Effects Of Body Mass Index And Preoxygenation In The 15°Head-Up Position On Tolerance To Hypoxia

Objective: To investigate the effects of body mass index and preoxygenation in the 15o head-up position on tolerance to hypoxia during induction and intubation of anesthesia.Methods: 62 patients with age ranged 21~63 years old undergoing surgery under general anaesthesia with well cardiorespiratory function and without special diseases were included . Firstly , they were assigned to one of four groups according to body mass index : normal weight group(18.5≤BMI <23㎏/㎡,n=17),overweight group (23≤BMI< 25㎏/㎡,n=13),1°obesity group (25≤BMI< 30kg/㎡,n=15 )and 2°obesity group (BMI≥30 kg/m2 ,n=17);Secondly, they were randomly assigned to one of two groups: supine group (n=30) or 15o head-up position group ( n=32). After preoxygenation was achieved with an oxygen flow of 10 litre/min as well as rapid sequence induction of anaesthesia within 4 minutes, the trachea was intubated and the patient was left apneic and 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 respectively when patients to enter the operating room and the end of induction of anaesthesia and SPO2 decreased to 90% for arterial blood gas(ABG) analysis.Results: Desaturation safety period (the time from the end of induction of anaesthesia to desaturation to 90%) was significantly differences between four groups with different body mass index (P<0.05) .The time respectively is 546.47±75.20s (normal weight group),465.77±32.20s (overweight group),355.13±44.36s(I°obesity group),227.53±34.23s(II°obesity group), Obviously ,the desaturation safety period was shorter with body mass index gradually growth .In addition, the desaturation safety period for the 15°head-up group and supine group After Preoxygenation were 430.00s±136.63s and 359.33s±124.42s,respectively (P<0.05). The desaturation safety period is 70s longer in the 25°head-up position than in the supine position for patientsConclusion: Different body mass index results in different potential tolerance to hypoxia for patients. With the body mass index of patients increasing, the desaturation safety period become shorter and shorter. Moreover, Preoxygenation is more effective in the 15°head-up position than in the supine position in patients.