BACKGROUND: Intrinsic PEEP (PEEPt) is frequently present during mechanical ventilation when expiratory times (te) are short. Some authors have begun to describe PEEP1, as a potentially therapeutic mechanism to be manipulated during pressure-controlled inverse ratio ventilation (PCIRV) much like ventilator-applied PEEP (PEEPappl). Other clinicians warn against PEEP, because of its potential side effects. Efforts to limit PEEP, or to apply it therapeutically have been hindered by the complications associated with the many ventilator adjustments required to effect a desired change in PEEPt. STUDY QUESTION: Does Equation 12 allow adequate prediction of the te necessary to achieve a desired PEEP1 once an initial PEEP1 has been measured?
METHOD: Using the exponential relationship between pressure and time during lung deflation, we developed a single, composite-function, logarithmic equation to predict the te necessary to achieve a desired PEEP, after the initial level of PEEP has been measured.
To test Equation 12 we used a test lung attached to a mechanical ventilator and recording pressure monitor attached to the alveolar port of the test lung. We used the pressure recordings to measure and set te. Two series of measurements were taken. RESULTS: In both series, the limits of agreement between the measured PEEP, and the predicted PEEPt were determined. The predicted value for PEEP demonstrated only a slight bias, underestimating measured (or actual) PEEP, by 0.79 (Series 1) and 0.39 (Series 2). IN CONCLUSION: In the laboratory, this technique appears to work well. More work is required to validate the equations with different ventilators and on various groups of patients.
