2.1 Design theory
The theoretical background of the development of the device includes CPR and tracheal intubation open airway. In CPR, the criterion of airway opening is the line between the external auditory meatus and the mandible is perpendicular to the horizontal plane. The core theory of tracheal intubation is keeping the head and neck of patients in an optimized position, including the three-axis alignment theory (The TAAT)6, sniffing position7,8, and ramped position9,10. Bannister et al. firstly introduced the TAAT, and suggested that the best glottic view would be obtained during laryngoscopy when the three axes of mouth, pharynx and larynx overlapped in 19446. Sniffing position is defined as the level of the head and face raised 15° and the neck flexed 35° through placing a 7 to 10 cm pillow or blanket behind their head or shoulder7,8. Generally, sniffing position is regarded as the preferred position for tracheal intubation during laryngoscopy because it can keep the three axes aligned to some extent. Ramped position is considered as a potential good position through raising the back of beds for 20° to 25° or raising the upper body and head until the line between the external auditory meatus and the sternal notch is aligned to the horizontal plane, which may facilitate tracheal intubation and ventilation9,10. Because the proper position is a decisive factor for successful airway opening11, so we designed the device based on these two reliable and feasible theories.
2.2 Compositions and materials
The device is designed as a mobile structure, including the mechanical controls and the electronic controls. The mechanical controls are composed of a head measurement and control equipment (HMCE), a head groove (HG), a neck lifting equipment (NLE), a neck brace (NB), electronic positioning adjustment equipment (EPAE), a back panel (BP), and a horizontal bottom plate (HBP). The electronic controls consist of an operation console (OC), programmable logic controller (PLC), and positioning control system (Fig. 1).
Specifically, the first part is the OC that is equipped with a liquid crystal display (LCD) touch screen, PLC, and power. The operation interface of the LCD touch screen includes the manual angle or height adjustment option, the automatic angle or height adjustment option, the auxiliary angle adjustment option, and the help option. The second part is the HMCE consists of a ring sleeve (RS), positioning reference plate (PRP), and dynamic inclinometer (DI, SDA126T-90-485, SN 01819100183, Rion-tech, Beijing, China). The RS is used to assist patients in wearing and fixing the HMCE, and the PRP and DI are used to measure the degree of an angle, called “the mandibular angle” (MA), which is formed by the line between the mandible and the external auditory meatus and the horizontal plane. Besides, another DI (SN 01819100184) is designed to measure the degree of an auxiliary angle formed by the line between the external auditory meatus and the sternal notch and the horizontal plane, but its function remains to be developed. The third part is an HG and a guide rail (GR). The GR is longitudinally parallel to the human body under the HG, enabling the HG to better support the head of patients when their position is changed. The fourth part is the NLE connected to the EPAE, which contains a support plate (SP), NB, guide post (GP), lever, and electric cylinder (EC). The NB is used to protect the cervical spine. The end face of the SP passes through the GP and slides up or down with it. One end face of the lever is below the SP and the other end face has a chute. The end face of the telescopic rod of the EC is equipped with a driving pin, which is located in the chute of the EPAE. The EPAE is controlled by EC and its functions of setting and measuring the values of angle and height are carried out by the PLC. The final part is a BP which is hinged with the SP through the bolt, so we can choose to insert the bolt to make the BP linkage with the NLE, or remove it to align the BP with the HBP. To make the head extent and neck flex for airway opening, the NLE, BP, and EPAP will be used in combination.
The device is made of 304 stainless steel, polytetrafluoroethylene, and polyester fiber. The type of the device is YT/QD-100Z with a voltage of 220 V, a frequency of 50 Hz, and a power of 300 W. The length, width, and height of the mechanical controls and the electronic controls are 65*54*40.5 cm and 42.6*37.8*6.5 cm, respectively. And the weight of the mechanical controls and the electronic controls are 25 kg and 8 kg, respectively.
The main efficacy of the device is to open the airway of patients with their head extended, neck flexed, and upper body raised through adjusting the values of angle and height automatically or manually. The method of automatic adjustment is to preset parameters of the automatic angle or height adjustment option on the LCD touch screen. To adjust manually, select the manual angle or height adjustment option, and then click the up or down option. Its specific functions are as follows.
2.3.1 Measure the degree of angle
The device can measure three important values of angle through DI and software. The first angle is the MA. The second angle, named “the angle of the BP” (BPA), is formed by the line between the BP and the horizontal plane. The last angle, called “the angle of position” (PA), is generated by the line between the BP and the projection line of the end face of the MA. As the PA is associated with the MA and the BPA, we determined to set the degree of the PA as the key parameter in the process of opening the airway of patients. Based on the airway opening criterion of CPR, we defined the degrees of the PA range from 90 to 100. Besides, medical staff can preset some alternative degrees of the PA in the operation interface, such as 90 degrees, 95 degrees, or 100 degrees, to facilitate the application of the device easier and briefer.
2.3.2 Adjust height
The device can measure the distances between the lift or lower of the BP to its initial position. The relative lifting distances (RLD) of the BP range from0 to 50 mm, and the absolute lifting distances of the BP range from 10.3 to 15.3 cm, which is calculated with the distances between the BP and the HBP plus the height of the HBP itself. The limits of the lifting distances are to avoid adverse effects and avoid hindering the implementation of other clinical practices.
2.3.3 Position accurately
The device uses the automatic tracking model of setting error values to control the deviation, so the differences between the real and preset values of these angles and heights are less than 5%. Thus, the device can open the airway accurately and reduce some airway injuries by correctly adjusting these values of angle and height. Besides, the maximum working speed of the device can reach 20 mm/s, and the maximum RLD can be reached in just 2.5 seconds. Therefore, when a clinical emergency occurs, medical staff can select the maximum working speed to shorten the time of airway opening.
2.3.4 Maintain patent airway
The device can maintain the patient’s airway in a permanent patent state, which prevents medical staff from repeating the airway opening process, saves manpower and time, and facilitates the implementation of other clinical practices.
2.3.5 Protect the cervical spine
The device can protect and support the cervical spine of patients through the NB.
2.3.6 Dynamic display
The device can dynamically monitor and display the values of angle, height, working speed, and time, which help medical staff observe, record, and adjust these important parameters.
2.4 Application methods
The operation of the device contains six steps. The first step is to start the OC to keep the device in a standby state. The second step is to help patients wear and fix the HMCE, and slowly place their head, neck, and upper body on the device. The third step is to adjust the degrees of the PA or the heights of the BP by selecting the automatic or manual option. The fourth step is that the device will automatically open the airway of patients and keep it open when the third step is finished. After this step, some clinical practices, such as tracheal intubation and bronchoscopy, will be routinely performed. When the treatment is completed, the final step is to remove the HMCE, click the reset option, and turn off the power.
2.5 Preliminary application
All experimental protocols were approved by the First Affiliated Hospital of Chongqing Medical University Institutional Review Board (No.
All methods were carried out in accordance with relevant guidelines and regulations.
This study was conducted in the Simulation Teaching Center of Clinical Skills, the First Affiliated Hospital of Chongqing Medical University, and written informed consent was obtained from 15 students in the third year of the Nursing degree.
Before the study started, all participants received standard training on the operation of the device and the one-hand bag-valve-mask (BVM) ventilation skill12,13
in the form of a lecture and teaching lasting about 15 minutes. The participants were then allowed to practice the techniques until they passed muster.
According to the basic life support (BLS) guidelines for adult CPR1, participants were required to use the BVM (Adult, Tianzuo, Xiamen, China) to ventilate twice after the airway of opening a Resusci Anne® CPR manikin (Laerdal, Wappingers Falls, NY) once using the device at the degrees of the PA were 90(90° PA group), 95༈95° PA group༉, and 100༈100° PA group༉, respectively. Since one cycle of BLS demands implementing compressions-airway-breathes operations 5 times, so participants repeated these study procedures 5 times.
Therefore, each group of participants used the device to open the airway 5 times and then used the BVM to ventilate 10 times.
The primary outcome was the ventilation success rate of participants. Investigators recorded the number of successful ventilation using a SkillGuide electronic display (Laerdal, Wappingers Falls, NY) that is equipped in the Resusci Anne. Besides, investigators observed whether there are visible fluctuations in the Resusci Anne’s chest, which is considered as a supplementary indication.
2.6 Statistical analysis
Investigators double entered all data into Excel (version 16, 2019, Microsoft, Redmond, WA), and the statistical analyses were performed using SPSS (version 25.0, IBM, Armonk, NY). Normally distributed measurement data were expressed by mean ± standard deviation (± s) while non-normally distributed statistics were displayed as the median and interquartile range (IQR) or proportions. Friedman test was used to compare the differences in the ventilation success rate between the three groups. P < 0.05 was accepted as statistical significance.