Comparative Performance of Pulmonary Ultrasound, Chest Radiograph, and CT Among Patients With Acute Respiratory Failure

David M. Tierney, MD, FACP; Joshua S. Huelster, MD; Josh D. Overgaard, MD; Michael B. Plunkett, MD; Lori L. Boland, MPH; Catherine A. St. Hill, DVM, PhD; Vincent K. Agboto, PhD, MS; Claire S. Smith, MS; Bryce F. Mikel, MD; Brynn E. Weise, MD; Katelyn E. Madigan, MD; Ameet P. Doshi, MD; Roman R. Melamed, MD, FCCP

Disclosures

Crit Care Med. 2020;48(2):151-157. 

In This Article

Abstract and Introduction

Abstract

Objectives: The study goal was to concurrently evaluate agreement of a 9-point pulmonary ultrasound protocol and portable chest radiograph with chest CT for localization of pathology to the correct lung and also to specific anatomic lobes among a diverse group of intubated patients with acute respiratory failure.

Design: Prospective cohort study.

Setting: Medical, surgical, and neurologic ICUs at a 670-bed urban teaching hospital.

Patients: Intubated adults with acute respiratory failure having chest CT and portable chest radiograph performed within 24 hours of intubation.

Interventions: A 9-point pulmonary ultrasound examination performed at the time of intubation.

Measurements and Main Results: Sixty-seven patients had pulmonary ultrasound, portable chest radiograph, and chest CT performed within 24 hours of intubation. Overall agreement of pulmonary ultrasound and portable chest radiograph findings with correlating lobe ("lobe-specific" agreement) on CT was 87% versus 62% (p < 0.001), respectively. Relaxing the agreement definition to a matching CT finding being present anywhere within the correct lung ("lung-specific" agreement), not necessarily the specific mapped lobe, showed improved agreement for both pulmonary ultrasound and portable chest radiograph respectively (right lung: 92.5% vs 65.7%; p < 0.001 and left lung: 83.6% vs 71.6%; p = 0.097). The highest lobe-specific agreement was for the finding of atelectasis/consolidation for both pulmonary ultrasound and portable chest radiograph (96% and 73%, respectively). The lowest lobe-specific agreement for pulmonary ultrasound was normal lung (79%) and interstitial process for portable chest radiograph (29%). Lobe-specific agreement differed most between pulmonary ultrasound and portable chest radiograph for interstitial findings (86% vs 29%, respectively). Pulmonary ultrasound had the lowest agreement with CT for findings in the left lower lobe (82.1%). Pleural effusion agreement also differed between pulmonary ultrasound and portable chest radiograph (right: 99% vs 87%; p = 0.009 and left: 99% vs 85%; p = 0.004).

Conclusions: A clinical, 9-point pulmonary ultrasound protocol strongly agreed with specific CT findings when analyzed by both lung- and lobe-specific location among a diverse population of mechanically ventilated patients with acute respiratory failure; in this regard, pulmonary ultrasound significantly outperformed portable chest radiograph.

Introduction

Acute respiratory failure (ARF) requiring mechanical ventilatory support is the most common reason for ICU admission and has high mortality.[1,2] Initial misdiagnosis of ARF etiology is common and increases mortality.[3] With the broad differential of diseases causing ARF, efficiency of diagnosis is not only related to accuracy of the chest imaging modality, but also its ability to anatomically localize a process and monitor for change with treatment.

Portable chest radiograph (pCXR) lacks the sensitivity and specificity of CT,[4–6] yet may be favored in some settings due to speed, lower cost and radiation, and risk associated with ICU patient transport especially with technologically complex support modes such as extracorporeal membrane oxygenation (ECMO).[7,8] Pulmonary ultrasound (PU) has demonstrated the benefits of pCXR's portability, speed, and lower cost while approaching accuracy of chest CT for pneumonia, interstitial processes, acute respiratory distress syndrome (ARDS), pleural effusion, and pneumothorax.[9–15] The Society of Critical Care Medicine and international guidelines support incorporation of point-of-care ultrasound (POCUS) in diagnosis of these conditions.[16,17] In addition to its initial diagnostic ability, POCUS offers clinicians a radiation-free tool to repeatedly reassess for progression or regression of pulmonary findings in real-time at the bedside which can further aid in tailoring treatment and differential diagnosis.

The majority of research reporting diagnostic accuracy of PU has defined agreement as compatible ultrasound findings anywhere within the correct lung as identified by CT. However, two small studies (n = 32 and 20) conducted in patients with ARDS have demonstrated a refined ability of PU to accurately localize findings beyond the correct lung to distinct lung zones on CT defined not by anatomic lung lobe (i.e., right lower lobe, right middle lobe), but by zones corresponding to contemporary protocolized ultrasound examination regions.[18,19]

The goal of this study was to concurrently evaluate the accuracy of both PU and pCXR with CT not only for agreement of findings within the ipsilateral lung or a correlating CT zone, but within the specific anatomic lobe using a previously published, quick, pragmatic, 9-zone PU protocol[20] among diverse medical/surgical, cardiac, and neurologic ICU patient populations with a wide array of ARF diagnoses.

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