Often referred to as, “the sixth vital sign,” the routine use of capnography appears to be lacking in hospitals, both across the United States as well as globally. 

By Paul Nuccio, MS, RRT, FAARC

RT’s Three Key Takeaways

  1. Capnography, often called “the sixth vital sign,” is not consistently used outside the operating room despite its benefits in patient care.
  2. The lack of capnography utilization is due to various factors, including misconceptions about its benefits compared to pulse oximetry and limited access to equipment and education.
  3. Efforts to promote capnography use include addressing barriers such as lack of training and equipment availability, with the potential for respiratory therapists to play a crucial role in advocating for its implementation.


Often referred to as, “the sixth vital sign,” 1 the routine use of capnography appears to be lacking in hospitals, both across the United States as well as globally. Considered to be the standard of care by anesthesiologists in the operating room (OR), monitoring patients outside of the OR with capnography has not been embraced by clinicians at the level that has been done in the surgical suite.2 The purpose of this article is to examine the reason(s) why there has been such a reluctance to utilize this technology, both on a local and a global scale.

Capnography vs Oximetry

There is a common misconception that if pulse oximetry is being monitored there is no additional benefit of adding capnography to the mix.  Although the abilty to use pulse oximetry as a monitoring device has been a great addition to our toolbox, it is important to understand that although the device provides great information regarding a patient’s oxygenation status, it does not provide information about a patient’s adequacy of ventilation, which can be provided with capnography.  Therefore, both pulse oximetry and capnography provide important, but very different physiologic measurements, and as such should be used in conjunction with each other, rather than instead of the other.

Where Should Capnography be Used?

In an editorial published in 2011 in Anesthesia,3 D. K. Whitaker described how although utilized routinely in operating rooms since 1988, it has failed to gain routine acceptance outside of the surgical area, despite the “significant contributions to patient safety”.  Whitaker was speaking about its lack of adoption in areas such as critical care units (ICU), during resuscitation efforts, during patient transport, during postoperative care, as well as when using procedural sedation, and neonatal resuscitation.  He also spoke of the importance of utilizing this technology in the emergency departments to monitor patients experiencing an exacerbation of their pulmonary disease.

Why Is the Use of Capnography Lacking?

It has been well documented that capnography is highly utilized in operating rooms in high income countries (HIC), including the United States, although that has not been the case with low and middle-income countries (LMIC), where it has been reported that the “lack of access to capnography likely contributes to more frequent and serious airway events and higher rates of perioperative mortality”.  This phenomenon has been described as the capnography gap.  The development of less-costly equipment should help to minimize or eliminate the expense barrier, thus making more equipment available to many LMIC’s, minimizing the capnography gap, and help to improve patient outcomes in those areas.4

Unfortunately, the use of capnography is not only lacking in low and middle-income countries.  In many high-income countries, capnography use outside of the operating room is still inconsistent at best.  In the INTUBE study,5 an international observational study looking at both intubation practices and peri-intubation morbidity, published in 2022, showed that despite the vast amount of literature showing that capnography is the ideal method of identifying esophageal intubation, 68.9% of those who incorrectly received esophageal intubation, 115 patients, were not monitored using capnography.  Most of these patients were intubated in either the intensive care unit (ICU) or the emergency department (ED).  Other adverse effects were identified also in this study that involved 197 sites across 29 countries (including the United States).

In a 2021 editorial by Russotto and Cook,6 the authors discuss the finding of the 4th National Audit Project (NAP4) which identified “waveform capnography as the single intervention with the highest potential for reducing morbidity and mortality during tracheal intubation and maintenance of an artificial airway.”  They also discussed the lack of capnography usage identified in the INTUBE study described previously. 

One of the issues that they identified, which may be related to our current focus, and for some perhaps an obsession with, evidence-based medicine, was their lack of awareness of any large randomized controlled trial (RCT) that shows that the use of capnography reduces morbidity and mortality.  The authors also pointed out that the same can likely be said of any type of monitoring device utilized in the critical care setting.

Another issue they noted was that in some hospitals, capnography equipment simply was unavailable outside of the operating room.  In many instances clinicians rely on other things to determine appropriate tube position such as direct visualization, which can, be problematic during a chaotic emergency intubation.  Chest auscultation and chest expansion are often used, although they have been shown to perform inadequately when used to confirm proper endotracheal tube placement.

The authors also spoke about what they called “confirmation bias”, when clinicians tend to see and hear what they expect to see and hear, as has been described in several medicolegal cases.  Regardless of the reason(s) for the lack of use, proponents of capnography need to work towards improving equipment access and making widely available appropriate education and training.

In a controlled before-and-after implementation study performed at two urban hospital EDs,7 the target audience for the intervention (use of capnography) were the staff of the emergency department.  The study utilized the knowledge transfer framework concept.  The focus of the intervention was on patients in the ED who required intubation and/or CPR.  The control site was an academic tertiary care center, and the experimental site was a community hospital.  Both sites have a fairly large (>80,000) annual volume of patients in their ED’s, and both use the same electronic medical record (EMR).  Although the control site had a capnography guideline in place for intubated patients, the experimental site did not have such a document.  The availability of capnography equipment, knowledge about capnography, and an awareness of potential benefits of using capnography in the clinical setting were the focus of the intervention, based on barriers that were identified in a previous study.8

A multi-disciplinary team made up of staff from both hospitals was created to engage with staff and that group also created and deployed an educational video and other materials, consistent with their knowledge transfer framework principles.

The results of the survey showed that although most staff were willing to use capnography, many felt uncomfortable with interpreting the data provided by capnography.  Many felt they required more training, and some were unsure of where to find the equipment.  Another interesting finding was that although providers were open to modifying their clinical practice regarding the implementation of capnography in intubated patients or those receiving CPR, most failed to actually put this into practice.  The authors did acknowledge that the compilation of their data was primarily obtained through documentation in the EMR, and given the often-chaotic environment, particularly during emergencies, documentation lapses are quite common.  They also pointed out that the acceptance of pulse oximetry in the ED setting was very similar, only beginning to become routine back in the late 1980’s.  Pulse oximetry is now considered to be the standard of care for the monitoring of most patients, so there still may be hope for capnography.

What’s Next?

Capnography has been shown to be an excellent monitoring device for identifying inadvertent esophageal intubation, detecting accidental endotracheal tube dislodgment during patient transport, and for identifying return of spontaneous circulation (ROSC) during CPR. Capnography has also been shown to effective in monitoring non-intubated patients receiving pain-controlled analgesia and during procedural sedation.9

As mentioned previously, the use of capnography is the standard of care in the operating room by anesthesiologists. In fact, it is doubtful that an anesthesia provider in a modern hospital today would even consider providing anesthesia to a patient if capnography was unavailable.  One would think that the same would hold true for anyone caring for patients with an artificial airway, undergoing CPR, or receiving any type of opioids or other sedation.  However, without a strong knowledge and understanding of the device and its limitations, the routine use of this device will likely fail. 

The anesthesiologist is considered the expert with capnography in the OR, but they are not always available outside of that area.  Perhaps this is a great opportunity for the respiratory therapist to become or continue to play the role of capnography expert outside of the OR, advocating and teaching others about it’s use.  The days of discarding this device because the etCO2 doesn’t match the PaCO2 should be behind us.  The respiratory therapist, with a strong understanding of the arterial to end-tidal CO2 gradient, can help others to understand and appreciate the value of this life-saving technology.

RT

Paul Nuccio, MS, RRT, FAARC, is a former director of pulmonary services at Brigham and Women’s Hospital & Dana-Farber Cancer Institute in Boston and an adjunct faculty member at Boise State University.  He is presently semi-retired and working as an Independent Consultant/Educator.

  1. [i] Hunter C, et al. The sixth vital sign: prehospital carbon dioxide predicts in hospital mortality and metabolic disturbances. Am J Emerg Med. 2014; 32:160-65.
  2. [ii] Kodali BS. Capnography outside the operating rooms. Anesthesiology. 2013 Jan;118(1):192-201
  3. [iii] Whitaker DK. Time for capnography – everywhere. Anaesthesia. 2011; 66:544–9.
  4. [iv] Russotto V, Myatra SN, Laffey JG, et al. Intubation Practices and Adverse Peri-intubation Events in Critically Ill Patients From 29 Countries. JAMA. 2021;325(12):1164–1172.
  5. [v] Russotto V, Tassistro E, Myatra SN, et al. Peri-intubation Cardiovascular Collapse in Patients Who Are Critically Ill: Insights from the INTUBE Study. AJRCCM. 2022;206(4):449-458.
  6. [vi] Russotto V and Cook TM. Capnography use in the critical care setting: why do clinicians fail to implement this safety measure? BJA 2021;127(5):661-664.
  7. [vii] Shah R, Streat DA, Auerbach M, et al. Improving Capnography Use for Critically Ill Emergency Patients: An Implementation Study. J Patient Saf 2022;18(1):e26-e32.
  8. [viii] Langhan ML, Kurtz JC, Schaeffer P, et al. Experiences with Capnography in Acute Care Settings: A Mixed-Methods Analysis of Clinical Staff. J Crit Care 2014;29(6):1035-1040.
  9. [ix] Restrepo RD, Nuccio P, Spratt G, Waugh J. Current applications of capnography in non-intubated patients. Expert Rev Respir Med. 2014:1-11.