Capnography Gets Comfortable in Sleep Centers

Vol. 19 • Issue 10 • Page 28

Technology Trends

Sleep technologists are constantly faced with new equipment options and monitoring requirements. The use of end-tidal CO2 (ETCO2) monitoring, for example, has gradually increased in sleep centers with both pediatric and adult patients.

The scoring guidelines for sleep studies published by the American Academy of Sleep Medicine in 2007 lists ETCO2 or transcutaneous CO2 monitoring as a requirement on all pediatric and infant sleep studies. An increased PaCO2 value obtained immediately upon awakening from sleep is suggestive of alveolar hypoventilation.

The measurement also is advantageous because changes in the patient’s respiratory status are detected prior to the problem showing up on oximetry. This allows for a better correlation between events detected by the airflow pressure and oronasal thermal sensors.

As a result, many physician directors of sleep centers perform ETCO2 on their patients, including adults, especially when chronic obstructive pulmonary disease or other underlying pulmonary and cardiac conditions are present.

While both ETCO2 and transcutaneous CO2 monitoring are effective, transcutaneous monitors typically have a lag time after the event and, in general, are more costly than traditional ETCO2 monitors. Two main types of ETCO2 monitors are mainstream and sidestream.

Mainstream monitors make use of a sensor positioned in a respiratory apparatus close to the patient’s mouth or trachea. They analyze directly in the respiratory gas stream. Some technologists view these monitors as being too bulky, considering that other airflow sensors (thermistors, etc.) also are used on the patient’s face during sleep testing.

One upside of this technology is that it is less susceptible to condensation and secretions that can interrupt some sidestream monitors’ signals.

Sidestream monitors typically are located on the bedside, and the gas sample is traditionally drawn through a cannula that is connected to the patient. Sidestream monitors have the advantage of utilizing a traditional diagnostic pressure cannula and therefore are at times more appropriate for use with patients of various age groups.

Manufacturers have developed lightweight pressure-sensing cannulas that are easily tolerated and can simultaneously monitor airflow pressure signals and ETCO2 sampling for patients undergoing sleep testing. As a result, sidestream technology is more prevalent in clinical settings than mainstream options.

One of the most frustrating problems associated with ETCO2 monitoring in the sleep center is the presence of moisture and secretions in the patient’s exhaled breath. When coupled with longer term usage over several hours and cool room temperatures, which is the case in most sleep centers, it is common for the moisture to condense and pool as the sample makes its way down the tubing. This can affect the reading and may result in a temporary loss of signal.

Capnography manufacturers incorporate varying types of proprietary moisture management methods to remove and separate the moisture from the sample before it reaches the monitor. These options come in the form of a water trap or set of filters, and they usually work well; however, when increased moisture is present, it may be necessary for the technologist to monitor the capnography device closely and potentially replace or empty the water chamber.

As the need and demand for capnography usage expands in sleep medicine, capnography manufacturers continue to look for ways to make these devices and disposable patient interfaces more affordable to use on a daily basis. Ultimately, this will improve the adoption of capnography in sleep centers.

Walter R. Van Horn is the technical product specialist at Salter Labs in Arvin, Calif.

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