Probably no device has had such widespread and quick acceptance into clinical
instrumentation in the past 20 years as the pulse oximeter.
The modern pulse oximeter should not be confused with the ear oximeter, which was
marketed in the mid 1970s. The technology is quite different; the old system, which
used eight wavelength detectors, could only be used on the earlobe, required
heating of the area, and was not portable. Another early version used a fiber-optic
cable for light transmission and detection as it was too big to be put into a probe
that could be comfortably applied to the patient.
Much of the original work on pulse oximetry was to develop a noninvasive method of
determining cardiac output. The side effect of getting a good correlation on blood
oxygen levels (SpO2) proved to be the marketable product, and research on using
the technology for cardiac output basically stopped. An urban legend developed
saying that both the pulse oximeter and Viagra were side effects of the prime
objective of the engineering work, one measuring cardiac output and the other
increasing it.
The “modern” pulse oximeter owes much of its success to William New, MD, PhD,
who introduced the Nellcor unit in the mid 1980s. Ohmeda introduced the Biox II in
the mid 1980s, this time using microprocessors, another major factor in the
utilization of pulse oximetry. Additional credit must be given to the malpractice
insurance companies that told anesthesiologists that if they used pulse oximetry their
premiums would be reduced.
The pulse oximeter works on a reasonably simple principle of light absorption, as
defined by the Beer-Lambert law, sometimes called Bouguet’s law, depending on the
textbook. Basically, the law states that light is absorbed or passed through a solution
based on the concentration of the chemical in the solution for a certain light
wavelength. It was found that hemoglobin (Hb), nonoxygenated blood that is dark
red in color, and oxyhemoglobin (HbO2), oxygenated blood that is bright red in
color, have different light-absorption levels. By using two detectors—one in the 660
nm range to measure hemoglobin and the other in the 940 nm range to measure the
oxyhemoglobin—along with proprietary algorithms, the pulse oximeter can obtain
accurate clinical results on blood oxygen.
Pulse oximeters have some limitations, though, as ambient light can affect the
readings, as can shivering, low flow, very thick skin, and poor placement of the
sensors. Most of the newer designs (after 1998) have much better rejection systems
for motion artifacts. When the finger is used as the location of the probe, it is
important that the light source be placed on the nail and the detector on the soft
tissue of the finger. Needless to say, the patient should not have nail polish on. A
patient with carbon monoxide exposure will register falsely high on oxyhemoglobin
since the blood will be very red. For these patients, co-oximetry or end tidal CO2
(capnometry) will give better clinical results.
The widespread use of pulse oximetry has increased patient comfort in that far fewer
traditional blood gas measurements are taken now than in the past. If you have ever
had an arterial “stick” for a blood gas test, you know that it is quite painful. The use
of direct monitoring of blood pressure, another source of obtaining blood gas test
samples, is also down in many hospitals.
There are some problems that biomeds still have to respond to with pulse oximeters.
Bad sensors and cables are probably the most common. Some shops will “reprocess”
the sensors and detectors on disposable units; be careful on this, as you may
become a manufacturer in the eyes of the legal system and be without insurance
protection. Other common calls we get include problems with batteries, white tape
(white tape should be a controlled substance), “bounce tests” (most units do not
bounce well off the floor), and people saying, “We cannot find it on the floor so you
must have it in the shop.”
If a patient has a cardiac pacer, either internal or external, the pulse oximetry alarm
may become a secondary alarm on some monitoring systems. This can present a
problem as the patient monitor may not sound an alarm but only display a “screen
flash” if the alarm limit on the pulse oximeter is triggered. Take a little time during
the next PM cycle on the monitors to confirm how the alarms react when a patient is
being paced.
In closing, please be aware of where the alarm limits can be set for the low alarms
on your stand-alone devices, monitoring systems, and multipurpose stand-alone
units. Most of us just check the default setting and do not try to adjust the limit
down below 90. Some manufacturers will allow the user to have alarm limits as low
as 50. So take the time to check the limits.
Review Questions
1) What two light wavelengths does the modern pulse oximeter use?
a. 660 and 940 nm
b. 660 and 940 .m
c. 730 and 970 nm
d. 530 and 560 nm
2) Which of the following can affect the accuracy of a pulse oximeter?
a. low blood pressure
b. low cardiac output
c. carbon monoxide in the blood
d. all of the above
3) The 660 nm wavelength light is used to measure ____________.
a. carbon dioxide
b. hemoglobin
c. oxyhemoglobin
d. none of the above
4) The 940 nm wavelength is used to measure __________.
a. carbon dioxide
b. hemoglobin
c. oxyhemoglobin
d. all of the above.
Answers: 1-a; 2-c; 3-b; 4-c
http://liveconcerns-waleed.blogspot.com/
instrumentation in the past 20 years as the pulse oximeter.
The modern pulse oximeter should not be confused with the ear oximeter, which was
marketed in the mid 1970s. The technology is quite different; the old system, which
used eight wavelength detectors, could only be used on the earlobe, required
heating of the area, and was not portable. Another early version used a fiber-optic
cable for light transmission and detection as it was too big to be put into a probe
that could be comfortably applied to the patient.
Much of the original work on pulse oximetry was to develop a noninvasive method of
determining cardiac output. The side effect of getting a good correlation on blood
oxygen levels (SpO2) proved to be the marketable product, and research on using
the technology for cardiac output basically stopped. An urban legend developed
saying that both the pulse oximeter and Viagra were side effects of the prime
objective of the engineering work, one measuring cardiac output and the other
increasing it.
The “modern” pulse oximeter owes much of its success to William New, MD, PhD,
who introduced the Nellcor unit in the mid 1980s. Ohmeda introduced the Biox II in
the mid 1980s, this time using microprocessors, another major factor in the
utilization of pulse oximetry. Additional credit must be given to the malpractice
insurance companies that told anesthesiologists that if they used pulse oximetry their
premiums would be reduced.
The pulse oximeter works on a reasonably simple principle of light absorption, as
defined by the Beer-Lambert law, sometimes called Bouguet’s law, depending on the
textbook. Basically, the law states that light is absorbed or passed through a solution
based on the concentration of the chemical in the solution for a certain light
wavelength. It was found that hemoglobin (Hb), nonoxygenated blood that is dark
red in color, and oxyhemoglobin (HbO2), oxygenated blood that is bright red in
color, have different light-absorption levels. By using two detectors—one in the 660
nm range to measure hemoglobin and the other in the 940 nm range to measure the
oxyhemoglobin—along with proprietary algorithms, the pulse oximeter can obtain
accurate clinical results on blood oxygen.
Pulse oximeters have some limitations, though, as ambient light can affect the
readings, as can shivering, low flow, very thick skin, and poor placement of the
sensors. Most of the newer designs (after 1998) have much better rejection systems
for motion artifacts. When the finger is used as the location of the probe, it is
important that the light source be placed on the nail and the detector on the soft
tissue of the finger. Needless to say, the patient should not have nail polish on. A
patient with carbon monoxide exposure will register falsely high on oxyhemoglobin
since the blood will be very red. For these patients, co-oximetry or end tidal CO2
(capnometry) will give better clinical results.
The widespread use of pulse oximetry has increased patient comfort in that far fewer
traditional blood gas measurements are taken now than in the past. If you have ever
had an arterial “stick” for a blood gas test, you know that it is quite painful. The use
of direct monitoring of blood pressure, another source of obtaining blood gas test
samples, is also down in many hospitals.
There are some problems that biomeds still have to respond to with pulse oximeters.
Bad sensors and cables are probably the most common. Some shops will “reprocess”
the sensors and detectors on disposable units; be careful on this, as you may
become a manufacturer in the eyes of the legal system and be without insurance
protection. Other common calls we get include problems with batteries, white tape
(white tape should be a controlled substance), “bounce tests” (most units do not
bounce well off the floor), and people saying, “We cannot find it on the floor so you
must have it in the shop.”
If a patient has a cardiac pacer, either internal or external, the pulse oximetry alarm
may become a secondary alarm on some monitoring systems. This can present a
problem as the patient monitor may not sound an alarm but only display a “screen
flash” if the alarm limit on the pulse oximeter is triggered. Take a little time during
the next PM cycle on the monitors to confirm how the alarms react when a patient is
being paced.
In closing, please be aware of where the alarm limits can be set for the low alarms
on your stand-alone devices, monitoring systems, and multipurpose stand-alone
units. Most of us just check the default setting and do not try to adjust the limit
down below 90. Some manufacturers will allow the user to have alarm limits as low
as 50. So take the time to check the limits.
Review Questions
1) What two light wavelengths does the modern pulse oximeter use?
a. 660 and 940 nm
b. 660 and 940 .m
c. 730 and 970 nm
d. 530 and 560 nm
2) Which of the following can affect the accuracy of a pulse oximeter?
a. low blood pressure
b. low cardiac output
c. carbon monoxide in the blood
d. all of the above
3) The 660 nm wavelength light is used to measure ____________.
a. carbon dioxide
b. hemoglobin
c. oxyhemoglobin
d. none of the above
4) The 940 nm wavelength is used to measure __________.
a. carbon dioxide
b. hemoglobin
c. oxyhemoglobin
d. all of the above.
Answers: 1-a; 2-c; 3-b; 4-c
http://liveconcerns-waleed.blogspot.com/
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