Measuring Temperature and Oxygen Saturation
Pick the right thermometer and site, use a pulse oximeter correctly and recognize readings you cannot trust.
Table of contents
Temperature and oxygen saturation are two of the fastest checks you can do, and they tell you a lot. A temperature can reveal an infection before a person feels sick. Oxygen saturation, or SpO2, shows how well the blood is carrying oxygen. Both devices can also be wrong for simple reasons, so knowing the limits of each is part of the skill.
What You Will Be Able to Do
- Choose the best site for a temperature.
- Use each type of thermometer correctly.
- Convert and compare readings from different sites.
- Use a pulse oximeter and spot an unreliable reading.
- Know when to report.
Choosing a Temperature Site
Normal oral temperature for an adult is about 97.8 to 99.1°F (36.5 to 37.3°C). A temperature of 100.4°F (38°C) or higher is generally considered a fever, and you should report it. Some older adults do not run high fevers even when they are very sick, so report any rise from their usual temperature. Report a temperature under 95°F (35°C), too.
| Site | How it compares | Best for | Avoid when |
|---|---|---|---|
| Oral | The usual standard | Alert adults and older children | Confused or unconscious, recent mouth surgery, breathing through the mouth |
| Rectal | About 1°F (0.6°C) higher than oral | Infants, when a precise reading is needed | Diarrhea, recent rectal surgery, low platelet count |
| Axillary (armpit) | About 1°F lower than oral | When other sites cannot be used | When an accurate reading is essential |
| Tympanic (ear) | Close to oral | Quick checks, adults and older children | Ear pain, heavy earwax, infants under 6 months |
| Temporal artery (forehead) | Close to oral, varies by device | Quick checks for all ages | Sweaty forehead |
Record the site along with the number, such as "99.2°F, axillary." Without it, nobody can compare readings over time.
Taking a Temperature
Always use a clean probe cover where one is provided, and clean the device between people.
Oral:
- Wait about 15 minutes after the person has had a hot or cold drink, food or a cigarette.
- Place the probe under the tongue, to one side.
- Ask them to close their lips and not bite down.
- Wait for the signal.
Tympanic:
- Use a new probe cover.
- For an adult, gently pull the ear up and back to straighten the ear canal.
- Aim the probe toward the eardrum and press the button.
Temporal artery: Follow the manufacturer's instructions. Most scanners are swiped across the forehead, and some also need a touch behind the ear.
Axillary: Dry the armpit, place the probe in the center and hold the arm close against the side until the signal.
Rectal: Only do this if you are trained and it is ordered. Use gloves, a rectal probe with a lubricated cover and the person's side-lying position. Insert it only as far as you were taught, hold it in place the entire time and never leave the person.
Warning: A rectal thermometer that is pushed too far can injure the bowel. Never force it, and never use it on someone it is not ordered for.
Using a Pulse Oximeter
A pulse oximeter is a clip that shines light through a fingertip to estimate how much oxygen the blood is carrying. Normal SpO2 for a healthy adult at rest is 95 to 100 percent.
- Choose a warm finger with good circulation. Remove dark nail polish or an artificial nail if needed, or use another finger or the earlobe if the sensor is designed for it.
- Clip the sensor on so the light faces the nail.
- Have the person sit still and rest the hand on a surface.
- Wait for the number to settle, which can take up to a minute. A pulse reading or waveform that matches the person's actual pulse shows the signal is good.
- Record the number and the oxygen status, such as "SpO2 94 percent on room air" or "96 percent on 2 liters."
Readings You Should Doubt
Several things can cause a wrong number.
| Cause | Typical effect |
|---|---|
| Cold hands or poor circulation | Weak signal, falsely low |
| Dark nail polish or artificial nails | Falsely low |
| Movement or shivering | Unstable or falsely low |
| Bright light on the sensor | Error reading |
| Darker skin tones | Can read falsely high |
| Carbon monoxide poisoning | Falsely normal or high |
The Food and Drug Administration has warned that pulse oximeters may be less accurate in people with darker skin. Do not rely on a single number. If the person looks unwell, is confused or is struggling to breathe, report it even if the reading looks normal.
When to Report
- A temperature of 100.4°F (38°C) or higher, or under 95°F (35°C).
- Any fever in an infant under 3 months, which is an emergency.
- An SpO2 under 92 percent, or the limit in the care plan. People with chronic lung disease such as COPD may have a lower normal, and their plan should state it.
- A sudden drop from the person's usual number.
Warning: Never change a person's oxygen setting. If the SpO2 is low, check that the tubing is connected and the machine is on, sit the person up if that is allowed and call the nurse. Call 911 if they are struggling to breathe, blue or confused.
Keeping Equipment Clean
Thermometers and oximeters move from person to person, so they can carry germs between patients. Wipe them with a hospital-grade disinfectant wipe between uses and let them stay wet for the time shown on the label. Use a new probe cover each time.
Common Mistakes
| Mistake | What it costs |
|---|---|
| Taking an oral temperature right after coffee | A falsely high reading |
| Leaving out the site when you record | Nobody can compare readings |
| Trusting a low SpO2 on a cold finger | A false alarm, or a real one that gets ignored |
| Trusting a normal SpO2 when someone looks ill | A real emergency can be missed |
| Reusing a probe cover | Spreads germs |
Check Your Understanding
1. A patient's rectal temperature is 100.0°F. How does that compare with an oral reading?
Rectal readings run about 1°F higher, so it is about the same as 99.0°F oral. Record the site with the number.
2. A resident's SpO2 reads 87 percent, but her hand is cold and she looks comfortable. What do you do?
Warm her hand or try another finger, and check the reading again. If it is still low, tell the nurse right away.
3. A man just drank hot coffee and is due for an oral temperature. What do you do?
Wait about 15 minutes, or use a different site.
4. A patient with COPD reads 90 percent. His care plan says his usual range is 88 to 92 percent. What do you do?
Record it. It is inside his care plan limits, but report it if he looks worse or the reading changes from his usual.
Key Takeaways
- Normal oral temperature is about 97.8 to 99.1°F, and 100.4°F or higher is a fever.
- Rectal runs about 1°F higher than oral, and axillary about 1°F lower.
- Always record the site.
- Normal SpO2 is 95 to 100 percent, and under 92 percent is a call unless the plan says otherwise.
- Cold fingers, movement and dark polish can make readings wrong.
- Never change an oxygen setting yourself.