A Laboratory Model and Scope of Three Dimensional Printing in Pediatric Airway Surgery Practice for Developing Nations Like Nepal

Abstract

Pediatric airway surgery, one of the complex procedures in otolaryngology, often demands a good surgical dexterity. To improve the surgical skills, a simulation laboratory can be a good option. Here we present a model of an airway surgery laboratory which is very minimalist and can be easily established in any hospital setup. Also, we discuss briefly on how a three dimensional (3D) model of an airway can be generated and printed from the digital imaging and communications in medicine (DICOM) CT imaging data of the patients along with the scope of 3D printing in airway surgery.

Introduction

Airway surgery in pediatric population is very complex and technically challenging. The children need to be handled with high delicacy and the surgery often demands a good dexterity. In Nepal, Tribhuvan University Teaching Hospital only has a dedicated Pediatric airway surgery unit so far which is being backed up a with team of experts in the field from the United States of America [1].

A rarity in the cases requiring airway surgery often makes it difficult for the surgeons to develop a good surgical skill within a short period of time. Also, unavailability of human cadavers in our country makes it very difficult for teaching hospitals to organize frequent airway surgery workshops to train the surgeons. In this scenario we felt a dire need of a simulation laboratory to practice airway surgery. This article summarizes a model of airway surgery laboratory which is very minimalist and also the scope of 3D printing in Nepal, which can generate airway specimens from the digital imaging and communications in medicine (DICOM) CT imaging data of the patients. We strongly believe it to be of significant benefit for the surgeons with a keen interest in airway surgery.

1. Laboratory model

   This model of ours (Fig. 1) can be easily established anywhere and is very minimalist. Figure 1 shows a gross overview of how a practice station looks. We consider the following as the necessary requirements for an airway surgery laboratory:

   1. Laryngeal stand: In Fig. 2 we depict a customized laryngeal stand which was designed by the author himself. The stand comprises of two sockets; one for holding the laryngoscope and the another for holding the specimen. Unlike the real scenario, the laryngoscope in this model has to be hold reversely. However, this doesn’t compromise the view. Considering the variation in size of laryngeal specimens and the need for appropriate laryngoscope, the distance to be set between the laryngoscope and the specimen is often dynamic. To facilitate this, the lower socket rests on a mobile base which can be moved back and forth. With the laryngoscope and laryngeal specimen in place, this set up allows practice of a wide range of airway surgeries e.g., laryngotracheal evaluation, assessment of cricoarytenoid joints, balloon dilation of stenosis, infiltration of steroids in tracheal wall, etc.
   2. Endoscope: The majority of the airway surgeries these days are endoscope guided. Thus, it will be very effective for a simulation lab to have a rigid endoscope along with camera and light source. A 0° rigid telescope would suffice most of the endoscopic procedures. Figure 1 depicts a custom made rigid endoscope set which is easily available  in the market at affordable price.
   3. Suction machine: A suction machine in the laboratory is an alternate option (Fig. 1). However, having a suction will allow procedures like injection laryngoplasty, injection of steroids in the tracheal wall etc., to be carried out in a neat and tidy way and at the same time it also provides  a simulation of real scenario.
   4. Micro laryngeal surgery (MLS) equipment: It won’t always be necessary, feasible, and cost-effective to procure all the MLS equipment. For an effective practice, we would suggest a laboratory to have atleast a laryngoscope, micro cup forceps, micro scissors, disposable syringe (3 cc or 5 cc) and a spinal needle.
   5. Dissection set and laryngeal specimen: To practice an open surgery, a dissection tray would be useful along with a dissection set of blade (size 15), blade handle, sutures (Vicryl 3.0 round bodied and Prolene 3.0 round bodied), suture holding forceps, needle holder and mosquito forceps (Fig. 3). Laryngeal specimen from goat cadaver can be easily procured from the local market which bears a close anatomical resemblance with the pediatric larynx. Three dimensional printed laryngeal specimen is another choice for practicing open airway surgery. They serve as a mirror image of the patient’s larynx, which are reconstructed via DICOM CT scan image data (Fig. 3).
   6. Facility for sterilization of the instruments and disposal of sharp instruments and cadaveric laryngeal specimens: This is one of the essential requirements for any simulation laboratory using cadaveric specimens as goats are known to harbor Scrapie, a prion disease [2]. Every instrument after its use needs to be sterilized. Sterilization can be done chemically e.g. Glutaraldehyde, Orthophthaldeyde, etc. or by using autoclave. Similarly, all the sharp instruments and used cadaveric specimens should have a proper disposal and should preferably be incinerated.
   7. Room for scrubbing and gowning: As discussed earlier, handling cadaveric animal tissues often carries a risk of transmission of prion disease. Thus, every surgeon needs to put on a gown, gloves and mask before entering the lab. Also, following the work, there should be a facility to scrub hands prior to leaving the laboratory.

Fig. 1.

An overview of airway surgery laboratory

Fig. 2.

BR Laryngeal stand

Fig. 3.

Dissection set along with 3D printed model of human larynx

Scope of 3D Printing in the Field of Pediatric Airway Surgery in Nepal

Three dimensional reconstruction and printing in today’s world have  a wide range of application and their scope in medical science is also expanding. With the emergence of pediatric airway surgery services in Nepal, 3D reconstruction and printing will have a lot to offer in the coming days. Various 3D printing facilities are now available in the nation. The charges applied depend on the size of the file and time required for the print.

On one hand, these printed specimens help the surgeons to plan their management, provide a simulation for surgical practice, design the prosthesis, etc. and on the other, they are a very effective teaching tool for the medical students as well as the patients to help them understand the pathology going on and the plan for management [3, 4]. Below we briefly discuss on how we did the 3D print of a pathological airway for the first time in Nepal.

With the advancement in technologies, multidetector computed tomography (MDCT) these days provide a high-resolution imaging. The gap between 2D images created by the CT scan can be filled up by interpolation and thus creating a 3D image [5]. A range of freely downloadable software is available these days which can read the DICOM CT imaging data and allow 3D reconstruction of the required segment or an organ. We used ITK-SNAP^® for 3D reconstruction of the larynx (Fig. 4) [6]. This is an open source software. After uploading the standard DICOM data to this software, we used manual segmentation to reconstruct the larynx and trachea going through each slice which were of 1 mm thickness. Each tissue in the body has a specific density and the segmentation uses this property to separate different tissues. The bone and air can be easily separated having a very high and low density respectively and allow an easy automatic segmentation. However, the cartilage and soft tissues have a narrow difference in their density thus, to completely delineate cartilage from the surrounding structures, manual segmentation is often necessary. After the reconstruction of 3D image, it was converted to stereolithography (STL) file which is the printable format (Fig. 4).

Fig. 4.

Sequence of process for 3D printing

The STL file of the reconstructed model after some cleanup was sliced using a slicing software (Ultimaker Cura^®, Ultimaker B.V., Utrecht, Netherlands). The GCODE file (Fig. 4) thus generated was finally ready for printing using a 3D printer (Ultimaker Cura^®, Ultimaker B.V., Utrecht, Netherlands). The print process was carried out in a heated bed with temperature of 60 °C. Glass plate was used as a build surface and the extruder temperature was kept around 200 °C. The print was cooled continuously during the entire process using a cooling fan kept at a maximum speed. Support structures were added for overhangs and the print job was finished in about 15 h at a speed of 60 mm/s with an infill density of the structure kept at 35%. The final print is shown in Fig. 4.

The material we used for the printing was polylactic acid (PLA), which is very hard. The specimens generated from this material are not suitable for practicing procedures like resection and anastomosis or application of the suture. However, in these specimens, endoscopic procedures can be done. Also, the specimens confer a good tool for teaching the medical students as well as helping the patients and their guardians understand the pathology better. The framework of these printed specimens can be used as a cast to generate specimens with soft texture using liquid silicone which can be easily cut and sutured. Moreover, printing materials like thermoplastic elastomers (TPE) or thermoplastic polyurethane (TPU) are also available which can be used to yield specimens with soft texture.

Conclusion

Incorporation of simulation laboratory and 3D printing in clinical practice will undoubtedly have a huge role for pediatric airway surgeons in refining their surgical expertise as well as in better understanding of the pathology.

Funding

None

Compliance with Ethical Standards

Conflict of interest

None