When is oxygen therapy performed in a sleep lab?

For many patients facing the challenges of using some form of positive airway pressure (PAP) to treat their sleep breathing disorders, the question is often asked: 

"Why not just use oxygen at night?"

After all, one major problem with untreated sleep apnea is the precipitous drop in oxygen levels in the blood, known as hypoxia

However, when it comes to obstructive breathing patterns, O2 therapy is not the go-to treatment (for a reason). But that doesn't preclude its use in the sleep lab for certain patients during their studies.

Blood oxygen basics

When you visit the doctor, most likely they check your blood oxygen by way of a small fingertip clip called a pulse oximeter.

Using a special infrared technology, this device quickly determines the oxygen saturation of your blood.

Healthy people maintain an oxygen saturation of 90 percent or higher at any time of day or night. 

When blood oxygen drops, it indicates an imbalance in blood gases (that is, there may be too little oxygen—hypoxemia—or too much carbon dioxide—hypercapnia—or both).

If these conditions are sustained, a lot of chronic health problems can and will develop. 

People with restrictive lung diseases like COPD struggle to maintain proper amounts of oxygen in their blood because they have mechanical obstacles that prevent efficient breathing. They often struggle to maintain healthy blood oxygen levels (above 90 percent) during the day, and at night, their levels may drop even further as they sleep.

Meanwhile, people with obstructive sleep apnea (OSA) may have healthy lung function and enjoy normal blood oxygen while they are awake, but severe obstructions at night may lead to these dangerous and sustained drops in their blood oxygen.

Why not treat sleep apnea with oxygen therapy?

It seems appealing, at first. Why wear a mask delivering air pressure when wearing a small nasal cannula that delivers a gentle stream of oxygen might do just as well?

The truth is, oxygen therapy alone cannot treat sleep disordered breathing. It's the very obstructions which negate the effects of oxygen therapy for people with OSA.

Since OSA is a mechanical dysfunction of the upper airway, it really doesn't matter how much oxygen is available for inhalation; the airway has become blocked or collapses, creating a roadblock for its entrance into the lungs. 

This is why continuous positive airway pressure (CPAP) is so effective; it literally splints open the upper airway with air pressure so that the person using it can breathe freely on their own.

CPAP is not a form of oxygen therapy, after all. It does not breathe for its users and it does not provide concentrations of oxygen. What it does do is make it possible to breathe, and this is why it's still considered the most effective therapy for treating OSA. 

For people with cardiovascular concerns, CPAP is also highly recommended over nocturnal supplemental oxygen after results of the HeartBEAT study, published in the New England Journal of Medicine in 2013, showed its use resulted in significant improvements in blood pressure for those with serious nighttime breathing problems. 

When might oxygen therapy be used in the sleep lab?

This is not to say that oxygen therapy is never used during sleep studies.

For some patients, even the application of CPAP to keep the airway open is not enough to offset sustained periods of low blood oxygen.

Remember those COPD patients we mentioned earlier? Their lung dysfunction makes it even more challenging if they also have sleep apnea. This combination of chronic conditions is referred to as Overlap Syndrome.

If they aren't getting oxygen during the day because of problems with gas exchange in their lungs, they most certainly will not be getting adequate oxygen at night if their upper airway introduces an additional roadblock to breathing. 

Patients trialing CPAP for Overlap Syndrome may also be given oxygen therapy in the form of an "O2 bleed." This entails bringing a medical oxygen supply tank into the room and administering a steady stream to the patient through cannula-like tubing that connects with their CPAP mask.

This way they receive both the air pressure of the CPAP therapy as well as supplemental oxygen to avert dangerous drops in blood oxygen that they may be sustaining as they sleep. 

It's not a perfect solution, but...

Oxygen therapy for CPAP users has its own challenges.

One of the ways in which our brains work with our lungs to maintain adequate oxygen in the blood supply is through what is known as the hypoxic drive.

In a nutshell, this means that when there's too much carbon dioxide and not enough oxygen in the bloodstream, the brain automatically sends out signals to the body to breathe to correct this imbalance.

This is true for all of us, but for those with compromised lung function, the hypoxic drive can go haywire. 

Oxygen therapy has influence over hypoxic drive. The brain, sensing there is enough oxygen in supply because of this artificial administration of it, does not send out these necessary signals to breathe regularly. These signals are meant to shorten the apneas as a defense mechanism, after all. 

Breathing patterns for those who are already struggling, but who are using oxygen therapy, may be further disrupted, and the severity of episodes of apneas may actually increase, leading to cardiovascular stress over the long haul. In addition, daytime sleepiness—one of the main side effects of OSA—will not be addressed by using oxygen therapy alone.

However, use of nocturnal O2 can still be very beneficial for some patients. It has been shown to improve overall arterial oxygen saturation during sleep. The overall outcome for those using oxygen therapy is generally quite high, so these rewards typically outweigh the concerns. 

For those who have Overlap Syndrome, sleep is going to be challenging, but there are options that can be explored in the sleep clinic, including use of supplemental O2 by itself and in combination with PAP therapy.

Your best option for addressing this combination of problems is to work with your sleep specialist to find the right therapeutic formula to meet your unique nighttime breathing needs.


Sources:

CHEST
Journal of Clinical Sleep Medicine
New England Journal of Medicine

Pulmonary & Critical Care Medicine (PulmCCM)
Respiratory Care

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