What is a Respiratory Therapist?
people take breathing for granted. It's second nature, an involuntary
reflex. But for the thousands of Americans who suffer from breathing
problems, each breath is a major accomplishment. Those people include
patients with chronic lung problems, such as asthma, bronchitis, and
emphysema, but they also include heart attack and accident victims;
premature infants; and people with cystic fibrosis, lung cancer, or
In each case, the person will most likely receive treatment from a
respiratory therapist (RT) under the direction of a physician.
Respiratory therapists work to evaluate, treat, and care for patients
with breathing disorders. Learn more about this exciting profession
from the AARC, the U. S. Department of Labor (just select your state for local information), and the National Bureau of Labor Statistics.
What is COPD?
Chronic obstructive pulmonary disease, or COPD, is an umbrella term for
two respiratory illnesses -- chronic bronchitis and/or emphysema.
There are 16 million Americans who have been diagnosed with COPD, of
whom 14 million have chronic bronchitis and 2 million have emphysema.
COPD results primarily from smoking tobacco. Years of smoking cause damage to the airways in the lungs. This lung damage continues to progress with the use of tobacco.
Average current and former smokers will likely not notice or
acknowledge symptoms for several years. Typically, they will begin
noticing the first symptoms of shortness of breath when they reach
However, earlier signs of COPD are often present. These include chronic
cough and increased mucus production. Recognizing these early signs is
important because lifestyle modifications, such as smoking cessation
and avoiding respiratory irritants, can be made to prevent additional
damage to the airways.
In technical terms, COPD is a slowly progressive disease that is
characterized by a decrease in the ability of the lungs to maintain the
body's oxygen supply and remove carbon dioxide.
As a result of this decrease in lung function, COPD patients alter
their lifestyles because they become short of breath after minimal
exertion. For example, instead of climbing a flight of stairs COPD
patients take the elevator. Physical activities also take longer to
complete. Lawn mowing that a COPD patient might have finished in 40
minutes only a year ago may now take an hour to do.
Pulse Oximetry InterpretationSynonyms
Oximetry, oxygen saturation check, oxygen sat
check, exercise oximetry, oxygen titration by oximetry, oxygen
saturation measured using pulse oximetry (SpO2), oxygen desaturation
No contraindications exist.
Standard pulse oximeter probes may be placed on fingers or earlobes of
ambulatory patients. Some oximeters use reflectance probes that can be
placed on the forehead. Fingernail polish should be removed, and
peripheral circulation should be maximized by warming or by applying
vasodilating cream, if necessary.
Although widely used, the practice of assessing oxygen desaturation by
pulse oximetry is poorly standardized. The principle of oximetry
measurement by spectrophotometry, although improving, is not as
reliable as many practitioners believe. One side of the oximeter probe
acts as a light-emitting source, and the other side acts as a
photodetector. The probe is placed on a finger or earlobe. A forehead
reflectance probe may also be used. The relative absorption of red
(absorbed by oxygenated blood) and infrared (absorbed by deoxygenated
blood) light of the pulsatile (systolic) component of the absorption
waveform correlates to arterial blood oxygen saturation.
Resting readings should be made for at least 5 minutes, and the
stability of the reading should be characterized on the report. If a
finger probe is used when standing, the hand should be placed on the
chest at the level of the heart to minimize venous pulsation, which can
falsely lower the reading. Correlation of the heart rate displayed on
the oximeter with an ECG rate or a manually palpated pulse can help
characterize the quality of the signal. Agreement within 5 or more
beats per minute generally rules out significant motion artifact.
Ideally, correlation of pulse oximetry saturation should be made with a
measured oxygen saturation by multiple wavelength spectrophotometry on
a simultaneously obtained arterial blood gas sample.
Documentation of the type of pulse oximeter used, probe type, and probe
site should be included on each report. The heart rate and SpO2
readings at rest should be reported.
When obtaining pulse oximetry readings during exercise, the type and
intensity of exercise (eg, walking speed, duration of activity) along
with the heart rate and SpO2 at the end of the activity should be
reported. When desaturation is detected, the activity should be
repeated with supplemental oxygen in place to demonstrate improvement
in SpO2 values.
Pulse oximetry is often performed (though optional) in the setting of
the 6-minute walk test, a standardized measure of functional exercise
capacity.8 This test is a measure of the maximum distance the patient
is able to walk in a hallway with a minimum of 100 feet marked in
5-foot increments. The patient is permitted to slow down or even stop,
if required; however, the elapsed time counter continues during rest
periods. This test should be performed while exercise oxygen needs are
being adequately met with portable oxygen delivery. Borg dyspnea and
fatigue scores are collected immediately after completion of the walk.
Interpretation of oximetry studies, while seemingly simple, generally
is not possible without characterizing oximeter accuracy by correlating
SpO2 with at least one simultaneously obtained arterial oxygen
saturation (SaO2). Laboratories should characterize the average
oximeter bias (SpO2 - SaO2) through pooled data to better understand
the limitations of using the oximeter, but this does not eliminate the
possibility that oximeter readings on individual patients may exhibit
larger biases. While SpO2 readings greater than 95% make the
probability of clinically significant hypoxemia unlikely, clinical
suspicion of hypoxemia should initiate the examination of ABGs. The
goal of titration of supplemental oxygen should be a stable SpO2
reading of 93% or higher. Arterial desaturation can be considered
present when the pulse oximeter saturation falls more than 4% below the
The role of pulse oximetry in the Medicare guidelines for reimbursement
for continuous supplemental oxygen therapy are demonstration of one of
the following while at rest and breathing room air: PaO2 less than or
equal to 55 mm Hg, SaO2 less than or equal to 88%, or SpO2 less than or
equal to 88%.
If supplemental oxygen is prescribed at a flow rate of greater than 4
liters per minute (LPM), the results of a PaO2 or oxygen saturation
(SaO2 or SpO2) taken on 4 LPM supplemental oxygen must be provided.
Patients may qualify for supplemental oxygen therapy reimbursement even
if the PaO2 is greater than 55 mm Hg and the SaO2 or SpO2 is greater
than 88% if one of the following conditions is met: (1) dependent edema
due to congestive heart failure; (2) cor pulmonale documented by P
pulmonale on an ECG or by an echocardiogram, gated blood pool scan, or
direct pulmonary artery pressure measurement, and (3) hematocrit
greater than 56%.
Carboxyhemoglobin (CoHb) and methemoglobin (metHb) absorb light at the
same wavelength as deoxyhemoglobin, causing a very significant
overestimation of SaO2 when these are elevated. Pulse oximetry has
other shortcomings. It does not provide information about the oxygen
content of the arterial blood. Tissue hypoxia can exist when SpO2 is
normal when anemia is present. Elevated levels of dysfunctional
hemoglobins (CoHb, metHb) can cause significant overestimation of the
Additionally, pulse oximetry does not address the adequacy of
ventilation, which can be assessed only by evaluation of the partial
pressure of carbon dioxide in arterial gas (PaCO2). Motion of the
finger within the probe can cause a motion artifact secondary to equal
rhythmic absorption of red and infrared light that most oximeters
interpret as an SpO2 reading of 85%. Disposable finger probes fixed to
the probe site with adhesive and fixed positioning of the probe site
during walking can minimize this.
Pulse oximetry tends to overestimate SaO2. One reason for this is the
fact that pulse oximetry expresses the percentage of oxyhemoglobin,
typically without consideration for CoHb or metHb (see below). One
pulse oximetry manufacturer now offers options that allow reporting of
total hemoglobin, oxygen content, CoHb and metHb, but these are not yet
in widespread use.
This significant difference generally results in pulse oximeters
reporting an oxyhemoglobin value that is 2-3% higher than the
spectrophotometrically determined oxygen saturation, even when the
pulse oximeter is functioning perfectly.
While the accuracy of pulse oximetry generally is good in population
studies (SaO2 - SpO2 <2%), SpO2 values in individual patients may
show a much greater bias, even when dysfunctional Hb levels are normal.
Anemia and polycythemia can cause greater oximeter overestimation. SaO2
from simultaneously obtained ABG determinations should be used to
characterize oximeter bias in individual patients, although this is not
ABG determinations should be considered whenever the clinical suspicion
of hypoxemia exists, even when the oximeter displays a value over the
threshold of 88%. Finally, the shape of the oxygen dissociation curve
causes the pulse oximeter to be inherently insensitive to mild
hypoxemia because relatively large changes in PaO2 in the flat upper
portion of the curve cause very small changes in blood SaO2.
Advantages of pulse oximetry include that it is noninvasive, simple,
and can be used to evaluate trends (evaluation of oxygenation during
exercise, sleep, during procedures).
Disadvantages of pulse oximetry include that it cannot be used to
assess oxygen delivery (anemia) or adequacy of ventilation (PaCO2) and
that accuracy is lessened in the presence of elevated dysfunctional
hemoglobin levels (CoHb, metHb), with a tendency to overestimate SaO2
by an average of 2-3%.
Factors that influence the accuracy of pulse oximetry readings
Overestimation of SaO2 is possible with bright sunlight on the probe,
fluorescent lights, operating room lights, infrared heat lamps,
elevated CoHb, elevated metHb, anemia, and motion artifact if the
actual SaO2 is less than 85%.
Underestimation of SaO2 is possible because intravascular dyes, such as
methylene blue and indocyanine green, produce transient reductions in
SpO2. Fingernail polish, increased venous pressures, and motion
artifact if the actual SaO2 is greater than 85% also can cause
underestimation of the SaO2.