Comparison of 2 Correction Methods for Absolute Values of Esophageal Pressure in Subjects With Acute Hypoxemic Respiratory Failure, Mechanically Ventilated in the ICU

摘要

BACKGROUND: A recent trial showed that setting PEEP according to end-expiratory transpulmonary pressure (P-pl,P-ee) in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) might improve patient outcome. P-pl,P-ee was obtained by subtracting the absolute value of esophageal pressure (P-es) from airway pressure an invariant value of 5 cm H2O. The goal of the present study was to compare 2 methods for correcting absolute P-es in terms of resulting P-pl,P-ee and recommended PEEP. METHODS: Measurements collected prospectively from 42 subjects with various forms of acute hypoxemic respiratory failure receiving mechanical ventilation in ICU were analyzed. P-es measured at PEEP (P-es,P-ee) and at relaxation volume of the respiratory system Vr (P-es,P-Vr), obtained by allowing the subject to exhale into the atmosphere (zero PEEP). Two methods for correcting P-es were compared: Talmor method (P-pl,P-ee,P-Talmor = P-es,P-ee - 5 cm H2O), and Vr method (P-es,P-ee,P-Vr = P-es,P-ee - P-es,P-Vr). The rationale was that P-es,P-Vr was a more physiologically based correction factor than an invariant value of 5 cm H2O applied to all subjects. RESULTS: Over the 42 subjects, median and interquartile range of P-es,P-ee and P-es,P-Vr were 11 (7-14) cm H2O and 8 (4-11) cm H2O, respectively. P-pl,P-ee,P-Talmor was 6 (1-8) cm H2O, and P-es,P-ee,P-Vr was 2 (1-5) cm H2O (P = .008). Two groups of subjects were defined, based on the difference between the 2 corrected values. In 28 subjects P-pl,P-ee,P-Talmor was >= P-es,P-ee,P-Vr (7[5-9] cm H2O vs 2 [1-5] cm H2O, respectively), while in 14 subjects P-es,P-ee,P-Vr was > P-pl,P-ee,P-Talmor (2 [0-4] cm H2O vs -1 [-3 to 2] cm H2O, respectively). P-pl,P-ee,P-Vr was significantly greater than P-pl,P-ee,P-Talmor (7 [5-11] cm H2O vs 5 [2-7] cm H2O) in the former, and significantly lower in the latter (1 [-2 to 6] cm H2O vs 6 [4-9] cm H2O). CONCLUSIONS: Referring absolute P-es values to Vr rather than to an invariant value would be better adapted to a patient's physiological background. Further studies are required to determine whether this correction method might improve patient outcome.