Monitoring Oxygen In Bloodstream: Hospital Techniques

Hospitals use two main methods to detect oxygen in the bloodstream: pulse oximetry and blood draw tests. Pulse oximetry is a widely used method in hospitals, where a small, clip-like device called a pulse oximeter is attached to a body part, typically a finger, to measure oxygen levels in the blood. This method is painless, non-invasive, and provides rapid results. Alternatively, blood draw tests, such as arterial blood gas (ABG) tests, involve taking a blood sample to measure oxygen and carbon dioxide levels directly. While blood draw tests provide more comprehensive information, pulse oximetry is often preferred for its convenience and accuracy, especially in critical care settings.

Pulse oximetry

While pulse oximetry is typically precise, especially with high-quality equipment, it is important to note that various factors can affect the accuracy of readings, including skin tone, nail polish, artificial nails, dyes used for diagnostic tests, excessive motion, skin temperature, and tobacco smoking. Recent evidence suggests that pulse oximetry may be less accurate for people with darker skin pigmentation, failing to detect low oxygen saturation levels in some cases.

Blood draw test

Blood oxygen levels refer to the amount of oxygen circulating in the blood. Normal blood oxygen levels fall between 75 and 100 mm Hg on arterial blood gas (ABG) test results.

There are two main ways to measure or test blood oxygen levels: through a blood draw test and through pulse oximetry (using an oximeter). A blood draw test provides much more information about your oxygen levels than an oximeter does.

A blood oxygen level test blood draw includes the following steps:

• You’ll sit in a chair or lie in a medical bed, and a respiratory therapist will look for an artery—usually in your inner wrist. They might use ultrasound imaging to help find an artery.
• Once they’ve located an artery, they’ll clean and disinfect the area.
• They’ll then insert a small needle into your artery to take a blood sample. You may feel a sharp pain as the needle goes into your artery.
• After they insert the needle, a small amount of blood will collect in a syringe. Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
• They may apply pressure for 5 to 10 minutes or longer if you’re taking blood-thinning medication.
• They’ll place a bandage over the site, and you’ll be finished.

A respiratory therapist usually performs blood draws for arterial blood gas tests from an artery in your wrist, arm, or groin. The sample is then either processed by the respiratory therapist or sent to a lab very quickly where medical laboratory scientists process the sample.

If you’re on supplemental oxygen therapy, your provider may turn off your oxygen for about 20 minutes before the blood draw. This is called a room air test. If you’re unable to breathe without supplemental oxygen, your provider will not do this test.

An arterial blood gas (ABG) test measures the oxygen and carbon dioxide levels in your blood, as well as your blood's pH balance. The test usually includes the following measurements:

• Oxygen content (O2CT): This measures the amount of oxygen in your blood.
• Hemoglobin: This measures the amount of hemoglobin, the protein responsible for carrying oxygen to your cells, in your blood.
• Oxygen saturation (O2Sat): This measures how much hemoglobin in your blood is carrying oxygen.
• Partial pressure of oxygen (PaO2): This measures the pressure of oxygen dissolved in your blood. It helps show how well oxygen moves from your lungs to your bloodstream.
• Partial pressure of carbon dioxide (PaCO2): This measures the amount of carbon dioxide in your blood and how well carbon dioxide can move out of your body.
• PH: This measures the balance of acids and bases in your blood, known as your blood pH level.

Oxygen saturation levels

Healthcare providers can measure blood oxygen levels through a blood draw test or pulse oximetry. A blood draw test provides much more information about oxygen levels than pulse oximetry. Doctors carry out arterial blood gas (ABG) tests in hospitals, but a person cannot perform an ABG test at home. Pulse oximetry is an alternative, non-invasive method to measure blood oxygen saturation. People can test themselves at home using a pulse oximeter, a small clip that attaches to a finger, ear, or toe. It measures blood oxygen indirectly by light absorption through a person's pulse. Although the pulse oximetry test is easier, quicker, and less painful than the ABG test, it is an estimation of blood oxygen levels.

Pulse oximetry can rapidly detect even small changes in oxygen levels. These levels show how efficiently blood is carrying oxygen to the extremities furthest from the heart, including the arms and legs. Pulse oximetry tests are typically precise, especially when using high-quality equipment found in most medical offices or hospital settings. With this equipment, medical professionals can carry out the tests accurately. The pulse oximeter will be able to tell you your oxygen saturation levels along with your heart rate.

An oxygen saturation level of 95% is considered typical for most healthy people. A level of 92% or lower can indicate potential hypoxemia, which is a seriously low level of oxygen in the blood. Various factors can affect readings, including a person's skin tone. Tests like these were developed without considering a diversity of skin tones. Once the test is over, the doctor will have the readings available immediately, helping them determine if other testing or treatment is necessary.

Oxygen therapy

Healthcare providers will monitor a patient's blood oxygen levels to ensure they are getting the right amount of oxygen. This can be done through a blood draw test or pulse oximetry (using an oximeter). Pulse oximetry is a non-invasive method to measure blood oxygen saturation. It is a small, clip-like device that attaches to a body part, most commonly a finger.

Blood gas test

Hospitals use a blood gas test to detect oxygen in the bloodstream. This test is also called an arterial blood gas (ABG) test. It is a safe, simple, and low-risk procedure that requires only a small sample of blood from an artery. It is often carried out in hospitals, but doctors can also perform the test in their offices or clinics.

During the test, a doctor or healthcare worker will use a small needle to draw blood from an artery in the wrist, arm, or groin. Before the test, they may apply pressure to the arteries in the wrist for several seconds to check that blood flow to the hand is normal. This procedure is called the modified Allen test. If a person is receiving oxygen therapy, they may need to stop using it for 20 minutes or more before the test.

The blood sample is then analyzed by a portable machine or in an on-site laboratory. The test measures the amount of oxygen and carbon dioxide in the blood, as well as the blood's pH level or acid-base balance. The oxygen content (O2CT) measures the amount of oxygen in the blood, while oxygen saturation (O2Sat) measures how much hemoglobin (a protein in the blood) is carrying oxygen. Partial pressure of oxygen (PaO2) measures the pressure of dissolved oxygen in the blood and how well oxygen travels from the lungs to the blood.

The results of the blood gas test can help doctors diagnose the cause of breathing difficulties and identify lung, heart, or kidney problems. It can also be used to monitor treatment for certain conditions, such as lung and kidney diseases.

Frequently asked questions