Oxygen FAQ

Poor oximeter performance (i.e. either inaccurate or absence of a reading) during low perfusion is a known phenomenon in clinical and laboratory settings. If a patient is cold or has peripheral vasoconstriction and poor perfusion, the pulse oximeter may have difficulty detecting a good pulse signal on the fingertip. This affects some oximeters more than others. Some oximeters perform wandering readings while others may produce steady but inaccurate results. At present, there is no requirement by certifying bodies to test oximeter accuracy under controlled or standardized conditions of low perfusion. Nonetheless, some manufacturers and labs do this testing routinely. The OpenOximetry.org Project is working to publish these data in our database while developing and advocating for standards for performance during low perfusion.

References: Lifebox Pulse Oximetry Learning Module 

Keywords: vasoconstriction, poor perfusion, cold

Different models of pulse oximeters will look slightly different and may have some variation, but many devices will operate in a similar way. The screen of the device will show a reading of the SpO2, the pulse rate, and often the waveform. 

• If possible, first remove any nail polish and warm the hands if they are cold. 
• Ensure that the probe is connected to the oximeter and that the device is charged. 
• Power on the device, and then clip the probe onto the fingertip while keeping the patient’s hand still.  
• After a few moments, the screen will display the SpO2. 
• If the device shows a pleth, it is important to check that the waveform looks appropriate. 

Many pulse oximeters also have buttons which allow the user to control alarm volume, screen display, and turn the device on and off. Now, the patient can continue to be monitored and checked for signs and symptoms of hypoxemia. It is always important to follow the manufacturer’s instructions for use if these are available. Finally, if the device does not seem to be working, try to troubleshoot the issue.

References: Lifebox Pulse Oximetry Learning Module

Keywords: how to use, instructions

SpO2 is the functional oxygen saturation measured by pulse oximetry. A normal SpO2 reading is usually considered to be above 94%. An SpO2 of 90-94% can signal that a patient may have a new or chronic respiratory problem, or that they may be progressing to hypoxemia. Many clinical definitions of hypoxemia (i.e. low oxygen concentration in the blood) use a cutoff of 90%, though depending on the context, SpO2 values above 90% may be abnormal (e.g. a healthy, young adult at sea level should be 96-100%. Similarly, depending on the context, an SpO2 less than 90% may be physiologically appropriate (e.g. at high altitude). Read more about the “Optimal SpO2 target for Patients with Respiratory Failure”

References: Lifebox Pulse Oximetry Learning Module

Keywords: normal SpO2, hemoglobin

Ideally, it is best to place the probe on a warm finger on the patient’s non-dominant hand so that the patient can still use their dominant hand without hindrance. For patients with decreased levels of consciousness (e.g. emerging from sedation), the middle finger is a good finger to place the probe because patients are less likely to scratch their face or eyes with this finger.  However, if you are unable to get a good reading on this finger, try the other fingers or the other hand until a good waveform is obtained.

References: Lifebox Pulse Oximetry Learning Module

Keywords: finger, placement, location

Recent studies using data from 54 countries have shown that about 77,700 operating rooms worldwide do not have pulse oximeters. When accounting for other clinical practice settings such as post-op recovery units and intensive care units, the ‘oximetry gap’ is likely much greater. Barriers to access include cost, supply chain, and incorporation into local practice guidelines.

References: Funk et al, Lancet 2010; Gibbs et al, What is the real oximeter gap?, Anaesthesia, 2017

Keywords: access, operating rooms, equipment

Spectrophotometry is a type of quantitative measurement technique that is used to measure the reflection or transmission properties of a substance as a function of wavelength. Every type of substance absorbs light over a specific range of wavelengths. This type of measurement allows us to assess the intensity of light that a substance (such as hemoglobin in blood) absorbs, and therefore has clinical and bioengineering applications. 

Clinically, spectrophotometry is used in pulse oximeters to determine the proportion of oxygenated hemoglobin in arterial blood. Since different wavelengths of light are absorbed by oxygenated and deoxygenated blood, pulse oximeters can use this technique to determine a patient’s peripheral oxygen saturation (SpO2).

Keywords: spectroscopy, spectrophotometry, wavelength, light

As patient status can change rapidly during anesthesia, a qualified anesthesia provider should be present continuously to monitor the patient and provide anesthetic care. The American Society of Anesthesiologists has determined standards for basic anesthetic monitoring, which state that “during all anesthetics, the patient’s oxygenation, ventilation, circulation and temperature shall be continually evaluated.” 

Regarding blood oxygenation and SpO2 measurement during anesthesia, ASA standards state that “a quantitative method of assessing oxygenation such as pulse oximetry” should be used at all times. It is important that the volume, pitch, and low threshold alarm noises be audible to the anesthesia care team personnel throughout the duration of anesthesia.

References: ASA Monitoring Requirements

Keywords: anesthesia, monitoring, frequency

Pulse oximeters can be used to measure many different clinically important values. Some (but not all) pulse oximeters can measure the following:

• Respiratory rate
• Perfusion
• Carboxyhemoglobin
• Methemoglobin
• Hemoglobin concentration
• Pulsatility variation

Keywords: measurement, respiratory rate, pulsatility variation

To receive FDA approval on a new device intended for human use, a premarket submission called a 510k must be made to the FDA. This must demonstrate that the device is substantially equivalent to a legally marketed device, meaning that it is just as safe and effective.

According to the FDA, a device is considered “substantially equivalent” if the following criteria are met: 

• Has the same intended use as the predicate device; and
• Has the same technological characteristics as the predicate;
  OR
• Has the same intended use as the predicate; and
• Has different technological characteristics and does not raise different questions of safety and effectiveness; and
• The device is demonstrated to be as safe and effective as the legally marketed device

Once this information has been submitted to the FDA, the FDA will determine whether the device is safe and effective through a thorough review process, including evaluation of performance data and technological characteristics. In the US, a device may not be marketed until the FDA determines that substantial equivalence is present.

References: FDA Premarket Notification 510(k)

Keywords: substantially equivalent, SE, FDA, 510k

An IP rating, also known as the ingress protection rating, is the rating of a product’s ability to withstand liquid and dust. IP ratings were defined and developed by the International Electrotechnical Commission (IEC), and are recognized all over the world.

The IP code is composed of two numbers:

• The first number rates the device’s protection against solid particles (i.e. dust). It is rated from 0 (no protection) to 6 (full protection).
• The second number rates the device’s protection against liquids. It is rated from 0 (no protection) to 9 (protection from high-pressure, high-temperature liquid).

References: IEC: IP Ratings

Keywords: IP, ingress protection, dust, liquid, IEC