全身麻醉诱导期正压通气对Ⅰ度肥胖患者氧储备的影响

Effect of positive pressure ventilation during induction of general anesthesia on oxygen reserve in Ⅰ degree obese patients

目的观察Ⅰ度肥胖患者全身麻醉诱导期应用持续气道正压（CPAP）和呼气末正压（PEEP）通气模式对氧储备的影响。方法选择拟在气管插管全身麻醉下行择期腹部手术的Ⅰ度肥胖患者45例，采用随机数字表法将患者分入纯氧机械通气组、CPAP＋纯氧机械通气＋PEEP组、体积分数0．6氧气机械通气组，每组15例。纯氧机械通气组患者麻醉诱导前在自主呼吸下通过面罩吸纯氧5min，麻醉诱导后行面罩下普通机械通气3min。CPAP＋纯氧机械通气＋PEEP组患者通过面罩行CPAP吸氧5min，麻醉诱导后行面罩机械通气加用PEEP（6cmH2O，1cmH2O=0．098kPa）3min。体积分数0．6氧气机械通气组的操作步骤和通气参数与纯氧机械通气组相同，仅将吸入氧体积分数调整为0．6。气管插管后暂不连接通气环路，待脉搏血氧饱和度（SpO2）降至93％时迅速连接环路通气供氧。记录气管插管后SpO2降至97％、95％、93％的时间。根据气管插管后即刻的血气分析值计算肺内分流率和氧合指数，记录胃部胀气时的视觉模拟评分。结果CPAP＋纯氧机械通气＋PEEP组SpO2降至97％、95％、93％的时间均显著长于另两组（P值均〈0．05），纯氧机械通气组又显著长于体积分数0．6氧气机械通气组（P值均〈0．05）。3组间SpO2降至97％与93％的时间差的差异无统计学意义（P值均〉0．05）。纯氧机械通气组的肺内分流率显著高于另两组（P值均〈0．05），氧合指数显著低于另两组（P值均〈0．05）。体积分数0．6氧气机械通气组的氧合指数又显著高于CPAP＋纯氧机械通气＋PEEP组（P〈0．05）。3组患者行机械通气后均存在不同程度的胃部胀气，CPAP＋纯氧机械通气＋PEEP组胃部胀气视觉模拟评分0～2分的患者构成比显著低于另两组（P值均〈0．05），3～5分的患者构成比显著高于另两组（P值均〈0．05）。结论应用正压通气模式可显著降低肺内分流率，提高氧储备，但应警惕胃胀气的风险。

Objective To observe the effect of continuous positive airway pressure （CPAP） and positive end-expiratory pressure （PEEP） ventilation during induction of general anesthesia on oxygen reserve in Ⅰdegree obese patients. Methods Forty-five Ⅰdegree obese patients scheduled for abdominal surgery under general anesthesia were randomized into 3 groups according to random digits table （n = 15 each）. In group A, patients inhaled 100% oxygen via face mask under spontaneous breathing for 5 min before induction of anesthesia and underwent mechanical ventilation for 3 min after induction of anesthesia. In group B, patients inhaled 100 % oxygen via face mask with CPAP for 5 min and then received ventilation with PEEP （6 cmH2O, 1 cmH2O=0. 098 kPa） for 3 min after induction. In group C, patients inhaled 60% oxygen via face mask under spontaneous breathing for 5 min before induction of anesthesia and underwent mechanical ventilation for 3 min after induction of anesthesia.After intubation, patients were ventilated until saturation pulse oxygen （SpO2） decreased to 93%. The apnea duration until SpO2 reached 97%, 95% and 93 % were recorded. Pulmonary shunt fraction and oxygenation index were calculated based on the blood gas analysis data instantly after intubation. Visual analog score （VAS） was used to evaluate gastric flatulence. Results The durations of SpO2 decreasing to 97%, 95% and 93% were significantly longer in group B than those in the other two groups （all P〈0.05） ; furthermore, the duration in group A was significantly longer than those in group C （all P〈0.05）. There was no significant difference in time interval of SpO2 97% to 93% between groups （all P〈0.05）. Compared with the other two groups, the pulmonary shunt fraction was significantly increased while oxygenation index was significantly decreased in group A （all P〈0.05）. The oxygenation index in group C was significantly higher than that in group B （P〈0.05）. Gastric flatulence occurred after mechanical ventilation in three groups. The constituent ratio of VAS of 0- 2 in group B was significantly lower than that in the other two groups （both P〈0.05）, while the constituent ratio of VAS of 3-5 in group B was significantly higher than that in the other two groups （both P〈0.05）. Conclusion Positive pressure ventilation can significantly reduce intrapulmonary shunt and improve oxygen reserve. Meanwhile, the risk of gastric flatulence should be noted.