Development of a Rapid, Safe, Fiberoptic Guided, Single-Incision Cricothyrotomy Method using a Large Ovine Model: A Pilot Study.

Authors: Lorenzo Paladino, M.D.1, James DuCanto, M.D. 2,

Seth Manoach, M.D. 1

1. Department of Emergency Medicine, SUNY Downstate Medical Center (450 Clarkson Avenue, Box 1228 Brooklyn, NY 11203.2. Departments of Anesthesiology, Medical College of Wisconsin (8701 Watertown

Plank Road, Milwaukee, WI 53226), and Aurora St. Luke's Medical Center (2900 West Oklahoma Ave., Milwaukee, WI 53213).

Abstract:

We present a pilot study in which we use an Ovine model to develop a rapid, safe cricothyrotomy (CT)technique utilizing a fiberoptic stainless steel optical stylet as a delivery system for a Melker 5.0 cricothyrotomy catheter. This technique is referred to as the “Single-Incision Cricothyrotomy with Fiberoptic Stylet” or SICFOS, and it requires a single incision followed by passage of the optical stylet through the incision in the CT membrane. The optical stylet allows visual confirmation of intra-tracheal placement, and easy placement of the Melker cricothyrotomy catheter.

During our pilot study, we discovered three additional methods of confirming intra-tracheal placement of the optical stylet in the event that the optics of the scope were occluded due to blood or secretions (tactile trapping of the scope tip between tracheal rings and their connective membranes, trans-illumination of the trachea in the midline, and stylet-driven tracheal displacement from side to side).

The principal strengths of the SICFOS technique are that it permits visual confirmation of intra-tracheal placement of the guiding stylet, as well as providing a reliable method of entering the trachea through a single puncture incision. The Melker catheter is advanced into the trachea over the optical stylet, following confirmation of intra-tracheal placement.

The SICFOS procedure was successful in each of the four experimental subjects, and none of the animals were subjected to hypoxemia greater than 60 seconds during all 4 of the procedures.

We recorded this process on video to facilitate the development of the procedure and to allow others to replicate it for further research or refinement. All devices used in this technique are currently employed in clinical practice.

Methods:

We performed the SICFOS procedure in 4 anesthetized sheep, introducing several subtle variations into the technique which allowed us to explore methods that maximized the speed of the procedure, demonstrated areas that create pitfalls for the technique, and optimized the various methods of intra-tracheal confirmation using the video recording of confirmation methods.

We recorded each case using a 4-channel digital video recorder, along with the audio of the investigators' discussions during the experiment.

Results:

After making a single scalpel incision in the cricothyroid membrane of the sheep, we inserted the optical stylet and confirmed intra-tracheal placement by visualization, transillumination, "click" palpation, and gentle stylet-driven tracheal displacement. We passed the cricothyrotomy tubes without difficulty and easily ventilated the animals.

Specific time points during the procedure were noted later following review of the video footage from the procedures. The time points of interest were:

1. Time to create incision in cricothyroid membrane (or incision time),2. Time to pass optical stylet through CT membrane (stylet insertion time),3. Time to visual identification of tracheal placement (Tracheal ID time),4. Time to advancement of the Melker CT catheter (Melker advancement time),5. Time to ventilation through Melker CT catheter.

Conclusion:

The SICFOS procedure is rapid, incorporates redundant safety features, and uses equipment increasingly available to anesthesiologists, emergency physicians, intensivists and surgeons. The promising outcome of this pilot study should be verified in a larger controlled, comparative trial.

Introduction:

Improved primary airway management techniques have decreased the incidence of cricothyrotomy in Emergency Medicine and Anesthesiology.1,2 Inexperienced personnel have difficulty performing standard surgical and wire-guided seldinger procedures.3 Despite all the recent historical improvements in airway management, patients with significant supraglottic pathology may still require emergent cricothyrotomy. As a result, investigators continue to suggest modifications to existing techniques of cricothyrotomy to simplify and accelerate the technique.4

Our research5 and clinical experience6 leads us to believe that optical stylets can facilitate relatively easy, safe, and fast cricothyrotomies in anatomically challenging patients who fail intubation through conventional as well as alternative methods.

Optical stylets are stainless steel, self contained endoscopes that function as stylets for tracheal intubation alongside laryngoscopes during direct laryngoscopy, or they can be utilized independently in the same manner as a flexible fiberoptic bronchoscope. These devices are inexpensive, firm, narrow (4.8-5 mm outer diameter), offer precise control, and closely match the inner diameter of cuffed seldinger-kit cricothyrotomy tubes. Optical stylets have been used to facilitate percutaneous dilatational tracheostomy procedures18, but to date, they have not been described as being used to perform percutaneous cannulation of the airway.

Our pilot study suggests that clinicians could insert a 5 mm optical stylet through the cricothyroid membrane after a single incision, perform both visual and tactile confirmation maneuvers for redundant safety, and advance a Melker 5.0 CT ventilation catheter without a separate dilation maneuver.

We performed a pilot study of optical stylet-guided cricothyrotomy in sheep using the Levitan optical stylet paired with the Melker 5.0 CT catheter. The purpose of the study was to develop this novel approach in a relevant live model and present a standard method to other clinicians and investigators, who may wish to compare it with existing approaches to cricothyrotomy or further refine the technique.

Methods:

Choice of Animal Model:We used a live anesthetized animal model to simulate

the adverse conditions we would anticipate to encounter during actual clinical use: bleeding at incision site and into the trachea, mucous soiling, and other conditions that only such models can duplicate. We chose 61-74 kilogram sheep (Barton West End Facilities, Oxford NJ) because we have experience working with them,5,7 they provide a well-accepted model of human airway and respiratory physiology and pathophysiology,8,9,10,11,12,13 and the anatomic dimensions relevant for modelling cricothyrotomy are comparable to humans.14,15

The most detailed paper on comparative anatomy utilized sheep larynxes obtained from a slaughterhouse and human cadaver data from an earlier publication.15,16 Although there were meaningful differences in laryngeal anatomy, the dimensions relevant to this work were similar. The anterior-posterior diameter of the inferior aspect of the ovine thyroid cartilage was slightly smaller than the male human specimens. The superior border of the ovine cricoid ring was slightly larger in sheep. Lateral dimensions measured at the inferior cornu and across the superior border of the cricoid ring were also comparable.

Because the ovine larynx specimens were obtained from a slaughterhouse (likely near the University of Iowa15) the authors do not provide sheep weights. The US Department of Agriculture reports that the average live weight of sheep slaughtered in the US is 142 pounds17, close to that of the sheep used in the present study.

Care of Animal Participants This study was approved by the SUNY Downstate

Medical Center Animal Care and Use Committee as well as the Institutional Review Board of this institution.This study followed American Association for Laboratory Animals care guidelines.

Melker Cuffed Emergency Cricothyrotomy Catheter SetManufactured and supplied by Cook Medical

(Indianapolis, IN), this kit consists of a pre-shaped airway catheter approximately 87.5 mm in length, (109 mm in total length including the integral female 15 mm connector), whose internal diameter measures 5 mm (15 french, or 0.197 inches) and whose outer diameter measures 7.40 mm (approximately 22 french, or 0.288 inches) at its widest point. The catheter comes supplied with a 14 french dilator of 12 cm length, 2 needles for CT membrane puncture, a short #15 scalpel blade and a guide wire of 0.038 inch diameter, 40 cm in length. The short scalpel blade was utilized during the SICFOS procedure on sheep #2 to investigate its effectiveness.

Levitan Optical StyletManufactured by Clarus Medical (Minneapolis,

MN), this device is a fully self contained fiberoptic scope approximately 30 cm in length, 40 cm including eyepiece and illumination interface. The stylet is approximately 5 mm at its distal rounded tip, and immediately decreases in diameter to 4 mm proximal to this tip along the distal on-third of the stylet to allow for this length of the stylet to be malleable. The optical stylets used in this study were the personal property of Dr. DuCanto.

Multi-Channel Digital Video Recorder We used a 4 channel digital video recorder (Model

DMR-5, Supercircuits, Austin, Texas) to display and collect all images. The recorder employed a capture rate of 30 frames/second with an overall resolution of 720 x 480 lines/inch for all 4 channels. This device integrated the images of the two exterior cameras and the two endoscopic images into the same monitor display. Stryker model 810 medical endoscopy cameras were used to collect images from the optical stylets.

Development and Documentation of the Technique Following the establishment of the proper depth of

anesthesia, monitoring, vascular access and airway control in the experimental animals, the equipment was readied for use.

The Levitan optical stylet (Clarus Medical, Minneapolis MN) was loaded with a Melker 5.0 mm ID cuffed cricothyrotomy tube (Cook, Bloomington IN), its light source and video connections checked, and the video recording system was activated to record as many details as possible.

We then performed a cricothyrotomy by palpating the cricothyroid membrane, making a single horizontal incision through it, then inserting the Levitan optical stylet through the incision and cricothyroid membrane, and confirming tracheal placement.

We then advanced the pre-loaded Melker 5.0 mm ID cuffed cricothyrotomy tube over the fiberoptic stylet (figure 1), and withdrew the stylet. To clear the optical stylet of blood and mucus, we wiped the lens against the tracheal mucosa. This method is routinely used by otolaryngologists during endoscopic nasal sinus surgery.

Results: Sheep #1:

Utilizing a #20 scalpel, a single incision was performed in the cricothyroid membrane, and the optical stylet was inserted the stylet into the trachea. Time to placement of the Melker tube was 8.3 seconds, including 4.3 seconds to make the #20-blade stab incision, and 4.1 seconds to insert the optical stylet and advance the tube.

Time to ventilation, including inflating the cuff and connecting the ventilation bag, was 28 seconds.

Visualization through the primary optical stylet was not utilized in this experimental subject. Confirmation of tracheal placement was performed with a second optical stylet placed through a tracheostomy incision prior to the start of the cricothyrotomy procedure.

Sheep #2: The #15 scalpel blade was utilized in this experimental subject to investigate the effectiveness of the scalpel supplied in the Cook-Melker cricothyrotomy kit. The incision we made with this scalpel was too small to pass the optical stylet and did not appear to have completely penetrated the cricothyroid membrane. All four confirmation techniques; vision, palpation, transillumination, and displacement, indicated that we entered the pre-tracheal soft tissue. We then performed a second incision with the small scalpel, which caused significant bleeding.

We were able to visually confirm tracheal placement after opposing the optic against the anterior tracheal mucosa to clear the blood. This maneuver also allowed us to appreciate clicking rings (the tactile and audible feedback of moving the tip of the optical stylet caudad and cephalad between the cartilaginous rings and their membranous interspaces between the tracheal rings) and midline transillumination.

Due to the inadequate incision with the small, # 15 scalpel, time to ventilation was 2 minutes in this experimental subject.

Sheep #3: Utilizing a #20 scalpel, we made a single

incision, inserted the stylet, and obtained fiber-optic confirmation of tracheal placement in 10 seconds. We then demonstrated the presence of tracheal rings, hanging tracheal mucous, deformation and rebound of the trachea, side-to-side displacement, transillumination, and palpation of clicks. Passing the Melker over the stylet and into the trachea over the Levitan took 4 seconds.

Time to ventilation was 48 seconds.

Sheep #4: Using a #20 scalpel, we made a single incision, inserted the stylet, and obtained fiber-optic confirmation of tracheal placement in 10 seconds.

We performed the same maneuvers discussed in experimental subject #3, namely, demonstrating the presence of tracheal rings, deformation and rebound of the trachea, side-to-side displacement, transillumination, and palpation of clicks.

Time to ventilation was 48 seconds due to the extra time spent performing all of the above tracheal placement confirmation maneuvers,

Before advancing the Melker Cricothyrotomy tube, we confirmed cricothyroid membrane puncture and tracheal placement by:

1) Tracheal visualization: tubular shape/rebound/rings (figure 2).

2) Transillumination (figure 3). Tracheal visualization: tubular shape/rebound/rings (figure 2). 3) Palpation of clicks, enhanced by trapping the tracheal cartilage and skin between the operator's finger and stylet tip. 4) Gentle side-to-side tracheal displacement using the stylet.

Discussion Like a bougie or wire,3,4an optical stylet can be used

to introduce a cricothyrotomy tube. The optical stylet is substantially more rigid than a bougie or a guidewire, and as a result, it can be inserted after a single incision, and a cuffed Melker catheter can be easily threaded over it, without dilation.

Unlike bougies or wires, fiberoptic stylets provide visualization, illumination, and precise control. These features allow clinicians to confirm placement by visualizing the trachea, transilluminating, trapping the anterior trachea to enhance the sensation of clicking rings, and by displacing the trachea from side-to-side with the stylet. This pilot study has several important limitations. The most serious is that it is not a standardized comparative trial and therefore can not establish efficacy and safety as such a trial could.

Weighing against this is that animals should be used judiciously in research, and that presenting information gained in the development process will be useful to others who seek to advance our knowledge of airway rescue techniques. Another important limitation is the animal model. Although the cricothyroid membrane-level dimensions are similar, sheep and human airways differ significantly with respect to other laryngeal dimensions and to tracheal length visible in the neck. The latter is important because it may be easier to demonstrate transillumination in the sheep trachea as compared to the human trachea.

Although we have not performed the SICFOS technique in humans, the distance between the cricothyroid membrane and sternal notch is sufficient so the bend of the video stylet can be manipulated to bring the light to the anterior trachea.

Finally, although we used a Levitan stylet, other rigid 5.0 mm diameter rigid optical stylet scopes could probably be used in its place, such as the Shikani optical stylet and the Storz Bonfils optical stylet.

References 1. Chang RS, Hamilton RJ, Carter WA. Declining rate of cricothyrotomy in trauma patients with an emergency medicine residency: implications for skills training. Academic Emergency Medicine 1998: 5: 247-51.

2. Timmermann A, Russo SG, Rosenblatt WH, Eich C, Barwing J, Roessler M, Graf BM. Intubating laryngeal mask airway for difficult out-of-hospital airway management: a prospective evaluation. British Journal of Anaesthesia 2007; 99: 286-91.

3. Schaumann N, Lorenz V, Schellongowski P, Staudinger T,Gottfried LJ, Burgmann H, Pikula B, Hofbauer R, Schuster E, Frass M. Evaluation of seldinger technique emergency cricothyroidotomy versus standard surgical cricothyroidotomy in 200 cadavers. Anesthesiology 2005; 102: 7-11.

4. MacIntyre A, Markarian MK; Carrison D, Coates J, Kuhls D, Fildes JJ. Three-step emergency cricothyroidectomy. Military Medicine 2007; 172: 1228-30. 5. Manoach S, Corinaldi C, Paladino L, Schulze R, Charchaflieh J, Lewin J, Glatter R, Scharf B, Sinert R. Percutaneous transcricoid jet ventilation versus surgical cricothyroidotomy in a sheep airway salvage model. Resuscitation 2004; 62: 79-87. 6. Manoach S, Paladino L. Trauma airway salvage using an optical stylet with oxygen insufflation. Journal of Clinical Anesthesia 2008; 20: 217-218

7. Paladino L, Charchaflieh JG, Eason JK, Wright BJ, Palamidessi N, Arquilla B, Sinert R, Manoach S. Increasing ventilator surge capacity in disasters: ventilation of four adult- human-sized sheep on a single ventilator with a modified circuit. Resuscitation 2008; 77: 121-126.

8. Wanner A. Utility of animal models in the study of human airway disease. Chest 1990; 98: 211-7.

9. Cissik JH, Ehler WJ, Hankins GD, Snyder RR. Cardiopulmonary reference standards in the pregnant sheep (Ovis aries): a comparative study of ovine and human physiology in obstetrics. Comp Biochem Physiol A1991; 100: 877-80. 10. Abraham WM, Ahmed A, Serebriakov I, et al. A monoclonal antibody to alpha1beta1blocks antigen-induced airway responses in sheep. Am J Respir Crit Care Med 2004;169: 97-104. 11. Tsai LW, Hoffman AM, Mazan MR, Ingenito EP. Bronchoscopic measurement of collateral ventilation in a sheep model of emphysema. Respiration 2007; 74: 565-71.

12. Ingimarsson J, Bjorklund LJ, Curstedt T, Larsson A, Robertson B, Werner O. A lung recruitment maneuver immediately before rescue surfactant therapy does not affect the lung mechanical response in immature lambs with respiratory distress syndrome. Acta Anaesthesiol Scand 2003; 47: 968-72.

13. Maybauer MO, Maybauer DM, Traber LD, et al. Gentamicin improves hemodynamics in ovine septic shock after smoke inhalation injury. Shock 2005; 24: 226- 31.

14. Zrunek M, Happak W, Hermann M, Steinze W. Comparative anatomy of human and sheep laryngeal skeleton. Acta Otolaryngol 1998; 105: 155-62.

15. Kim MJ, Hunter EJ, Titze IR. Comparison of human, canine and ovine laryngeal dimensions. Acta Otol Rhin Laryngol 2004: 112: 60-8.

16. Tayama N, Chan RW, Kage K, Titze IR. Geometric characterization of the laryngeal cartilage framework for the purpose of biomechanical modeling. Ann Otol Rhinol Laryngol 2001; 110: 1154-61.

17. Agricultural Statistics Board. “Livestock Slaughter”. Washington D.C., U.S. Department of Agriculture, 2009. (Accessed 1 May 2009 at http://www.usda.gov/nass/PUBS?TODAYRPT/lstk0309.txt).

18. U. Buehner (1) , J. Oram 1 , S. Elliot (2) , A. Mallick (3) and A. Bodenham (3). (1) Specialist Registrar , (2) Research Nurse , (3) Consultant in Anaesthesia and Intensive Care, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK.Bonfils semirigid endoscope for guidance during percutaneoustracheostomy. Anaesthesia 2006; Volume 61 Issue 7, Pages 665 - 670.

Conflict of interest statement None of the authors have conflicts of interest that could in any way bias this work.

Figure 1: A 5.0 mm ID Melker cuffed cricothyrotomy tube mounted on a Levitan optical stylet. Note the #20 scalpel.

Figure 2: Monitor display of trachea obtained during cricothyrotomy procedure, showing the characteristic round shape of the trachea, tracheal rings and and mucous dripping from anterior wall of the trachea.

Figure 3: Transillumination of the trachea, seen in well-lit room (image taken from video).

Size 10 Surgical Blade (DeRoyal)

Size 11 Surgical Blade (DeRoyal)

Size 15 Surgical Blade (DeRoyal)

Size 20 Surgical Blade (DeRoyal)

Figure 4: Scalpel Shapes and Dimensions

Width appropriate to place Melker CT Catheter (7.3 mm O.D.)

Depth from scalpel tip to blade lock appropriate to penetrate CT membrane without over penetration (posterior wall of trachea).

Width not appropriate to place Melker CT Catheter (7.3 mm O.D.)

Depth from scalpel tip to blade block appropriate to penetrateCT membrane, but potential for over penetration exists.

Width not appropriate to place Melker CT Catheter.

Depth adequate to penetrate CT membrane.

Width appropriate to place Melker CT Catheter.

Depth adequate to penetrate CT Membrane.

6.9 – 7.1 mm

16 mm

5.42 mm

20 mm

4.1 mm

13.5 mm

9.1 mm

11.3 mm