal mucosa. Laryngoscope 2005;115: Steehler MK, Hesham HN, Wycherly BJ, Burke KM, Malekzadeh S. Induction of tracheal stenosis in a rabbit model endoscopic versus open technique. Laryngoscope 2011;121: Yildirim G, Haliloglu T, Sapçi T, et al. Tracheal reconstruction with porous high-density polyethylene tracheal prosthesis. Ann Otol Rhinol Laryngol 2000;109(10 pt 1): Miles WK. Tubeless canine tracheostomy for laryngeal experimentation. Arch Otolaryngol 1970;92: Paniello RC, Dahm JD. Long-term model of induced canine phonation. Otolaryngol Head Neck Surg 1998;118: Natvig K, Olving JH. Tracheal changes in relation to different tracheostomy techniques. (An experimental study on rabbits). J Laryngol Otol 1981;95: Miller FR, Guay ME, Bauer T, Tucker HM. Long-term flap tracheostomy in a pediatric animal model. Arch Otolaryngol Head Neck Surg 1995; 121: Baek C-H, Chung Y-J, Jeong H-S, Kim S-W. Comparison of open dilatational tracheostomy with conventional pediatric tracheostomy in a growing animal model. Laryngoscope 2005;115: Loewen MS, Walner DL. Dimensions of rabbit subglottis and trachea. Lab Anim 2001;35: Swanson ER, Abdollahian D, Ohno T, Ge P, Zealear DL, Rousseau B. Characterization of raised phonation in an evoked rabbit phonation model. Laryngoscope 2009;119: Myer CM, O Connor DM, Cotton RT. Proposed grading system for subglottic stenosis based on endotracheal tube sizes. Arch Otolaryngol 1194; 103(4 pt 1):