How O2 Sensors Play a Part in Ventilator Performance

Alarm fatigue can have a harsh psychological impact on a clinician’s mind. Research shows that 72% to 99% of alarms are false, leading to alarm fatigue. Alarm fatigue occurs when a clinician experiences frequent alarms during patient care and grows increasingly desensitized to the alarms, and therefore less likely to take action during a critical time. This false alarm rate is staggering, and could also explain why we find that the same alarm tone on your phone becomes less effective waking you up each morning.

We will come back to alarm fatigue after we go over oxygen sensors. Oxygen sensors allow the clinician to know how much oxygen is being delivered to the patient during ventilation, and therefore prevent hypoxia, hypoxemia or oxygen toxicity. An oxygen sensor is one of those “when you need it to work, it should work” kind of devices. 

A bad oxygen sensor in the best case is a quick change for a nurse or respiratory therapist and the biomed. At worst, it can lead to adverse consequences – these adverse events are not unheard of unfortunately. There are 35 reports on the FDA Maude database regarding oxygen analyzers in the last 10 years. Improper oxygen sensing coupled with pipeline gas hooked incorrectly has led to fatalities (see examples here and here). To mitigate such occurrences, AARC guidelines recommend analyzing any blended medical gas that is being delivered. 

There are different types of medical oxygen sensors, the most common one being the galvanic cell that has an electrolyte with a cathode and an anode; it reacts with a small amount of the oxygen flowing through to the ventilator to create an electrical output that is proportional to the amount of oxygen (see how this works here). Other technologies to sense oxygen in medical applications may use paramagnetic technology or ultrasonic technology, such as the Maxtec UltraMaxO2. Each of these technologies have their advantages and disadvantages, and may be a great choice for one application, but not another. Of course when you look at other industrial applications like automotive, or dissolved oxygen sensing there are optical sensors and electrochemical sensors that fall outside the scope of this topic.

With a plethora of ventilators and medical devices being designed and manufactured, and different therapies being used, the need for oxygen remains constant. Regardless of which therapy you consider, oxygen sensors are always critical to allow the clinician to observe crucial data. This data is imperative so the clinician can decide whether to increase or decrease the amount of oxygen delivered to the patient. Depending on the situation, the patient may need 100% oxygen or they may need much lower levels; what’s important is that oxygen needs can change at any time. Weaning protocols (best practice protocols set with the intent to gradually get a patient off mechanical ventilation) are quite common and without the ability to know how much oxygen is being delivered, the clinician will find it extremely difficult to provide the best care.  

When the time comes to decide on which oxygen sensor to use, you will need to consider the following:

Which sensor has the right specs for your ventilator, analyzer or anesthesia machine?
Use our cross reference guide to find out the sensor you need based on the manufacturer or the sensor you are trying to replace.

Lifetime of the Sensor
The life of a galvanic oxygen sensor can be most accurately expressed in terms of percentage O2 hours. For instance, if a sensor claims to have a 500,000 %O2 hour life, you can determine the actual time with this formula:

Lifetime (years)  = 500,000/(24*365*x) 

Where x is the percentage of oxygen flowing through the patient circuit. If left in air, you would replace x with 20.9 (atmospheric O2 is roughly 20.9%). If you are delivering 100% oxygen at all times, you would replace x with 100. The sensor begins utilizing its lifetime capacity the moment it is made. Maxtec accounts for a storage time prior to shipping, so that the rated lifetime is guaranteed from the moment a sensor is shipped out. Maxtec has also implemented some unique designs to allow a longer lifetime for oxygen sensors than what you might see on average in the market. See what Maxtec does to create sensors with a longer lifespan. 

Stability, Accuracy, & Response Time
Oxygen sensor specifications mention certain parameters like zero offset, stability/drift and linearity that affect the accuracy and/or life of the sensor. These parameters are all products of the sensor design, chemistry, and quality of materials. Drift and linearity can impact the accuracy of the sensor and should have a low value for best performance. Zero offset is the offset voltage the sensor outputs in 0% oxygen. This parameter can have an effect on the accuracy and life of the sensor, and tends to increase as the sensor ages. Response time is the time the sensor takes to stabilize on a reading when the input oxygen level changes. It is largely dependent on the electrode and electrolyte design. Find out how Maxtec optimizes these factors to produce a high quality product. 

The cost of a sensor often indicates the quality and what you get out of it. You would be better off from a budget standpoint to buy a sensor with high quality and long life. A high quality sensor will mean fewer product related issues, fewer complaints from the clinicians and less frequent preventative maintenance. With longer-life sensors, you wouldn’t have to worry about frequent replacements. Consider how often you want to replace sensors, cost of holding stock, spending time placing POs, and disposing of the sensors after use before making a buying decision.

Unplanned maintenance can be painful. To alleviate this, almost all oxygen sensors come with a warranty period depending on how long they expect it to last. Warranties typically range from 6 months to 12-14 months and some even have warranties up to 24 months. You may have experienced changing a patient from a ventilator or an anesthesia machine because the oxygen sensor alarm keeps beeping. Longer life sensors with long warranty periods could help mitigate such issues. Longer warranties will allow you to have less frequent planned maintenance, but more importantly it speaks to the quality of the sensor. Try to be cautious of how exactly the warranty works. The last thing you would want to do is negotiate with companies who might not replace sensors immediately.

Now let’s talk about alarm fatigue: poor quality sensors can cause false positive alarms, and the more this happens, the less sensitive people tend to be to alarms. This can be quite dangerous, because when we become insensitive to an alarm – we may neglect to respond in a crucial time. 

The responsibility of providing high quality healthcare is something we all share. Respiratory therapists and nurses are on the frontlines and the first call they make when something goes wrong with equipment is to the clinical engineering department or the biomed department. Albeit a small part, choosing the right oxygen cell will allow you to have one less thing to worry about. The high quality and long-life sensors provided by Maxtec can help you with that. Maxtec sensors come with a lengthy warranty as well. We achieve this long life by using unique materials:

  1. Gold Cathode: Being a noble metal, gold doesn’t degrade with the reaction inside the galvanic cell. Cathode degradation can affect the reaction and measured oxygen concentration, which can lead to dire consequences or early death of the oxygen cell. Others may use lower quality metals for their cathode. 
  2. Hydrophobic Membrane: Uncontrolled moisture can cause a lot of problems in devices. Maxtec uses a hydrophobic membrane that can keep condensed moisture away from the primary diffusion membrane. This adds an extra protective layer to mitigate wear and tear on the oxygen sensor. 
  3. Red Tape: As soon as the sensor is made, it starts measuring room oxygen – meaning, its usage time starts ticking. We make use of a unique tape that limits the amount of ambient oxygen exposure from 20.9% to 7-8%. When you are about to use the sensor, you can simply remove the red tape. The red tape ensures that our oxygen sensor’s life isn’t wasted when it is not in use. 

Through these methods, we are able to offer sensors with strong warranty periods. In addition to this, if there comes a time when you need to replace a sensor under warranty, we have a hassle-free process and will do this for you without asking any questions. You can depend on our customer service to help you with replacements and technical support. You will be put in touch with our in-house team of technical experts who have a combined 50+ years of experience with oxygen sensors. 

Have you ever wondered how to dispose of your oxygen sensors? You must follow state and local laws when disposing of an oxygen sensor, given the materials in it (similar to disposing of batteries). If you’d like to avoid any disposal inconveniences, you can send your sensors to us and we will dispose of them in an environmentally responsible manner. 

The sensors we manufacture have been tried and tested by users like you for over 20 years. Is it time to replace the oxygen sensors for your equipment? Reach out to us to get an oxygen sensor right away. Also reach out if you are interested in participating in our frequent buyer program (return 15 sensors to get one sensor free of charge).

TIP: A good practice that a lot of respiratory therapists and nurses have is to carry a handheld oxygen analyzer to check oxygen supply quickly if they think something is off. It is an extra precautionary step before they decide to make any major changes. Check out our Handi+ oxygen analyzer that can be used to do quick checks like this.