Default to PEEP
Where I work, the anesthesia machines still default to a PEEP of zero, and I don’t understand why. I always perform positive-pressure ventilation with a minimum PEEP of 5 cm H2O. Even if the patient is breathing without assistance from the anesthesia machine (negative-pressure ventilation), I try to dial in some PEEP; depending on the machine this is easier (Dräger, for example) or more difficult (GE). If the patient is obese, undergoing laparoscopic surgery, or in Trendelenberg, I routinely increase the PEEP to 8 or 10. In doing so, with or without recruitment maneuvers, I usually see the SpO2 improve without increasing the inspired oxygen concentration.
PEEP has many benefits and little downside. It improves pre-oxygenation in obese patients. It decreases atelectasis and post-operative pulmonary complications and it can improve oxygenation. To anyone not routinely using PEEP, I ask, why not?
Why would someone want to avoid PEEP? High levels of PEEP can impede venous return and worsen hypotension. If a patient has significant hypotension, lowering the PEEP to 5 may be reasonable, but I would argue vasopressors, fluid, and blood are more effective treatments depending on the cause. If a patient has a significant air leak (e.g. bronchopleural fistula) or a tension pneumothorax, PEEP could worsen the condition.
A new systematic review and network meta-analysis from March 2025 reaffirms the benefits of PEEP. Their findings showed any PEEP is better than no PEEP for reducing postoperative pulmonary complications including pneumonia. Higher PEEP (defined in the study as > 5 cm H2O) is better than lower PEEP at preventing atelectasis.
The study defined low tidal volume as 4-8 mL/kg of ideal or predicted body weight and high tidal volume as > 8 mL/kg of ideal or predicted body weight. PEEP was chunked into three categories: 0, 1-5, and > 5 cm H2O. Postoperative pulmonary complications was a composite of many different outcomes which were defined differently by various studies included.
For preventing post-op pulmonary complications and pneumonia:
Any PEEP is better than no PEEP (moderate certainty)
Low tidal volume is better than high tidal volume (moderate certainty)
Low tidal volume with PEEP is better at reducing hypoxemia compared to high tidal volume with no PEEP (high certainty)
PEEP > 5 cm H2O is superior to no PEEP for prevention of atelectasis (moderate certainty)
As with all studies there are limitations. I would have liked to see PEEP of 5 as a standalone group since that is probably the most commonly used PEEP setting. Recruitment maneuvers with PEEP did not show clear benefit over PEEP alone, however, this was probably inadequately parsed out. I would like to see it tested in specific populations (obesity, morbid obesity, laparoscopic surgery, Trendelenberg positioning, and combinations of the previous characteristics). I suspect recruitment maneuvers combined with increasing PEEP would show more benefit in obese and morbidly obese individuals in Trendelenberg than in people with normal BMI regardless of positioning.
My conclusions from this study are: use at least a PEEP of 5 and tidal volumes not greater than 8 mL/kg of ideal body weight for all patients. If you don’t use PEEP or if you use high tidal volumes, please share your evidence for supporting such practices.
As always, if you notice any errors, please reach out to me.