The Airway Pressures During Bag-Valve-Mask Ventilation

Introduction:

Emergency department (ED) patients are considered to have an elevated risk of gastric distention and aspiration of gastric contents, making rapid sequence induction (RSI) the preferred intubation procedure. Pre-oxygenation is likely the most critical step in RSI, as it extends the duration of safe apnea time, providing the operator with more time for the intubation process. Although a facemask with a high FiO2 oxygen reservoir is recommended for pre-oxygenation, bag-valve-mask (BVM) ventilation is frequently used in emergency airway management.

Since its development during the polio epidemic in 1953, the BVM has been used for oxygenation and ventilation of critically ill patients. However, the positive pressure generated by the BVM can increase the risk of regurgitation and aspiration of gastric contents into the lungs. Excessive volumes and flow generated with the BVM can not only lead to gastric distention but also increase intrathoracic pressures, potentially causing negative cardiovascular effects.

The aim of this randomized crossover manikin study is to investigate how airway pressures change during ventilation with a BVM using different scenarios and techniques.

Methods:

This is a randomized crossover trial performed in the simulation lab of a tertiary care facility between 15.07.2024 to 15.08.2024. The ethical committee of XXX approved the study and informed consent was obtained from the participants. The participants were emergency medicine residents ranging from postgraduate year 1 (PGY) to PGY4.

In this study, airway pressures during BVM ventilation were continuously recorded using a calibrated pressure sensor placed between the facemask and the bag. All participants were requested to ventilate the Resusci Anne QCPR airway mannequin (Laerdal Medical, Stavanger, Norway) in a randomized manner using one-hand, two-hand (CE method), and modified two-hand (TE method) techniques, while the airway pressures were measured. Two different scenarios were applied to simulate normal and difficult airways while ventilating the airway mannequin. For the difficult airway scenario, a cervical collar was applied to the airway mannequin. To reduce potential bias, the purpose of the study was not explained to the participants Each participant was asked to provide a sufficient amount of air with the BVM to raise the mannequin's chest and to repeat these 10 times in a randomized order. All the pressure values measured during ventilation were recorded as cmH2O. The highest-pressure value measured during ventilations, as well as the number of ventilations during which the pressure exceeded 20 cmH2O, were recorded.

The differences in the pressure values measured using different hand techniques in normal and difficult airway scenarios were evaluated. Additionally, it was assessed which scenario and technique resulted in pressures exceeding 20 cmH2O, based on the theoretical assumption that pressures above this value would open the lower esophageal sphincter and inflate the stomach with air. This assumption was based on previous studies indicating that lower esophageal sphincter pressure is typically exceeded, and gastric inflation begins, when airway pressure surpasses 20 cmH₂O.

Statistical analysis:

The study data were analyzed using the SPSS software version 16.0 for Windows (SPSS Inc., Chicago, IL, USA). Demographic and baseline characteristics were summarized as a mean ± standard deviation for continuous variables and as a percentage of the group for categorical variables. Non-normally distributed data are presented as medians (interquartile range). For each scenario and technique, the participant was considered the unit of analysis. For every participant, the highest pressure value among the 10 ventilations and whether ≥5 of 10 ventilations exceeded 20 cmH2O were used in the analyses The chi-square test was used to compare the ventilations exceeding the 20 cmH2O pressure value with PGY levels. P < 0.05 was accepted as statistically significant.