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

The amount of water consumed per day by active humidification depends upon several factors including minute ventilation requirements and the ability of a specific humidification system to reach and maintain the goal of providing between 33 to 44 mgH2O/L of ventilation. Under ideal conditions (use of a heated wire circuit to prevent rainout) at low (5L/min), average for critical-illness (10L/min) and high (15 L/min) minute ventilation demands, the estimated daily consumption would be approximately the following: For the gas conditioning criteria of 33-44 mgH20/L estimated H2O consumption would be approximately 250-300, 500-600 and 700-1000 mL/day, respectively.

Elimination of a machine mounted inspiratory filter – If a bacterial viral filter is used between the circuit Wye and the patient, then an additional inspiratory filter between the machine and the inspiratory limb may not be necessary to protect the patient (so long as the machine is kept clean and an airway mounted filter and/or expiratory limb filter is used). That is a big “if,” and the use of an inspiratory limb filter at the circuit takeoff is to eliminate this chance of error.  

A single inspiratory filter setup (at the wye) has been suggested as an option in settings of severe shortage. This setup may create potential for error and subsequent contamination of the machine. Additionally, the use of one instead of two filters in series significantly decreased viral filtration efficiency. The impact on risk of viral contamination is unknown. 

Expiratory limb filter extended use (i.e. not changing between patients) has been suggested by some as an option if severe shortage is faced and appropriate bacterial viral filter is used at the patient. APSF

Passive systems using Heat and Moisture Exchangers (HME) trap moisture and prevent it from being lost from the patient.

  • Efficacy of these devices drop over time, causing increased resistance. Manufacturers may suggest a change every 24 hours, but studies have shown that an unsoiled device in some circumstances be used for several days or up to 1 week (Ricard et al, AJRCCM 2000; Thomacot et al, CCM, 2002; AARC. Resp Care. 2012).
  • Signs of an increase in resistance include an increase in PIP but no change in Plateau pressure or a prolonged expiratory flow time.  
  • The most common cause of HME partial occlusion or rise in resistance is from pulmonary edema fluid or blood.  Mucus generally clumps in a dependent portion of the device without increasing resistance appreciably. (Davis et al Crit Care Med. 2000)

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

There are six main types of pulse oximeters: 

  • Fingertip
  • Handheld
  • Benchtop
  • Phone-based
  • Wearable (e.g. watches)
  • Multimodal (e.g. integrated into other types of monitors)

References: Lifebox Pulse Oximetry Learning Module

Keywords: probe, screen, device 

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

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