How to Read a Pulse Oximeter: Pulmonologists Explain in Detail

How To Read A Pulse Oximeter

The pulse oximeter is used to determine the oxygen condition of patients in a wide range of medical settings and is becoming an increasingly common element of monitoring devices. It provides constant, non-invasive control of oxygen saturation of hemoglobin in the blood. With each heart rate, the reports are updated.

Pulse oximeters do not provide data on the concentrations of hemoglobin, cardiac activity, oxygen performance in the tissues, oxygen intake, oxygen sufficiency of ventilation adequacy. However, they offer an opportunity to quickly identify variations from a patient's oxygen base as an early warning signal to doctors to avoid the effects of desaturation and to diagnose hypoxemia before cyanosis occurs.

How a Pulse Oximeter Works

A pulse oximeter is a non-invasive method of measuring both the heart rate and the external capillary rate of hemoglobin's arterial oxygen saturation. It includes a portable display and a photoelectric sensor, which clips on the fingertip, toes, or earlobe of the patient.

The photoelectric sensor device calculates the amount of infrared and red light received when arterial oxygen enters the capillary beds when more light is received, during systole, and when less light is received, during diastole.

The monitor measures the period between the light absorption spikes and shows a pulsing frequency in bpm (beats per minute). It also measures a value to show a peripheral oxygen saturation percentage (SpO2) based on the amount of light consumed at diastole and systole.

Factors Which Affect The Accuracy Of Readings

Various conditions can affect pulse oximetry measurements. Weak peripheral perfusion due to cold or hypotension is the main reason for the failure to get an adequate signal, primarily due to insufficient pulse waves. The oximeter could not record a signal due to cold extremities, hypothermia, and weak peripheral perfusion. Peripheral pulses can be so low at cardiac arrest that they can not be detected by the device, so the measurement of SpO2 by  pulse oximeter might be contraindicated.

Pulse oximetry with blood pressure levels higher than 80 mm Hg is considered to be accurate. Hypotensive blood pressure measurements lower to 80 mm Hg generate unreliable and inaccurate pulse oximetry measurements. Hypotension, low heart rate, vasoconstriction, dobutamine, and dopamine also decrease blood flow to the tissues.

How to Use a Pulse Oximeter

A pulse oximeter is distributed either as a tiny device with a clip for finger or a toe or as a smallholding device with a wire sensor that can be attached or placed on the toe, finger or earlobe. The small model is cheaper and more comfortable for home use. Light rays from the unit penetrate the finger or toe through the blood to calculate the oxygen.

The light beams are "interpret" to measure the percentage from the blood which carries oxygen. This also lets you monitor the heart rate, as like the  smart band that monitors heart rate. To ensure that the oximeter reads accurately, calculate the heartbeat for a minute, and estimate the number on the oximeter to the pulse number you calculated. When they are identical, then you will get a good signal.

1. How To Read A Pulse Oximeter

First, you should locate the SpO2 values. This result can be identified on the pulse oximeter's electronic readings and will be presented as a percentage, usually within 90 and 100 percent. The exact position can vary based on the type of oximeter that is used. Certain pulse oximeters might also have a label indicating signal strength, which is a representation of the signal intensity produced by the sensor.

After that, you must find the pulse rate. In addition to  oxygen saturation, pulse oximeters usually calculate a patient's heart rate. The heartbeat is expressed as a number with two or three digits, usually within 60 and 100 in adults and higher in children and infants.  Baby heart monitors are used to measure the upcoming baby's heart rate.  That is often displayed in connection with a heart pattern or BPM letters that refer to beats per minute.

You should also find any other indicators on the monitor. Many pulse oximeters often present an ECG and a plethysmograph of a patient. The ECG, that monitors the electrical activity produced by the heart when beating, could be used to control cardiac function and to determine arrhythmias. In comparison, a plethysmograph indicates the variations in the level of oxygen in the blood that happens with each heartbeat. These pulse oximeters are not commonly available for domestic use.

2. Getting The Best Readings

Unlike  reading a thermometer, you have to ensure that enough blood flows to the arm and the finger is wearing the device to have the best reading from the oximeter. Moreover, the strongest readings are obtained when your hand is relaxed, warm, and placed below your heart's level. If you smoke the results on the oximeter can be higher than the real oxygen saturation. That's because smoking raises the levels of carbon monoxide in your bloodstream, and the oximeter can not determine the differences between the oxygen and carbon monoxide. If you smoke, consult your healthcare professional on how to read a pulse oximeter results. Try to avoid smoking by taking the help of an  acupressure smoking patch.

Besides the unreliable readings mentioned above, you can often get irregular readings from your oximeter because the oximeter sensor is not working properly. You should carry your oximeter to the clinic of your medical provider for accuracy tests.


  1. What do the numbers mean on a pulse oximeter?

The pulse oximeter calculates two separate things. The pulse rate is the first number that appears. The second number that turns up is the oxygen level of the blood.

  1. What is a normal SpO2 level?

Standard blood saturation of oxygen is classified between 97 and 99 percent. Some people, particularly long-time smokers, usually have SpO2 ranging from 93 to 95 percent. Measurements of 90 percent or less that suggest that the person needs additional oxygen and additional tests to confirm hypoxia.

  1. Which finger do you use for pulse oximeter?

Researchers assume that the middle finger of the dominant hand has the largest and probably the most precise SpO2 readings, according to the findings of several studies. They believe that the middle finger has by far the most exact value representing the saturation of arterial oxygen.

  1. Does drinking water increase oxygen in the body?

Yes. Water molecules or H2O contain two atoms of hydrogen and one atom of oxygen. Drinking enough water will make it easier for you to remain hydrated and it is faster for your bloodstream to supply the rest of the body with oxygen.

  1. What is a normal reading on an oximeter?

Regular pulse oximeter measurements are usually between 95 and 100 percent, based on several studies. Values below 90 percent are viewed as low hence the need for supplementary oxygen is suggested. That diagnosis is also known to as hypoxemia, with extreme shortness of breath, elevated heart rate and pain in the abdomen.


As every clinical monitoring device, the pulse oximeter has to be used appropriately and the findings interpreted correctly. The purpose of a pulse oximeter is to be a diagnostic tool in health care by making a sporadic and consistent evaluation of SpO2 of a patient. It is a non-invasive, simple-to-use device that provides important data about a patient's blood oxygenation.

Medical professionals have to understand pulse oximetry limitations. The pulse oximeter is an additional evaluation tool and not a substitution for other evaluation devices. Pulse oximeters will improve patient health by alerting the health care professional to hypoxia. The reading should therefore always be viewed with the clinical condition of the patient.



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