Objective:To investigate the effects ofbody mass index on duration of non-hypoxic apnoea during induction and intubation of anesthesia.Methods:80 patients undergoing surgery with general anaesthesia aged 21～63 years old with ASA Ⅰ-Ⅱgrade and without special diseases were included.they were assigned to one of four groups according to body mass index:Group 1(normal

n=20)

Group 2 (overweight

n=20)

Group 3(Ⅰ° obesity

n=20)and Group 4(Ⅱ°obesity

n=20).Preoxygenation was achieved with an oxygen flowof10 litre/min within 4 minutes.After rapid sequence induction of anaesthesia

the trachea was intubated and the patient was left apneic with disconnected from the anaesthesia circuit until SpO2 decreased to 90%.The time taken for desaturation to 90%from the end of induction of anaesthesia was recorded.Arterial blood samples were drawn when patients to enter the operating room and the end of induction of anaesthesia and SpO2 decreased to 90%respectively for arterial blood ga(sABG)analysis.Results:Desaturation safety period(the time to desaturation to 90%)were significantly differences between four groups with different body mass index(P<0.05).The time were (542.47±48.24)(sGroup 1)

(465.77±32.20)(sGroup 2)

(355.13±44.36)(sGroup 3)

(227.53±34.23)s(Group 4).Conclusion: Different body mass index of patients results in different desaturation safety period and potency of tolerance to apnoea.With the body mass index of patients increasing

the desaturation safety period become shorter and shorter.