Respiratory mechanics at different PEEP level during Anaesthesia in elderly: a pilot study

Background. General anaesthesia 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 anaesthesia (PEEP test); 2) if anaesthesia could be associated with the development of EFL; 3) if the use a small amount of PEEPe is able to reverse the possible negative effects of low lung volume ventilation. Method. Fifty two patients scheduled for abdominal surgery were prospectively randomized in: 1) group ZEEP, ventilated at PEEPe 0 H2O and 2) group PEEP ventilated at PEEPe 5 cm H2O. The presence of EFL was determined by the 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 anaesthesia. Results. 1) The PEEP test allows the detection of EFL; 2) Anaesthesia 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 anaesthesia is a valuable phenomenon. The use of 5 cmH2O of PEEPe was helpful to prevent the deterioration of lung mechanics that occurs during surgery.