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

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Abstract:

BACKGROUND: A recent trial showed that setting PEEP according to end-expiratory transpulmonary pressure (Ppl,ee) in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) might improve patient outcome. Ppl,ee was obtained by subtracting the absolute value of esophageal pressure (Pes) from airway pressure an invariant value of 5 cm H2O. The goal of the present study was to compare 2 methods for correcting absolute Pes values in terms of resulting Ppl,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. Pes was measured at PEEP (Pes,ee) and at relaxation volume of the respiratory system Vr (Pes,Vr), obtained by allowing the subject to exhale into the atmosphere (zero PEEP). Two methods for correcting Pes were compared: Talmor method (Ppl,ee,Talmor = Pes,ee ‐ 5 cm H2O), and Vr method (Pes,ee,Vr = Pes,ee ‐ Pes,Vr). The rationale was that Pes,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 Pes,ee and Pes,Vr were 11 (7‐14) cm H2O and 8 (4‐11) cm H2O, respectively. Ppl,ee,Talmor was 6 (1‐8) cm H2O, and Pes,ee,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 Ppl,ee,Talmor was ≥ Pes,ee,Vr (7 [5‐9] cm H2O vs 2 [1‐5] cm H2O, respectively), while in 14 subjects Pes,ee,Vr was > Ppl,ee,Talmor (2 [0‐4] cm H2O vs −1 [−3 to 2] cm H2O, respectively). Ppl,ee,Vr was significantly greater than Ppl,ee,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 Pes 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.

Keywords: ARDS; acute lung injury; esophageal manometry; esophageal pressure; transpulmonary pressure

Document Type: Research Article

DOI: http://dx.doi.org/10.4187/respcare.01883

Affiliations: Service de Réanimation Médicale, Hôpital de la Croix Rousse, france

Publication date: December 1, 2012

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