Our device consists of mechanical controls and electronic controls. The mechanical controls contain a head groove that is used to support the head of patients under the head measurement and control equipment. The head measurement and control equipment is used to measure the values of angles. The mechanical controls also include a neck lifting equipment, a neck brace, an electronic positioning adjustment equipment, a back panel, and a horizontal bottom plate. The above structures work together to protect the cervical spine, elevate the upper body, extend the head, and flex the neck of patients. The electronic controls include an operation console, programmable logic controller, and a positioning control system. It is mainly used to adjust the parameters for airway opening and display relevant data.
The device is used to open the airway of patients and maintain airway patency by automatically measuring the values of three important angles and/or adjusting the relative lifting distance (RLD) of the back panel, based on the design theory of the airway opening principle of CPR and endotracheal intubation. On the one hand, the first angle is called “the mandibular angle” (MA) and formed by the line between the mandible and the external auditory meatus and the horizontal plane. The second angle is “the angle of the back panel” (BPA) and formed by the line between the back panel and the horizontal plane. The third angle is named “the angle of position” (PA) and generated by the line between the back panel and the projection line of the end face of the MA. Because the form of PA is associated with MA and BPA, so we take the degrees of PA as the primary parameter in the process of using the device to open the airway. Besides, we defined the degrees of PA range from 90 to 100, based on the airway opening criterion of CPR that is MA need to near 90°. On the other hand, the device can extend the head of patients, flex the neck, and rise the upper body by lifting the back panel. The range of RLD of the back panel is 0 to 50 mm, and the absolute lifting distances range from 10.3 to 15.3 cm.
2.2 Study design and participants
We conducted a prospective randomized, non-blind study to compare the effects of the device with the HT/CL manoeuvre in opening the airway of a Resusci Anne CPR manikin (Laerdal, Wappingers Falls, NY). The financial source of this work was supported by the Chongqing Science and Technology Commission under project number cstc2016shmszx130038. After the approval of the First Affiliated Hospital of Chongqing Medical University Institutional Review Board (No. 20205401), the study was conducted in the Simulation Teaching Centre of Clinical Skills of the First Affiliated Hospital of Chongqing Medical University. We recruited a convenience sample of volunteers to participate in this study. The volunteers were all college students who aged 18 years or older and majoring in medicine. We obtained written informed consent from all participants.
2.3 Study procedures
Before the study began, all participants were trained in standard operating procedures for the device, HT/CL manoeuvre, and bag-valve-mask (BVM) ventilation technique provided by one medical personnel with rich experience in emergency treatment and teaching. The above training format included lectures and teaching, lasting approximately 30 minutes. At the end of the training, participants would practice the above training content on their own. When they passed the rigorous test, they began to participant in our study.
The airway of the same manikin was then opened by each participant using the device at 3 different levels of PA (Fig.1) and using the HT/CL manoeuvre in random order (Fig.2). The 3 different levels of PA were 90°, 95°, 100°, respectively. Randomization was based on computer-generated random sequences that were stored in sealed opaque envelopes. One researcher generated the random sequences and was not involved in the enrolment of participants and the implementation of study procedures. After the participants passed the test of the training, the envelope was opened. The sequence of airway opening for any participant was known. After the airway of the manikin was opened, ventilation was administrated by the participants using BVM by squeezing the bag over 1 second and then allowing adequate bag inflation. Each time the airway of the manikin was opened, participants ventilated the manikin twice. What’s more, each participant was required to repeat these above procedures 5 times, based on the BLS guidelines for adult CPR that is recommended implementing five compressions-airway-breathes cycles . Therefore, each participant opened the airway of the manikin 5 times and then ventilated it 10 times in each condition. After completed the study under 4 different conditions, each participant needed to open the airway 20 times and ventilate 40 times in all. After the procedure of one condition was completed, participants rested for 2 minutes. Finally, within 10 minutes after the end of the study, all participants completed a brief online questionnaire regarding their preference for the device. Data collation was performed by independent observers who were not involved with the performance of the study procedures.
2.4 Study outcomes
The primary outcome was the number of ventilation success as mainly measured by the SkillGuide electronic display (Laerdal, Wappingers Falls, NY) which is equipped in the manikin. Besides, the visible elevated chest of the manikin was considered as an assistant measurement method of the primary outcome. The secondary outcome was the preference of participants for the device, which was assessed by an online questionnaire. This questionnaire consisted of 5 items, including “The device is easy to use.”, “The device provides a better ventilation effect than the manual method does.”, “I would be willing to use the device in an emergency case.”, “Which method would you prefer to choose in an emergency case.”, and “Which method would you prefer to choose in a non-emergency case.” Participants responded to the first three items on a 1-5 Likert scale ranging from “strongly disagree” to “strongly agree” [17,18], and responded to the last two items in selecting the device or the manual method.
2.5 Statistical analysis
We used SPSS (version 25.0, IBM, Armonk, NY) to perform all statistical analyses. Continuous data were reported as mean ± standard deviation, or median and interquartile range (IQR). Categorical variables were presented as frequencies. The number of ventilation success under 4 different conditions was analysed by the Friedman test, and which was combined with Bonferroni’s adjustment to compare the number of ventilation success for each condition. P-value < 0.05 was accepted as statistically significant, and P-value < 0.008 was considered significant after Bonferroni’s adjustment.