In Reply
As we discussed in our article,1 the use of auto-PEEP to establish PEEP always results in different PEEP levels occurring in various lung units based on the lung mechanics of the unit. Lung units with long time constants (high airway resistance and/or high compliance) always develop the greatest auto-PEEP, whereas lung units with the shortest time constants (low compliance and/or low resistance) always develop the least auto-PEEP. As shown in the mathematical discussion by Chatburn and Kallet, lung units that are really stiff, as in severe ARDS, may have such short time constants that they fully collapse, even with a very short low CPAP time. This, as discussed, results in a repetitive opening and closing of lung units, causing atelectrauma.
Attempting to base the needed PEEP level on the use of auto-PEEP is always physiologically unsound and always has the potential of causing more lung injury. In our opinion, one should never establish PEEP by the use of auto-PEEP, because the risks always outnumber the potential benefits.
Footnotes
Dr Mirelea-Cabodevila has a patent on mid-frequency ventilation with no monetary gain. Dr Kacmarek has disclosed relationships with Covidien, Orange Med, and Venner Medical.
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Reference
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