Setting intraoperative positive end expiratory pressure: how to be protective

General anesthesia and mechanical ventilation are required to perform most surgical procedures. Several study groups conducted observational and randomized trials to improve ventilator management and better understand how the setting of certain ventilator parameters may prevent postoperative complications. This review is focused on the role of positive end expiratory pressure (PEEP), summarizing the evidence in the general surgical population and in specific settings such as obese patients, laparoscopic procedures and thoracic surgery requiring one-lung ventilation. Several functional changes occur in the respiratory system following the induction of general anesthesia, which result in respiratory mechanics alterations, mainly airway closure and atelectasis formation. The application of a certain level of PEEP can limit the formation of atelectasis and avoid repetitive opening and closing of the alveoli, but these beneficial effects in respiratory mechanics do not necessarily translate into improved clinical outcome. On the other hand, higher levels of PEEP can impair patients’ hemodynamic and require more intraoperative fluids and vasoactive drugs. Setting PEEP level can be guided by patient’s characteristics and other parameters of respiratory system, in a tailored way. Several methods have been investigated, comprising setting PEEP to achieve the highest compliance of the respiratory system. However, tailored techniques so far failed to show benefits in terms of reduced incidence of postoperative complications. Applying an initial fixed minimal PEEP level of 2 to 5 cmH2O seems to be a pragmatic approach suitable for most surgical patients, to avoid excessive atelectasis formation while avoiding the negative effects of higher PEEP levels. Higher levels might be considered in long surgical interventions, laparoscopy and extreme Trendelenburg positioning.