Sir,
We read with interest the article written by Sehgal et al[1] and want to raise certain issues pertaining to the important topic:
In Case 1, an end-expiratory transpulmonary pressure of 0–10 cm of H2O and end-inspiratory transpulmonary pressure of <25 cm of H2O were targeted. As a result, the patient received positive end expiratory pressure (PEEP) of 13 [transpulmonary pressure (Ptp) PEEP of 3 or 4] though his FiO2 was 1 throughout the hospital course. Should a higher PEEP and hence a higher Ptp PEEP been targeted in this case (though the patient had hypotension)? Talmor et al.[2] had studied application of esophageal pressure values for titration of ventilator strategies in acute respiratory distress syndrome (ARDS) patients and had used an algorithm to determine the Plexp (end-expiratory pleural pressure) and PEEP (targeting a minimum PaO2 of 55 mm of Hg) which is provided in Table 1. Trials such as ALVEOLI have also suggested a higher PEEP at a FiO2 of 1. Table 2 portrays the PEEP–FIO2 combination used in the said trial (in the lower PEEP group). Thus, it seems that the authors have measured the esophageal pressures but have not used them for appropriate PEEP titration
The authors have attempted to tailor the ventilator strategy based on the esophageal pressure monitoring, but they have not indicated how the strategy should be altered based on the subtype, namely, ARDSp versus ARDSexp. It is seen that application of PEEP results in increased recruitment and decreased elastance of the respiratory system in ARDSexp as compared to the ARDSp as suggested by Gattinoni et al.[3] However, whether the above findings should dissuade intensivists to apply PEEP in cases of ARDSp can be ardently debated due to lack of evidence in its favor. ARDSNet and ALVEOLI had consistently used PEEP in all ARDS patients (both ARDSp and ARDSexp) based on Table 2. Talmor et al.[2] had around 23% patients having ARDSp in the esophageal pressure group for which they had used the same strategy as in ARDSexp
Of the two cases described by the authors, poor chest wall compliance in Case 2 appears to be predominantly due to increased abdominal pressures (as a result of hemoperitoneum). This, however, might not be true for all extrapulmonary ARDS patients, as also highlighted in a study by Pelosi et al,[4] indicating that ARDSexp may not be a homogenous group by itself
Finally, a few caveats about using esophageal pressure for titrating PEEP – the esophageal pressure may not represent the pleural pressures in normal individuals as also in critically ill patients. Arbitrarily, correction factors (Talmor et al. had subtracted 5 cm of H2O from the esophageal pressure value to correct for the effects of mediastinal weight and balloon air volume on the observed pressures) have been used which can be variable and can make the interpretation difficult.[5] Furthermore, esophageal pressures can lead to increased PEEP administration and better oxygenation parameters in subjects but its effect on mortality, ventilator-free days, etc., is still unclear.[5]
Table 1.
FiO2 and Plexp combination used by Talmor et al2
Table 2.
FiO2 and PEEP combination used in ARDSNet trial
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References
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