Effects of different oxygen concentrations on oxygenation index of obese patients during non-ventilation period after general anesthesia induction

Objective To evaluate the effects of different oxygen concentrations on the oxygenation index of obese patients during the non-ventilation period after general anesthesia induction. Methods 75 American Society of Anaesthesiologists （ASA） gradeⅡ-Ⅲobese patients （30 kg/m22）， aged 18-65 years， were recruited and divided into H， M and L groups according to the inhaled oxygen concentration during anesthesia induction. Induction drugs were given according to the ideal body weight. After the patients’ eyelash reflex were absent and spontaneous respiration was terminated， the oropharyngeal airway was placed， the mandibular mask was supported with both hands and mechanical ventilation was pre-administered with oxygen （100% oxygen concentration in group H， 80% oxygen concentration in group M， and 60% oxygen concentration in group L）. The tracheal tube was intubated under the guidance of a visual light rod， and oxygen was temporarily not connected. The ventilator was connected when O2 saturation declined to 92%. The main outcome indexes included the oxygenation index of obese patients before anesthesia induction （T0）， after preoxygenation （T1）， and before PACU entry （T2）. The secondary outcome indexes included the number of cases of attasis at each time point of T0， T1， and T2. The time of SpO2 decreasing to 92% （time interval between SpO2 decreasing to 92% and the start of intubation）， the time of SpO2 restoring to 100% after ventilator connection， intubation time and operation time were recorded. The incidence of postoperative pulmonary complications and the length of hospital stay were compared among different groups. Results Compared with group H， oxygenation indexes at T1 were lower in groups M and L （both P < 0.05）. At T1 and T2， the incidence of atelectasis in groups M and L was significantly lower than that in group H （both P < 0.05）. Among the three groups， the time of SpO2 declining to 92% in group H was （197±57） s，（157±31） s in group M， and （131±23） s in group L， respectively. Compared with group H， the time of SpO2 declining to 92% in groups M and L was significantly shortened （both P < 0.05）. The time of SpO2 restoring to 97% in group H was shorter than that in groups M and L （both P < 0.05）. No significant differences were observed in the incidence of postoperative pulmonary complications and the length of hospital stay among three groups （all P > 0.05）. Conclusions During general anesthesia induction in obese patients， the oxygenation index at 100% oxygen concentration is higher than those at 80% and 60% oxygen concentrations， which is conducive to the restoration of SpO2 after oxygen administration. The incidence of postoperative pulmonary complications and the length of hospital stay do not significantly differ among three groups.