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Effects of weights applied to the apex of a bag-valve-mask and pinch strength on tidal volume: a prospective simulation study – Scientific Reports

Study design

This prospective simulation study was conducted using quasi-experimental and equivalent time series designs.

Sample size and setting

To achieve a reasonable sample size, we performed a power analysis using G*Power for linear mixed model (LMM) analysis. The sample size for computation of a test power (1 − β) of 0.80 with seven predictors was 68, with an effect size of 0.15 and alpha of 0.05. Considering the dropout rate, 75 students were recruited to achieve a reasonable sample size. During the study, three students withdrew owing to personal problems. In total, 72 students were included in the analysis.

Using convenience sampling, participants were recruited from three universities in three large cities in the Republic of Korea. The inclusion criteria were undergraduate paramedic students aged 18 years or older who had completed a basic life support provider course, according to the 2020 American Heart Association guidelines3. The participants were held the mask in their left hand. This study was conducted during the COVID-19 pandemic. Therefore, students who contracted COVID-19 and hence needed to be quarantined were excluded.

The principal researcher contacted the directors of the paramedicine departments of the three universities to obtain permission for recruitment. Data were collected between November 14, 2022 and February 28, 2023.

Ethical considerations

This study was conducted in accordance with the principles of the Declaration of Helsinki and was approved by the institutional review board of Kyungdong University (No. 1041455-202210-HR-015-01). Participation was voluntary and anonymous. Before conducting the study, we received informed consent from all participants, who were informed that consent could be withdrawn at any time during the study without any consequences.

Measurements and procedures

General characteristics (such as sex, grade, height, and weight), and major variables included handgrip strength, three pinch strengths (tip, key, and tripod), and Vt were measured in this study. First, general characteristics were measured using a self-reported questionnaire. The handgrip strength (kg) and three pinch strengths (kg) of the objective variables were then measured using an electronic hand dynamometer (Lavisen KS-301, Lavisen Co. Ltd., Namyangju, Republic of Korea) and Jamar Pinch Gauge (PG 60, Sammons Preston, Bolingbrook, IL, USA), respectively. Handgrip strength (kg) and pinch strength (kg) were measured twice with the left hand, and the average values were obtained. The pinch strengths included tip, key, and tripod pinch strengths (Fig. 1). Each participant was measured pinch strengths in three types of finger shapes (postures) as shown in Fig. 1. Tip pinch strength is the force between the base of the thumb and the tip of the index finger, and key pinch strength is the force between the anterior of the thumb and the inner side of the index finger. The tripod pinch strength is the force between the anterior of the thumb and the anterior surfaces of the index and middle fingers19.

Figure 1

Pinch strength position. (a) Tip pinch, (b) key pinch, and (c) tripod pinch.

Vt (mL) was measured via BVM bagging (Adult Laerdal Silicone Resuscitator, Laerdal Medical Corporation, Stavanger, Norway). In this study, Brayden Pro manikin (Innosonian, Inc., Seoul, Republic of Korea), which has a built-in software that can automatically measure Vt, was used. Based on previous studies, the Brayden Pro manikin was placed at the same height as the middle of the femur of the participants22.

Machine usage was demonstrated and explained data collection. All participants were given the opportunity to practice BVM bagging for 1 min while maintaining the E–C technique with their left hand and holding the self-inflating BVM bag with their right hand. In addition, the participants were given a 5-min break after measuring each variable to minimize their difficulty. It took approximately 35–40 min to measure all the variables for each participant (Fig. 2).

Figure 2
figure 2

Flowchart of the study design.

Mean Vt was measured by BVM ventilation for 1 min for each pendulum (0 g, 100 g, 200 g, 300 g, respectively). The measured Vt was calculated 10 times for each weight placed on the mask, and the average value of Vt (mL) measured according to each weight was calculated. A metronome (Metronome Beats: BPM Counter, App Store, Stonekick Limited, London, United Kingdom) was used to accurately provide ventilation rates to measure the Vt (mL). It was set to 60 beats per minute, allowing participants to administer one ventilation every 6 s (Fig. 3).

Figure 3
figure 3

Experimental environment.

Statistical analysis

Data were analyzed using SPSS Statistics for Windows, Version 27.0 (IBM SPSS Inc., Chicago, IL, USA). To confirm the normal distribution of the data, kurtosis (< 10) and skewness (< 3) were calculated. Statistical analyses included descriptive statistics, t-tests, Pearson’s correlation analysis, and LMM analyses. To obtain accurate Vt in the correlation analysis, parameters such as the four weights, height, tripod pinch strength, and handgrip strength, which were found to display positive correlations, were treated as the control variables and included in the LMM analysis. For the independent variables, dummy (sex and grade) codes were created to run the LMM analysis.

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