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Pulse Oximeter Readings

Pulse Oximeter Readings: Working, Interpretation, and More

Pulse Oximetry is a simple, non-invasive method of monitoring a patient's oxygen saturation. It is commonly used in a pre-hospital setting and is an effective way of supervising the oxygenation status. It also helps in determining changes before they are clinically apparent. The upcoming article aims at helping you understand its readings.
Aakash Singh
Last Updated: Apr 22, 2018
A pulse oximeter is a small box-like device which consists of a computerized monitor and probe that can be connected to the patient's finger, toe, nose, or earlobe. The monitoring unit shows a digital percentage readout of a calculated estimate of the patient's hemoglobin (Hgb) that is saturated with peripheral oxygen (SpO2). Hemoglobin in the blood is the carrier of oxygen.
Each gram of hemoglobin can carry 1.34 milliliters of oxygen. This device also displays a calculated heart rate. For best and accurate results, the readings must be tallied with a person's respiratory rate. This instrument was designed to monitor the inability of oxygen intake by the body. It is used for the detection of hypoxia, a condition in which the body or a region of it is deprived of adequate oxygen supply.
Working of a Pulse Oximeter
This apparatus must be clipped onto those body parts, which enable light to pass through the blood flowing in the arteries. Normally, it employs a processor and a pair of small light-emitting diodes (LEDs) facing a photodoide through a translucent part of the patient's body, usually a fingertip or an earlobe. One LED is red with a wavelengthof 660nm, and the other is infrared with a wavelength of 940nm.
Absorption of light at these wavelengths differs greatly between blood loaded with oxygen and blood deficient of oxygen. Oxygenated hemoglobin absorbs more infrared light and permits more red light to pass through. Deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light. The LEDs blink about 30 times per second. The photodiode evaluates the amount of light that is not absorbed. The measurement vacillates in time because the amount of arterial blood that is present raises with each heartbeat.
By deducting the minimum transmitted light from the peak transmitted light in each wavelength, the effects of other tissues is amended for. The ratio of the red light quantification to the infrared light quantification is then calculated by the processor, which represents the ratio of oxygenated hemoglobin to deoxygenated hemoglobin. This ratio is then changed to SpO2 by the processor via a lookup table.
Interpreting Pulse Oximeter Readings
There may be a possibility that you get an inaccurate reading from your oximeter. The best way to get the most accurate reading is to compare the pulse rates shown on this instrument with the manual readings. The following conditions may get you inaccurate readings:
  • Carbon monoxide poisoning
  • A patient showing rapid movements
  • Patient suffering from hypothermia or anemia
  • Few types of seizures
  • Nail polish on the finger (may not allow the infrared light to pass through)
The readings depend on a number of factors, like oxygen percentage in the air, health condition, respiratory rate, the activity the person is performing, and a few other factors. Readings normally should be around 95 - 100%. Any reading above 90% is normal. Factors like altitude can also affect the reading.
A person who has respiratory problems should always make sure he gets a reading of 90 - 94%. If the reading goes below 90%, then the person must be given immediate medical treatment. You may be required to give oxygen supply for a reading less than 80%. Along with the readings, several other medical conditions are also monitored and acted upon.
The readings in children depend on various factors, including the heartbeat. For a normal adult, the heart rate is 60 to 80 beats a minute. The heart rate of infants and children is relatively higher. It can range from 120 to 150 a minute for infants and 60 to 120 beats per minute for children between 5 to 12 years of age.
Pulse oximeters can be considered as one of the best inventions to measure the blood oxygen saturation, as it does not require any blood sample to be taken. They are being used in various medical situations especially during a patients's recovery phase. Readings are most accurate under a few controlled settings.
Disclaimer: This HealthHearty article is for informative purposes only and should not be used as a replacement for expert medical advice.