pulse oximetry by Dr. Tracy Wolbrink.
Hi, my name is Traci Wolbrink. I'm one of the pediatric
intensivist at Children's Hospital Boston. In this video,
I'll be talking to you about pulse oximetry. I'll be
demonstrating some of the equipment and resources that we
have available at Children's Hospital Boston. In this video,
I'll talk to you about basic pulse oximetry. Some of the
indications for using pulse oximetry. I'll show you how to
apply a pulse oximeter probe, and we'll talk about some of the
pitfalls of pulse oximetry
mechanism of action.
In this segment, I'll be talking to you about how pulse oximeter
works. The pulse oximeter works by emitting infrared and red
light and having it passed through a tissue bed, which
includes pulse tile blood, the infrared and red light will pass
through the tissue bed over to a receiver which is on the other
side of the pulse oximeter. You can see that here. As the red
and infrared light passes through the tissue bed. The
hemoglobin which is fully saturated, and D saturated will
absorb different spectrum in different amounts of light. So
fully saturated hemoglobin will absorb infrared light more
readily, and fully desaturated hemoglobin will absorb more red
light. And by passing this information about how much light
is absorbed, both infrared and red light, the machine will be
able to calculate the percentage of fully saturated hemoglobin in
the patient's blood.
Indications. The indications
for using pulse oximetry in the clinical setting vary amongst
institutions, and may include routine oxygen monitoring for
all patients, or monitoring only when the provider is concerned
that the patient may have a low saturation based on the
patient's history, diagnosis or physical exam findings. Some
clinical signs that may make you worried about a patient's oxygen
saturation include nasal flaring, chest in drawing, or
subcostal, retractions, suprasternal, retractions, or
tracheal tugging intercostal, retractions, grunting, cyanosis,
or an ability of your child to feed. In most hospitals, in
oxygen saturation cutoff of 90% or less is considered an
indication for oxygen therapy. And if you have a patient that
has an oxygen saturation of less than 90% on pulse oximetry, your
patient should be placed on oxygen. However, this cutoff can
vary depending on an institution's oxygen
capabilities. That is in high resource areas, a higher oxygen
saturation threshold may be used. For example, here at
Boston Children's Hospital, our cutoff for oxygen therapy is
usually a saturation of less than 93%. A lower oxygen
saturation goal allows low resource settings to be more
aggressive about weaning. It should also be noted that
determining the best oxygen saturation target, while an
oxygen therapy is often patient dependent. For example, certain
conditions, such as sciatic congenital heart disease may
cause health care providers to consider withholding oxygen as
they have different oxygen saturation goals and oxygen can
actually make some of these patients sicker. The frequency
of ongoing oxygen saturation monitoring also varies depending
on the hospital access to oxygen, and the degree of
patient illness. In settings with limited oxygen resources,
monitoring is often done intermittently, or in settings
with ample oxygen resources. Monitoring is often done
continuously. If you don't have the capabilities for continuous
pulse oximetry monitoring, or if it is not appropriate for your
patient, you'll want to check the patient's oxygen saturation
frequently after initiating oxygen therapy. And this will
allow you to titrate the oxygen saturations to an appropriate
level and then adjust them intermittently throughout the
day. Once you have checked a patient's oxygen saturations,
and they have improved and no longer need oxygen therapy, you
should discontinue oxygen therapy at that time. However,
you should ensure that you continue to check saturations
frequently following discontinuation of oxygen
therapy to ensure that the patient is maintaining adequate
oxygen saturations. Please note that some studies performed in
the US have actually associated continuous pulse oximetry
monitoring in acute care with increased length of hospital
stay in costs.
Application of pulse oximeter probe
so there are multiple types of pulse oximeter machines made by
many different manufacturers. They're all very similar. And
you should use whatever you have available in your institution.
They have handheld monitors. There are also bench wear
tabletop monitors like the one you see in this picture. You can
also use these pulse oximeter probes like we have here to
connect to your bedside monitor. As you see above. All the
monitors will include the basic features, which include a area
for which you can see your SPO to or your saturation of oxygen,
and one area where you can see your beats per minute, or your
heart rate. They should also usually include an alarm setting
for which will denote to the health care provider when the
oxygen saturations are low. They all also will come with a probe
connector, which allows you to connect the probe to the device.
And then the probe itself is going to be your interface with
the patient. And there are two different main categories of
saturation probes, which include the reusable probe. Here's an
example of an alligator clip, reusable probe, or a disposable
type probe, meant to be for single use. With the disposable
probes, there's often a weight limit that suggested to be used
with these probes. For instance, in this one, you can see that
there, it's recommended for less than three kilogram infants, or
greater than 40 kilogram adolescents or adults. And the
three kilogram infant, it's recommended to put on the foot
or the hand, and then a 40 kilogram adult, it's meant to
fit on the finger. That being said, you can often find ways to
get these devices to fit on patients that are outside of
this range. But if you have the capabilities for having
different disposable and reusable oxygen probes, you're
going to have the capabilities to use these on a larger range
of patient ages and weights. When you go to apply your
saturation probe to your patient, there are several
locations that you will be able to use in a small infant or
child, you can use often the foot, the hand, toes, fingers,
or even sometimes ear lobes. The one thing that's most important
to remember is that you must make sure that the light source
and the receiver are opposite of each other, no matter where you
place this. So for example, if I'm going to place this on the
infant's foot, I want to make sure that the light source here
and the receiver here are indirect communication with each
other, I can then wrap the elastic around to make sure that
it stays on this patient. This probe here, as I showed you
before, is a neonatal probe. And so the distance between the
light source and the receiver is quite small. Some of the child
and infant probes that allow you to place them on the foot will
have a wider distance so that you can use them for larger
patients. So you can see I can apply this to the patient's foot
can also apply to the patient's hand in a similar fashion when
you apply it here. Again, you want to make sure that the light
source and the receiver are opposite of each other. And then
you'll be able to get an accurate reading. Alternatively,
you could use a reusable This is a finger reusable probe. It's
got a picture of a finger here. And it's meant for you to put
your finger inside and allow this to close over the device.
These as long as they're cleaned, can be used on multiple
patients. The disposable probes are meant to be used only on one
patient, but in certain environments, you may need to
reuse them. And as long as you clean them, they can sometimes
be reused must be said that, over time, the light source and
the receiver may get worn out and may give you not very
accurate readings over time. Other considerations for probe
use revolve around ways to ensure accurate readings. It is
important not to use the probe on the same extremity as the
blood pressure cuff, as the pulse oximeter depends on
pulsatile flow, which can be impeded by the blood pressure
cuff. Secondly, if the probe is used continuously, it should be
assessed often for signs of skin irritation below the line Each
skin should also be cleaned before probe application to
remove any dirt, markers or other possible causes of probe
inaccuracy. Finally, nail polish should be removed from the
finger or toenail to which the probe will be applied, as the
color can absorb light emitted by the oximeter and interfere
with the detection of oxygenated hemoglobin
pitfalls.
So now I'm just going to demonstrate some of the pitfalls
you might experience. When using pulse oximetry. I'm gonna place
this probe on my finger, placing the receiver on one side and the
light source on the other and wrap the plastic around. Then
I'm going to look at our monitor and observe to see a pulse a
tidal wave form, which you now see, along with a saturation of
99% and a heart rate of 8485. You can see here that there's a
very nice pulse otile tracing, which gives me an indication
that this is a good way for him. And that might, I should
probably trust my output reading. There are certain
circumstances when you have a low output reading that you want
to reevaluate whether or not your equipment is working
properly. And you should also assess clinically what's going
on with your patient to determine if the number is
accurate. For instance, if my if I move my finger around, you see
that you lose the normal pulse otile waveform. This can
interfere with your signal and can sometimes give a falsely low
reading. So if a patient is crying, screaming, kicking,
moving around, you may not have an accurate waveform. And then
you may not have an accurate pulse oximetry tracing, which
will give you a falsely low oxygen saturation level.
Additionally, some of the hemoglobinopathies can cause a
problem in terms of the sensing mechanism and the properties of
the pulse oximeter absorbing different wavelengths of light.
And finally, and most importantly, the low output
state can cause a lot of problems for using pulse
oximetry. So patients that are severely dehydrated patients
that are hypovolemic patients with sepsis, patients in shock
for any reason, and patients with low cardiac output can
often have a lack of peripheral pulses. And this lack of
peripheral pulsatility can lead to erroneous readings and your
pulse oximeter tracing. pulse oximetry includes the word pulse
and so you need pulsatile blood flow in order to get appropriate
tracings and to get appropriate values. So unless you have a
good pulse, you often see a lack of a good pulse tracing, and
either absent or erroneously low oxygen saturation level. In
these patients, it's important to try to change your probe to a
different site to make sure that you're doing everything to
resuscitate your patient and promote good oxygen delivery.
And these are the patients where you may have to invasively
measure what their oxygen levels are either through an arterial
blood gas or other means of sampling.
Other uses
so in addition to monitoring a patient's oxygen saturation, you
can use it non invasively. To look at other indices. For one,
you can look at a patient's volume status by looking at the
pulse pressure variation. As you see on the monitor, you notice
that during inspiration, the notch of the pulse waveform is
lower than during exhalation. This is often augmented, or the
difference is often larger in patients that are hypovolemic or
in patients that have significant obstructive lung
disease, like an asthma or COPD, or in patients that are having
significant intrathoracic pressure swings because of
breathing. Additionally, it can be a marker to look at cardiac
output. If you have a patient that has a very nice pulse
oximetry tracing, and all of a sudden the tracing is gone, you
should make sure that you're checking the patient clinically
for signs and symptoms of cardiac arrest. And you should
make sure that you feel both for peripheral and central pulse, as
this could be one indicator that a patient has just become
pulseless. Additionally, as you're doing chest compressions
in this patient, you can often see adequacy of chest
compressions by taking a look at your pulse waveform. But note
that the size of the waveform does not indicate adequacy of
chest compressions. You can actually use the waveform as a
marker but always examine the patient and feel for a pulse. So
this concludes the video on pulse oximetry. Thank you.
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