A tweetorial on optimal machine settings for B line image acquisition, with a focus on: focal position at pleura, harmonics off, and increased far gain.
Let's start with some polls
We will stick to low frequency probes here (i.e. curvilinear and phased array - linear has its own purpose for detailed pleural assessment)
Which preset do you prefer for B line assessment?
2/
What depth do you typically set?
3/
After selecting preset and selecting depth, do you ever adjust any other machine settings to optimize B line assessment?
4/
Importantly, there is no right answer to the above questions!
We won't discuss much about preset or probe type. But we will discuss machine settings to optimize B line quality, based on 1) Theory based on physical basis of B lines 2) In vitro study 3) Study in patients
5/
To start with the theoretical basis:
B lines are 1) reverberation artifacts 2) formed from the pleural interface when the interstitium is thickened 3) span the full depth of the field
See explanation in tweetorial on ABCs of lung ultrasound here
1) Artifact
Tissue harmonic imaging is a technology designed to minimize artifact. In theory, harmonics being "on" may reduce B line quantity. The same idea applies for cardiac presets, which tend to minimize artifact.
(Notably, there is conflicting literature here)
7/
2) Formed at the pleural interface
Thus it would make sense to put the focus at the pleural line. The focal position is the depth at which lateral resolution is highest, so interstitial thickening is more likely to be detected w pleural at focal position.
Here, focus at 10 cm 8/
Same site, but focus moved to pleura. Improved lateral resolution at the pleural line brings out more B lines.
9/
3) B lines Span the full depth of the field
Often the brightness of B lines fades deeper into the image due to loss of energy with subsequent reverberations. Increasing the far gain can theoretically improve ease of visualizing B lines in the far field (as shown here).
10/
Study using in-vitro B line model (tetrahedral air bubbles) found better quality w
-focus at pleura
-more far-gain
-lung preset (vs abd)
Did not acheive significance for "harmonics off"
Limitations: one machine (Sparq), needs further study in pts. pubmed.ncbi.nlm.nih.gov/31089845/
This study sought to test if adjusted settings (developed based on in-vitro experiments) were associated change in perceived quality (and quantity) of B lines.
12/
Adjusted settings were defined as focus at pleural line, harmonics off, and time gain compensation increased linearly in the far field.
In a retrospective study, most exams resembled the typical settings (and cardiac was most common preset).
13/
In the prospective study, reviewers (>100 prior lung ultrasound exams) were shown side by side clips of typical v adjusted settings (side randomized) and were asked to grade the quality and quantity of each.
Adj settings were reported to have better quality in ~97% of cases
14/
Conclusions
Though more data is needed, it seems reasonable that for B line assessment: 1) focus set at pleural line 2) harmonics off 3) increased fair gain
Limitations: these were studied as a bundle (not individual). Study not designed to compare probes or presets.
15/
Why does this matter? 1) Consistency is important, in both clinical practice and in research. 2) The utility of B lines lies in their high sensitivity for interstitial edema. If settings are suboptimum and limit sensitivity, that reduces the power of the B line assessment.
16/
Other points on B line acquisition
-remember to find the most perpendicular angle to the pleural line. Otherwise you may end up with a non-A non-B pattern, which is non-diagnostic.
-if ribs are obscuring view, can turn probe to remove ribs from view.
17/
After considering the above data and discussion, will you adjust machine settings for B line assessment?
18/
Thanks for reading, interested to hear all thoughts on experiences w B line assessment!
2/ Pre-procedure
Lung sliding on ipsilateral side - for a comparison to post-procedure
-use linear probe
-apical and lateral/anterior
3/ Check vessel
-confirm compressibility
-understand axis of vessel
-check prox and distal for stenoses
-optimize depth and gain (this image may be undergained)
Let's talk about placement of small bore nasoenteric feeding tubes and use of ultrasound for this (A thread)
Scenario: Pt with gastroparesis and COVID/ARDS, planning to prone, want post-pyloric tube. No dedicated team for this. Can we place safely w #POCUS guidance?
1/
How is small bore feeding tube (SBFT) different from standard NG?
Narrower (6-8 Fr vs 14-18 Fr), more flexible (but w rigid stylet for placement), longer. Thus: more comfortable, gastric or post-pyloric, ineffective for suction, prone to clogging, prone to PTX if placed in lung.
Some methods used for placement 1) Blind placement - NOT RECOMMENDED. 1-2% risk of PTX 2) 2 radiograph method (safe but time consuming) 3) Capnometry 4) Endoscopic visualization 5) Electromagnetic 6) Fluoroscopic 7) Ultrasound?
1/ Happy Monday everyone! We have a special case for you today written by UPMC PGY2 #POCUS enthusiast @MikeTao15.
A 52 yo M with hx of EtOH/HCV cirrhosis, VTE on Eliquis, HFrEF presents w worsening abd distention and pain. He is disoriented and unable to give much history.
2/ Cirrhosis previously complicated by esophageal varices, hepatic encephalopathy, and ascites. No follow up since last hospital admission at outside facility ~1 year ago. Has not been taking meds.
Vitals in the ED: Temp 38.1, HR 90, BP 98/70, Pulse Ox 96% on 2L
3/
He is lethargic, arousable to voice and oriented to self only
+scleral icterus
Cardiac + pulmonary exams normal
Abdomen distended, diffusely tender, no rebound/guarding
2+ b/l edema to thighs
Jaundiced, scattered ecchymoses
+asterixis
2/ HPI:
well until 3 months ago. Since then, progressive fatigue, nausea, mild diffuse itching without rash. Few weeks of early satiety, poor PO intake, and now increasing abdominal girth. Last BM 3 days ago. No vomiting. Weight unchanged over 3 months. No fevers/chills.
3/ No home meds. 2-3 etoh drinks per day (none for a few wks). Unable to work due to symptoms. Past 1-2 days he has become confused and unable to ambulate.
We will start with a hypothetical case for illustration
65 y/o f w HFpEF, COPD admitted 4 days ago with acute pancreatitis (now resolved). You are prepping her for discharge but she is now short of breath/hypoxic requiring 4 L O2.
2/
Reportedly coughed a lot after dinner yesterday. Has not gotten any inhalers or antiHTN meds this hosp stay.
Net positive 4L. HR 88 SpO2 90% 4L BP 165/90 RR 22 T 99.8. WBC 22 (from 12 a day ago).
JVP not seen RRR, +S1/S2, 2/6 SEM
Bibasilar crackles, No LE edema. BNP 150.
3/