Lung-protective Ventilation in the Operating Room

摘要

THE concept of lung-protective ventilation is well established in patients with acute lung injury and is now considered a fundamental approach when managing any patient under mechanical ventilation in an intensive care unit. The concept of lung-protective ventilation in the operating room has taken a little longer to develop, but data establishing the beneficial results of intraoperative lung-protective ventilation are increasing.1–3 Regardless of location, it has become well accepted that tidal volume (VT) should be maintained between 4 and 8 ml/kg of predicted body weight, that plateau pressure should be maintained at less than 28 cm H2O, and that driving pressure (plateau pressure minus end-expiratory pressure [PEEP]) should be maintained at less than 15 cm H2O. However, the establishment of guidelines for the setting of PEEP in any of these settings has been very challenging. There are no guidelines for PEEP setting based on the results of randomized controlled trials. In fact, the current literature is nonconclusive. The only established guideline is that patients with moderate-to-severe acute respiratory distress syndrome require “high” PEEP levels, whereas patients with mild adult respiratory distress syndrome require “low” PEEP.In this issue of the Journal, Pereira et al.4 performed a small physiologic trial to evaluate the ability of titrated PEEP to prevent intraoperative atelectasis using electrical impedance tomography. Optimal PEEP was selected based on the specific response of the given patient’s respiratory system. They selected 40 patients without previous lung disease undergoing elective abdominal surgery (20 under laparoscopy and 20 by open abdomen) admitted to the same institution during a 21-month period. All patients received a recruitment maneuver using pressure control ventilation to 40 cm H2O. Upon completion of the recruitment maneuver and before the initiation of the surgical procedure, the patients were randomized to be ventilated with 4 cm H2O PEEP or with the PEEP level that resulted in the least collapse and least overdistension using electrical impedance tomography. At the end of surgical anesthesia, patients in both arms were extubated without any adjustment of PEEP or fractional inspired oxygen tension; within 30 to 60 min of extubation, a chest computed tomography was performed. Compared with the 4 cm H2O group, the PEEP by electrical impedance tomography group had a lower intraoperative driving pressure, better oxygenation, and equivalent hemodynamics. No other postoperative pulmonary complications were recorded, and no adverse events associated with the recruitment maneuver were reported.Electrical impedance tomography is a portable, radiation-free imaging technique that can easily be used at the bedside. It provides real-time dynamic assessment of gas movement into and out of the respiratory system. As noted, it is very useful in identifying the PEEP level, resulting in minimal collapse and overdistention. The major problem with electrical impedance tomography is its availability. At present, no electrical impedance tomography device is commercially available in the United States. The only techniques that provide comparable information are the titration of PEEP postrecruitment using esophageal manometry or the best dynamic compliance PEEP.5,6 These techniques require invasive placement of an esophageal balloon or the careful assessment of compliance as PEEP is decreased. Limited data are available comparing these techniques, but electrical impedance tomography appears more precise in identifying the optimal PEEP level.Of concern is the fact that the results of the study by Pereira et al.4 seem to differ from the recently published Spanish study by Ferrando et al.7 The Spanish study did not find a difference in postoperative complications among groups.7 The design of the Spanish study at first glance is similar to that of Pereira et al.4 except (1) they enrolled 1,012 patients with healthy l