Download Pulse Oximeter

PULSE OXIMETER
BY
AHMAD YOUNES
PROFESSOR OF THORACIC MEDICINE
Mansoura faculty of medicine
Hypoxia and Oxygenation
• Hypoxia is low oxygen tissue content, resulting
from inadequate oxygen delivery to meet their
oxidative requirements.
• There are four basic types of hypoxia.
1- Hypoxic hypoxia occurs when there is a
deficiency in oxygen exchange in the lungs.
Some causes include:
• Decreased partial pressure of oxygen available
at altitude.
• Conditions that block the exchange at the
alveolar capillary level (e.g. pneumonia,
pulmonary edema, asthma, drowning).
Hypoxia and Oxygenation
2-Anemic hypoxia occurs when the body cannot
transport the available oxygen to the target
tissues. Causes include:
• Anemia from acute or chronic blood loss.
• Carbon monoxide poisoning.
• Medications such as sulfonamides and nitrites.
• Methemoglobinemia.
• Sickle cell disease.
Hypoxia and Oxygenation
3- Stagnant hypoxia occurs when there is
insufficient blood flow. Causes include:
• Heart failure.
• Decreased circulating blood volume.
• Vasodilatation.
• Continuous positive pressure ventilation.
Hypoxia and Oxygenation
4- Histotoxic (histologic) hypoxia occurs when the
body’s tissues are not able to use the oxygen that
has been delivered to them. This is not a “true
hypoxia” because the tissue oxygenation levels
may be at or above normal. Causes include:
• Cyanide poisoning.
• Alcohol consumption.
• Narcotics.
Hypoxemia
• Hypoxemia is a condition in which there is an
inadequate amount of oxygen in arterial blood
(decreased PaO2, SaO2, or hemoglobin content).
• Hypoxia (low O2 content, low cardiac output, or
low oxygen uptake at the tissue level) occurs
whether hypoxemia is present or not.
• In adults, children, and infants older than 28 days,
hypoxemia exists when the PaO2 is less than 60
mmHg or the arterial oxygen saturation (SaO2) is
less than 90% when breathing room air.
If the partial pressure of O2 (PaO2) is less than the
level predicted for the individual’s age, hypoxemia
is said to be present.
Predicted Pao2 = 105 - 1/2 age (year)
• oxygen is a treatment for “hypoxemia, not
breathlessness”. Further, “oxygen has not been
shown to have any effect on the sensation of
breathlessness in non-hypoxemic patients”
• The main goal of oxygen therapy is:“To treat or
prevent hypoxemia thereby preventing tissue
hypoxia which may result in tissue injury or
even cell death”
Some of the causes of hypoxemia are:
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Low inspired PO2 (e.g., at high altitude).
Hypoventilation, V/Q mismatch (e.g., COPD).
Anatomical Shunt (e.g., cardiac anomalies).
Physiological Shunt (e.g., atelectasis).
Diffusion deficit (e.g., interstitial lung disease).
Hemoglobin deficiencies.
What is a pulse oximeter ?
• Oxygen binds to hemoglobin in red blood
cells when moving through the lungs. It is
transported throughout the body as arterial blood.
• A pulse oximeter uses two frequencies of light
(red and infrared) to determine the percentage (%)
of hemoglobin in the blood that is saturated with
oxygen.
• The percentage is called blood oxygen saturation,
or SpO2.
• A pulse oximeter also measures and displays the
pulse rate at the same time it measures the SpO2
level.
Pulse oximetry
• Clinical recognition of decreased arterial oxygen
saturation of haemoglobin (SaO2) is subjective and
unreliable, with the classic sign of cyanosis appearing
late when Sao2 is between 80 - 85%.
• Pulse oximetry is simple to use, relatively cheap,
noninvasive and provides an immediate, objective
measure of Sao2.
• It is now used widely in all in-hospital settings and
increasingly in both primary care and the pre-hospital
environment.
• Oxygen saturation, ‘the fifth vital sign’, now also forms a
component of many early warning systems to identify
the deteriorating patient.
What can be learned by monitoring blood
oxygen saturation?
• Each lung contains nearly 300 million alveoli which are
surrounded by blood capillaries.
• Since alveolar walls and capillary walls are very thin, oxygen
passing into the alveoli immediately transfers into the blood
capillaries. (Usually in adults, the transfer would take about
0.25 seconds while resting.)
• A large proportion of the oxygen diffusing into the blood
binds to hemoglobin in the red blood cells, while a part of
the oxygen dissolves in the blood plasma.
• The amount of oxygen transported around the body is
determined mainly by the degree to which hemoglobin
binds to oxygen (lung factor), hemoglobin
concentration (anemic factor), and cardiac output
(cardiac factor).
What can be learned by monitoring
blood oxygen saturation?
• Oxygen saturation is an indicator of oxygen
transport in the body, and indicates if sufficient
oxygen is being supplied to the body, especially to
the lungs.
• The pulse oximeter can also measure pulse rate.
• The volume of blood being pumped by the heart
per minute is called the cardiac output.
• The frequency of pumping during one
minute is called the pulse rate. These
cardiac function indicators can be
determined by the pulse oximeter.
How does oxygen move around the body?
• Oxygen is transported throughout the body by the
blood.
• Oxygen is inhaled into the lungs, and carbon
(carbon dioxide) is exhaled from the lungs to the
air. This process is called ventilation.
• Inhaled air flows into the upper airway, then into
the peripheral airways, and is finally distributed
into the lungs. This process is called distribution.
• Oxygen is absorbed from the alveoli, then into the
lung capillaries via alveolar membranes, while
carbon dioxide moves from the lung capillaries to
the alveoli. This process is called diffusion.
How does oxygen get into the blood?
• Only about 0.3 ml of gaseous oxygen dissolves in 100 ml
blood per mmHg (pressure).
• This amount is only 1/20 of carbon dioxide solubility. This
suggests that a human could not get sufficient oxygen if
solubility were the only way to get oxygen in the blood. For
this reason, hemoglobin (Hb) has an important role as a
carrier of oxygen.
• One molecule of hemoglobin can bind to 4 molecules of
oxygen, and 1 g of hemoglobin can bind to 1.34 ml of
oxygen. Since 100 ml of blood contain about 15 g of
hemoglobin, the hemoglobin contained in 100 ml of blood
can bind to 20.1 ml of oxygen.
• Amount of oxygen contained in 100 ml of blood (20.4 ml) =
Dissolved oxygen (0.3 ml) + Hb-bound oxygen (20.1 ml)
How does oxygen get into the blood?
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Oxygen content of arterial blood (CaO2 [mL O2/100 mL])
CaO2 =1.34 mL /g X Hb (g/100Ml) XSaO2 + 0.003 X PaO2
SaO2 =100XO2Hb/(O2Hb + RHb)
The arterial oxygen saturation (SaO2) is usually expressed
as the ratio of oxygenated hemoglobin (O2Hb) to the total
amount of Hb that can bind oxygen. The amount of
hemoglobin that can bind oxygen is the sum of O2Hb and
deoxygenated (reduced) hemoglobin (RHb).
• The SaO2 value for a given PaO2 depends on the position of
the oxygen-hemoglobin saturation curve (also called the
oxygen-hemoglobin dissociation curve)
• At the usual body temperature and pH, a PaO2 of 60 mm Hg
corresponds to approximately an SaO2 of 90%.
How does oxygen get into the blood?
• A left shift results in a lower PaO2 being associated with
a given SaO2 and vice versa.
• A shift to the left can occur with decreasing
temperature, hydrogen ion concentration [H+],
PaCO2, or level of 2, 3-diphosphoglycerate (2, 3DPG).
What is oxygen saturation?
• Hemoglobin bound to oxygen is called
oxygenated hemoglobin (HbO2). Hemoglobin not
bound to oxygen is called deoxygenated
hemoglobin (Hb).
• The oxygen saturation is the ratio of the
oxygenated hemoglobin to the hemoglobin in the
blood, as defined by the following equation.
What is oxygen saturation?
• Since each hemoglobin molecule can bind to 4 molecules of
oxygen, it may bind with 1 to 4 molecules of oxygen.
However, hemoglobin is stable only when bound to 4
molecules of oxygen or when not bound to any oxygen. It is
very unstable when bound to 1 to 3 molecules of oxygen.
• Hemoglobin exists in the body in the form of deoxygenated
hemoglobin (Hb) with no oxygen bound, or as oxygenated
hemoglobin with 4 molecules of oxygen.
• Oxygen saturation can be assessed by SaO2 or SpO2.
• SaO2 is oxygen saturation of arterial blood, while SpO2 is
oxygen saturation as detected by the pulse oximeter. They
are called arterial blood oxygen saturation and percutaneous
oxygen saturation, respectively.
How does the pulse oximeter measure
oxgen saturation ?
• Hemoglobin bound to oxygen is called oxygenated
hemoglobin and has a bright red color.
• Hemoglobin with no oxygen bound to it is called
deoxgenated hemoglobin and has a dark red color. That
is why arterial blood has bright red color and venous
blood has dark red color .
• The pulse oximeter probe containing light-emitting
diodes (LEDs) and a photoreceptor situated opposite, is
placed across tissue, usually a finger or earlobe.
• Some of the light is transmitted through the tissues while
some is absorbed.The ratio of transmitted to absorbed
light is used to generate the peripheral arterial oxygen
saturation (SpO2) displayed as a digital reading,
waveform, or both.
How does the pulse oximeter measure
oxgen saturation ?
• As a result of rapid sampling of the light signal, the
displayed reading will alter every 0.5 - 1 s, displaying the
average SpO2 over the preceding 5 - 10 s.
• Most pulse oximeters are accurate to within +/- 2% above
an SaO2 of 90%.
• Tissue thickness should be optimally between 5 - 10 mm.
• Poor readings may be improved by trying different sites ,
warming sites or applying local vasodilators.
• Information about pulse rate and waveform
(plethysmographic waveform) may also be provided.
• A poor signal may indicate a low blood pressure or poor
tissue perfusion - reassess the patient.
The graph shows spectroscopic and absorptive properties
(properties regarding which color is absorbed) of oxygenated
hemoglobin (HbO2) and deoxygenated hemoglobin (Hb)
Oxygenated hemoglobin absorb more infra red while deoxygenated
hemoglobin absorb more red
How does the pulse oximeter
measure oxgen saturation ?
• The percentage of oxygenated hemoglobin and
deoxygenated hemoglobin is determined by
measuring the ratio of infrared and red light
detected by the pulse oximeter.
• The pulse oximeter emits red (R) and infrared
(IR) LED light that passes through the body,
receives data from a photodetector, and
calculates the oxygen saturation by determining
the ratio of the two waveforms.
How does the pulse oximeter measure
oxgen saturation ?
• When the amount of HbO2 is greater, the absorption of
red light becomes smaller and the absorption of infrared
light becomes larger, resulting in a lower ratio of
absorption of the two wavelengths.
• In contrast, when the amount of deoxygenated
hemoglobin is greater, the absorption of red light
becomes greater while the absorption of infrared light
becomes smaller, resulting in an increased ratio of
absorption of the two wavelengths. Thus, the pulse
oximeter determines oxygen saturation by measuring
the ratio of oxygenated hemoglobin to deoxygenated
hemoglobin.
How can the pulse oximeter measure oxygen saturation,
even though the light from the pulse oximeter has to pass
through layers of tissue before it reaches the blood?
• Arterial blood pumped from the heart moves
through vessels in the form of waves called
pulse waves resulting in a change in size of the
artery . However, venous blood does not move
in pulse waves.
• The light emitted into the body is absorbed by
arterial and venous blood as well as other
tissue, and some continues through the body.
However, tissues other than arteries experience
no change in size over time.
The following figure shows temporal change in
pulse wave signals.
How does the pulse oximeter measure oxgen
saturation ?
• Since tissues other than arterial blood experience no
change in size over time, the light passing though the
body changes in intensity over time depending on the
change in the size of arterial blood layers due to pulse
waves. The change in intensity results from the change
in size of the arterial blood layer, uninfluenced by
venous blood and other tissues.
• Monitoring changes in the components of the exiting
light provides data on arterial blood.
• Measuring the cycle of the changes in light components
also reveals the pulse rate.
• The pulse oximeter can measure oxygen saturation as
well as pulse rate based on the pulsing of arterial blood.
What factors cause errors in the pulse oximeter?
1. Abnormal hemoglobin :Blood may contain abnormal
hemoglobins such as carboxyhemoglobin and
methemoglobin which do not contribute to oxygen
delivery. The dual-wavelength pulse oximeter may be
affected by these abnormal hemoglobins.
2. Medical dyes :If dyes such as cardio green,
intravascular dyes, and indocyanine green have been
injected into the blood, they may influence the level of
transmission of the red and infrared light.
3. Manicure and pedicure : If users wear nail polish, it may
absorb the light emitted from the LED, and change the
light transmitted though the body, influencing the
values calculated.
What factors cause errors in the pulse
oximeter?
4. Major body motion :Body motion may cause noise that
affects the values calculated. When noise, including that
caused by body motion, reduces the reliability of the
values calculated, the pulse oximeter will display a
warning.
5. Blood flow blocked due to pressure on arms or fingers
:The pulse oximeter measures oxygen saturation based
on changes in the blood flow. Therefore, if the blood flow
is blocked, correct measurement becomes impossible. In
addition, if the fingers are flexed at a uniform pace (if, for
example, grip strength is intensified at a uniform pace on
an ergometer), the pulse oximeter may interpret the
pressure as changes in pulse rate, causing errors
(particularly pulse rate errors)
What factors cause errors in the pulse
oximeter?
6. Peripheral circulatory failures :The pulse oximeter utilizes
blood flow to monitor changes in the amount of light
transmitted to calculate values. If the peripheral blood flow
is reduced, adequate data may not be obtained, and the
result is inaccurate measurement. In this case, it is
necessary to promote blood flow by massaging or warming
the fingers or measuring other fingers with more regular
blood flow.
7. Excessive ambient light (panel lamp, fluorescent lamp,
infrared heating lamp, direct sunlight, etc.) The pulse
oximeter can usually cancel out the effects of ambient light.
However, if the ambient light is too strong, the device will
not be able to cancel out the effects, and this may cause
errors
What factors cause errors in the pulse
oximeter?
8. Ambient electromagnetic waves : If electric
appliances such as televisions, mobile
telephones, or medical devices which produce
high levels of electromagnetic waves are used
near the pulse oximeter, the electromagnetic
waves from these devices may interfere with
accurate measurement.
9. Probe attached incorrectly ; If the probe is not
properly attached, it may detect a variety of
noise, resulting in inaccurate measurement.
When in doubt, the technologist can place the
probe on her or his own finger as a test of
oximeter accuracy.
Why an ABG instead of Pulse oximetry?
• Pulse oximetry is non-invasive and provides
immediate and continuous data.
• Pulse oximetry does not assess ventilation
(pCO2) or acid base status.
• Pulse oximetry becomes unreliable when
saturations fall below 70-80%.
• Technical sources of error (ambient or
fluorescent light, hypoperfusion, nail polish,
skin pigmentation)
• Pulse oximetry cannot interpret methemoglobin
or carboxyhemoglobin
Why an ABG instead of Pulse oximetry?
• Pulse oximetry provides only a measure of
oxygen saturation, not content, and thus gives
no indication of actual tissue oxygenation.
• Readings from a pulse oximeter must not be
used in isolation: it is vital to interpret them in
light of the clinical picture and alongside other
investigations, and potential sources of error.
Pulse oximeters are not affected by:
• Anaemia (reduced haemoglobin)
• Jaundice (hyperbilirubinaemia)
• Skin pigmentation
Does the ratio of PaO2 to SpO2 always
remain the same?
• The amount of oxygen dissolved in the blood is
proportional to the partial pressure of oxygen.
• The amount of oxygen bound to hemoglobin will
increase as the partial pressure of oxygen
increases.
• The amount of oxygen bound to hemoglobin
does not increase in proportion to the partial
pressure of oxygen. The increase may be
indicated by an S-shaped curve.This is called the
oxygen dissociation curve.
In the following graph, the low pH curve shows that when
PaO2 is 80 mmHg (Torr), oxygen saturation is 80%.
Does the ratio of PaO2 to SpO2 always
remain the same?
• The sinusoid shape of the curve means that an initial
decrease from a normal PaO2 is not accompanied by a drop
of similar magnitude in the oxygen saturation of the
blood,and early hypoxaemia may be masked.
• At the point where the SpO2 reaches 90-92%, the PaO2 will
have decreased to around 60 mmHg. In other words, the
PaO2 will have decreased by almost 50% despite a reduction
in oxygen saturation of only 6-8%.
• The output from a pulse oximeter relies on a comparison
between current signal output and standardised reference
data derived from healthy volunteers.
• Readings provided are increasingly unreliable with
increasing hypoxaemia. Below 70% the displayed values are
highly unreliable.
Does the ratio of PaO2 to SpO2 always
remain the same?
• Because of the normal position on the flat portion of the
O2Hb dissociation curve, there is little change in the
SaO2 as a result of the fall in PO2 associated with sleep.
• If the baseline awake PaO2 is lower, the fall in SaO2 will
be greater for the same drop in PaO2. In patients with
lung disease and a lower awake PO2, even a normal
sleep-related drop in PO2 will be associated with a
larger decrease in the SaO2.
• The change in ventilation with sleep is due to a fall in VT
with minimal change in the RR.
Does the ratio of PaO2 to SpO2 always
remain the same?
• The position of the O2Hb dissociation curve is
often defined by the P50, which is the PaO2
corresponding to an SaO2 of 50%.
• For Hb A, the P50 is 26 mm Hg but is 42 to 56
mm Hg in sickle cell disease patients. The net
effect is a rightward shift in the O2Hb
dissociation curve for HbS. This means that for
a given SaO2, the PaO2 is higher in SCD
patients than would be expected based on the
normal O2Hb dissociation curve.
Does the ratio of PaO2 to SpO2 always
remain the same?
• The oxygen dissociation curve is called the
“standard oxygen dissociation curve” in which the
body temperature is 37°C, pH 7.4.
• The curve may shift to the right or left, depending
on patient conditions.
• If the body temperature decreases and pH
increases, the curve will shift to the left. If the
temperature increases and pH decreases, the curve
will shift to the right.
Does the ratio of PaO2 to SpO2 always
remain the same?
• Determining the oxygen-carrying capacity of Hb is
complicated by the fact that both carboxyhemoglobin (COHb) and met-hemoglobin (MetHb)
are forms of circulating Hb that do not bind oxygen.
• Carboxyhemoglobin occurs when carbon
monoxide (CO) binds to Hb. Smokers have
increased carboxyhemoglobin.
• MetHb occurs when the normal ferrous state (Fe2+)
of the iron moiety in Hb is oxidized to the ferric
stage (Fe3+). Significant methemoglobinemia can
occur after exposure to certain medications.
Does the ratio of PaO2 to SpO2 always
remain the same?
• The sum of the fractional concentrations of
O2Hb, RHb, COHb, and MetHb equal 100%.
• FO2Hb + FRHb + FCOHb + FMetHb = 100%
or
• FO2Hb = O2Hb X 100 /(O2Hb+RHb +COHb +
MetHb)
Does the ratio of PaO2 to SpO2 always
remain the same?
• The four fractions of Hb can be accurately measured by
co-oximeters that measure the absorption of 4 or more
wavelengths of electromagnetic radiation by blood .
This is possible because the four forms of Hb differ in
their absorption for the different wavelengths of
radiation.
• Pulse oximetry uses only two wavelengths: 660 nm (red)
and 940 nm (infrared) to measure the O2Hb and RHb .
• The absorption of radiation at 660 nm is much greater
with RHb than O2Hb, whereas O2Hb absorbs more
radiation at 940 nm.
• COHb has about the same absorbance at 660 as O2Hb
and, if present, increases the measured SpO2 value .
Does the ratio of PaO2 to SpO2 always
remain the same?
• In normal individuals, FCOHb is 2% or less but
can be 8% or more in cigarette smokers.
• Patients with SCD often have FCOHb values of
4% or more due to production of CO from
chronic hemolysis.
• In patients who are heavy smokers, it is
important to remember that the SpO2 may
overestimate the FO2Hb.
Does the ratio of PaO2 to SpO2 always
remain the same?
• If a patient has a lower than expected SpO2 while awake,
a number of possibilities should be considered
including a faulty oximetry probe, poor signal quality
due to poor perfusion, a shift in the O2Hb saturation
curve or an abnormal Hb.
• If oximetry issues are ruled out, an arterial blood gas is
needed to determine whether hypoxemia is really
present . In this situation, co-oximetry analysis could
also determine whether significant COHb or MetHb is
present and determine a true SaO2 and the fraction of
Hb that is oxygenated.
• If clinically indicated, analysis with a co-oximeter will
provide more accurate information.
Concerning mmHg and Torr
• Standard atmospheric pressure is 760 mmHg. This
means atmospheric pressure is the same as that
exerted by a 760 mm high column of mercury (Hg).
• The first measurement of atmospheric pressure
was performed by Torricelli, a student of Galileo
Galilei. One mmHg is referred to by the term “Torr”
after his name.
• The unit “mmHg” is the same as “Torr,” and one
atmospheric pressure is 760 mmHg = 760 Torr.
• Currently, Torr is generally used when measuring
PaO2.
Does the ratio of PaO2 to SpO2 always
remain the same?
• SpO2 is accurate down to about 70%. Whereas
values below 70% are often reported, one must
keep in mind that they probably do not
correspond accurately to the actual SaO2.
• In the case of COHb, the absorption of 660 nm is
similar to O2Hb and causes a falsely elevated
SpO2 estimate of the FO2Hb. It is estimated that
for every 1% of circulating COHb, the pulse
oximeter reading is falsely elevated by about 1%
compared with the FO2Hb.
Does the ratio of PaO2 to SpO2 always
remain the same?
• MetHb absorbs nearly equal amounts of red and
near infrared light, giving an R = 1. As the
concentration of MetHb increases, the pulse
oximeter reads closer and closer to 85%. Therefore,
methemoglobinemia may cause the SpO2 to give a
falsely low estimate of the SaO2 and, hence, the
PaO2. On the other hand methemoglobin shifts the
oxyhemoglobin saturation curve to the left and the
SaO2 is less than the FO2Hb as oxygen does not
bind methemoglobin . Methemoglobinemia can
occur from medications (e.g., benzocaine,
sulfonamides)
Factors that impair the accuracy of SpO2
• In sleep monitoring, an arterial oxygen
desaturation is usually defined as a decrease in
the SpO2 of 3% or 4% or more from baseline.
• Note that the nadir in SaO2 commonly follows
apnea (hypopnea) termination by approximately
6 to 8 seconds (longer in severe desaturations).
This delay is secondary to circulation time and
instrumental delay (the oximeter averages over
several cycles before producing a reading).
Apneas are followed by arterial oxygen desaturations.
Longer apneas are associated with more severe
desaturation. SpO2 = pulse oximetry.
Handheld Pulse Oximeter
Fingertip pulse oximeter
Portable pulse oximeter
Factors that impair the accuracy of SpO2.
• Oximeters may vary considerably in the number of
desaturations they detect and their ability to discard
movement artifact.
• Using long averaging times may dramatically decrease
the detection of desaturations. The ability of oximeters
to detect desaturations is especially important in light of
the definitions of hypopnea that depend on an
associated desaturation.
• The AASM scoring manual recommends a maximum
averaging time of 3 seconds at a heart rate of 80 bpm. In
patients with a slow heart rate, a slightly longer
averaging time (at least a 3-beat average) may be
needed.
A long averaging time impairs the ability of
oximetry to detect arterial oxygen desaturation.
SpO2 = pulse oximetry.
Uses
Pulse oximetry has four main uses:
1. detection of /screening for hypoxaemia; (SPo2 <
92%-94% should be referred to ABG to assess
elegibilty for LTOT).
2. targeting oxygen therapy;
3. routine monitoring during anaesthesia;
4. diagnostic (e.g. sleep hypnoea).
Targeted oxygen therapy in critically ill
patients
• In critically ill patients, the target of oxygen
therapy is SpO2 94-98% in non hypercapnic
patients and 88-92 % in hypercapnic patients .
Guidelines for long term use of oxygen
• Referral for assessment for long-term oxygen therapy is
considered if SPo2 <92 - 94% (need ABG )
• Patients potentially requiring LTOT should not be
assessed using pulse oximetry alone
• Each applicant's condition must be stabilized and
treatment regimen optimized before long-term oxygen
therapy is considered. Optimum treatment includes
smoking cessation.
• Applicants must have chronic hypoxemia on room air at
rest (Pa02 of 55 mmHg or less, or Sa02 of 88% or less).
Guidelines for long term use of oxygen
• Applicants with persistent Pa02 in the range of 56 to 60
mmHg may be considered candidates for long-term
oxygen therapy if any of the following medical
conditions are present: cor pulmonale ; pulmonary
hypertension; peripheral oedema or persistent
erythrocytosis (Haematocrit >55%).
• Persistent Pa02 in the range of 56 to 60mmHg may be
candidates for long-term oxygen therapy if the following
occurs: Exercise limited hypoxemia ; documented to
improve with supplemental oxygen ; Nocturnal
hypoxemia.
• LTOT should be for minimum 15 hours per day .and up
to 24 hours per day may be of additional benefits.
Guidelines for long term use of oxygen
• Type I: low PaO2 (< 60 mm Hg), normal PaCO2 (< 6 - 7
kPa).In these patients it is safe to give a high
concentration of oxygen initially with the aim of returning
their PaO2 to normal and then once clinically stable,
adjusting the inspired oxygen concentration to maintain
an SpO2 of 94 - 98%.
• Type II: low PaO2 (< 60 mm Hg), increased PaCO2 (> 6 - 7
kPa). This is often described as hypercapnic respiratory
failure and is usually caused by COPD. If given excessive
oxygen, these patients may develop worsening
respiratory failure with further increases in PaCO2 and the
development of a respiratory acidosis. If unchecked, this
will eventually lead to unconsciousness, and respiratory
and cardiac arrest. The target oxygen saturation in this at
risk population should be 88 - 92%.