Definitive airway control in the civilian prehospital setting is most often done by paramedics who have demonstrated a misplaced endotracheal tube rate of up to 25%.1 Airway management is also an issue in the military setting as well. According to the United States Army Institute of Surgical Research (USAISR), 90% of all combat deaths occur on the battlefield before the casualties ever reach a medical facility. Roughly 6% of these deaths are related to airway management issues.2 One of the most immediate life-threatening complications of any trauma is loss of airway patency. Maintaining oxygenation and preventing hypercarbia are critical in managing the trauma patient, especially if the patient has sustained a head injury. The circumstances surrounding these intubations are often less than controlled, with the prehospital setting posing perhaps the most adverse conditions both in terms of environmental factors and patient's clinical presentations. Several factors, for example facial trauma, neck tumors, or foreign material in the airway, can produce difficulty in performing the procedure. The consequence of not recognizing that an endotracheal tube has been placed into the esophagus rather than correctly placed into the trachea includes permanent brain damage or death.
The aviation industry realized long ago that training, performance, and safety could be enhanced by the use of flight simulators. The technological developments in computer processing and simulator development have resulted in high-fidelity flight simulation that permits pilots and flight crews to rehearse a wide variety of flight emergencies and to give students a competence in the use of specific aircraft and equipment. This same technology has now been applied to patient simulation for those involved with healthcare delivery at all levels of training.3–5 The ability to present patients of various complexities gives both teachers and students a means to review physiology in a clinical setting or to experience high-acuity, low-frequency clinical events in a realistic environment without putting themselves or actual patients at risk. Endotracheal intubation in the prehospital environment is considered a high-acuity, low-frequency procedure.
In a previous paper, we described the development of a cost effective and portable endotracheal intubation virtual reality simulator that can be used to improve the training opportunities for emergency medical service (EMS) providers.3 The prior PC-based simulator, developed by the authors, is a one-haptic device system. The current device uses a mouse to manipulate the laryngoscope as well as the position of the human model. The work presented here is a description of improvements made to this simulator. Many of the improvements discussed here deal with the realism of this type of simulator and its usefulness in comparison to mannequin simulators currently used in healthcare training.
For the endotracheal intubation simulator to be effective, objects in the simulated environment must respond to the user's actions dynamically, in real-time, with accurate visual representations in regards to changes in geometry and appearance. Interactivity includes the ability to manipulate objects, perform physics-based interaction and deformation of objects, incorporate force feedback through haptic device hardware, and allow immersive stereo visual output. Three key components of this project, currently under development, deal with the physical geometry, collision detection, and the visual realism of the model.
Basic measurements of head neck and chest position were taken from various mannequins and human volunteers to develop proper geometrical movement within the model. Figure 1 shows a side-by-side comparison of the patient model in both the supine position as well as the sniffing position. Proper positioning is key to visualization of the vocal cords during orotracheal intubation. In this simulation, we are able to accurately simulate visualization when optimal positioning is not achieved as well as change the anatomic relationships to provide a challenge to more experienced intubators.
There are various types of collision detection methods. For our application, we used a hierarchical oriented bounding box (OBB) method as described in our prior work.3 With this method, intersecting polygons are identified to detect a collision. In our model, we are concerned only with the collision detection of the tracheal tube and the laryngoscope blade with the relevant soft tissues of the virtual model, which are relatively small in terms of the number of intersecting polygons. With the small number of polygons and limiting the model to the laryngoscope blade, we are able to achieve the fine balance between the required accuracy and the necessary time complexity for real-time haptic update rates.
Visual realism demands complexity, or at least the appearance of complexity. Texture mapping is an efficient means to create the appearance of complexity without the tedium of modeling and rendering every three-dimensional detail of a surface. In general, texture mapping is the process of “painting” a picture onto a surface in a scene. Texture maps can be used to significantly enhance the appearance of a surface, giving a realistic appearance without adding large amounts of geometric detail. Images of a patient or test object are captured from several viewpoints and are combined into one texture mapping image. Using high-quality texture mapping the images are rendered, making the patient model look real. To allow for both basic and advanced skills assessment, the required perceptual fidelity is essential to capturing the natural behavior of the operator. The level of realism in terms of object and scene appearance determines the faithfulness and hence the degree of immersion experienced by the trainee in the virtual world. Figure 2 is a computer model of the vocal cords and trachea. This model is geometrically accurate but lacks visual realism. Figure 3 is the same model with an image taken from a real patient texture mapped over it. The benefits of texture mapping are obvious from this comparison.
The view of the vocal cords in the SimMan airway management trainer by Laerdal Medical is a nice representation of what the user would see while performing a tracheal intubation, but it is not as realistic as Figure 4, which is a texture map of the same view taken from the virtual reality airway management trainer.
A rigid fiber optic laryngoscope was used to acquire images from real patients undergoing tracheal intubation in the emergency department as well as cadaver specimens in the anatomy laboratory. Selected images were then used to texture map the patient model developed for the virtual reality tracheal intubation trainer (Fig. 5).
Orotracheal intubation by prehospital providers is a high-risk/low-frequency procedure that can have significant consequences when performed improperly. Simulation in general, and more specifically virtual reality simulation, has the potential to facilitate maintenance of proficiency and is a means for decreasing errors in the prehospital environment. This can occur by not only ensuring procedural and technical competency in performing the skill, but also ensuring cognitive competency for the skill in recognizing complications. While mannequin practice is useful for healthcare providers at all levels to hone their technical skill, it is difficult to simulate the actual environment in which this skill is performed using a mannequin, even with the current mannequin simulation technology. Virtual reality on the other hand can be used to develop highly interactive, physically and visually accurate training scenarios.
Situated cognition and learning has been discussed by many authors debating the concept of providing real world context to the learning situation.6–8 The virtual reality intubation simulator has the potential to expose both novice and experienced health care providers to situations that occur infrequently, for example massive facial trauma, to allow them to develop the cognitive framework and skills necessary to manage these patients. Sensory overload can easily occur when significant airway management difficulty is encountered in a critically ill patient, thus delaying care. Unfortunately, clinical education for prehospital students does not always afford the opportunities to care for every conceivable scenario. Through the use of a virtual reality tool such as the intubation trainer, healthcare providers can be exposed to these situations and learn how to intervene in an environment that is safe in regards to the virtual patient as well as for the provider.
One concern in the prehospital environment is the lack of live training opportunities for paramedic students and new paramedics. The opportunities to develop experience in operating rooms and emergency departments with live patients or high-fidelity trainers are generally lacking.9 Skills retention is also a concern as the opportunities to perform the skill by a practicing paramedic are generally few.10 Though critically important to quality patient care, this knowledge is often difficult to obtain due to limitations of cadaver or mannequin availability and low frequency of intubations while in practice. Medicolegal concerns of prehospital providers performing intubations in the operating theater or emergency department also results in a decreased frequency in the opportunity to learn.
Novice users can also benefit from virtual intubation task training. When the Commission on Accreditation of Allied Health Education Programs–accredited paramedic training programs were surveyed, 25% of the respondent programs had students that had not fulfilled the national curriculum recommendation of five oral intubations during their clinical training.9 Eight percent of the programs reported that less than half of their students had actually met the recommendations. While procedural competency in these situations is typically performed on an airway management mannequin, the mannequin does not take into account situations that are commonly encountered when performing routine oral intubation, namely blood or emesis in the airway or different body morphology. These factors which are common and do not often produce difficulty in performing the skill can provide a stumbling block for novice health care providers performing the skill with little prior experience. Simulation allows the trainer to manipulate the environment so that trainees are required to employ critical thinking skills to successfully manage the airway. While task transfer for complex tasks has yet to be elucidated, for simple tasks, task training in a virtual reality environment can afford improved real-world performance.11
There are several planned enhancements to the virtual airway management simulator, above and beyond those described here that will be made prior to its being tested in the field. In the background, video of actual scenes will be used to develop the periphery of the environment. These scenes will include actual footage taken from a variety of settings. A second haptic device, equipped with a laryngoscope handle, will be integrated into the virtual environment which when combined with the current endotracheal tube device, will allow the user to develop the psychomotor mapping skills necessary to properly perform the procedure. Finally, this will all be engineered into a three-dimensional stereo display to provide the most realistic and situated environment possible.
Realistic simulators are creating a paradigm shift in education and training throughout all of medicine. Virtual reality technology offers significant promise as a tool for the simulation of emergency resuscitation situations for EMS personnel. Virtual reality can provide highly realistic and engaging simulations of diverse patient populations. With continuing improvement in the fidelity of virtual reality systems, the virtual reality environment can mimic many of the critical elements of a training event leading to improved knowledge and skills to deal with these situations. Intubation airway training is such an event. Though critically important to learn, it is knowledge often difficult to obtain due to limitations of operating room time and low frequency of intubations while in practice. The three-dimensional viewing and interaction available through virtual reality make it possible for prehospital personnel and students to practice many endotracheal intubations without ever touching a patient.
In this paper, we have presented a model for a virtual reality airway management task training simulator that has the potential to not only facilitate the development of technical competencies but also the cognitive competencies associated with the skill. The core of a successful virtual reality simulation for emergency airway management is based on a realistic digital model of the human anatomy and airway structures with movement and functionality producing real-time interactivity coupled with realistic visualization. This work provides a solid foundation for future versions of the intubation simulator, which will incorporate an additional haptic device for laryngoscope blade manipulation.
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