Comparison of Optimal and Excess Fresh Gas Flow for Pre-intubation Oxygenation: A Randomized, Participant-Blind,...

The effect of different fresh gas flow (FGF) on achieving the target expired oxygenation (FeO₂) has been evaluated mainly with manual bag-mask ventilation, which provides variable minute ventilation (MV). The effect of machine-delivered consistent MV has yet to be well established. The present study evaluated the efficacy of pre-intubation oxygenation using optimal and excess FGF.

One hundred adult patients aged 18-60 years and with American Society of Anesthesiologists' physical status I-III were randomized to receive optimal FGF (=MV+500 mL) or excess FGF (i.e., +50%) for pre-intubation oxygenation targeted to FeO₂ of 85% and 90% or ventilated to maximum for five minutes. Concurrent fixed dial settings of volatile agents were used. Ventilation was done using an anesthesia machine in a pressure support (PS)-based technique. MV, fraction of inspired oxygen (FiO₂), and FeO₂ were collected and compared at different timepoints.

Both optimal and excess FGF groups showed similar efficacy in achieving FeO₂. The mean FeO₂ in the optimal and excess group at three minutes was 84.52 ± 3.38% versus 84.94 ± 3.73%; p = 0.368, while the same at five minutes was 86.02 ± 3.12% versus 85.98 ± 3.57%; p = 0.615. The mean time required to achieve an FeO₂ of 85% was 160.16 ± 67.15 seconds in the optimal FGF group and 147.81 ± 55.50 seconds in the excess FGF group (p = 0.335), with a mean difference of 12.35 seconds (8.36%).

Pre-intubation oxygenation using the optimal FGF is non-inferior to excess FGF, and is as adequate as using excess FGF to achieve FeO₂ levels exceeding 85% during machine-delivered PS-based ventilation. However, it was noted that three minutes was insufficient to achieve the target FeO₂ 90% using a closed circuit system and concurrent volatile agents.