The effects of different fractions of inspired oxygen during anesthesia recovery period on oxygen reserve and pulmonary gas exchange

Abstract

Background To observe the effects of different fractions of inspired oxygen(FiO2)during anesthesia recovery period on oxygen reserve and pulmonary gas exchange before extubation.Methods One hundred and fifty-two non-smoking patients with elective surgery done under general anesthesia were included in this study.After entering post anesthesia care unit (PACU),all the patients were mechanically ventilated with SIMV mode in FiO20.35.When a stable end-tidal oxygen concentration was achieved,a lung recruitment maneuver was performed and then the mode of ventilation went back to synchronized intermittent mandatory ventilation(SIMV).The patients were randomly assigned to 4 groups(n=38):FiO2=0.35,FiO2=0.5,FiO2=0.75,FiO2=1.0.The patients were ventilated with different concentrations of oxygen corresponding to their grouping for 5 min.The ventilator was stopped and the time of apnea tolerance was recorded.Blood samples were taken from dorsal artery of foot for blood-gas analysis.The shunt(Qs/Qt)and PaO2/FiO2 were calculated as well.Results The time to apnea tolerance were in turn(129±42),(178±61),(340±152),(421±153)s(P＜0.001)in group 0.35FiO2,group 0.50FiO2,group 0.75FiO2 and group 1.0FiO2.Compared with group 0.75FiO2,apnea tolerance in group 1.0FiO2 was longer,but it was not statistically significant.Apnea tolerance in group 1.0FiO2 was significantly longer than in group 0.35FiO2 or group 0.50FiO2.Apnea tolerance in group 0.75FiO2 was significantly longer than in group 0.35FiO2 or group 0.50FiO2.Apnea tolerance in group 0.50FiO2 was longer than in group 0.35FiO2,which was not statistically significant.Shunt after apnea were in turn(4.1±1.1),(4.6±1.3),(5.1±2.5),(13.1±4.5)％ in group 0.35FiO2,group 0.50FiO2,group 0.75FiO2 and group 1.0FiO2,respectively.Shunt in group 0.35FiO2,group 0.50FiO2 and 0.75FiO2 was significantly less than that in group 1.0FiO2(P＜0.001).PaO2/FiO2 after apnea were(494±75),(523±70),(536±80),(423±94)(P＜0.001)in the turn of group 0.35FiO2,group 0.50FiO2,group 0.75FiO2 and group 1.0FiO2.Pao2/FiO2 after apnea in group 0.35FiO2,group 0.50FiO2 and group 0.75FiO2 was significant larger than in group 1.0FiO2.Conclusions The use of 75％ oxygen can improve the pulmonary gas exchange,accompanied by shortened apnea tolerance. Key words: Fraction of inspired oxygen; Oxygen reserve; Pulmonary gas exchange; Apnea tolerance; Intrapulmonary shunt