By Melicent Lavers-Sailly

Capnography, the measurement of carbon dioxide (CO₂) in respiratory gases, has long been used to monitor the breathing of patients under anesthesia in the operating room. Now there is a growing recognition of its value as a reliable tool for monitoring patients under conscious sedation in ambulatory settings outside the OR.

Minimally invasive procedures are becoming more common in areas such as endoscopy clinics, cardiac catheterization labs, and interventional radiology labs, where nurses rather than anesthetists are responsible for sedation. These nurses need to have the right tools to ensure that patients are breathing properly.

In a recent Heart and Safety podcast focusing on the use of capnography outside the OR, Michael Wong of the Physician-Patient Alliance for Health and Safety interviewed Barbara McArthur, an advanced practice nurse at Sunnybrook Health Sciences Centre in Toronto with wide experience in the OR and ambulatory areas, including medical imaging, where she currently practices.

“In my area, we don’t have anesthesiologists administering the sedation,” said Barbara McArthur, “We have nurses giving the sedation, so we have to be more diligent. We know sedation is a continuum, so patients can easily slip from moderate levels into deep levels very quickly.”

Traditionally nurses in ambulatory areas have relied on visual assessment of breathing rhythm, which can be difficult if the patient is prone during the procedure or if comorbidities such as COPD or apnea are present.

Pulse oximetry may also be used to monitor the patient’s oxygenation (O₂) levels. However, patients under sedation are often given oxygen during a procedure, so if they begin having trouble breathing there may be a delay of a minute or more before their O₂ levels drop and the oximeter alerts the nurse.

Since a capnography monitor measures ventilation rather than oxygenation, it provides an immediate alert if expiratory CO₂ levels start falling, and thus an earlier indication of patient decline.

“Having the monitor can let you know the patient’s status sooner,” says McArthur. “If the patient is getting into respiratory problems, the nurses can intervene much more quickly.”

Capnography readings consist of a waveform graph showing expiratory CO₂ plotted against time, and a number representing the partial pressure of CO₂ at the end of the exhalation, which is known as end-tidal CO₂.

During a recent review of hospital policies at Sunnybrook, McArthur’s team reviewed the current literature on procedure sedation and found position statements or practice guidelines in favour of end-tidal CO₂ monitoring from clinical societies such as the Association for Radiologic and Imaging Nursing, the American Anesthesiology Society and the Association of periOperative Registered Nurses.

As a result, capnography monitoring is now recommended for use at Sunnybrook in all units that have the equipment. Those that do not will acquire it at the next opportunity and incorporate it into their practice.

Some hospitals may believe that the lack of a capnography port on their existing monitors may prohibit them from adopting capnography outside the OR as soon as they would like, says Cheryl Ha, Senior Marketing Manager, Respiratory and Monitoring Solutions, for Medtronic Canada, a supplier of both capnography and pulse oximetry equipment. “However, the availability of capnography modules that can be added to many multiparameter platforms has expanded dramatically, thus allowing most hospitals to add on the feature without having to replace their existing fleet.

“Another barrier to adoption may be the learning curve associated with reading and interpreting the capnography waveforms and then knowing how to properly intervene when appropriate.”

Nevertheless, Ha adds, “With strong recommendations coming from bodies such as the Canadian Anesthesiologists’ Society and Le Collège des Médecins du Québec, the benefits of including end-tidal CO₂ monitoring outside the OR are becoming better known in the clinical community — so much so that we’re seeing a growing interest for education and peer-to-peer support to help move past some of the barriers.

“We genuinely believe that down the road, capnography will be adopted as a standard of care in procedures requiring moderate to deep sedation outside the OR as a key measure for promoting increased patient safety and monitoring vigilance.”

Melicent Lavers-Sailly is senior manager of corporate communications at Medtronic Canada.