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Minimal Criteria for Lung Ultrasonography in Internal
Medicine
Janeve Desy, MD, MEHP, RDMS
1,2
, Vicki E. Noble, MD
3
, Andrew S. Liteplo, MD
4
, Paul Olszynski, MD, MEd
5
, Brian Buchanan, MD
6
,
Renee K. Dversdal, MD
7
, Shane Arishenkoff, MD
8
, Gigi Liu, MD, MSc
9
, Elaine Dumoulin, MD
10
, Irene W. Y. Ma, MD, PhD, RDMS, RDCS
1,2,4
1
Division of General Internal Medicine, Department of Medicine, University of Calgary, Calgary, AB, Canada;
2
W21C, University of
Calgary, Calgary, AB, Canada;
3
Department of Emergency Medicine, University Hospitals, Cleveland Medical Center, Case Western
Reserve School of Medicine, Cleveland, OH, USA;
4
Division of Emergency Ultrasound, Department of Emergency Medicine, Massachusetts
General Hospital, Boston, Harvard Medical School, Boston, MA, USA;
5
Department of Emergency Medicine, University of Saskatchewan,
Saskatoon, SK, Canada;
6
Department of Critical Care, University of Alberta, Edmonton, AB, Canada;
7
Department of Medicine, Oregon
Health & Science University, Portland, OR, USA;
8
Division of General Internal Medicine, Department of Medicine, University of British
Columbia, Vancouver, BC, Canada;
9
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA;
10
Division of Respiratory Medicine, Department of Medicine, University of Calgary, Calgary, AB, Canada
Author for correspondence: Janeve Desy: janeve.desy@ucalgary.ca
Received:
11 December 2020; Accepted after revision: 5 February 2021; Published: 21 June 2021
DOIhttps://doi.org/10.22374/cjgim.v16i2.507
Abstract
Background
Point-of-care lung ultrasound (LUS) examination is increasingly utilized in Internal Medicine.
To improve the standardization of LUS education and clinical use, explicit minimal criteria for
defining what is an acceptable and clinically useful image are needed.
Methods
A 97-item online survey of potential minimal criteria for common uses of LUS in Internal
Medicine was developed and sent to 10 international point-of-care ultrasound experts. Their
opinion on the inclusion of each item was sought and items not achieving consensus (defined
as agreement by at least 70% of the experts) were reassessed in subsequent rounds. A total of
three rounds were conducted.
Results
Seventy-four minimal criteria were agreed upon for inclusion, 24 were agreed upon for exclusion,
and two did not reach consensus.
Conclusions
Experts agreed on 74 minimal criteria for Internal Medicine LUS. The use of these minimal
criteria during teaching and clinical use is strongly recommended.
Résumé
Contexte
Léchographie pulmonaire au point d’intervention est de plus en plus utilisée en médecine
interne. Pour améliorer luniformisation de la formation sur léchographie pulmonaire et de
6 V o l u m e 1 6 , I s s u e 2 , 2 0 2 1 C a n a d i a n J o u r n a l o f G e n e r a l I n t e r n a l M e d i c i n e
Original Research
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Background
The role of point-of-care ultrasound (POCUS) in the care of
medical patients is being increasingly recognized.
1–3
Of the
recommended Canadian Internal Medicine POCUS applications,
3
lung ultrasound (LUS) is one of the easiest to learn and has
high clinical utility.
4
Its use in medical patients with dyspnea,
for example, is associated with increased diagnostic accuracy
at the bedside.
5–7
Its use may also be gaining importance in the
assessment of patients with coronavirus-19.
8
Despite it being
relatively easy to learn, to support the use of LUS clinically,
appropriate training in image acquisition and interpretation
is required. It is generally accepted by POCUS experts that
images not meeting minimal criteria, such as those that have
insufficient depth or inadequate optimization of the pleural
line, should not be used to support clinical decision-making,
9
as they may introduce serious diagnostic errors. Both achieving
minimal criteria during image acquisition and the recognition
of when these criteria have not been met are fundamental to
POCUS competency.
9
In addition, the use of minimal criteria
in POCUS training programs is considered a key indicator of
high-quality education.
10
Despite the critical importance of minimal criteria, existing
resources on learning LUS, while useful, focus primarily on
image acquisition and interpretation,
4,11,12
without an explicit
list of minimal criteria that an image must meet. As POCUS
education expands across the country, articulation of such criteria
becomes increasingly important if high-quality education is to
be standardized. Given that trained POCUS experts agree on the
importance of minimal criteria,
9
through consensus methods,
this study seeks to encapsulate this codex of expert knowledge
into an explicit list of minimal criteria for LUS. These minimal
criteria can then be used to guide clinical use as well as LUS
education for residency training programs.
Methods
Survey Development
This study received approval from the Conjoint Health Research
Ethics Board at the University of Calgary (#REB16-2452). Using
existing key reference resources for LUS,
11,13–22
two independent
investigators (J.D. and I.M.) drafted a list of minimal criteria for
all intended applications of LUS, to be as inclusive as possible.
Disagreements were resolved by discussion and if necessary
consensus from additional investigators. This 78-item list was
formatted into an online survey (www.surveymonkey.com,
SurveyMonkey Inc., San Mateo, CA, USA).
This draft online survey was piloted in May 2019 on 14
Internal Medicine and Family Medicine physicians with at least
1 month of formal ultrasound training for feedback on survey
length, clarity, response options, missing or redundant items,
and flow. Feedback was reviewed by both J.D. and I.M. and
incorporated into the final 97-item survey.
son utilisation clinique, il faut des critères minimaux explicites pour définir ce quest une image
acceptable et utile sur le plan clinique.
Méthodologie
Un sondage en ligne de 97éléments portant sur des critères minimaux possibles dans l’utilisation
courante de léchographie pulmonaire en médecine interne a été élaboré et soumis à 10experts
internationaux en échographie au point d’intervention. Leur avis sur l’inclusion de chaque
élément a été sondé, et les éléments pour lesquels il ny avait pas de consensus (défini par l’accord
dau moins 70% des experts) ont été réévalués lors de tours suivants. Au total, trois tours ont
été effectués.
Résultats
Soixante-quatorze critères minimaux ont été acceptés, 24 ont été exclus et deux nont pas fait
consensus.
Conclusions
Les experts se sont entendus sur 74critères minimaux relatifs à léchographie pulmonaire
en médecine interne. Lutilisation de ces critères minimaux au cours de lenseignement et de
lutilisation clinique est fortement recommandée.
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Desy J et al.
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Table 1. Baseline Characteristics of the 10 Participants on the Expert Panel
Characteristic N (%)
Country of Practice
Canada 5 (50)
USA 5 (50)
Specialty
Emergency medicine 3(30)
Critical care medicine 1 (10)
General internal medicine 6 (60)
Gender
Male 4 (40)
Female 6 (60)
Years of experience using POCUS*
3–4 1 (10)
5–6 3 (30)
7–8 1 (10)
9–10 1 (10)
>10 4 (40)
Years of experience teaching POCUS*
1–2 1 (10)
3–4 2 (20)
5–6 1 (10)
7–8 2 (20)
9–10 1 (10
>10 3 (30)
Years of experience assessing POCUS*
1–2 2 (20)
3–4 1 (10)
5–6 2 (20)
7–8 2 (20)
9–10 1 (10)
>10 2 (20)
Number of peer-reviewed publications related to
POCUS
1–2 1 (10)
3–4 5 (50)
>10 4 (40)
Completion of POCUS fellowship of 1-year duration or
more
Yes 6 (60)
No 4 (40)
* POCUS denotes point-of-care ultrasound.
Expert Panel
Our expert panel included 10 international POCUS experts who
had at least 1 year of fellowship training in ultrasonography OR
a 3-year track record of teaching and assessing POCUS AND a
minimum of three peer-reviewed POCUS-related publications.
The experts completed three rounds of the online survey between
June 2019 and September 2019, where they were asked regarding
specific minimal criteria and if a given item must or must not
be present to meet minimal criteria. We defined consensus as
agreement by at least 70% of the experts.
23
Open-ended response
options were also provided to capture missing items and additional
comments. Items that did not reach consensus were included in
subsequent rounds, which included new or revised items based
on expert feedback from the previous round. Results from survey
responses from prior rounds were provided to the participants
in the form of the percentages of those who chose each option,
as well as relevant comments that led to any item revisions.
Results
All 10 experts completed all rounds of the survey. Table 1 outlines
the baseline characteristics of the experts.
Round 1
In round 1, of the 97 items considered, consensus was reached
to include 50 items. For 18 items, consensus was reached for
being NOT mandatory (Table 2). No consensus was reached
for the remaining 29 items.
Round 2
Based on feedback from experts in round 1, two new questions
were added to the 29 items that were without consensus from
Round 1. The new questions were: (i) For a lung scan to be
considered acceptable, one of the following lung patterns/
findings MUST be present deep to the pleural line: A-lines,
B lines, consolidation, or pleural effusion and (ii) To rule out
pneumothorax, the least gravitationally dependent areas of the
chest MUST be scanned (e.g., anterior chest in a supine patient).
Of the 31 items considered in this round, 16 items reached
consensus to be included, 4 reached consensus for NOT being
mandatory, and 11 items did not reach consensus (Table 2).
Round 3
Round 3 included the 11 items from round 2 that did not meet
consensus as well as one new item on the need to scan the
posterolateral regions of the lungs for evidence of pneumonia/
consolidation. Of the 12 items considered, 8 reached consensus
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Minimal Criteria for Lung Ultrasonography
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Table 2. Minimal Criteria For Internal Medicine Lung Ultrasound
Minimal Criteria
% agreement
1 For a lung scan to be considered acceptable, one of the following lung patterns/findings MUST be present deep to the
pleural line: A-lines, B-lines, consolidation, or pleural effusion
90
2
2 Whenever possible, we recommend recording a minimum of a 6-s cineloop 80
3
3 Using a lung preset is NOT mandatory if abnormalities can be visualized 70
1
4 Turning off tissue harmonic imaging is NOT mandatory if abnormalities can be visualized 70
1
Assessing for Pleural Sliding
Acceptable transducer(s)
5 Linear 100
1
6 Curvilinear 90
1
7 Phased array 80
2
8 Microconvex 70
1
Minimal criteria for pleural sliding
9 Pleural line MUST be clearly visible 100
1
10 Pleural line MUST be clearly centered 80
1
11 Pleural line MUST be as echogenic as possible (by fanning) 80
1
12 To state that lung sliding is ABSENT, at least one rib MUST be visible 100
3
13 Showing two consecutive ribs is NOT mandatory 80
1
14 Lung zones MUST be labeled 80
2
15 If pleural sliding not seen, MUST use at least 1 maneuver 100
1
Acceptable maneuvers to improve pleural sliding visualization
16 Decrease depth 80
1
17 Change to a linear transducer 100
1
18 Adjust gain 70
1
19 Use M-mode 80
1
Maneuvers deemed not mandatory
20 Increasing frequency is NOT a mandatory maneuver 80
1
21 Moving the focus is NOT a mandatory maneuver 90
3
22 Using Doppler is NOT a mandatory maneuver 100
1
Still image archive for pleural sliding if cineloops not available
23 A still image of M-mode is acceptable to show the presence or absence of lung sliding 90
1
24 A B-mode still image is NOT acceptable to show the presence of lung sliding 90
1
25 A B-mode still image is NOT acceptable to show the absence of lung sliding 90
1
Assessing for Pleural Irregularities
Acceptable transducer(s)
26 Linear 100
1
27 Curvilinear 80
1
28 Microconvex 100
2
29 Phased array LEAST preferred 70
2
Minimal criteria for pleural irregularities
30 Pleural line MUST be clearly visible 100
1
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General Criteria
General Criteria
31 Pleural line MUST be clearly centered 80
1
32 Pleural line MUST be as echogenic as possible (by fanning) 100
1
33 Lung zones MUST be labeled 80
2
34 Showing two consecutive ribs is NOT mandatory 90
1
No consensus: At least one rib must be visible 50
Assessing for Lung Point/Pneumothorax Assessment
Acceptable transducer(s)
35 Linear 100
1
36 Curvilinear 100
1
37 Phased array 70
1
38 Microconvex 70
1
Minimal criteria for lung point/pneumothorax assessment
39 Pleural line MUST be clearly visible 100
1
40 Pleural line MUST be clearly centered 70
1
41 Pleural line MUST be as echogenic as possible (by fanning) 70
1
42 Lung zones MUST be labeled 80
2
43 Must scan bilaterally to rule out a pneumothorax unless clinically not indicated (e.g., post-procedure) 80
1
44 To rule out pneumothorax, the least gravitationally dependent areas of the chest MUST be scanned (e.g., anterior
chest in a supine patient)
90
3
45 Lung point is NOT mandatory to diagnose pneumothorax 90
2
47 Showing two consecutive ribs is NOT mandatory 80
1
No consensus: At least one rib must be visible 50
Still image archive for lung point/pneumothorax if cineloops not available
47 A still image of M-mode is acceptable to show lung point 80
2
48 A B-mode still image is NOT acceptable to show lung point 100
1
Assessing for B-Lines
Acceptable transducer(s)
49 Curvilinear 100
1
50 Phased array 100
1
51 Microconvex 70
1
52 Linear NOT acceptable* 89
1
Minimal criteria for B-lines assessment
53 Pleural line MUST be clearly visible 90
1
54 Pleural line MUST be clearly centered 100
2
55 Pleural line MUST be as echogenic as possible (by fanning) 90
1
56 At least one rib must be visible 70
1
57 Lung zones MUST be labeled 90
2
58 Must scan bilaterally to rule OUT pulmonary edema 100
1
59 To rule OUT pulmonary edema, we encourage learners to scan a minimum of eight lung areas (four on each side)
whenever possible
80
2
60 For the diagnosis of B-lines, we recommend a minimum depth of 10 cm below the pleural line be imaged 70
3
61 Showing two consecutive ribs is NOT mandatory 70
1
(continued)
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% agreement
Minimal Criteria
General criteria
Still image archive for B-lines if cineloops not available
62 A B-mode still image is acceptable to show positive B-lines 70
1
63 A B-mode still image is NOT acceptable to rule out presence of B-lines 90
2
Assessing for Consolidation
Acceptable transducer(s)
64 Curvilinear 100
1
65 Phased array 90
1
66 Microconvex 100
2
67 Linear acceptable if consolidation can be visualized 90
3
Minimal criteria for consolidation
68 Pleural line MUST be clearly visible 100
2
69 Lung zones MUST be labeled 90
2
70 Must scan bilaterally to rule out a pneumonia 100
1
71 To look for pneumonia/consolidation, we encourage learners scan a minimum of eight lung areas (four on each side) 70
3
72 To look for pneumonia/consolidation, posterolateral regions MUST be scanned 70
3
73 Pleural line being clearly centered is NOT mandatory 70
1
74 Pleural line being as echogenic as possible is NOT mandatory 70
1
75 If consolidation is visualized, having at least one rib visible is NOT mandatory 90
3
76 Showing two consecutive ribs is NOT mandatory 100
1
Minimal criteria for basal zone consolidation
77 MUST attempt to visualize the spine 70
1
78 Diaphragm MUST be visualized 90
1
79 Spleen or liver MUST be visualized 70
1
80 Lung zones MUST be labeled 70
2
81 Consolidation must show air bronchograms 70
1
82 Demonstrating the spleen/kidney or liver/kidney interface is NOT mandatory 80
2
83 Air bronchograms do NOT need to be dynamic 80
1
Still image archive for consolidation if cineloops not available
84 A B-mode still image is acceptable to show consolidation 100
1
Assessing for Pleural Effusion
Acceptable transducer(s)
85 Curvilinear 100
1
86 Phased array 100
1
87 Microconvex 70
1
88 Linear NOT acceptable* 100
1
Minimal criteria for pleural effusion
89 MUST attempt to visualize the spine 80
1
90 Diaphragm MUST be visualized 100
1
91 Spleen or liver MUST be visualized 80
1
92 Lung zones MUST be labeled 70
2
93 MUST scan bilaterally to rule out a pleural effusion 100
1
94 MUST scan a minimum of two zones to rule out pleural effusion 70
1
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General Criteria
% agreement
Minimal Criteria
General Criteria
t
95 To diagnose a pleural effusion, at least 25% of the diaphragm MUST be visualized 90
3
96 Demonstrating the spleen/kidney or liver/kidney interface is NOT mandatory 80
2
97 Sinusoid sign is NOT mandatory 70
1
Still image archive for pleural effusion if cineloops not available
98 A B-mode still image is acceptable to show presence of pleural effusion 100
1
* Only nine experts responded to these questions.
Expert responses to items and the round in which the items achieved consensus are shown as superscript numbers
to be included, 2 reached consensus for NOT being mandatory,
and 2 items remained without consensus (Table 2).
The final list of items is listed in Table 2 and included 74
mandatory items, 24 items that were considered NOT mandatory
and 2 items that never reached consensus.
Discussion
In this study, we defined 74 consensus-based minimal criteria
for key findings in Internal Medicine LUS. These criteria are
both explicit and practical, taking into consideration potential
equipment limitations such as commonly available transducers
and machine functions (e.g., options for focus and transducer
frequency modulation). It also takes into consideration the
LUS findings in question. For example, while experts generally
agreed that for most findings the pleural line should be visible,
centered, made as echogenic as possible by fanning, and with at
least one rib visible, in the presence of certain findings, such as
an obvious consolidation, centering of the pleural line was not
deemed mandatory (#73) nor was it necessary that the pleural
line itself be optimized (#74). In another example (#12), experts
made it clear that if pleural sliding is visible, the presence of at
least one rib may not be necessary. However, to state that lung
sliding is ABSENT, at least one rib MUST be visible, so that
the pleural line can be properly identified in such cases. Also,
the group explicitly outlines image storage requirements. For
example, while the presence of B-lines can be confirmed and
documented with a still image (#62), their absence cannot be
so confirmed (#63) due to the respiratory movement of B lines,
making it possible to miss a positive finding with a still image.
Such key information, while inherently known to LUS experts,
has not been previously outlined and is vitally important for all
learners and training programs to recognize.
There are some limitations to our study. First, a few of our
items required significant revisions. For example, while 100%
of our experts agreed that a minimal depth must be achieved
for the assessment of B-lines, (to avoid mistaking these for
z-lines),
24
it was challenging to derive consensus on what this
minimal depth should be, as it is partially dependent on the
patient’s body habitus (e.g., the more subcutaneous tissue depth
present, the deeper the distance required). Ultimately, only by
the third round were our experts able to achieve consensus
once our revisions reflected this variability in subcutaneous
tissue depth (#60: a minimum of 10 cm required, starting
from below the pleural line, rather than at the skin surface).
We encountered similar wording issues when describing the
amount of diaphragm required to be imaged in the assessment
for pleural effusions. Rather than describing exactly which
portions of the diaphragm were required to be visualized
(medial vs lateral), experts were ultimately able to agree on
the overall percentage of a diaphragm that must be visualized
(#95). Second, the online survey design did not allow for rich
discussion amongst experts, and comments were limited to
open text boxes only. However, despite this limitation, our
experts were very engaged, and key comments from them led
to significant wording revisions and additional items. Third,
our minimal criteria are intended to be exactly that—minimal
criteria. While using a lung preset and turning off tissue
harmonic imaging should be performed whenever possible,
if findings are seen, our group was willing to forego these
settings (#3, #4). However, from a learner’s perspective, it may
still be prudent to be consistent in the use of an optimal preset
or demonstrate the presence of both ribs using a curvilinear
transducer whenever possible, even though these are not
considered mandatory. Fourth, we did not perform a systematic
review. However, our experts are true experts of LUS, including
a number who participated in national and international
consensus statements that did include an extensive literature
strategy.
8,11
Lastly, although not every expert answered every
question in our survey, only two questions in all three rounds
of the survey had missing responses.
In conclusion, our experts agreed upon 74 items required
for meeting minimal criteria for LUS uses relevant to internal
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Minimal Criteria for Lung Ultrasonography
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% agreement
Minimal Criteria
medicine, and 24 items were NOT required. In the teaching of
LUS, adherence to these criteria is recommended.
Statement of Contributions
JD, VEN, ASL, and IWYM contributed to conception and
design, and procurement of data; JD and IWYM contributed
to the analysis of data, to the initial draft of the manuscript, and
critical review and drafting of the manuscript.
Statement of Funding
This study was funded by the 2017 Canadian Society of Internal
Medicine Education and Research Fund. The funder had no
role in study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Conflict of Interest Statement for All Authors
Dr. Ma is funded by the John A. Buchanan Chair of General
Internal Medicine, University of Calgary.
Dr. Liteplo had received a grant from GE/EMF to perform
ultrasound research, has consulted for Philips Healthcare, and is
involved in ultrasound-related research sponsored by Fujifilm/
Sonosite unrelated to this research.
Dr. Buchanan is a clinical advisor for MEDO.Ai, in developing
artificial-intelligence-based software for common point-of-care
ultrasound applications.
Dr. Dversdal is employed part-time by Vave Health in
the Chief Medical Officer’s role. Primary contributions to this
manuscript were all prior to this role.
Drs. Arishenkoff, Dumoulin, Desy, Noble, Liu, and Olszynski
have no conflicts of interest to report.
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