Respiratory: Pulse oximetry (for nursing assistant training)

As a nursing assistant, you will help provide safe care to clients who have or are at risk for hypoxia, which is when there is not enough oxygen to meet the needs of the body.

These clients require pulse oximetry, which is a non-invasive, easy, and pain-free method of measuring the amount of oxygen carried by the hemoglobin in the red blood cells.

This is known as arterial blood oxygen saturation, or SaO2 for short. Maintaining a normal SaO2 ensures that the amount of oxygen that travels through the bloodstream to tissues around the body is adequate.

Now, a pulse oximeter consists of a probe, which is attached by a cable to a pulse oximeter. That probe has a light source on one side and a photodetector, or sensor, on the other side.

So, when it gets clipped onto a body part, a light shines through the tissues on one side, and on the other side, the sensor detects how much light has been absorbed by the arterial blood in the tissues.

The principle is that, when hemoglobin is bound to oxygen, it absorbs more light than when it’s not. Now, there are several types of probes, depending on the site they can be placed.

The most commonly and easily used ones are digit probes, which can fit onto a finger or a toe. There are also earlobe probes, which attach to the client's ear.

Less commonly, if the digits or earlobes are inaccessible, a pulse oximetry probe can be applied across the forehead and secured with a headband.

Both earlobe and forehead probes tend to be more accurate than digit probes in cases when blood flow to the extremities is compromised or if the client moves their hands or feet frequently, creating motion artifacts.

There are also sensor pads that can be used on several different sites, including an adult's earlobe or nose bridge and a newborn's palms or soles.

Now, all these probes can be either disposable, which are preferred when multiple clients need to be checked using the same oximeter, or reusable when used for a single client.

They also come in two types: adhesive and clip sensors. In general, adhesive sensors are better for younger children or if you need to place the sensor on an earlobe, nose bridge, or toe.

Clip sensors might not be the best for children because they are very easy to take off. A pulse oximeter reading, also called SpO2, of 95% or greater is considered normal.

Anything below that is considered low for most clients. But, if it falls below 85%, it can get really dangerous for the client.

This may occur in clients with various lung conditions that interfere with gas exchange, meaning movement of oxygen and carbon dioxide between the blood, lungs, and tissues.

In other cases, though, readings can be falsely low because of poor blood flow to the extremities, which makes it hard for the pulse oximeter to pick up a proper signal.

Now, this could be due to peripheral vascular disease, which happens when one of the arteries supplying the extremities becomes narrowed, as well as hypotension, or low blood pressure; hypothermia, or decreased body temperature; several medications; peripheral edema, or accumulation of fluid and swelling of the limbs; smoke inhalation; or carbon monoxide poisoning.

Readings can also be inaccurate due to motion artifacts, like when the client is shivering or restless, meaning that false signals are generated when they shouldn’t be.

Readings may also be inaccurate if the client is wearing nail polish, or if bright light, such as sunlight, is shining on the probe, making it harder to measure the oxygen saturation.

Now, before we talk about how to assist with pulse oximetry, here are some common care tips to keep in mind.

In general, depending on the condition of the client, pulse oximetry can be used intermittently, meaning that you go and check the client’s SpO2 at certain times, or continuously, where the client is continuously connected to the pulse oximeter.

In the latter case, an alarm can notify you if SpO2 falls below a certain level or if the probe falls off. If the client is a child, remember that they will probably love to move, so it might be best to place the probe on their finger or toe; otherwise, you may get inaccurate readings. Also, avoid using forehead or nose probes with these clients.