To Explore The Effect Of Fresh Gas Flow On Patients’ Oxygen Reserve During Mask Assisted Ventilation

ObjectiveBy exploring the effect of different fresh oxygen flow on patients’oxygen reserve during mask assisted ventilation under general anesthesia,a valuable reference value is provided for setting the fresh oxygen flow during mask assisted ventilation in clinical anesthesia practice.MethodsSeventy two ASA I-II patients,aged 18-60 years,with BMI between18-30kg/m~2,male and female,who underwent elective general anesthesia in our hospital from October 2021 to January 2022 were selected.After entering the operating room,the patients in each group began anesthesia induction after preoxygenation with tidal volume method for 3 minutes.After the patients stopped breathing,they began mask assisted ventilation for 2 minutes.According to the order of admission,the patients were randomly assigned to the experimental group with fresh gas flow of 1L/min,2L/min,4L/min and 8L/min during mask assisted ventilation.18 people were included in each group.The primary outcome measures were the time when the pulse oxygen saturation decreased to 90%after endotracheal intubation,i.e.safe apnoea time.The secondary indicators were the pulse oxygen saturation,end expiratory oxygen concentration,heart rate,carbon dioxide partial pressure after mask assisted ventilation and carbon dioxide washout during mask assisted ventilation,as well as the end expiratory carbon dioxide partial pressure at the beginning of mechanical ventilation and the time from the beginning of mechanical ventilation to the recovery to the pulse oxygen saturation after preoxygenation,that is,reoxygenation time.Results1)In patients who received 3-min tidal volume preoxygenation under the same conditions,when the fresh gas flow of mask assisted ventilation was1L/min,2L/min,4L/min and 8L/min,the safe apnoea time of face mask assisted ventilation was 305.1±97.0s in FGF=1L/min group,315±112.5s in FGF=2L/min group,381.3±118.6s in FGF=4L/min group and 359±104.4s in FGF=8L/min group.There was no significant statistical difference by multi sample mean comparison（P=0.139>0.05）.Correlation analysis showed that there was no significant correlation between the flow of fresh oxygen during mask assisted ventilation and the safe time limit without ventilation（P>0.05）.2)The EtO₂of patients in each group was different after 3 minutes of preoxygenation and 2 minutes of mask assisted ventilation.The comparison of multiple mean values showed that there was no significant statistical difference in EtO₂between FGF=1L/min group and FGF=2L/min group（P=0.456）;there was no significant difference in EtO₂between FGF=4L/min group and FGF=8L/min group（P=0.116）;there was significant difference between FGF=1L/min group and FGF=4L/min group and FGF=8L/min group（P=0.021 and P<0.001）;there was significant statistical difference in EtO₂between FGF=2L/min group,FGF=4L/min group and FGF=8L/min group（P=0.003and P<0.001）.The comparison of multiple means showed that there was significant statistical difference in EtO₂among FGF=1L/min group,FGF=2L/min group,FGF=4L/min group and FGF=8L/min after mask assisted ventilation for 2min（P<0.05）.Correlation analysis showed that there was a positive correlation between fresh oxygen flow and end expiratory oxygen concentration during mask assisted ventilation（P<0.001,correlation coefficient r=0.52）.3)During mask assisted ventilation,there was significant statistical difference in CO₂elution under different fresh gas flow.The CO₂elution in FGF=1L/min group and FGF=2L/min group was greater than that in FGF=8L/min group（P=0.010 and P=0.015）,while there was no significant statistical difference between FGF=4L/min group and the other three groups（P>0.05）.4)There was no significant statistical difference in the Et CO₂of patients in each group after 3 minutes of preoxygenation,2 minutes of mask assisted ventilation and mechanical ventilation（P>0.05）.5)There was no significant statistical difference in reoxygenation time among the groups（P=0.947>0.05）.6)There was no significant statistical difference in Sp O₂after entering the operating room,3 minutes of preoxygenation,2 minutes of mask assisted ventilation and the lowest Sp O₂after stopping ventilation（P>0.05）.7)There was no significant statistical difference in HR of patients in each group after entering the operating room,mask assisted ventilation for 2minutes and pulse oxygen saturation of 90%（P>0.05）.Conclusion1)In patients who received 3-min tidal volume preoxygenation under the same conditions,there was no significant statistical difference in the effects of FGF=1L/min,FGF=2L/min,FGF=4L/min and FGF=8L/min on oxygen reserve.2)During mask assisted ventilation,when the fresh air flow is 1-8L/min,the fresh oxygen flow has a positive correlation with the end expiratory oxygen concentration.3)For patients who receive preoxygenation before anesthesia induction,when mask assisted ventilation,it is recommended that the fresh oxygen flow be greater than 4L/min,which can significantly reduce the repeated inhalation of gas in the respiratory circuit and maintain the patient’s EtO₂.