Patients with severe pain who use opioid-based medications may suffer sleep apnea and its complications, including greater likelihood of death, according to a study in Pain Medicine, the journal of the American Academy of Pain Medicine.

The research shows that three-fourths of patients on chronic opioid therapy have some degree of sleep apnea, said Dr. Lynn R. Webster of Lifetree Clinical Research and Pain Clinic in Salt Lake City, who is lead author on the study. They also found a "direct dose-response relationship" between central sleep apnea and methadone used with benzodiazepines.

Webster said sleep apnea may be an underlying factor in the increase in unintentional overdose deaths linked to opioid pain medications, especially methadone.

The research also showed that as many as one-third of patients being treated with opioids had a component of sleep apnea called central sleep apnea, rather than the more common obstructive sleep apnea. Central apnea is when the body makes no effort to breathe, the part of the brain responsible for respiration malfunctioning. It's also harder to spot, because some of the telltale hints with obstructive sleep apnea, such as being overweight and loud snoring, are absent.

"With central sleep apnea, we don't know what the indicators are," Webster said.

Anyone with sleep apnea is at greater risk of heart disease and stroke. And Webster said it also has been shown that people with sleep apnea have more intense pain, "which makes pain medicine less effective, which leads to more pain medicine, which leads to more sleep apnea, which increases the risk of heart disease and stroke. ... It's a cycle. There are a lot of different factors that are interrelated that can contribute to other problems."

While someone on moderate to high-dose opioid medications may have significant problems with sleep apnea, Webster said, not all of them will. It is important that patients are assessed to spot cases of sleep apnea and treat it.

"If you can't modify the sleep apnea and make sure it's safe, you may have to provide less medication," he said. However, he noted the research is not a call to reduce use of opioids, but rather to understand the risks they may bring and deal with them.

There are a number of treatments for patients with sleep apnea, including a continuous positive airway pressure (CPAP) mask, use of oxygen and others. "The best treatment for this we do not know yet. You can't necessarily use the treatments used for other populations for this problem, because the mechanisms are different for them."

Central sleep apnea in the past has been most strongly linked to heart failure or neurologic disorders like stroke. In these cases it's presumably a combination of chronic pain and the opioid treatment prescribed for it.