Abstract:  Objective · To investigate the effects of low tidal volume mechanical ventilation and low level of positive end expiratory pressure (PEEP) on respiratory function in patients with asthma under general anesthesia.  Methods · Forty-five patients with asthma undergoing upper abdominal surgery under general anesthesia were selected and randomly divided into three groups, with 15 cases in each group. Group A received a regular tidal volume of 10 mL/kg, group B a low tidal volume of 6 mL/kg and group C a low tidal volume of 6 mL/kg combined with 5 cmH2O PEEP. Ppeak was recorded at different time points, including the time of induction under anesthesia and the time of 5, 30 and 60 minutes after anesthesia induction. Based on such parameters, Cdyn were also calculated. Moreover, blood gas analysis index (PaO2 and PaCO2) were documented at the time of deoxidation period for 5 minutes before induction and 60 and 120 minutes after induction of anesthesia.  Results · The Ppeak values in goup C were significantly lower at all times (P<0.01) and Cdyn at the time of 60 and 120 minutes after induction were significantly higher (P<0.05) than group A. At the time of 60 and 120 minutes after induction, the levels of PaO2 were also increased (P<0.01) while the levels of PaCO2 was significantly decreased (P<0.05) in group C compared to group A and group B respectively.  Conclusion · The intermittent positive pressure ventilation of low tidal volume combined with low level of PEEP is a safe and effective mechanical ventilation method for asthma patients under general anesthesia, which can reduce airway peak pressure, enhance pulmonary dynamic compliance and improve the oxygenation index.

Key words:  low tidal volume, intermittent positive pressure ventilation, positive end expiratory pressure, asthma