Oxygen FAQ

Up to date, expert answers to frequently asked questions (FAQ) about oxygen supply systems, respiratory care and pulse oximetry written by OCC & collaborators.

Top 10 most popular FAQs

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;
  • 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

  • Always see manufacturer’s specifications. 
  • All external filters should be inspected at least daily
  • For turbine and compressor ventilators, external inlet filters and fan filters must be cleaned (if cleanable per manufacturer) or replaced at least monthly. For ventilators that allow, bacterial/viral filters should be placed proximal to external inlet filters. 
  • For example, the LTV-1200:  The external inlet filter should be removed and cleaned once a month and can be reused. If operated in high dust or humidity environments, it may need to be cleaned more often. The filter can be cleaned  with mild detergent and warm water by using a soft cleaning brush. The filter must be rinsed thoroughly of all detergent residue and must be dried completely prior to re-insertion. If the filter is damaged or cannot be thoroughly cleaned, it should be replaced. The external inlet filter appears to be a proprietary item (Reticulated Foam P/N 10258)
  • The fan filter should be removed and cleaned at least once a month (same cleaning procedure as described for the inlet filter). It also can be reused. If the ventilator is being operated in high dust or humidity environments, it may need to be cleaned more often. If the filter is damaged or cannot be thoroughly cleaned, it should be replaced. 
  • The LTV-1200 model also has an oxygen inlet filter that must be inspected and cleaned on a regular basis. It also is cleaned using a mild cleanser, warm water and a soft brush. Rinse the filter thoroughly to remove all traces of the cleanser. Allow the filter to dry completely before replacing it in the ventilator. Inspect the filter for damage. If it is not intact, or shows signs of damage or cannot be completely cleaned, it should be replaced. The filter is a proprietary item (O2 Inlet Filter (P/N 19845-001) and the accompanying O-Ring (P/N10609)
  • The Zoll 731 ventilator: has an internal 2-stage filtration system (an outer foam filter and inner disk filter) to protect the gas flow. External filters should be visually inspected on a daily basis (or more frequently) for dust build up during extended operation in harsh environments and changed when they appear dirty. Use of external filters will preserve the life of the proprietary internal filters (foam filter REF#: 465-0028-00, Air Intake Disk Filter (REF # 465-0027-00). If external filters are not (or cannot be) used, the internal filters must be visually inspected on a regular basis and replaced when dirty. Note: proprietary internal filters cannot be cleaned and reused: they must be replaced. 
  • The Medtronic PB560 has an external air inlet filter that is intended to be replaced (~monthly or more often) rather than reused

Below is a partial list of items to consider when caring for patients on a mechanical ventilator. Also included are partial lists of manufacturers’ ventilator accessories for two ventilators to serve as examples.

Parts inventory

There are two main types of pulse oximeter: transmittance devices and reflectance devices. Transmittance pulse oximeters are the most common and work by transmission (i.e. shining a light) through tissue, usually a fingertip or ear. As the light passes through the body part, the amount of oxygen in the blood determines how much light is absorbed in the tissue. A light detector on the other side of the probe detects light that is not absorbed, and a microprocessor calculates the oxygen saturation in the blood. Reflectance pulse oximeters are placed on the skin surface and measure the light reflected off the tissues rather than through the tissue. In this way, absorption is measured to calculate oxygen saturation. Of note, reflectance devices are inherently more difficult to design to perform well.

References: Lifebox Pulse Oximetry Learning Module

Keywords: transmittance, reflectance, light, absorption

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

Nail polish or nail varnish can impact pulse oximeter accuracy, so it is best to remove the polish to allow the light from the probe to pass through the tissue. If it cannot be removed, placing the probe on the toe or on the fingertip sideways can be an option. 

Certain colors of nail polish may lead to underestimation of SaO2 by pulse oximetry. Studies have shown that in healthy adults, blue, green, black, and brown nail polish appear to interfere the most with pulse oximeter SpO2 readings. In fact, they can cause readings of up to a 3-5% underestimation in oxygen saturation.

Another study, which examined different nail polish colors on 50 critically ill patients, showed that all colors interfered with pulse oximetry readings, but that the most significant interference was due to black, purple, and dark blue polish. All other nail polish colors had a lesser effect on pulse oximeter readings. 

Regarding gel nail polish, a study in 17 healthy adults tested several colors of gel-based manicure, and concluded that certain colors of gel polish resulted in a significant overestimation of SpO2, although their results varied when using different brands of pulse oximeter.

References: Lifebox Pulse Oximetry Learning Module, Ralston et al, Anaesthesia 1991; Adler et al, Acad Emerg Med 1998; Hinkelbein et al, Resuscitation 2007; Yönt et al, Intensive Crit Care Nurs 2014; Coté et al, Anesth Analg 1988; Yek et al, Singapore Med J 2019

Keywords: nail polish, varnish, nail color

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