Restricted accessResearch articleFirst published online 2000-9
Measuring Intra-Esophageal Pressure to assess Transmural Pulmonary Arterial Occlusion Pressure in Patients with Acute Lung Injury: A Case Series and Review
BACKGROUND: Positive end-expiratory pressure (PEEP) may interfere with accurate assessment of cardiac function. PEEP may decrease left ventricular volume by lowering the transmural gra-dient between ventricular and pleural surface pressure (PPL) around the heart while raising the absolute pulmonary arterial occlusion pressure (PAOP). Clinical formulas used to predict the transmural PAOP (PAOPTM) require subtracting 25-50% of the PEEP level from the PAOP. However, both PAOP and PPL are influenced by transmitted PEEP and transmitted intra-abdom-inal pressure (IAP). We compared PAOPTM calculated by measuring intra-esophageal pressure (PES) with PAOPTM estimated by clinical formulas. METHODS: Twenty-two PES 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 PPL. RESULTS: PES (14.6 ± 5.0 mm Hg) exceeded PEEP; 9 of 11 patients had clinical evidence of increased IAP. PAOPTM predicted by clinical formulas were 13.5-17.7 mm Hg, whereas PAOP.TM calculated by PES was 6.2 ± 3.6 mm Hg (p < 0.05). Linear regression revealed a moderate corre-lation between PAOP and PEEP (r = 0.49, p = 0.02). In contrast, there was a strong correlation between PAOP and PES (r = 0.83, p < 0.0001). A review of data derived from the literature did not show a consistent pattern of PEEP transmission. CONCLUSION: PAOPTM calculated by PES may reflect transmitted IAP to the pleural surface. Using PES to calculate PAOPTM may provide a more accurate assessment of hemodynamic status than predicting PAOPTM using clinical formulas based solely on estimated PEEP transmission.
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