Chest
Volume 136, Issue 4, October 2009, Pages 1014-1020
Journal home page for Chest

Original Research
Critical Care Medicine
A-Lines and B-Lines: Lung Ultrasound as a Bedside Tool for Predicting Pulmonary Artery Occlusion Pressure in the Critically Ill

https://doi.org/10.1378/chest.09-0001Get rights and content

Background

The risk of pulmonary edema is the main limiting factor in fluid therapy in the critically ill. Interstitial edema is a subclinical step that precedes alveolar edema. This study assesses a bedside tool for detecting interstitial edema, lung ultrasound. The A-line is a horizontal artifact indicating a normal lung surface. The B-line is a kind of comet-tail artifact indicating subpleural interstitial edema. The relationship between anterior interstitial edema detected by lung ultrasound and the pulmonary artery occlusion pressure (PAOP) value was investigated.

Method

We performed a prospective study in medicosurgical ICUs of university-affiliated teaching hospitals. We enrolled 102 consecutive mechanically ventilated patients who all underwent pulmonary artery catheterization. We defined A-predominance as a majority of anterior A-lines and B-predominance as a majority of anterior B-lines. These patterns were correlated with PAOP.

Results

For diagnosing PAOP ≤ 13 mm Hg, A-predominance had 90% specificity, 67% sensitivity, 91% positive predictive value, and 65% negative predictive value. For diagnosing PAOP ≤ 18 mm Hg, A-predominance had 93% specificity, 50% sensitivity, 97% positive predictive value, and 24% negative predictive value, respectively.

Conclusions

A-predominance indicates dry interlobular septa. Specific to predicting a low PAOP value, A-predominance suggests that fluid may be given without initial concern for the development of hydrostatic pulmonary edema. B-predominance indicates interstitial syndrome, which is usually related to interstitial edema. B-predominance is observed in a wide range of PAOP values, precluding conclusions about the need for fluid therapy. This bedside potential will be appreciated by those intensivists who envision fluid therapy based on low PAOP values and who consider that using the concept of a safety factor provided by lung ultrasound is logical.

Section snippets

Methods

A prospective 5-year study evaluated 103 critically ill patients receiving a PAC in medicosurgical ICUs. These patients required hemodynamic measurements at the discretion of the managing team faced with instability or complex hemodynamic situations (Table 1). Patients were consecutive in the context of the part-time presence of the ultrasound operators (DL and GM), who were blinded to the hemodynamic measurements made by other members of the managing team. Hindrances to an examination

Results

Of 103 patients, 1 patient experienced a pneumothorax and was excluded. The study enrolled 102 patients (Table 1), resulting in 102 comparisons of PAOP and lung ultrasound.

Discussion

Until now, lung ultrasound has been used for diagnosing the lung disorders: pneumothorax, pneumonia, COPD, asthma, and pulmonary embolism,7, 9, 10, 11, 12 for which it showed high accuracy, as has been confirmed by other studies.13, 14, 15, 16, 17, 18, 19 In particular, ultrasound proved to be an accurate test for diagnosing interstitial syndrome.6 Pulmonary edema combines respiratory and hemodynamic phenomena. The present study extends the potential of lung ultrasound to the hemodynamic

Conclusions

Lung ultrasound provides a new approach for interstitial edema detection. A-predominance indicates dry anterior interlobular septa. Specific to predicting a low PAOP value, A-predominance suggests that fluid may be given without initial concern for the development of hydrostatic pulmonary edema. B-predominance indicates interstitial syndrome, possibly related to interstitial edema. B-predominance is observed in a wide range of PAOP values, precluding firm conclusions for the need for fluid

Acknowledgments

Author contributions: Dr. Lichtenstein collected the data and wrote the article. Dr. Mezière collected the data and cowrote the article. Dr. Lagoueyte reviewed the article. Dr. Biderman was the advisor. Dr. Goldstein collected data. Dr. Gepner was the advisor and collected data.

Financial/nonfinancial disclosures: The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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