Answer:

An extensive literature has evaluated the role of limiting tidal volumes to prevent VILI. Ventilation with tidal volumes greater than 8 mL per kg ideal body weight (IBW) is a risk factor for postoperative pulmonary complications in thoracic and abdominal surgery. Moreover, a randomized controlled trial in major abdominal surgery demonstrated that restricting tidal volumes from 6 to 8 mL per kg IBW decreased the incidence of postoperative respiratory failure. This intervention was part of a lung-protective strategy, which combined restricted tidal volumes with PEEP as compared to large tidal volumes without PEEP. Because the intervention also included PEEP, we cannot ascribe the full benefit to tidal volume restriction. A recent meta-analysis that included 19 studies comparing patients receiving tidal volumes of 6 to 8 mL per kg of IBW to those greater than 10 mL per kg of IBW showed a reduction in postoperative pneumonia and need for postoperative ventilatory support. In sum, the current data support targeting tidal volumes to less than 8 mL per kg IBW. However, there may be situations where these tidal volumes are inadequate. The optimum dose of intraoperative PEEP is less clear. A meta-analysis revealed that a no-PEEP approach was a risk factor for postoperative pulmonary complications in thoracic and abdominal surgery. However, randomized trials during high-risk abdominal surgery did not demonstrate a benefit from high PEEP and recruitment maneuvers. Another observational study compared the effect of PEEP ≥5 cm H₂O on patients undergoing abdominal surgery and craniotomies. The beneficial effect of PEEP in reducing postoperative respiratory complications was observed in the abdominal surgery group but not in those undergoing craniotomies. As a whole, the current evidence supports the use of moderate PEEP (approximately 5 cm H₂O) during surgery in patients at risk of atelectasis, and higher PEEP and recruitment maneuvers when the patient’s physiology suggests derecruitment.

Driving pressure is calculated as the plateau pressure minus the PEEP. The driving pressure is a factor of both the tidal volume and the set PEEP. A high driving pressure (>15 cm H₂O) is associated with an increased risk of postoperative pulmonary complications. Observing the effect of ventilator settings on driving pressure may be a useful strategy. However, this approach has not yet been fully evaluated in prospective studies.

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