PULSE OXIMETER

A pulse oximeter is a device that tells you the percentage of oxygen circulating in the blood, by measuring the oxygen saturation (called the SaO2), of the hemoglobin.

It consists of a small and portable monitor and a sensing unit that clips onto the patients finger. Along with the SaO2, the meter also gives you a pulse rate.

According to the manufacturer:

Noninvasive arterial oxygen saturation measurement is obtained by directing red and infrared light through a pulsating vascular bed. The pulsating arterioles in the path of the light beam causes a change in the amount of light detected by a photodiode. The oximeter measures within the pulse wave form the ratio of transmitted red to infrared light and thereby determines the oxygen saturation of the blood. The nonpulsatile signal is removed electronically for the purpose of calculation and, therefore, skin, bone, and other nonpulsating substances do not interfere with the calculation of arterial saturation.

There are several things to keep in mind when using the pulse oximeter:

  1. The measurement becomes inaccurate in hypothermic patients, and in patients in decompensated shock.
  2. The device will give false high readings in patients with carbon monoxide poisoning. (Read the appendix in your text, page 733-734 to find out why.)
  3. Chronic smokers have residual carbon monixide in their blood, so their readings may give false highs.
  4. Extremely bright lights might interfere with the sensor's function.
  5. Inadequate perfusion due to poor arterial circulation, or the use of a blood pressure cuff on the same extremity as the sensor, may prevent proper operation of the device.
  6. Patient movement, dysfunctional hemoglobin, and certain intravascular dyes, can also affect the reading.
  7. Very dense fingernail polish or acrylic nails may interfere with sensor function.
  8. Anything that compromises venous return may alter the reading. Keep the sensor at heart level whenever possible.

The pulse oximeter is useful to prod the EMT to be more aggressive in oxygen therapy and possibly ventilations of a patient. The text says:

It should be used with all patients complaining of dyspnea or respiratory problems. As a general rule, if the oxygen saturation is less than 95% with a good pulse wave, increase the oxygen concentration being delivered to the patient and consider assisting the ventilations with a bag-valve-mask unit with a reservior. If the SaO2 reading is greater than 95%, continue the current oxygen therapy.

The State EMS in their practical examination says if the reading is:

less than 90%, the rescuer should indicate high flow oxygen usage. If the reading is greater than 90% the rescuer indicates low flow oxygen usage.

Probably the most important thing to remember about the pulse oximeter is that it is just a machine, just another tool to help you. Don't let it dictate your treatment.

"Treat the patient, not the oximeter"

 

References:

Model 300 Pulse Oximeter User's manual. Palco Labs, Santa Cruz, CA.
Brady Emergency Care, 6th edition. Grant, Murray and Bergeron.
Bureau of EMS - State practical Examination