Understanding the Link Between CHF, OSA and Increased Mortality
Congestive Heart Failure (CHF) is a condition where the heart is in a weakened state and cannot handle all the blood it receives, which results in congestion of the lungs. CHF has different levels of severity, and it is responsible for a large number of hospital admissions and healthcare costs. Therefore, it’s in the best interest of the patient and the healthcare system to identify all risk factors that would cause worsening of CHF or CHF decompensation, which raises the risk of mortality.
The association between Obstructive Sleep Apnea (OSA) and increased mortality from CHF has been established with the large Sleep Heart Health Study. In spite of what is known, there has not been a concerted effort to screen for OSA in CHF patients. This is not to say that strong efforts are not made in regularizing and individualizing treatment, and closely monitoring these patients. It’s just that sleep-related breathing disorders are not routinely part of the screening and management of CHF.
With this in mind, a new study published in the Journal of Clinical Sleep Medicine called the SOMA study looked at a group of hospitalized patients with CHF who were screened for sleep apnea.
The significance of this special situation is that it (naturally) selects the individuals who have a more serious form of the disease, since they needed to be hospitalized. The idea behind the study was to identify those in which treatment (that targeted the apnea component of the disease) would result in less chance of readmission. It’s worth noting that sleep labs that typically conduct these screening studies are not available in hospitals but rather in an outpatient setting. That’s because the equipment and personnel necessary to perform the sleep study are not really appropriate for a hospital’s “serious disease treatment” setting.
So within this study, a new technology was also analyzed. It’s called high resolution pulse oximetry (HRPO). This technology involves the placement of a device on the patient’s finger or earlobe to monitor and capture changes in the spectrum composition of the color of blood circulation (associated with oxygen saturation of the blood). This information is actually routinely monitored in intensive care units (ICUs) as a measure of the adequacy of oxygen delivery. The HRPO not only measures the oxygenation in real time, but the curves it shows are associated with the patient’s respirations, so this information allows the doctor to identify apnea periods, which are intervals where there is cessation of breathing.
One potential problem of using this type of screening is that it does not identify the types of apnea, namely:
- Central sleep apnea, which results from the failure of the brain to stimulate the lungs to breathe
- Obstructive sleep apnea, which results from a blockage in the throat that limits passage of air to the lungs.
Unlike other oximetry devices that only measure oxygen saturation without providing the curve information, HRPO did not pose a common problem — errors in readings due to the sensor moving out of place. Unlike portable sleep-testing devices that offer an apnea home screening option, but would not work in a complicated monitored ICU setting, HRPO can be added to existing cardiac-monitored units. One more plus: There’s no need for additional health personnel to monitor or attend to the equipment.
The results of the SOMA study showed a high correlation between abnormal HRPO findings and positive findings in subsequent and separate sleep studies.
One other problem associated with this type of screening is that CHF patients frequently have other conditions like hypertension, atrial fibrillation, and COPD so it’s hard to attribute the effect of the apnea on mortality without controlling for all other variables.
Nevertheless, this procedure is cheaper and more practical to perform on a large group of people, specifically those who are sick enough to require hospitalization, in order to screen for the possibility of apnea, which would clearly require further intervention if diagnosed.
Positive findings for apnea with an HRPO in-hospital screening still require post-hospitalization formal sleep studies after hospital discharge. The breathing problems that occur during sleep in CHF patients are more complex and need further evaluations with sleep studies, and then individualized treatment. In some cases, treating patients merely classified as having sleep apnea with regular CPAP for obstructive apnea can end up suppressing the brain’s regulatory function on breathing, causing central apneas.
It is important to recognize that apnea is not the only dangerous type of breathing pattern in patients who have CHF. There are other types of abnormal breathing patterns in these patients. One is an alternating fast and slow breathing called Cheyne Stokes breathing which is associated with increased risk of dangerous arrhythmias. The addition of HRPO screening to the monitoring equipment can be useful in preventing complications, which lead to higher mortality rates, directly caused by abnormal breathing events during sleep.
What is quite surprising is that based on what is already known about sleep disorders and how they complicate heart disease, little effort has been made to aggressively identify and then treat these sleep disorders, especially apneas in this class of patients.
It is clear that more research is needed to formalize and validate apnea diagnostic results from the SOMA study using HRPO as a method to screen for apnea. The idea of finding a simple device that works in the hospital setting to screen CHF hospitalized patients with high risk for apnea is a good first step.