B1 Intermediate US 44 Folder Collection
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Spirometry is important in several ways. Firstly, we can use it as a diagnostic tool, so, commonly,
when somebody presents with cough or breathlessness, we'd use spirometry to see if there's
a problem with the lungs rather than, for example, with the heart.
Secondly, we might use it for monitoring disease. So, somebody who has got pre-existing COPD,
or even asthma, we might want to see how their airflow is carrying on.
Thirdly, and increasingly so, we're encouraged to screen for people who are at higher risk.
So, for example, smokers or ex-smokers, who are aged over 35 may be presenting with recurrent
cough or wheeze, we might look to see if they might have evidence of airways disease, for
example, COPD.
Spirometry measures the flow of air in and out of the lung. What we're actually measuring
is not just expiration; it's a function of inspiration as well. We're not measuring
the total volume of the air in the lung, because there's a little bit left here at the bottom,
the residual volume. But what we're effectively measuring is the amount of useful air that
goes in and out of the lung.
There are various types of spirometer available, ranging from quite cheap, hand-held spirometers,
which don't have a display, to this rather more sophisticated one that we use for diagnostic
purposes.
Many of the spirometers are the same; this is a spirometer in the mouthpiece, which measures
flow. You can see this little vane whizzes round, which sends off electrical impulses
to the computer, which integrates this into a volume/time or into a flow/volume curve.
It can also do several other more sophisticated techniques, but it still does the basics of
a Forced Vital Capacity manoeuvre.
It's important to prepare a patient before carrying out diagnostic spirometry. First
of all, a patient may already have been taking short-acting bronchodilators, for example,
because they've been symptomatic, but we really need to stop any drugs that might interfere
with the diagnostic spirometry.
The general advice is, stop any short-acting bronchodilators four hours before and then
your long-acting bronchodilators for about 24 hours before the procedure. So, that's
very important.
Secondly, in general terms, it's important that the patient doesn't wear any tight
clothing, for example, tight corsets. They shouldn't have a large meal for six hours
before. They should avoid smoking an hour before the procedure and avoid any strenuous
exercise for 30 minutes before. A patient leaflet, given beforehand, explaining the
procedure can be a very useful way of preparing the patient for spirometry.
There is certain information that we need to record before we carry out the procedure.
We need to record the patient's age, their height, their ethnicity, because a correction
factor might have to be made for patients who are non-Caucasian. It's also useful
to know when they did last take any medication or did last smoke, for example.
Once we've recorded the details, we need to carry out the procedure. The first thing
is to make sure that the patient is comfortable. They must be seated, mainly for a practical
reason that sometimes, elderly people who are frail, when they carry out a forced manoeuvre
may actually become very dizzy and occasionally fall. So there are very practical reasons
for getting people seated.
They need to be comfortable and they need to have loosely fitting clothes. They shouldn't
have tight clothes, which might affect the values. Also, they should remove any loose
fitting dentures, which again, could interfere with the procedure.
Before we carry out spirometry it's a useful idea to demonstrate to the patient the actual
manoeuvre. For the forced manoeuvre, the patient takes a deep breath in, to maximal inspiration,
pauses briefly, and then breathes out as hard and as long as they can. It's a good idea
to encourage them all the way, “Keep going, keep going, keep going,” until they get
to at least six seconds minimal expiration for adults and three seconds for children.
Ideally, until they get to residual volume.
Quality control is very important in carrying out spirometry and in its interpretation.
Many of the modern, computerised systems will tell you whether it was a good blow and whether
it meets international standards, usually, using American Thoracic Society, European
Respiratory Society standards. But if you haven't got that bit of sophistication,
then it's very important that you get three repeatable blows. Three repeatable blows means
that there is a sharp upstroke on the volume/time curve and a smooth curve without any interruption,
for example, a cough.
Sometimes this is very difficult to do. Often, you have to go up to eight blows before you
get three decent readings. One has to accept, very occasionally, especially for frail people,
this may not be possible.
Usually, for diagnostic spirometry we need post-bronchodilator readings. For example,
when we're diagnosing COPD, the NICE guidelines say that we should use post-bronchodilator
values. But often, in General Practice, we may be not quite sure what's going on, whether
it's asthma, or COPD. In order to diagnose asthma, we have to make sure that there are
pre- and post-bronchodilator readings.
Once the pre-bronchodilator procedure is carried out, we then need to administer the bronchodilator.
There are no set guidelines regarding exactly what sort of bronchodilator we should give,
but it's generally accepted that one gives 100 micrograms of Salbutamol, administered
via a large-volume spacer and this should be repeated four times. In other words, four
times 100 microgram puffs. Then, repeat the diagnostic spirometry 20 minutes later.
It's very important to get good quality traces to look at when interpreting the results.
I can't emphasise too much how important it is to have the graphs in front of you and
not just look at a series of results. The reason for this is two-fold. There are some
quite common pitfalls, which can be picked up on the trace, but also, the computer is
sometimes wrong. It's a bit like ECG machines. I'm sure many of you will have had the experience
that you have an ECG result, which says the trace is normal, or the trace is abnormal
and you look at it and you disagree. Usually you're right. It's likewise with spirometry.
It's very important to look at the trace.
There are some quite common pitfalls with spirometry. One of the most common is that
patients fail to take a deep inspiration or deep expiration outwards, either because they're
too tired or they're just unable to do it. This can sometimes give a false picture.
Another common problem is that the fit of the mouthpiece into the patient's mouth
isn't correct, isn't tight, so they lose air around the mouthpiece, again, giving a
falsely low reading. Make sure that you look at the trace, look at the patient.
Spirometry is a vital tool to be used in general practise in the diagnosis of the breathless
patient and is mandatory when diagnosing a patient with COPD. It's extremely useful
in monitoring disease, especially with COPD and with asthma.
But it's very important that when interpreting results, that we make sure that the results
are of high quality, preferably by looking at the traces, so make sure that the procedure
has been carried out properly.
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Spirometry from BMJ Learning

44 Folder Collection
yao published on February 2, 2019
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