The standard for diagnosing pneumonia is a combination of the clinical history, physical examination, and chest x-ray (CXR) findings. However, lung ultrasound (US) has been shown to be a reasonable alternative to CXR in children, and may be an appropriate alternative diagnostic imaging modality in the Emergency Department (ED).
Probe: High resolution linear probe with frequencies ranging from 6-12 MHz
Max Depth: 8 cm
Scanning Scheme: Scan through 6 zones (3 per side)
- Midclavicular line on the anterior chest
- Midclavicular line on the posterior chest
- Mid-axillary line from the axilla to the diaphragm
Each of these lines is scanned in 2 perpendicular planes, transverse and longitudinal.1
Findings on Lung Ultrasound
In a healthy patient
Lung US shows reverberations of the pleural line, called A-lines.
In a fluid filled lung
Lung US shows B-lines that are perpendicular to the pleural line. Fluid-filled parenchyma create vertical B-lines.
- Focal areas of B-lines = pneumonia
- Diffuse B-lines = pulmonary edema or ARDS
- If the consolidation caused from pneumonia reaches the pleura, the consolidation can be seen in its entirety as solidified, uniformly hypoechoic, wedge-shaped lung tissue (video below).
- Irregular pleura lines can also indicate pneumonia.
Lung Ultrasound vs Chest X-ray
Study 1: Pediatric Pulmonology 2013
A study comparing lung US to CXR required that all patients undergo lung US by an expert pediatric sonographer as well as a CXR.2
- Of the 89 children diagnosed with pneumonia, lung US showed pneumonia in 88 children, whereas the CXR was positive for pneumonia in 81 children.
- In this study, lung US was repeated throughout the course of disease and demonstrated in most cases a decrease in size or disappearance of consolidation in concordance with clinical improvement.
Study 2: Pediatrics 2015
This meta-analysis summarized studies on the diagnostic accuracy of lung US for childhood pneumonia. Ultimately 15 of 1,475 studies met inclusion criteria. The sensitivity, specificity, and positive and negative likelihood ratios were as follows:3
- Sensitivity 96%
- Specificity 93%
- Positive LR 15.3
- Negative LR 0.06
Benefits of Lung US: Rapid, portable, non-ionizing
Radiation exposure is particularly important the younger the patient is. Children with chronic co-morbidities (e.g., inflammatory bowel disease, cancer, frequent asthma exacerbations) may have an increased risk of radiation exposure (future XRs or CTs). US avoids this risk.
Lung US is estimated to cost approximately $140 per scan versus CXR cost of approximately $370, leading to a potential savings of $230 per scan.2
Length of Stay
Given that lung US is a point of care test, some studies have shown decreased ED visit times.2
Lung US Can Be Learned With Brief Training
A major hesitation to performing lung US in the ED is provider comfort with performing it. As can be seen in studies below, lung US appears to be a technique that can be rapidly acquired and reliably utilized with limited training.
Study 1: JAMA Pediatrics 2013
15 pediatric emergency medicine attendings and fellows underwent a 1-hour training session (30 minute lecture and 30 minute hands-on scanning session using normal models) to determine test performance characteristics in diagnosing pneumonia compared to CXR (reference standard).4
- 200 prospectively enrolled patients
- Sensitivity 86%
- Specificity 89%
- Positive LR 7.8
- Negative LR 0.2
- There were 3 true misses and 2 operator errors.
- There were 12 sub-1 cm consolidations identified that were consistent with pneumonia that were not seen on CXR.
Study 2: Chest 2016
15 pediatric emergency physician attendings and fellows with varying levels of ultrasound experience underwent a 1-hour training session. Pediatric patients, who were suspected to have a pneumonia, were enrolled into the randomized controlled trial comparing lung US versus CXR.1
- “Novice” sonologists (defined as people who had performed ≤25 lung US previously) achieved a 30% reduction in CXRs.
- “Experienced” sonologists (defined as people who had performed >25 lung US) achieved a 60.6% reduction in CXRs.
- Conclusion: “It may be feasible and safe to substitute LUS [lung ultrasound] for CXR when evaluating children suspected of having pneumonia with no missed cases of pneumonia or increase in rates of adverse events.”
The Bottom Line
- Lung US is as good as CXR in the hands of an expert sonographer.
- Emergency physicians can be trained to be good at lung US with brief training.