Respiratory mechanics at different PEEP levels during general anesthesia in the elderly: A pilot study

Background. General anesthesia could imply that the closing capacity exceed the functional residual capacity. This phenomenon, associated with a reduction of maximal expiratory flow, could lead to expiratory flow limitation (EFL). The aim of our study was to verify 1) a new method of determining EFL during anesthesia (PEEP test); 2) if anesthesia could be associated with the development of EFL; 3) if the use a small amount of PEEP is able to reverse the possible negative effects of low lung volume ventilation. Methods. Fifty two patients scheduled for abdominal surgery were prospectively randomized in: 1) group ZEEP, ventilated at PEEP 0 H₂O and 2) group PEEP ventilated at PEEP 5 cm H₂O. The presence of EFL was determined by the negative expiratory pressure (NEP) test the day before surgery and by the PEEP test during surgery. Data of respiratory mechanics were calculated at the beginning and at the end of anesthesia. Results. 1) The PEEP test allows the detection of EFL; 2) anesthesia was associated with EFL: 8 patients developed EFL after induction. At the end of surgery, 7 more patients became flow limited in the group ZEEP, while only 1 in the group PEEP. The group ZEEP exhibited a marked decrease of expiratory flow and a worsening of respiratory mechanics at the end of surgery. Conclusion. The PEEP test allowed to verify that EFL during anesthesia is a valuable phenomenon. The use of 5 cmH₂O of PEEP was helpful to prevent the deterioration of lung mechanics that occurs during surgery.