well welcome to another MedCram lecture we're going to talk about lab analysis
and this really is the opening of a long series that we're going to do on the
analysis of laboratory results especially in patients that are in the
hospital labs our objective data you know that whenever we see a patient we
talked about a soap note right we've got the subjective we've got the objective
we have the assessment and the plan and this squarely fits within the objective
so we have physical exam findings we have signs and symptoms and things of
that nature but we also have objective data like CBC a CMP different types of
labs and things that come back and if you've ever had those things come back
and maybe you felt a little bit less than adequate in terms of interpreting
this and how to follow this in a organized way of looking about it and
how to act on it well this is the series that's going to be for you this is going
to hone your skills in understanding and applying and actually doing something in
writing orders about labs that come back so we're going to go through this in a
methodical way and we're going to talk about the CBC which you might have seen
or we have a WBC a hemoglobin hematocrit and a platelet count with an MC V and
we're also going to talk about in this series the chem 7 specifically the
sodium the potassium the chloride the co2 or the bicarb the B UN the
creatinine and the glucose so objective measurements how to read them how to
look at them and what to do about them and the way I'd like to start out
philosophically with these things I want you to imagine that you are flying a
plane and as with all analogies sometimes these things break down but
the way I like to look at this is you're flying a plane and the patient is your
passenger you're at a pilot and as you're flying this plane you can look
out the window and that's kind of a clinical view when you look at the
patient you can kind of see how they're doing but you know for some very
difficult Asians and the analogy is that you're
flying through a storm sometimes visibility isn't that great and what you
need to rely on is your instruments so I like to think of lab analysis as your
instruments and for those of you who are pilots you know that some people are
instrument rated and other people are not instrument rated and that's because
there's a whole science to being able to fly by instruments and that's kind of
what you're doing when you're looking at labs any type of labs x-rays or things
of that nature these are your instruments when you're flying the plane
so you can see what the CBC is the human globe and the Saudi and the potassium it
gets you a better look at what's going inside the patient but they have to be
interpreted in light of what's going on clinically with the patient and the best
example that I can think of is imagine you have a plane that is taking off and
you have a plane that is coming in for landing okay in both of these situations
the airspeed is less the flaps are down in both cases and the altitude is also
about the same so in other words the instruments would look almost identical
even the wheels are down but the planes are doing completely different things
one is taking off and the other one is landing for instance you can have the
same sodium let's say the sodium is 140 on one patient and it's 140 on the other
but let's say it came down from 145 down to 140 but in the other situation it was
135 and it was going up to 140 so the point here is is that whenever you get
labs back on a piece of paper it's a snapshot it's a point in time of what's
going on with your patient and the most powerful way to look at Labs is looking
at previous labs so I always like to trend because in most situations there's
a range around some sort of normalcy so let's take sodium for instance the low
limit for sodium is 135 the high limit is 145 and of course 140 is right in the
middle so you can look at that lab and let's say you've got a
1:44 and that's a normal value and you might not think anything of it but if
you were to look the previous day and saw that it was 139 and the previous day
to that it was 135 all of those technically are normal values but you
can clearly see that by tomorrow you're going to have a problem with
hypernatremia and so that's the example that I use and we can do an example for
each one of these so again you need to look at the trends on these things
and be proactive especially if you're dealing with patients in the intensive
care unit all right the other thing too is of course when you're flying a plane
you can continuously look at these instruments you can see how fast the
altimeter for instances is increasing or decreasing you can see how fast your
airspeed is changing well that's a different situation than when you're
doing labs you are the one who chooses what labs you get and you are the one
that chooses how frequently you get those labs so part of analyzing labs is
knowing how frequently you need to have these labs checked and which labs it is
that you need to have so obviously a pilot sitting in this plane doesn't
decide what instruments are going to be working those are the instruments that
come with the plane and those are the ones that are there and they're there
all the time it's a little bit trickier with Laos because you have to decide
what labs you get and there's some diagnoses for instance like a pulmonary
embolism where unless you think about the diagnosis of pulmonary embolism you
typically won't get the right diagnosis you usually won't get the diagnosis of
pulmonary embolism unless you get a CT angio you're typically won't know if a
patient is anemic unless you order a CBC and usually won't know if a patient is
hypercapnia unless you order an ABG so that's the added complexity to what
we're going to discuss in this whole series is knowing when to order tests
and knowing how to utilize those tests so that brings us to another situation
and that's lab errors so you know when you're flying on a plane and you have
instruments it's pretty obvious if the instrument is failing you or it's not
work correctly not-so-obvious in the lab
world so the published data is that about 0.45 percent of all the labs have
a significant error rate to them and are therefore incorrect and most of those
have to do not with the machine itself that's running the labs but how it's
drawn or if patients blood samples get mixed up so in other words you might
have let's see here on a graph a potassium that's going along like this
and then all of a sudden it goes up and then it comes back down again
okay that's just not clinically feasible it could be that a patient sample got
mixed up with a nearby patient resulting in a lab error so here's another
difference between pilots and yourself who's looking at these lab values pilots
generally speaking are told to trust their instruments okay why is that
because when they're up there and they can't see it feels like they're the
right-side up but they may not be because of centripetal forces and things
of that nature so they're always told to trust their instruments even when what
they see outside the window is telling them something different well that's a
little bit different here in clinical medicine because errors can happen
you've got to couple that with what you're seeing clinically so if it
doesn't make sense clinically my advice is to repeat the
lab test to confirm it before acting on something that's clearly out of the
ordinary so in other words don't put a hundred percent trust and the lab values
that you get so for instance what can happen is you draw blood in a patient's
arm and there may be an IV infusing or maybe a central line for instance and
you're taking blood out of that central line if for instance that patient has a
lot of d5 running through it and you draw blood up here you're going to
notice that your glucose is going to be high okay the other thing can happen if
there's potassium runny you might have a high potassium or if you draw it out of
a central line and you don't waste enough blood that could cause a
difference in potassium and we'll get into some examples of this for instance
if the potassium is really high and kind of at the ordinary what you can do is
you can always order an EKG and see if there are peaked t-waves if there are
peaked t-waves that confirms and triangulates the fact
that perhaps you've got a hyper kelly in this situation if it doesn't then you
know you've probably got some time and you may want to repeat it as opposed to
just acting on it immediately with kayexalate and bicarb and in fact the
patient's potassium is normally you cause a different problem with
hypokalemia instead okay so the four points that I want you to get out of
this first lecture sort of the introduction and the philosophy of lab
data is these are objective measurements and they're meant to complement the
clinical impression so you need to put together this data with what it is that
you see in front of you that's number one number two is always trend this data
because it's in the trends that tells you where things are moving not just the
snapshot data that you get to trend it is much more powerful number three labs
can't be wrong so remember to trust the lab data but to verify it so if it looks
wrong repeat it and then the other thing that I want you to be aware of in terms
of the complexity is you've got to think about what it is that you want to see on
the patient and what blood tests you want to order but also how often you
need to see it so how often do you think it's gonna change and when do you want
to know that change is it good to know eight hours after the events if not then
order q4 and be cognizant of that and then you should probably as a number 5
think about your outliers in other words how low does something have to be or how
high does something have to be before you're gonna act on it
so for instance a hemoglobin of less than 7 is going to make you want to
transfuse blood just make sure you put in in order for that so you get the call
on that ok thanks for joining us for this first video we're gonna jump in
with CBC next video