in this video we're gonna discuss pneumothorax, okay well you remember your
Anatomy we zoomed in on the pleura in lung sliding and we took our image and
rotated it to depict how it would appear on ultrasound and remember we thought of
the anatomy from the outside-in we looked at the skin layer we let the the
subcutaneous layer we looked at the muscular layer we looked at the
intercostal segments including the muscles in the neurovascular bundle we
looked at the rib with rib shadowing and the rib with rib shadowing and then only
then did we say that this was the pleural line then we took our high
frequency probe scanned and sagittal orientation with the indicator
superiorly at the most anterior portion of the chest and we focused our
attention on the pleural line here and we saw that there was lung sliding and
that was our normal lung
so what happens in the setting of a pneumothorax in a pneumothorax as we've
discussed before since it's a non dependent process we see that air comes
most anteriorly in the pleural space so if we place our ultrasound transducer on
the anterior of the patient and interrogate first of all all of the soft
tissues anterior to the pleural line will be imaged the same but when the
ultrasound beam hits the parietal pleura it reflects back in images that the same
as the pleural line but now air is interposed between the visceral in the
parietal pleura so when the ultrasound beam hits that air it scatters and it
does not reflect back to the ultrasound transducer so we do not see the visceral
pleura and since there's no visceral pleura
there's no lung sliding let's see what that looks like on ultrasound so this is
a video clip of no lung sliding and the anatomy is the same we see our skin
layer here we see our subcutaneous layer we see our muscular layer with our
intercostal segments we see rib and rib with rib shadowing and now we're
convinced below the ribs here this is the pleural line but now let's look at
that pleural line do you see any movement along it no there's no ants
marching along it there's no shimmering or twinkling and if we look at the
compartments above and below the pleural line as we've done previously they're
static there's movement of the chest wall because the patient is still
attempting respiration but there's no dynamic movement and difference of the
compartment above and below the pleural line now remember this is because as the
ultrasound beam comes down and hits that parietal pleura it reflects back it
visualized normally but now there's air interposed between the visceral and
parietal pleura so when the ultrasound beam hits that air it's scattered does
not come back to the probe and so we see no dynamic movement
between the two plural layers creating the lung sliding appearance in the lung
sliding artifacts so what would we expect to see on M mode if there is no
lung sliding and remember M mode is motion over time we've taken a slice of
this 2d video and we've displayed it over time and if we divided the
compartments into everything above the pleural line and everything below the
pleural line as we've done previously you'll notice that in this example
they're the same they're both static there's relatively straight lines across
and the only motion that you see is in the intercostal and muscular segments
and this is chest wall motion of respiration notice below the line it's
the same straight across and the only motion that you see is actually chest
wall motion that's transmitted down through this motion here is not
indicative of lung sliding in the way that you know that is is exactly the
same above and below so both of these are static showing that there's no lung
sliding along the pleural line in this M mode appearance has been called the
Stratosphere sign because of the way that streams from a jet linear streams
appear as a jet flies through the stratosphere others have called it a
barcode sign but with the advent of nonlinear two-dimensional barcodes this
could be confusing so now if we compare the M mode appearance side-by-side it
should become more apparent here lung sliding is present and here lung sliding
is absent here we have the sandy beach appearance and here we have the
stratosphere appearance and if we look at the pleural line here outlined in
yellow and if we look above it and below it here there's a significant difference
this is static other than chest wall movement this is dynamic that appears
sandy and fuzzy different above and below where here we look above
below they're both static other than the chest-wall movement now that you
understand lung sliding I want to make three points and the first one is that
the presence of lung sliding effectively rules out a pneumothorax at the
intercoastal level that you're scanning and so in a supine trauma patient if
you're concerned about a tension pneumothorax and you're scanning at the
anterior portion of the lung and they have lung sliding you've effectively
ruled out a tension pneumothorax and this does so with a negative predictive
value of 99 to a hundred percent the second point is that the lack of lung
sliding does not rule in a pneumothorax and this is because there's multiple
disease states that produce a lack of lung sliding and if you think about it
anything that would cause the pleural layers to stick together or cause lack
of lung sliding at a certain point could produce this so for example if you have
a large emphysema as a bleb that's not really moving
there's no slung sliding created at that level that could create lack of lung
sliding or a passed pleurodesis in which the pleural layers are scarred together
or scarring for any reason for that matter or if you have an infection that
causes the layers to stick together like in pneumonia all of those things will
cause a lack of lung sliding but they're not a pneumothorax so that begs the
question then what rules in a pneumothorax and a lung point which
we're going to discuss next effectively rules in a pneumothorax with a 100%
positive predictive value a hundred percent specificity in all the studies
up-to-date so then what is the lung point
well the lung point is simply the transition between normal lung sliding
and air in the pleural cavity aka pneumothorax so in this patient if we
were to place our ultrasound transducer here and interrogate we would see that
here there's no lung sliding again if we were
to place our transducer over here and interrogate we would see that
there's no lung sliding but if we were to place our transducer post eerily and
interrogate here there we would see lung sliding present and if we were to slide
up and place our transducer right here at this point we would see the lung
point or lung siding present and lung sliding absent in the same intercostal
space and not only is this a hundred percent specific for pneumothorax it
also defines its borders so here is a video clip of a lung point and if you
notice let's first do our exercise skin sub-q muscle intercostal rib rib and so
now we know for sure this is the pleural line that we're looking at and if you
look on one side of this pleural line we see lung sliding if you look on the
other side of the pleural line we see lack of lung sliding and in between the
two we see this transition point right here this is the lung point so let's
look at that again I want you to also engrave this video clip into your memory
as this is a hundred percent specific for pneumothorax there's nothing else in
ultrasound that produces this picture you may not see the transition point
extremely clearly on ultrasound so another way that a lung point may
present itself on ultrasound is that in the same intercostal segment you see
lung sliding present temporarily then absent present absent and this is
because the changes with respiration in the chest wall in the lungs can cause
that visceral pleura to come up and touch the parietal pleura temporarily
then you have lung sliding and then drop away again no lung sliding in the
setting of pneumothorax so what does a lung point look like then on m-mode well
if we remember we're going to take a slice of the 2d image display it over
time and we're gonna look at everything above and below the pleural line and
above is going to look the same but below see how we see this grainy
appearance this dynamic movement well this is indicative of lung sliding
but on the other half we see no lung sliding so this is that off-and-on
phenomenon of the lung point in the same intercostal segment lung sliding present
lung sliding absent lastly I want to discuss one important point about lung
point you know that I said that it was a hundred percent specific for
pneumothorax and defined its borders but one caveat to that is if there's a
complete pneumothorax you will not see a lung point and you can see why here if
you interrogate from any of these directions with the ultrasound probe
you're never going to see that transition point because there is none
because this is a 100% or a complete pneumothorax and the lung edges never
touch the chest wall now we'll discuss the clinical implications of this in
future videos but this is an important point to note all right well that was
pneumothorax and lack of lung sliding in the lung point and in the next video
we're going to discuss the clinical application of all of this in the
extended fast exam you