The Ryan Report

Home Oxygen Guru – The HO₂G Pen

Ready for Spring!

I don’t know about you, but I’m ready for spring and summer. Time to get out after being stuck inside for most of the winter. To those of you affected by spring flooding and weather-related disasters, I send positive vibes your way.

With spring comes the travel season, and only portable oxygen concen- trators (POCs) can be used during airline travel. The FAA requires anyone using a POC during flight to carry enough batteries to last 1.5 times the length of the trip. If possible, carry a fingertip pulse oximeter with you so you can monitor your saturations and lower your device setting if you are getting enough oxygen – saving some battery life. Carrying an up-to-date prescription from your doctor may save some headaches at the gate.

A “New” Player Has Entered the Arena

In the next issue will be the updated guide to POCs. New POCs are not being introduced as frequently, so much of the data will remain the same as last year. One “new” addition is the ResMed Mobi POC. The Mobi really isn’t a brand new product, but rather an updated version of the Inova Labs LifeChoice Activox 4L model, which ResMed acquired a couple of years ago. I know several users of the LifeChoice line of POCs had recurring issues with the devices, including frequent low purity problems requiring replacement of the sieve beds. With ResMed’s purchase and retooling of the Activox 4L into the Mobi, the hope is that these problems have been resolved.

ResMed increased the amount of oxygen produced by the device. The Activox 4L generated about 480 mL/min of oxygen, less than half a liter per minute; the provider’s Mobi manual says it can output about 680 mL/ min of oxygen at its highest setting–an improvement over the Activox 4L of 200 mL/min. It’s not a lot of added volume, but it is an upgrade. The Mobi will be able to generate more oxygen than the smaller Inogen One G4 and Precision EasyPulse 3 POCs, but will not match the output by similarly sized POCs like the Inogen One G3 and GCE Zen-O Lite. Keep this in mind if you have tried these other devices and are interested in the Mobi.

88% Is the Magic Number

I recently was asked to participate in a webinar for Dr. Noah Greenspan’s Pulmonary Wellness Online program (https://pulmonarywellnessonline.com). I had the opportunity to discuss home oxygen with Dr. Greenspan, and to do a live question and answer session with oxygen users across the country. One question was about 88% being the threshold for oxygen saturation when determining the need for supplementary oxygen.

Perhaps the simplest and most common answer I’ve seen shared is along the lines of, “because that’s what Medicare requires when determining eligibility for home oxygen equipment.” Which is true to an extent, a person will have to demonstrate that they experience blood oxygen desaturations at or below 88% while breathing room air at rest and/or activity. But this doesn’t really answer the question of “Why is it 88%?” To understand why 88% is an important number, we need to look a little deeper into the physiology of blood oxygenation.

When we breathe in, oxygen in the air passes through the alveoli deep in the lung into the bloodstream. When the oxygen enters the blood, the volume of oxygen that is coming in adds a level of pressure to the bloodstream. The amount of pressure that is created directly affects how much of the oxygen coming in is picked up by the hemoglobin in the blood (hemoglobin is a blood protein that carries the oxygen). The more oxygen pressure created, the more hemoglobin attaches the oxygen to itself for transport to the rest of the body. Saturation refers to how much oxygen the hemoglobin is carrying relative to its full capacity. If saturation is 100%, then the hemoglobin in the blood is carrying as much oxygen as it possibly can. But if the oxygen pressure in the blood is in- adequate, hemoglobin will not be able to attach as much oxygen as possible, and thus the saturation level will be lower than 100%.

The oxyhemoglobin disassociation curve relates the amount of oxygen pressure in the blood- stream (PO2) to the oxygen-hemoglobin satura- tion level (% saturation, or SaO2%.) An important distinction: SaO2 is estimated when using pulse oximetry.

The normal PO2 is 80- 100, which equates to saturations of 95%-98%. Individuals who have mildly de- creased PO2 values in the 60-80 range, will equate to about 91%-95% saturations. A PO2 of 55 results in a saturation of 88%. Note, then, that you can have a PO2 ranging from 55-100, a difference in PO2 of 45, and have saturations in a relatively acceptable range from 88%-98%.

If you look at the graph closely, though, you can see that the saturation drop that occurs between a PO2 of 55 and PO2 of 40, a PO2 difference of only 15, is about 18% (from 88% to 70%, which is, let’s say, not good). Compare that to the drop in PO2 from 100 to 55, a difference in PO2 of 45 that results in only a 10% drop in saturation (from 98% to 88%), and you can see that things can go south very quickly once that PO2 55/SaO2 88% threshold is crossed.

Think of the upper PO2 range as the top of a snowy hill, where you are on a sled. You can move around on this PO2 hilltop quite a bit, going back and forth between 55 and 100, but you aren’t going to get enough momentum to really start heading down the hill and have your saturations fall below 88%. However, once you pass the point where PO2 drops below 55, the oxygen pressure in the blood is not enough for the hemoglobin to grab as much of that available oxygen, and so saturation drops below 88%. And, unfortunately, the further below 55 you get, the steeper the drop becomes, and the easier that sled starts careening out of control down the hill. To top it off, once you DO stop, the further down the hill you are, the harder it is to get back up that hill on your own.

Please note that this is a basic explanation of the relationship between inspired oxygen and saturation levels. There are numerous variables that can affect how well one is oxygenated that are not mentioned here. I hope it is somewhat clearer why 88% is such a crucial number when assessing the need for supplemental oxygen. 88% is, essentially, the tipping point where things can start spiraling out of control, as your body begins to increasingly lose its ability to effectively transport oxygen to tissues and organs the further down the hill you go. That is why monitoring your oxygenation via pulse oximetry during your daily activities should be an important part of your reg- imen. Understanding when you need oxygen and how much oxygen you need to stay in a healthy saturation range is a vital component to living well with supplemental oxygen. It also can be a critical source of information when experiencing changes in health status – the more information you have on your daily oxygen use and its effectiveness, the better you and your doctor/pulmonologist/ family can assess any changes and relate them to changing oxygen needs.