Lung Ultrasound Score Can Adequately Diagnose Acute Respiratory Distress Syndrome

By Vibhu Sharma, MD

Associate Professor of Medicine, University of Colorado, Denver

SYNOPSIS: In this prospective, observational study, lung ultrasound showed comparable diagnostic performance to standard diagnostics but better accuracy.

SOURCE: Smit MR, Hagens LA, Heijnen NFL, et al. Lung ultrasound prediction model for acute respiratory distress syndrome: A multicenter prospective observational study. Am J Respir Crit Care Med 2023;207:1591-1601.

This prospective, observational study enrolled mechanically ventilated patients with respiratory failure. Lung ultrasound (LUS) was performed with a linear array probe (a phased array or curvilinear probe also was allowed) using a previously published 12-region protocol.¹ An “aeration score” was generated based on the LUS pattern: A lines were scored as 0 per quadrant, B lines were scored as 1 if more than two lines were seen per quadrant filling < 50% of the pleural line in that quadrant, and 2 if B lines extended to over 50% of the pleural line. A C pattern (consolidation on LUS) was scored as 3. C patterns with a pleural effusion were scored as a 0 (deemed “atelectasis rather than an intrinsic pulmonary process”). Each of 12 lung quadrants also was scored as a 1 if there was an abnormal pleural line, subpleural consolidations, dynamic air bronchograms plus a pleural effusion present; in the absence of pleural effusion, this was scored as a 0.

LUS was completed on day 1 or 2 after onset of mechanical ventilation. An expert panel adjudicated a final diagnosis of acute respiratory distress syndrome (ARDS) based on all available clinical and radiographic evidence. Categories generated included: “certain no ARDS,” “certain ARDS,” and “uncertain ARDS.” The latter group was, by consensus, adjudicated to a “likely ARDS” or “likely no ARDS” category. Another panel scored ARDS present or not based on chest X-ray (CXR) and chest computed tomography (CT). Diagnostic accuracy of LUS was compared to clinical assessment by a physician based on all available clinical and radiographic data (CXR and chest CT), which was the reference standard for diagnosis of ARDS.

A derivation cohort (n = 324) and a validation cohort (n = 129) were included. An LUS-ARDS score was developed based on regression coefficients derived from the final model: 2.5 × left LUS aeration score + 1 × right LUS aeration score + 3.5 × number of anterolateral regions with an abnormal pleural line. The score could range from 0-91. Finally, the LUS- ARDS score was compared with physician assessment based on clinical data and CXR alone.

The findings of the study included an area under the receiver operator curve (AUROC) for the LUS-ARDS score of 0.82 (95% confidence interval [CI], 0.85-0.95) when compared to the current reference standard (clinical assessment plus chest CT imaging, which was comparable to clinical assessment and CXR). A high cutoff LUS-ARDS score of 27 led to a specificity for a “certain ARDS” diagnosis of 0.94 (95% CI, 0.90-0.97). A low cutoff of 8 led to a sensitivity of 0.94 (95% CI, 0.87-1.00). A higher LUS-ARDS score made ARDS more likely when there was uncertainty about the diagnosis of ARDS. The LUS-ARDS score had low interobserver variability when compared to assessment of the diagnosis based on clinical assessment and CXR alone.

COMMENTARY

There are a few noteworthy findings from this study by Smit et al. First, the LUS-ARDS score performs as well as clinical assessment and CXR assessment by clinical experts. Second, a high score may be able to sway an uncertain clinical diagnosis toward a diagnosis of ARDS and a low score away from ARDS and may lead to consideration of an alternative diagnosis. Generation of the LUS score, however, requires substantial training and time at the bedside as well as an assessment of quadrants that typically are dependent and require turning the patient if supine. The score cannot be generated if a patient is proned. Clinicians may find generation of this score cumbersome as well, with no impact on clinical management if the diagnosis of ARDS is not in doubt. The real value of the LUS-ARDS score may be that it operationalizes and quantifies ultrasound findings that strongly suggest a diagnosis of ARDS and may be a good test to perform if there is disagreement about the diagnosis.¹

REFERENCE

1. Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point of care lung ultrasound. Intensive Care Med 2012;38:577-591.