title: Measuring intra-esophageal pressure to assess transmural pulmonary arterial occlusion pressure in patients with acute lung injury: a case series and review.
abstract: BACKGROUND
  Positive end-expiratory pressure (PEEP) may interfere with accurate assessment of cardiac function. PEEP may decrease left ventricular volume by lowering the transmural gradient between ventricular and pleural surface pressure (P(PL)) around the heart while raising the absolute pulmonary arterial occlusion pressure (PAOP). Clinical formulas used to predict the transmural PAOP (PAOP(TM)) require subtracting 25-50% of the PEEP level from the PAOP. However, both PAOP and P(PL) are influenced by transmitted PEEP and transmitted intra-abdominal pressure (IAP). We compared PAOP(TM) calculated by measuring intra-esophageal pressure (P(ES)) with PAOP(TM) estimated by clinical formulas.
  
  
  METHODS
  Twenty-two P(ES) measurements were made with a bedside pulmonary mechanics monitor (BICORE CP-100) on 11 patients with acute lung injury who had an elevated PAOP (mean +/- standard deviation) of 21.1 +/- 6.2 mm Hg and PEEP of 13.0 +/- 3.8 mm Hg. Paired comparisons were made with the Wilcoxon signed-rank test and multiple comparisons were made using one-way analysis of variance (ANOVA) and the Student-Newman-Keuls test. Pearson product-moment correlation coefficients were calculated. A MEDLINE literature search was done to survey the reported range of PEEP transmitted to P(PL).
  
  
  RESULTS
  P(ES) (14.6 +/- 5.0 mm Hg) exceeded PEEP; 9 of 11 patients had clinical evidence of increased IAP. PAOP(TM) predicted by clinical formulas were 13.5-17.7 mm Hg, whereas PAOP(TM) calculated by P(ES) was 6.2 +/- 3.6 mm Hg (p < 0.05). Linear regression revealed a moderate correlation between PAOP and PEEP (r = 0.49, p = 0.02). In contrast, there was a strong correlation between PAOP and P(ES) (r = 0.83, p < 0.0001). A review of data derived from the literature did not show a consistent pattern of PEEP transmission.
  
  
  CONCLUSIONS
  PAOP(TM) calculated by P(ES) may reflect transmitted IAP to the pleural surface. Using P(ES) to calculate PAOP(TM) may provide a more accurate assessment of hemodynamic status than predicting PAOP(TM) using clinical formulas based solely on estimated PEEP transmission.
authors.affiliation: Department of Anesthesia, University of California, San Francisco, USA. richkallet@earthlink.net
authors.forename: R H
authors.initials: RH
authors.lastname: Kallet
authors.forename: J A
authors.initials: JA
authors.lastname: Katz
authors.forename: J F
authors.initials: JF
authors.lastname: Pittet
authors.forename: J
authors.initials: J
authors.lastname: Ghermey
authors.forename: M
authors.initials: M
authors.lastname: Siobal
authors.forename: J A
authors.initials: JA
authors.lastname: Alonso
authors.forename: J D
authors.initials: JD
authors.lastname: Marks
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001794:Blood Pressure; D004947:Esophagus / Q000503:physiopathology*; D005260:Female; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011312:Pressure; D011651:Pulmonary Artery / Q000503:physiopathology*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy; D012189:Retrospective Studies