Pulse Oximetry and Oxygen Saturation

Definition of Pulse Oximetry

Pulse oximetry is the noninvasive measurement of oxygen that flows through the hemoglobin inside the blood vessels.

How Pulse Oximetry Works

The color of the blood varies depending on how saturated it is with oxygen due to the optical properties of the hemoglobin molecule.

When hemoglobin releases an oxygen molecule it loses its pink color, acquiring a bluish tone and therefore restricting the amount that is reflected under a red light.

Thus the pulse oximeter determines the oxygen saturation by measuring the "degree" of arterial blue blood and expresses this "blueness" in terms of saturation.

Since light absorption of the tissues and venous blood are constant, any change in the absorption of light within a given period of time should be exclusively due to the blood pressure.

Pulse oximeters measure the relationship in a time interval between the differences in absorption of red and infrared lights. This relationship is directly linked to the oxygen saturation.

Technical Application

A pulse oximetry is device with a clip-shaped sensor. In the clip is a light that is reflected onto the fingertip and a sensor that measures the amount of light absorbed by hemoglobin circulating in the patient.

As a first step massage the patient's fingertip, then put the clamp with the sensor and receive the information displayed on the screen of the device.

The information that is displayed is:

• Oxygen saturation index
• Heart rate
• Pulse curve

Limitations of pulse oximetry

• Changes in hemoglobin
• Dyes and pigments in the reading area (nail polish).
• External light sources.
• Peripheral hypo perfusion.
• Anemia.
• Increased venous pulse.
• It does not detect hypoxia.
• It does not detect hypo ventilation.

In general they are useful for the care of patients where an alteration in oxygenation is foreseen:

• Respiratory distress in asthma.
• Cyanosis.
• Assessment of exercise tolerance.
• Evaluation or control of oxygen therapy.
  

Uses of Pulse Oximeters

• You must first obtain information on the proper use of each model.
• Remove nail polish for finger pulse oximeters.
• Make the measurement far from a major light source, light bulbs, etc.
• In case of continuous measurements over a period of time change the place of measurement 8finger for example), at least every 8 hours to prevent skin lesions.
• Clip sensors should not apply excessive pressure, as it could alter the measurement.

Oxygen Saturation Normal Range

Oxygen saturation should be greater than 95%.

Evaluation of Abnormal Results in Oxygen Saturation

The mesurement figure presented by an Oximeter, can be both above or below normal levels. For patients on oxygen therapy the norm is that they are below, however it is important to be aware of risks in higher oxygen saturation.

Increased levels of oxygen saturation:

• Hyperventilation
• Anxiety

Decreased values of oxygen saturation:

• Chronic lung disease.
• Offset or asthma attacks.
• Heart disease.