Two recently published studies seem to point to completely different results on the benefit of monitoring with capnography.
In the article, “ETCO2 Concentration Correlates With Trauma Mortality,” Anesthesiology News discusses the research by Danielle K. Bodzin, MD (anesthesiologist, University of Miami/Jackson Memorial Medical Center) and her colleagues:
Dr. Bodzin and her colleagues retrospectively queried the Anesthesia Information Management System at the Ryder Trauma Center in Miami. The researchers used an algorithm to identify patients (between years 2005 and 2015) who underwent emergency surgery after trauma with a maximum or average ETCO2 sustained for at least five minutes below or equal to 30 mm Hg. Neurologic cases were excluded.
Over the 10 years evaluated, researchers found 413 patients who met the inclusion criteria. Of these, 133 patients met the primary outcome of death or cardiac arrest. Two receiver operating characteristic curves were plotted for maximum and average less than or equal to 30 mm Hg within the predefined time frame.
Presenting their findings at the 2015 annual meeting of the American Society of Anesthesiologists (abstract 5007), the researchers concluded that ETCO2 of less than or equal to 20 mm Hg was highly predictive of mortality. Dr. Bodzin said:
Our results suggest that end-tidal carbon dioxide is a valuable short-term prognostic indicator in trauma patients underdoing emergency surgery. We suggest that continuous end-tidal carbon dioxide monitoring early on in the resuscitation bay and during transport prior to entering the operating room [OR] could be a very useful practical marker of successful resuscitation, and may help us determine which trauma patients might benefit from early, aggressive resuscitation.
In other words, ETCO2 is a surrogate measure of cardiac output. By identifying which trauma patients may be in need of “early, aggressive resuscitation”, clinicians would be able to allocate time and resources in a optimal manner.
Contrast the Dr. Bodzin research with that of John J. Vargo, MD, MPH (Digestive Disease Institute, Cleveland Clinic) and his colleagues. In the Medscape article, “Capnographic Monitoring Unhelpful for Routine Endoscopy.” In Dr. Vargo’s study:
To investigate the potential benefit of the new standard, Dr. John Vargo of Cleveland Clinic in Ohio and colleagues randomly assigned 452 healthy patients (ASA Physical Classification l and ll) undergoing routine outpatient EGD (218 patients) or colonoscopy (234 patients) under moderate sedation to a blinded capnography alarm or open capnography alarm group. Standard cardiopulmonary monitoring devices were used in both groups, in addition to capnographic monitoring.
In the open arm, an independent observer signaled all respiratory abnormalities — for example, hypoventilation, disordered respirations, pseudo-apnea — on the capnography monitor. In the blinded arm, no signals were given for any ventilatory abnormalities, although for patient safety the endoscopy team would be alerted if a patient experienced apnea lasting 30 seconds or more. The endoscopy team was blinded to the capnography findings in both arms.
There was no significant difference in rates of hypoxemia between the blinded and open capnography arms, and the authors concluded that “capnographic monitoring in routine EGD or colonoscopy for ASAPS l and ll patients does not reduce the incidence of hypoxemia.”
Dr. Vargo and his colleagues found hypoxemia rates of about 50% in both the blinded and open capnography EGD groups. However, the statistical difference observed was not significant:
Hypoxemia rates were 54.1% and 49.5% in the blinded and open capnography EGD groups, respectively (P = .05), and 53.8% vs. 52.1% for the blinded and open capnography colonoscopy groups, respectively (P = .79).
The researchers therefore concluded that “capnographic monitoring in routine EGD or colonoscopy for ASAPS l and ll patients does not reduce the incidence of hypoxemia.”
Commenting on the research by Dr. Vargo and his colleagues, David Greenwald, MD (director of clinical gastroenterology and endoscopy, The Mount Sinai Hospital) cautioned that the study results may be applicable to healthy patients. He would recommend capnography monitoring for at-risk patients, saying:
However, it is also important to note that capnography measures apnea more reliably than does pulse oximetry, and so the use of capnography may provide benefit in some high-risk populations, particularly in obese patients undergoing colonoscopy.
For more case studies on capnography monitoring, please click on the images below: