Effects Of Preoxygenation With N₂O-O₂ On Duration Of Non-Hypoxic Apnea

OBJECTIVE We investigated the effect of preoxygenation with 50% N₂O-O₂, 50% O₂-N₂ and 100% O₂ on duration of non-hypoxic apnea.METHODS 150 patients（ASAⅠ-Ⅱ） undergoing selective operation were randomized into three groups:50% N₂O-O₂（Group A, n=50）, 50% O₂-N₂（Group B, n=50）, and 100% O₂（Group C, n=50）. Preoxygenation and mask ventilation with 50% N₂ O, 50% O₂, and 100 % O₂ were used in Group A, Group B and Group C for 3 min, Fresh inflow air 10L/min. After anesthesia induction,patients were orotracheal intubated with video laryngoscope, and disconnect patients from the ventilator. The duration from the moment rocuronium given to patients（SpO₂=100%） to SpO₂ fall to 95%（T95）、 92%（T92） and 90%（T90） was recorded. During the induction, we did not use any assistant or controlled mechanical ventilation until SpO₂ falling to 90%.RESULTS The duration of preoxygenation in 3 groups is similar（193s vs.190 s vs.189 s, P>0.05）. The duration of non-hypoxic apnea is longer in Group C than that in Group A（464±103s vs. 250±67s,P<0.05）, the duration in Group A longer than Group B（250±67s vs. 223±46s, P<0.05）.CONCLUSION In the induction of general anesthesia, after preoxygenation with mask tightly closed for 3 min, the duration of non-hypoxic apnea of patients given with 100% O₂ is significantly longer than that in patients given with 50% N₂O-O₂, and the latter is longer than that in patients given with 50% O₂-N₂.