The study results revealed significantly better results with 3D-PVL and SVL in intubation time, glottic imaging, and ease of use in the normal airway scenario and glottic imaging in the difficult airway scenario than with MCL. Conversely, no significant difference was found between the three ETI devices investigated within the scope of this study in the rates of successful intubation attempts and accurate ETT placement variables, regardless of airway scenarios.
The duration of intubations performed by medical school students with MCL reported in the literature ranged between 14 and 40.8 s for normal airway scenarios and between 10.5 and 38 s for VL[13–17]. This study revealed comparable intubation times. A review of the relevant studies indicated that Ray et al. and Pieters et al. revealed no significant difference between MCL and VL in both normal and difficult airway scenarios. In contrast, Rendeki and Maharaj revealed that VL was superior to MCL in both scenarios, and Shin et al. revealed that the VL provided a shorter intubation time after repeated trials in the normal airway scenario but not in the difficult airway scenario. The discrepancies between the studies might be attributed to the differences between the respective studies’ methodologies and the use of different devices and manikins. In fact, a VL can even be found superior to another VL in certain parameters[13]. Conversely, a meta-analysis of studies conducted with actual patients revealed shorter intubation times with the use of VL[18].
The study results indicated SVL as the easiest ETI device to use among the three devices investigated, whereas the most difficult was MCL, regardless of airway scenarios. Similarly, relevant studies available in the literature reported that VL was easier to use than MCL in both normal and difficult airway scenarios[13 − 17]. The thicker blade and the less ergonomic blade handle created difficulties in using 3D-PVL in the difficult airway scenario based on the unstructured feedback received from the participants. These drawbacks were also mentioned by Gorlan et al., and a channeled 3D-PVL with oxygen and suction features was developed to overcome these drawbacks[19].
SVL and 3D-PVL gave better results than MCL in terms of glottic imaging. A good glottic view may not be obtained in the DL technique when viewed from a limited mouth opening, even if the axes are aligned correctly. Conversely, the video camera helps the VL technique overcome obstacles such as the tongue, teeth, and limited mouth opening. The camera at the end of the VL blade eliminates the need to align the oral, pharyngeal, and laryngeal axes. Previous studies have demonstrated that VL improved Cormack − Lehane grades and glottic imaging regardless of user experience[13–17, 20–23].
Comparable results were obtained with all three ETI devices in terms of the rate of successful intubation attempts, regardless of airway scenarios. SVL and 3D-PVL provided significantly better glottic imaging than MCL, but this difference was not reflected in the rate of successful intubation attempts. Hence, obtaining a good glottic view does not always imply accurate ETT and successful ETI placement[24]. A good glottic view, as well as correct positioning and advancement of the ETT in the mouth and good hand-eye coordination, are required for accurate ETT and a successful ETI placement. The rate of successful intubation attempts in the manikin studies in which medical school students’ ETI successes were compared according to VL and MCL use were not significantly different, whereas a meta-analysis conducted by Nalubola et al. revealed that medical school students had higher intubation and first entry success in real patients, especially using channeled VL[13–16, 18]. Training medical school students first with VL while gaining ETI skills reportedly increased their intubation success by 14–19% and shortened the intubation time[25, 26].
An easily accessible option in the production of devices and tools is 3D printing technology, the costs of which are difficult to meet in many countries. Offering the designed devices open access as downloadable files would allow these devices to be produced globally when needed[10]. The need for 3D printing and VL production has increased because of the disadvantages of limited transportation during the pandemic period. However, studies on this subject remain limited. Studies available in the literature produced new VLs based on the existing VLs and DLs as examples, in addition to developing their own unique devices[4, 9, 10, 19, 27–30]. PLA material, which is considered biocompatible, was generally used in manufacturing these devices. Cohen compared 3D-PVL with MCL and reported the superiority of 3D-PVL over MCL in terms of first entry success rate, glottic imaging, and intubation time[29]. Papanaoum et al. revealed that 3D-PVL was more successful than MCL[27]. Similarly, Lambert et al. compared 3D-PVL with MCL and Pentax-AWS® and revealed that 3D-PVL is superior to MCL in terms of intubation time and success, glottic imaging, and ease of use[4]. Conversely, Ataman compared AirAngel® with Glidescope® and concluded that Glidescope was more successful in terms of the first entry success rate in both normal and difficult airway scenarios and intubation time in the normal airway scenario[9]. All the included participants in these studies were experienced practitioners. The heterogeneity in the outcomes reported by these studies might be because of the differences between the selected endpoints, the devices used (both standard VLs and 3D-PVLs), and manikins. A thorough literature review conducted during the writing of this study revealed no other study on the efficiency of 3D-PVL in inexperienced users.
ETI is one of the basic competencies that should be taught in medical school. However, many difficulties and obstacles exist in teaching ETI to medical school students. First, more than fifty attempts are needed to gain competency in conventional DL[11]. Then, performing this training on actual patients is often not possible, considering the busy operating room and emergency room conditions[25]. Gaining this competence to medical school students with VL offers safer, faster, and easier alternative training that can be completed in six or seven attempts[14, 31, 32]. The steps of the intervention can be controlled under the mentorship of an experienced laryngoscopist, and anatomical structures can be understood more easily due to the real-time feedback provided by the video camera[32]. However, the 40% access rate to VLs even in developed countries and much lower in developing and underdeveloped countries constitutes the biggest obstacle to giving this training[5, 6].
This study did not include a direct measurement that assessed the use of 3D-PVL in real patients. Studies on the subject matter reported that 3D-PVL should theoretically withstand a force of 100 N during ETI[28]. Other studies on PLA durability demonstrated that PLA could withstand a force of approximately 200 N[33]. Mendes et al. reported that the 3D-PVL model they developed for pediatric and adult patients could withstand forces of > 400 N[10]. Gorman et al. reported that the 3D-PVL they produced complied with ISO7376:20 standards both in terms of rigidity and strength[19]. In comparison, > 750 manikin intubations were performed with the single 3D-PVL specifically produced for this study, yet no breakage or macroscopic deformation was observed. Additionally, 3D-PVL can be reused after sterilization by 1% Rely + OnTM Virkon solution or hydrogen peroxide or via methods such as gas plasma and gamma radiation[4, 19]. However, the number of sterilizations that the structural properties of 3D-PVL will withstand is not reported. In sum, 3D-PVL was not validated on real patients, but the findings suggest its use in real patients in the near future because of the fast pace of technological developments in this field.
4.1 Limitations of the Study
This study is a manikin study. Therefore, directly adapting the study results to real patients is impossible. It would be unethical to recommend using this device, which results from a new idea and the durability and efficiency of which have yet to be standardized on real patients other than a manikin. The structure of the manikins used in the study can simulate the airway anatomy of a patient with a normal airway to a certain extent. However, a manikin can simulate only one of the difficult airway scenarios, i.e., cervical immobilization, because of the numerous difficult airway scenarios in real life. The devices and manikins used in this study were adult models and, thus, unsuitable for assessing pediatric airways.
This study was not a blind study as the type of laryngoscope used could not be concealed from the participant or the researcher measuring the intubation times. The Hawtorn effect, referring to the possibility that subject monitoring could enhance the outcomes, may have contributed to the study’s outcomes being better than they otherwise would have been[34]. However, the Hawtorn effect might not have significantly affected the results because the robust endpoints (tracheal and esophageal intubations and intubation times) were clearly defined in this study.
Additionally, the study participants, who were inexperienced, might have gained experience with each intubation attempt, which might have improved the results obtained at subsequent stations, as pointed out in the literature[17]. This situation was foreseen during the study’s planning phase, and the device order was randomized to negate the said effect. However, it is unclear how much the results were affected.
The Cormack − Lehane classification was used to evaluate glottic imaging. This classification was developed for DL and thus the subjective nature of the evaluations made with this classification might have affected the results[23]. However, it remains one of the best options available for comparing different techniques.
The principle of creating material in layers is the basis of 3D printing, and the layers’ thickness can affect the material’s strength. Additionally, 3D-printed video laryngoscope models do not come out of a standard production line and thus the 3D printer used in production may affect the material quality which is a limitation of this technology.
The qualities of the images produced by 3D-PVL and SVL may have been different because these two techniques have different video camera resolutions. 3D-PVL has a resolution of only 640 × 480 pixels, whereas SVL has a resolution of 1280 × 800 pixels. However, the difference in terms of pixels did not cause a significant difference in glottic imaging on the manikin. The manufacturer declares that the endoscope camera is resistant to fogging and wetness, but the effects of secretions and liquids available in a real patient on the images produced thereof are unknown. However, the study results did not reveal any disadvantage for that matter, when performing ETI training on a manikin.