ARDS Patient is on APVcmv (pressure regulation) with TV of 400, PEEP of 8 and RR of 20. Esophageal pressure monitoring shows expiratory transpulmonary pressure of -6 indicating the need to increase PEEP from 8 to at least 14. The goal of the expiratory transpulmonary pressure is to be maintained at 0-5 cm H2O.
The application of transpulmonary pressure in clinical practice has sound physiologycal basis, but it can cause some confusion because it has quite diverse interpretations:
1) as in this post, there is the possibility to increase Paw with PEEP to balance the value of Ppl in order to have 0-5 cmH20 of end exp transpulomonary pressure to keep the dependent lung recruited (an end insp transpulmonary pressure below 20 should prevent damage on the non dependent lung);
2) some authors reccomend to correct for the "gravitational factor" provided the fact the esophageal balloon does not reflect the Ppl neither of the dependent nor that of the non dependent lung but rathar the Ppl of the "mid lung" . So they suggest to add /subtract 5 cmH20 to the Ppl measured with the baloon to derive the transpulmonary pressure of the dependent /non dependtent lung respectively
3) other authors proposed to compute the value of Ppl with the ratio between chest wall and RS elastance x Paw particularly to explore the non dependent lung.
When trying to compare the 3 methods with real measurments the results can be substantially different and the ambition to protect the non dependent lung with one approach (the ratio between elastance proposed by Gattinoni) keeping at the same time recruited the dependent lung with an other (the method proposed by Talmor) can be absolutely impossible....
What method do you suggest us to adopt in clinical practice and what's your opinion about the degree of uncertainty of the value of Ppl we get.