Mar 11, 2019
From Essentials of Emergency
Medicine NYC 2017, Reuben Strayer explains how the pulse ox might
be the most useful bit of tech in the ED.
- The pulse ox waveform is an
excellent indicator of mechanical heart rate and peripheral
- For patients breathing room air, pulse oximetry
can be used to monitor for hypoventilation.
- Nail polish has minimal impact on the accuracy of pulse
- If you are unable to get a good pulse ox waveform by adjusting
or repositioning the probe, be concerned that the patient is poorly
- “The respiratory rate is the most vital of the vital
signs.” Experienced doctors look at a patient who seems
well, but understands that they’re not truly well, because they
subconsciously notice tachypnea. Subconsciously is the only way to
notice tachypnea, because respiratory rate is often not measured
accurately. Since we don’t always have access to
reliable respiratory rate, Strayer’s go-to vital sign is the oxygen
- “Reusable pulse oximeter probes are gross.” One study found that even when these probes are
cleaned by standard procedure, ⅔ had bacteria cultured from them.
Strayer recommends using single use probes in your
- Wilkins MC. Residual bacterial
contamination on reusable pulse oximetry
sensors. Respir Care. 1993 Nov;38(11):1155-60.
PubMed PMID: 10145923.
- Data is conflicting about the effect of nail polish on pulse
oximetry readings, but overall it is felt that the impact is
- Earlier data suggested that
nail polish decreased sat readings by 2-10%, but more recent
studies found minimal effect.
- If it seems that the waveform
is affected by nail polish, you can remedy the situation by turning
the probe 90 degrees, so it goes sideways through the
- Yamamoto LG, et al. Nail polish
does not significantly affect pulse oximetry measurements in mildly
hypoxic subjects. Respir Care. 2008 Nov;53(11):1470-4.
PubMed PMID: 18957149.
- As long as a patient is breathing room air, pulse ox can
monitor ventilation and function as a hypoventilation alarm.
- Significantly hypercapnic patients saturate
less than 95% when they’re breathing room air. So if you need to
monitor a patient for hypoventilation, such as due to intoxication
or procedural sedation, the pulse ox will do a great job of telling
you if the patient is still breathing.
you need to give supplemental oxygen, then use capnography to
- The pulse oximeter does so much more than provide
- It provides the
photoplethysmogram (PPG) which is a waveform that tells you the
“mechanical” heart rate.
While telemetry gives the electrical heart rate, what really
matters to your organs is the mechanical rate. This can be
especially helpful during transvenous or transcutaneous pacing.
When you have reliable tracing, the pulse ox heart rate is more
reliable than the telemetry heart rate.
- The pulse ox can measure the peripheral perfusion index
which is a more sensitive and earlier indicator of hypoperfusion
than blood pressure. This is a
numerical value which indicates the strength of the pulsations read
by the pulse oximeter. It is based on the amplitude of the pulse ox
waveform and expressed as a number between 1 (low) and 10 (high).
The perfusion index dips before the stroke volume drops and
long before the heart rate rises. Many monitors will report the
perfusion index in tiny print after the word
- Lima AP, Beelen P, Bakker J.
Use of a peripheral perfusion index derived from
the pulse oximetry signal as a noninvasive
indicator of perfusion. Crit Care Med.
Jun;30(6):1210-3. PubMed PMID: 12072670.
- van Genderen ME, et al.
Peripheral perfusion index as an early predictor for central
hypovolemia in awake healthy volunteers. Anesth Analg. 2013
Feb;116(2):351-6. PubMed PMID: 23302972.
- What if you don’t have a reliable pulse ox tracing?
of the time this is because the probe is poorly positioned, the
patient is moving too much, or there’s a lot of ambient
you’ve corrected for these problems and you still don’t have a good
tracing, you should be concerned that the patient is poorly
study of 20,000 anesthesia cases showed that pulse ox failure was
directly related to worsening physical status.
- Moller JT, et al. Randomized evaluation of
pulse oximetry in 20,802 patients: I. Design, demography, pulse
oximetry failure rate, and overall complication rate.
Anesthesiology. 1993 Mar;78(3):436-44. PubMed PMID: 8457044.
- How does the pulse ox measure oxygen saturation and
what is the best way to position the oximeter probe on the
side of the pulse ox puts emits visible (red) light and infrared
light. On the other side is the detector. The percent oxygen
saturation is calculated based on the different way in which
oxyhemoglobin absorbs visible and infrared light compared with
pulse ox measures carboxyhemoglobin as if it were oxyhemoglobin,
giving a falsely elevated pulse ox reading for a victim of carbon
best spot for a peripheral pulse ox is a place with a lot of
capillaries and arterioles, like the fingertips, earlobes, nose, or
- Functionally, it doesn’t seem to matter
whether the emitter is on the dorsum, volar aspect, or even side of
the finger. For convenience sake, most find it ergonomically
superior to have the cord and emitter on the dorsum of the
- Mannheimer PD. The
light-tissue interaction of pulse oximetry. Anesth
Dec;105(6 Suppl):S10-7. Review. PubMed PMID: 18048891
- Vegfors M, Lennmarken C.
Carboxyhaemoglobinaemia and pulse oximetry. Br J
Anaesth. 1991 May;66(5):625-6. PubMed
- DeMeulenaere, Susan. "Pulse oximetry: uses and
Journal for Nurse Practitioners 3.5 (2007): 312-317.
ED, et al. Pulse oximetry: understanding its basic
facilitates appreciation of its
limitations. Respir Med. 2013 Jun;107(6):789-99.