[Effect of fraction of inspired oxygen baseline level on the mask ventilation time before intubation in emergency patients by monitoring of expiratory oxygen concentration].

Objective: To investigate the effect of different fraction of inspired oxygen (FiO) baseline levels before endotracheal intubation on the time of expiratory oxygen concentration (EtO) reaching the standard in emergency patients with the EtO as the monitoring index.

Methods: A retrospective observational study was conducted. The clinical data of patients receiving endotracheal intubation in the emergency department of Peking Union Medical College Hospital from January 1 to November 1 in 2021 were enrolled. In order to avoid interference with the final result due to inadequate ventilation caused by non-standard operation or air leakage, the process of the continuous mechanical ventilation after FiO was adjusted to pure oxygen in patients who had been intubated was selected to simulate the process of mask ventilation under pure oxygen before intubation. Combined with the electronic medical record and the ventilator record, the changes of the time required to reach 0.90 of EtO (that was, the time required to reach the standard of EtO) and the respiratory cycle required to reach the standard after adjusting FiO to pure oxygen under different baseline levels of FiO were analyzed.

Results: 113 EtO assay records were collected from 42 patients. Among them, 2 patients had only one EtO record due to the FiO baseline level of 0.80, while the rest had two or more records of EtO reaching time and respiratory cycle corresponding to different FiO baseline level. Among the 42 patients, most of them were male (59.5%), elderly [median age was 62 (40, 70) years old] patients with respiratory diseases (40.5%). There were significant differences in lung function among different patients, but the majority of patients with normal function [oxygenation index (PaO/FiO) > 300 mmHg (1 mmHg ≈ 0.133 kPa), 38.0%]. In the setting of ventilator parameters, combined with the slightly lower arterial partial pressure of carbon dioxide of patients [33 (28, 37) mmHg], mild hyperventilation phenomenon was considered to be widespread. With the increased in FiO baseline level, the time of EtO reaching standard and the number of respiratory cycles showed a gradually decreasing trend. When the FiO baseline level was 0.35, the time of EtO reaching the standard was the longest [79 (52, 87) s], and the corresponding median respiratory cycle was 22 (16, 26) cycles. When the FiO baseline level was increased from 0.35 to 0.80, the median time of EtO reaching the standard was shortened from 79 (52, 78) s to 30 (21, 44) s, and the median respiratory cycle was also reduced from 22 (16, 26) cycles to 10 (8, 13) cycles, with statistically significant differences (both P < 0.05).

Conclusions: The higher the FiO baseline level of the mask ventilation in front of the endotracheal intubation in emergency patients, the shorter the time for EtO reaching the standard, and the shorter the mask ventilation time.