Pulse Oximetry Essential In Diagnosing Sleep Apnea
This is a great article in regards to overnight oximetry and OSA.
Heidi Nye is a contributing writer for RT Magazine. For further information, contact firstname.lastname@example.org.
Incidences of sleep-disordered breathing continue to rise as America faces an obesity epidemic that some experts believe could soon exceed 50% of the population in some states. Overnight oximetry, a standard monitoring tool in respiratory care, plays a key role in diagnosing obstructive sleep apnea and other sleep disorders before oxygen desaturation contributes to comorbidities like GERD, type 2 diabetes, and cardiovascular disease.
By 2030, obesity rates for American adults are projected to exceed 50% in 39 states, adding $66 billion to the already exorbitant cost of treating obesity-related diseases.1 One of those related diseases is sleep-disordered breathing, specifically obstructive sleep apnea (OSA), which has seen an enormous increase in diagnoses in recent years.
Sleep apnea is marked by episodes of hypopnea (partial occlusion of the airway) and apnea (full occlusion). Central sleep apnea (CSA) is characterized by daytime drowsiness, frequent nighttime arousals, pauses in breathing of 10 seconds or more, and at least 10 to 15 apneas and hypopneas per hour with no respiratory effort. CSA occurs primarily in patients with heart failure. The far more common obstructive sleep apnea—approximately 84% of all cases, affecting 15 million Americans2—manifests the same signs, except the patient is making an effort to breathe during the episodes.
Overnight pulse oximetry, an essential tool in clinical and home sleep testing, is key to diagnosing sleep apnea before nighttime blood oxygen desaturation worsens existing comorbidities such as cardiovascular disease, type 2 diabetes, and GERD, or perhaps even contributes to their onset.2-4
“It’s the gold standard in home apnea testing,” said David Baker, CEO of SleepImage, which recently formed a partnership with Nonin Medical Inc to add pulse oximetry to its existing devices. Results from Nonin’s WristOx2 oximeter are integrated with those from the SleepImage device. The addition of oximetry to its sleep testing devices has increased system accuracy by 25% to 30%, Baker said.
“Cardiopulmonary sleep disorders, essential sleep apnea, obstructive sleep apnea, upper airway resistance all require the use of pulse oximetry for diagnosis,” said Braebon CEO Richard Bonato, who added that pulse oximetry also can be used as an ongoing monitoring tool after the initial diagnosis.
“Pulse oximetry is one of the parameters used for diagnosis, but it can also be a tool to monitor ongoing treatment. A case in point—a doctor with breathing problems used pulse oximetry one night to establish a baseline. The next night he again monitored his blood oxygen with pulse oximetry while wearing a CPAP. He had essential sleep apnea, and so continued to monitor with pulse oximetry to determine his optimum air pressure level,” Bonato explained.
Postdiagnostic readings make sure that the patient using continuous positive airway pressure (CPAP) is receiving the optimal flow of compressed air to keep the airway open and thereby prevent the obstructed breathing that characterizes sleep apnea.
On its own, however, pulse oximetry is rarely sufficient, said Bonato. “Sure, if a guy walks into your clinic at 400 pounds with a 22-inch neck, it’s pretty obvious what’s going on, so pulse oximetry monitoring may be enough,” he said, adding that most cases aren’t so clear-cut and require other data such as ECG, respiratory rate, heart rate, and snore.
Since Medicare and Medicaid require corroborating desaturation data before patients can be put on CPAP, Nonin sales rep Steve Carey sees the need for pulse oximetry growing. “As more people begin to understand that sleep apnea can cause other problems, it becomes more important for the medical community to screen patients,” said Carey. “There’s been a shift from sleep labs to companies like SleepImage that are doing four or five parameters with a home device.”
Correct Application Makes All the Difference
“Pulse oximetry is more than a number,” said Shari Angel Newman, RPSGT, clinical director at Spartanburg Regional Medical Center’s Sleep Disorders Center in South Carolina. “Diabetics or congestive heart failure patients tend to have poor perfusion,” which can result in false negatives or false positives. Because blood flow is diminished, pulse oximetry “may not show depth of variation in the ups and downs” of blood oxygenation.
In heavy smokers, the body makes extra hemoglobin in an attempt to deliver sufficient oxygen to the cells, something that also must be taken into account when looking at pulse oximetry readings. A diabetic may have diminished blood flow in the fingertips, and an oximeter placed there could give false readings. Even dark nail polish or ambient light shining on the sensor can result in inaccuracies.
Conventional pulse oximetry considers only the pulsation of arterial blood at the measurement site, but when the patient moves, venous blood also moves, which can result in an underestimation of oxygen saturation levels.5,6 Signal Extraction Technology (SET), pioneered by Masimo Corporation, isolates the venous blood signal, which has a lower oxygen saturation level, and extracts only the arterial signal to more accurately report oxygen saturation and pulse rate. “The biggest hurdle is convincing sleep labs to use measure-in-motion pulse oximetry,” said Gary Clawson, Masimo’s senior director of global professional education, “so they don’t get a lot of oxygen drops” that aren’t diagnostically significant.
If you have values generated only once per second, you typically are given readings in whole percentages, said Compumedics marketing and product management consultant Jeffrey Kuznia. “But the body doesn’t step down in whole percentages,” said Kuznia. “Pulse oximetry generally has 2% to 3% accuracy, but if you instead went down to the tenth place, you’d get a response curve that was physiologically much closer to what the body is actually doing.”
Focus on Sleep
A poor night’s sleep can mean low energy levels and a decrease in exercise, which can contribute to weight gain and obesity. With excess weight comes depression, an ever-diminishing inclination to exercise, further weight gain, and potentially more episodes of sleep-disordered breathing. Because of resulting hormonal, chemical, and metabolic changes, type 2 diabetes, cardiac and cardiovascular problems, GERD, and other diseases are more likely to manifest or worsen.2-4 For example, 86% of type 2 diabetics have OSA.3
“The reality is that if you have diabetes and sleep apnea, your treatment will be impeded if you don’t treat the sleep apnea,” said Kuznia. Interruptions in sleep affect the body’s ability to metabolize glucose, so treating OSA improves glucose control and helps with weight loss, which further improves control.3
If blood flow to the kidneys and the brain is interrupted, desaturation can cause a number of adverse events, including elevated blood pressure, arrhythmia, and increased incidence of stroke. The American Heart Association reported that 50% of patients with OSA are hypertensive, and 50%+ of those with heart failure, arrhythmia, and arterial fibrillation are likely to have OSA, compared with approximately 30% in the general cardiac population.2
If sleep apnea could be treated at its onset, the United States could reduce the occurrence of diabetes, hypertension, and heart disease, while saving many billions of healthcare dollars in the process. “But the system doesn’t always lend itself to that,” said Henry L. Johns, BS, RTSGT, CRT, CPFT, program manager for Clinical Specialty Labs at the Veterans Administration’s Eastern Kansas Health System.
Several years ago, Johns petitioned Medicaid on behalf of pediatric patients who needed pulse oximetry home testing and treatments for sleep apnea. The oximetry, CPAP, and ongoing care would have been approximately $2,500 per patient. Medicaid refused to cover the testing; however, it does cover other life-saving procedures that cost much more, like tracheostomies, which can cost upwards of $300,000, according to Johns. “[It] makes no sense” to disallow immediate, low-cost care because diabetes and its complications may not manifest for another decade, Johns said.
Medicare requires a 4% drop in blood oxygen saturation in order for a patient to qualify as having sleep apnea, but Johns said clinicians know that a 2% to 3% drop can be “very clinically significant, especially if it occurs in a cyclical fashion. Some aggressive physicians will put their patients on CPAP, but the majority will say, ‘Let’s watch it.’ But what does that mean if they’re not testing? Most insurers watch what Medicare is paying. If they’re not paying, insurance companies won’t allow for testing.”
Ideally, primary care physicians would screen all at-risk patients with pulse oximetry. Those who reported being awakened by their own snoring, disturbing their significant other’s sleep, or not feeling rested would be sent home with a pulse oximeter or multichannel sleep monitors to take a closer look. According to Johns’ calculations, every accredited sleep lab in the country would have to handle 7,000 cardiac and cardiovascular patients a week in order just to take care of the 50%+ of those patients who are likely to have sleep apnea.
The awareness of attending clinicians and physicians plays a major role in helping to diagnose sleep disorders. An estimated 85% of patients with clinically significant, treatable OSA are undiagnosed.2 Where some can let warning signs slip away, the most diligent physicians can overload a sleep center. “Of the two hospitals I oversee,” said Johns, “three primary care physicians keep the sleep center booked 3 months out. They’re very attentive to asking basic questions of every patient with hypertension or diabetes: Do you snore or stop breathing? Are you sleepy during the day?”
In addition, though it once may have been the case, sleep apnea is not just about the obese anymore. While OSA and obesity have been clearly linked, clinicians can’t just single out heavy patients for scrutiny. “That’s where we were 30 years ago, thinking only obese people snored; 70% of my patients are obese,” said Newman, but added that not every person with sleep apnea suffers from obesity, and that she is aware that healthy-looking patients also may suffer from sleep-disordered breathing.
Ultimately, diagnosing and treating sleep apnea and obesity early on could ease the personal suffering and public healthcare costs of ongoing care for cardiac patients and type 2 diabetics, the latter of whom are predisposed to a long list of complications, including kidney failure, blindness, and amputation.
What’s more, arresting OSA at onset might even prevent sleep apnea-related changes in the body from developing these conditions in the first place. A technology as inexpensive yet effective as pulse oximetry can and should play a role in expanding sleep disorder screenings and diagnoses, but for now, such an aggressive regimen only exists in an ideal world. RT
Heidi Nye is a contributing writer for RT Magazine. For further information, contact email@example.com.