Problem With Nocturnal Oxygen Qualifications

Generally speaking, we consider an SpO2 of 90% as acceptable. This is because an SpO2 of 90% typically correlates with a PaO2 of around 60 mmHg, and anything below a PaO2 of 60 mmHg is considered hypoxia that requires treatment with supplemental oxygen.

Medicare, in setting guidelines for oxygen qualification, aims to ensure that people truly need oxygen. So, they set the qualification threshold at 88%. If your oxygen saturation is 88% or less while resting or with exertion, you qualify for home oxygen therapy.

In this case, I have no issue with the guideline—it makes sense. However, qualifying for nighttime or sleep oxygen is a different story. During the day, a saturation of 88% means you qualify for oxygen. But at night, you not only need to drop below 88%, it also has to remain that low for a minimum of five minutes.

For example, in a study we did last night, a patient's SpO2 dipped to 83%, which is considered low. But because of Medicare’s nighttime oxygen requirements, this person doesn’t qualify for oxygen. Even if their SpO2 dropped to 70%, they wouldn’t qualify unless it stayed below 88% for at least five minutes.

I believe this is a flaw in the system. Granted, lower oxygen levels during sleep are often considered normal, but setting a time-based threshold seems unnecessarily rigid. Perhaps Medicare could instead adopt a threshold like 85%—and if anyone’s SpO2 falls below that, even briefly, they should qualify for nighttime oxygen therapy. This would account for those whose saturation dips significantly, even if the drop doesn’t last the full five minutes.

Truly, Medicare does not always have the patient’s best interests in mind when setting qualification policies. What seems to guide their decision-making more is how they can save money. While the guidelines ensure that only those who really need oxygen get it, the rigid thresholds—especially for nighttime oxygen—can leave some patients without necessary support. It seems less about patient care and more about cutting costs.

Calculations: How Long Will An Oxygen Tank Last?

Your question. 

My dad wears 3 LPM oxygen at home oxygen. When he goes out of the house he has these little tanks. I think they are ML6 tanks. He is always stressed that they won't last very long. Tomorrow we have to go from the hospital to our house, which is about a 30 minute drive. He insists that I bring two tanks for the journey, but I'm wondering if we need that many. So, I am wondering how you determine how long tank will last on 3 LPM. 

My humble answer.

I completely understand your concern, and it's great that you want to ensure your dad has a comfortable journey. To estimate how long an ML6 tank will last at a flow rate of 3 liters per minute, you can use a simple formula:

Duration (minutes)=Flow Rate (in liters per minute)Tank Capacity (in liters)​×60

For an ML6 tank with a capacity of around 170 liters:

$\text{Duration (minutes)}=\frac{170}{3}\times 60$

$\text{Duration (minutes)}\approx 56.67\times 60$

$\text{Duration (minutes)}\approx 3,400.2$

Calculating this further, we can use another formula to convert this to minutes. 

        Duration (hours)=60Duration (minutes)​

For example:

$\text{Duration (hours)}=\frac{3,400.2}{60}$

$\text{Duration (hours)}\approx 56.67$

So, 3,400.2 minutes is approximately 56.67 hours.

So, at a flow rate of 3 liters per minute, one ML6 tank is estimated to last approximately 3,400.2 minutes or 56.67 hours. For a 30-minute drive, one tank should be more than sufficient. 

However, it's always a good idea to bring a spare for unexpected delays or emergencies, providing peace of mind during the journey. So, in my humble opinion, you are your father are both correct. You are correct in that one tank should be efficient to make the journey. But, your father is right in that it is always a good idea to have a spare tank just in case something unexpected happens.