Lung Ultrasound for Acute Chest Syndrome

By Delia Gold

Acute ChestI

Utility of Point-of-Care Lung Ultrasonography for Evaluating Acute Chest Syndrome in Young Patients With Sickle Cell Disease

Ann Emerg Med Sept 2020 - Pub Med Link


Take Home Points

1. POCUS can be used to diagnose ACS in the setting of clinical concern with good accuracy compared to chest xray.

2. Using POCUS to evaluate for ACS in this chronically ill patient population is well-tolerated and associated with positive ED interactions and satisfaction.

3. Future research needed to determine if there are populations in which ultrasound can safely be used in place of chest xray.


Background

Acute chest syndrome affects approximately 30% of patients with sickle cell disease (SCD) in their lifetime and is a significant cause of morbidity and mortality. Acute chest syndrome = fever or respiratory symptoms + new infiltrate on CXR. Children with ACS often present with symptoms similar to pneumonia (PNA), vs just pain. Studies demonstrate that more than 50% of patients with ACS have a normal physical exam and vital signs, which necessitates some form of imaging to determine the diagnosis. Because of this, young patients with SCD are repeatedly exposed to radiation via CXR to rule out ACS. Vetter study reported that on average a child with SCD with have >26 radiographic tests by age 18. Many hospitals have clinical protocols to try to decrease the number of CXRs performed on these patients, however they may miss some of these ACS patients. POCUS on the other hand can limit radiation exposure while simultaneously identifying ACS patients. Authors argue that CXR is not an ideal screening test for ACS due to radiation, and that POCUS should be considered instead.


See our last podcast on this topic on an article from 2016. In this study, POCUS was 94% specific compared to CXR.


Questions

What is the accuracy of POCUS as compared to CXR (reference standard) in the diagnosis of acute chest syndrome in SCD patients?

Secondary outcomes of the study included agreement of findings between novice and expert sonographer, patient and parent satisfaction, and ability to tolerate the POCUS examination.


Population

Convenience sample of patients with SCD (any genotype) ages 0-21 years at two affiliated freestanding pediatric hospitals.


Inclusion:

  • Symptoms of acute chest + getting chest xray

Exclusion

  • Hemodynamic instability

  • Had chest radiographic from outside facility prior to arrival

  • Study sonographer unavailable


Design

Prospective observational study with enrollment between November 2015 - July 2017.

A study sonographer blinded to the physical exam (except anything visual such as tachypnea, tachycardia on monitor) performed a POCUS scan before the CXR was performed.

No clinical decisions were made based on the ultrasound images.

After the scan, parents/guardians asked to fill out a 10-question survey to assess satisfaction with their experience using Likert scale. Questions focused on both the ED visit and their experience with the POCUS scan.

Demographics, medical hx, hospital data were extracted.

Expert sonographer reviewed all scans and was blinded to any previous interpretation.

Reference standard was the pediatric radiologist’s interpretation of the CXR. Equivocal CXRs were considered negative to avoid inflating test characteristics.

Accuracy defined by proportion of observation for which the CXR (standard) and POCUS scan agreed (correct classification rate). Analyzed agreement between novice and expert by calculating interobserver agreement (Cohen’s k) for the diagnosis of lung consolidation.


Primary outcome was stated as accuracy of POCUS compared to chest xray. Unclear if it was the novice or expert values they were most interested in.


Who did the ultrasounds?

Study sonographers included 5 novice trainees and 1 expert sonographer with specialized training and > 5 years experience.

Novice sonographers received training from the expert sonographer, with training similar to previous studies. Training included 1-hour lecture on lung ultrasound and 1-hour practical hands-on imaging session. Novice sonographers performed 5 point-of-care lung exams before enrolling patients in the study.


The Scan

Curvilinear or Linear (depending on habitus)

Curved

Linear

Scanning technique used a standardized protocol (Copetti study) with scanning of anterior, lateral, and posterior lung fields in transverse and longitudinal orientations. Lungs were scanned from inferior to superior to ensure that the diaphragm was identified first.

Consolidations > 1 cm were used to determine positivity.


Learn how to do Ultrasound for Pneumonia from 5 Minute Sono! - Acute Chest Syndrome will have similar appearance to pneumonia

5minsono


Check out Pediatric POCUS Pathology on the POCUS Atlas!

thePOCUSAtlas


Results

N = 191

  • 220 eligible for enrollment, 21 declined, POCUS scan incomplete for 7, 1 patient left study mid-scan due to discomfort

  • Median age 8 years

  • 51% admitted

  • An infiltrate was identified by CXR in 32 patients (17%) while POCUS identified lung consolidation > 1 cm in 40/191 (21%).


Primary Outcome

POCUS was able to recognize ACS with accuracy of 89% in novice sonographers and 92% on review by expert sonographer.

Novice:

LR+ 8.39 (2.85-15.61)

LR- 0.20 (0.01-0.40)

Expert Reviewer:

LR+ 12.65 (CI 7.05-22.70)

LR- 0.13 (0.05-0.34)


Secondary Outcomes

Interobserver agreement between novice and expert 0.67 (CI 0.54-0.80).

They also compared the presence of clinical risk factors with POCUS to determine its ability to identify ACS - only the presence of tachycardia and tachypnea were statistically significant between with groups with positive and negative CXRs. POCUS was superior to all clinical criteria in determining the presence of ACS.


Questionnaires were filled out by 141/191 families (73%), although not completely filled out.

  • 90% reported no pain with POCUS scan

  • 93% reported being satisfied with their ED care.


False positives (n = 11)

  • 4 were “scarring” on xray

  • 1 was equivocal on xray

  • 2 were misinterpreting the spleen and air in the stomach as air bronchograms

  • 4 were actually <1 cm but were called positive on POCUS → ¾ ended up having acute chest

False negatives (n=4)

  • 3 were misinterpretation by novice (but picked up by expert)

  • 1 was due to error in technique (apparently did not get the image needed)


Strengths

Prospective study

Good test characteristics for POCUS vs. CXR

Used novice sonographers to show how “easy” this is to do, but then had an expert reviewer with similar accuracy between those groups

Focus on patient satisfaction was novel and very important in this patient population as they are in the ED often, can be quite sick (cannot move to radiology suite), and are already in pain so more likely to not tolerate a POCUS scan (in theory)


Limitations

Convenience sample based on study sonographers’ availability, may have contributed to selection bias.

CXR is an imperfect reference standard ➝ but better than CT scanning or bronching all patients, also makes the argument that any limitations regarding POCUS should not be more concerning than CXR. The comparison to chest xray was also a bit unfair as radiologists had access to prior studies so they could identify scars or prior lesions and identify them as not a new finding. 4 of 11 false positives were “scarring” on xray.

Difficulty distinguishing acute from chronic lung changes on POCUS scans➝ if sonographers weren’t blinded, they could easily compare their POCUS scans to prior CXRs which likely would help with this.

Sonographers weren’t completely blinded to the clinical status of patients, able to observe tachypnea or tachycardia (on monitor). Important point from a research perspective that they weren’t blinded but reflects the reality and benefit of POCUS - the clinician gets to incorporate clinical information into sonographic study.

No review of efficiency, LOS, time to perform scan, time to disposition ➝ this was not a study aim but I think that this is always one of the concerns regarding POCUS so should be evaluated if possible on studies comparing POCUS to a reference standard.


Discussion

ACS is a high risk diagnosis with significant morbidity and mortality and is diagnosed with clinical symptoms in the setting of abnormalities on imaging. CXR works but has radiation. POCUS works but might miss more that 10% of cases based on this study. It has a great NPV which is ideal for a screening test.

Multiple studies evaluating accuracy of POCUS for detecting pleural and lung disease in the setting of PNA. Wide variability in test characteristics, this study adds support to novice sonographers being able to use POCUS clinically with accuracy. POCUS has also been used to diagnose ACS, but this is the largest pediatric study to date. Prior studies had similar test characteristics as this study (Daswani, Razazi). This study and one other provide some evidence that POCUS may detect ACS earlier than by CXR.

First study to examine patient and parent satisfaction with POCUS used in SCD patients for ACS. Families were highly satisfied and even reported that the POCUS scan improved their ED visit overall. This is in line with what we experience anecdotally on “US rounds” in EDs. The POCUS scans did not improve efficiency but this was not formally studied and no data recorded on time to scan, LOS in ED, etc. It is interesting that some parents reported the POCUS study was not useful and didn’t improve efficiency of hospital visit. That makes sense as it did not always provide a definite answer (not to mention it was not used for decision making in this study). I wonder what they would have said if they were told that history and physical exam has been shown to provide no benefit in diagnosis of acute chest in children.

Similarly, POCUS causing pain in 10% of children seems high. This may be due to the manner in which pain was assessed in nonverbal children (and the limitations of a parent’s intuition of pain), but also could be related to the population of sickle cell disease patients who were currently likely in a vasoocclusive crisis.


Summary

This was a prospective study of 191 patients <21 years old with sickle cell disease and concern for acute chest syndrome. POCUS was able to detect ACS with high sensitivity and specificity compared with CXR. Using POCUS on this patient population was well-received by patients and families.


Take Home Points

1. POCUS can be used to diagnose ACS in the setting of clinical concern with good accuracy compared to chest xray.

2. Using POCUS to evaluate for ACS in this chronically ill patient population is well-tolerated and associated with positive ED interactions and satisfaction.

3. Future research needed to determine if there are populations in which ultrasound can safely be used in place of chest xray.


More Great FOAMed on This Topic

EM DOCS US Probe: Ultrasound for Diagnosis of Acute Chest Syndrome

Internet Book of Critical Care - Sickle Cell Acute Chest Syndrome


Our score

3 Probes


Expert Reviewer for this Post

Panebianco

Nova Panebianco, MD, MPH @Novaleda

EM Ultrasound Division Director, Associate Professor, Department of Emergency Medicine, University of Pennsylvania


Cite this post as

Delia Gold. Lung Ultrasound for Acute Chest Syndrome. Ultrasound G.E.L. Podcast Blog. Published on March 15, 2021. Accessed on May 06, 2021. Available at https://www.ultrasoundgel.org/108.
Published on 03/15/21 04:00 AM
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