ΔP-Guided PEEP in the Operating Room--Do We Need More Guidance?

To the Editor

Intraoperative higher positive end-expiratory pressure (PEEP) can prevent atelectasis, which could translate into less postoperative pulmonary complications (PPCs). However, ventilation with higher PEEP can also induce overdistension, which could in part negate these positive effects. A “personalized” PEEP approach may be more appropriate, as the balance between prevention of atelectasis and induction of overdistension probably differs between patients. Since ΔP is a “digital” biomarker for both atelectasis and overdistension, a ΔP-guided PEEP strategy has been proposed before,[1] and recently in your journal, Zhang et al[2] presented the findings of a randomized clinical trial confirming benefit of a ΔP-guided PEEP strategy in patients undergoing open abdominal surgery.

However, it remains uncertain how to titrate “best” PEEP to ΔP––for instance, we can use an incremental PEEP trial, wherein PEEP is gradually increased and set at the level at which ΔP is lowest, or a decremental PEEP trial after a recruitment maneuver, in which PEEP is gradually decreased to find the level at which the ΔP, after an initial decrease, again starts to increase. These 2 approaches may very well result in different levels of “best” PEEP––the first approach favors prevention of atelectasis but may conceal PEEP-induced overdistension and the second approach could result in less prevention of atelectases but takes notion of overdistension caused by PEEP. Advantages of an incremental PEEP trial are that it takes far less time than a decremental PEEP trial, and may also result in less hemodynamic instability induced by the high intrathoracic pressures during a recruitment maneuver.[3,4]

In their study, Zhang et al[2] used the first approach, ie, they used incremental PEEP trials. The “Driving PrESsure DurIng GeNeral AnesThesIa for Open AbdOmiNal Surgery” (DESIGNATION) study is an international multicenter ongoing randomized clinical trial in which a decremental PEEP trial is used to select the best PEEP, after an initial incremental PEEP trial to 20 cm H2O as a recruitment maneuver.[5] In an interim analysis for study conduct, we compared the ΔP at the recruitment maneuver, ie, at 20 cm H2O PEEP, and the nadir for PEEP in the successive decremental PEEP trial in a total of 290 patients. While ΔP was 10 (9–12) cm H2O at the end of the incremental PEEP trial, the nadir ΔP in the decremental PEEP trial was much lower, only 7 (6–8) cm H2O (P < .01).

One interesting finding in the study by Zhang et al[2] was that mechanical power (MP) of ventilation was higher in the ΔP-guided PEEP group. MP can be seen as the amount of energy transferred from the ventilator to the lung, and has been proposed, alongside ΔP, as an additional biomarker to guide ventilation. Given the fact that the MP is calculated from the ΔP, it is surprising to see that while ΔP declines, the MP increases.[6] In fact, the MP is expected to move in the same direction as ΔP. Could the authors provide more insight on how the MP was calculated, and how the other parameters used to calculate the MP differed between the groups?