| Background Preoxygenation during induction of general anesthesia can substitute intrapulmonary nitrogen and increase the oxygen reserves to reduce the incidence of hypoxemia during intubation. Because functional residual capacity (FRC) is lower than normal body weight patients,obese patients oxygen reserve is declined and more easily lead to hypoxemia during induction of general anesthesia. A large number of researches suggested that patients with morbidly obesity(BMI>35kg·m-2) during the induction of anesthesia using the level of10cmH2O PEEP can prolong the safe duration limits of non ventilation. There are differences for diagnostic criteria for obesity between Asian populations and the WTO, I degree obese patients takes up a large proportion of the obese people, the application of positive pressure ventilation in the clinical effects and side effects in these patients are unclear.Objective To observe the effect of continuous positive airway pressure(CPAP) and positive end-expiratory pressure(PEEP) ventilation during induction of general anesthesia on apnea duration in I degrees obese patients, and with a low concentration of oxygen groups were compared to evaluate its clinical value.Methods Forty-five obese patients undergoing general anesthesia were enrolled in this prospective randomized study. Patients were randomized into3groups (n=15each):Pure oxygen ventilation group,combined pure oxygen ventilation and CPAP/PEEP group,0.6volume fraction of oxygen ventilation group. All the patients were intramuscularly injected atropine0.5mg30minutes before entering the operation room, and they didn’t be given a sedative. The patients were continuously monitored of non-invasive blood pressure (NIBP), electrocardiograph(ECG), heart rate (HR), pulse oxygen saturation (SpO2), peripheral vein channel was opened under local anesthesia, radial artery and internal jugular vein was punctured and cathetered. In Pure oxygen ventilation group, patients breathed100%O2via face mask continuously for5min, the headband was used to make their face with the oxygen mask tightened mildly, connect the anesthesia machine and the breathing circuit, adjust the fresh gas flow rate to10L.min-1, switch mode selector to manual mode, adjust the loop APL pressure valve limit into0. anesthesia induction:0.3mg-kg-1of etomidate,4μg.kg-1of fentanyl,0.6mg.kg-1of rocuronium were injected into intravenous, anesthesia practitioners used hands to maintain airway patency and the mandibular closed in patients, controlled by hand assisted ventilation. Keep the airway pressure<25cmH2O during the hand assisted ventilation. While BIS<50, turn on the muscle relaxation monitor. When the T4/T1=0, use anesthesia respirator mask to control ventilation in3minutes, set ventilation parameters:FiO2=100%, RR=12bpm, Vt=10ml×standard body weight (Kg). Assistant through the application of Sellick technique may prevent gas into the esophagus. In combined pure oxygen ventilation and CPAP/PEEP group, the patients spontaneous breathing with the oxygen mask, set the loop APL pressure valve limit into6cmH2O (1cmH2O=0.098kPa) to execute CPAP, after induction, based on the parameter of mechanical ventilation of the pure oxygen ventilation group plus PEEP 6cmH2O. The ventilation parameter of0.6volume fraction of oxygen ventilation group was the same with pure oxygen ventilation group except that the oxygen concentration was set to60%. After induction, a senior anesthesiologist performed peroral tracheal intubation, fiber bronchoscope to ensure the position of the endotracheal tube without error quickly. Anesthesia was maintained with propofol.No patients were not ventilated until SpO2decreased to93%. The apnea duration until SpO2reached97%,95%and93%were measured with a stopwatch; the pulmonary shunt fraction and oxygenation index were calculated based on the blood gas analysis data instantly after intubation; stomach flatulence was evaluated by surgeons.Results The duration of SpO2dropped to97%,95%and93%were significantly longer in combined pure oxygen ventilation and CPAP/PEEP group than the other two groups (all P<0.01), furthermore, pure oxygen ventilation group were significantly longer than0.6volume fraction of oxygen ventilation group (all P<0.01). There were no significant difference in duration of SpO297%to93%among the three groups(P=0.047). The pulmonary shunt fraction in pure oxygen ventilation group was significantly higher than the other two groups (all P<0.01). The oxygenation index in pure oxygen ventilation group was significantly less than the other two groups (all P <0.01), moreover, which in0.6volume fraction of oxygen ventilation group was significantly higher than combined pure oxygen ventilation and CPAP/PEEP group (P <0.01). There were varying degrees of stomach flatulence after mechanical ventilation in three groups. In combined pure oxygen ventilation and CPAP/PEEP group stomach flatulence visual analog score (VAS) of0-2was significantly lower than the other two groups (all P<0.05).Conclusion Application positive pressure ventilation can reduce intrapulmonary shunt and increases nonhypoxic apnea duration significantly, but should be alert to the risk of stomach flatulence. |
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