The purpose of this study is to investigate the clinical application value of inverse ratio ventilation in obese patients during induction of general anesthesia by studying the effect of inverse ratio ventilation on the safe apnea time.

Inverse ratio ventilation(IRV) can produce mean airway pressure(Pmean)similar to external positive end expiratory pressure(Peep) by increasing inspiratory time. Moreover, the increase of Pmean was not accompanied by the further increase of peak airway pressure (Ppeak) and airway plateau pressure (Pplat), while the application of external peep accompanied with the increase of Pplat increased the risk of barotrauma . High level of Peep increased cardiac load and decreased cardiac output. A number of studies have found that the hemodynamic stability of patients can be achieved when IRV regulates the inspiratory / expiratory ratio in an appropriate range (I: E < 2:1). Therefore, the inverse ratio is considered to be superior to Peep in terms of gas exchange and respiratory mechanics.

Inclusion Criteria:

• Obese patients, aged 18-65 years, of either gender, ASA grade II-III, body mass index (BMI) > 30 kg / m2, scheduled for general anesthesia under tracheal intubation, signed informed consent.

Exclusion Criteria:

• Patients who need rapid sequence induction (RSI); patients with expected difficult airway; severe chronic respiratory diseases, such as tuberculosis, bronchitis, bronchial asthma and COPD; patients with severe cardiovascular diseases, such as severe ischemic heart disease and pulmonary hypertension; patients with severe cerebrovascular diseases, such as cerebral hemorrhage and cerebral infarction; patients with abnormal basal metabolic rate, such as pregnancy, thyrotoxicosis, pheochromocytoma; and severe stomach reflux disease; patients with abnormal hemoglobin and hematocrit.