Pain management/conceptCapnography for Procedural Sedation and Analgesia in the Emergency Department
Introduction
Procedural sedation and analgesia is the standard of care for the management of acute procedural pain and anxiety in the emergency department (ED).1 Patient safety monitoring during ED procedural sedation and analgesia currently includes pulse rate, blood pressure, respiratory rate, oxygen saturation, ECG, and clinical observation. Noninvasive monitoring of ventilation with capnography has been studied as a research tool but is not part of routine procedural sedation and analgesia monitoring. Although standard practice in anesthesia, the use of capnography in emergency medicine has primarily been limited to intubated patients for verification of endotracheal tube placement and for cardiac arrest. There has been little emphasis on the use of capnography for assessing ventilatory status and on waveform interpretation in spontaneously breathing patients.
Capnography is a well-studied technology in anesthesia and has been used in the operating room for more than 35 years.2, 3 Anesthesiologists and respiratory physiologists began using capnography as a research tool in the 1950s. Modern capnography was developed in the 1940s by Luft4 and commercialized in the 1960s and 1970s after the development of mass spectroscopy. Through the pioneering work of Smalhout and Kalenda,2 capnography became a routine part of anesthesia practice in Europe in the 1970s and in the United States in the 1980s. In 1999, the American Society of Anesthesiologists issued Standards for Basic Anesthetic Monitoring,5 delineating the role of capnography for all patients receiving general anesthesia: “Every patient receiving general anesthesia shall have the adequacy of ventilation continually evaluated. Qualitative clinical signs such as chest excursion, observation of the reservoir breathing bag and auscultation of breath sounds are useful. Continual monitoring for the presence of expired carbon dioxide shall be performed unless invalidated by the nature of the patient, procedure or equipment.”
Capnography provides continuous, real-time, breath-to-breath feedback on the clinical status of the patient and allows the clinician to determine the baseline ventilatory status and track changes over time.3, 6 Capnography, like ECG, is a diagnostic monitoring modality because changes in the shape of the waveform are diagnostic of disease conditions.2, 3 This article discusses the use of capnography as a diagnostic monitoring tool for procedural sedation and analgesia, focusing on the physiology and interpretation of the CO2 waveform and recognition of normal, abnormal, and drug-induced ventilatory patterns.
Section snippets
Terminology
Capnography is the noninvasive measurement of the partial pressure of carbon dioxide in exhaled breath. The ancient Greeks believed there was a combustion engine inside the body that gave off smoke (capnos in Greek) in the form of the breath. A capnometer is a CO2 monitor that displays a number (ie, end-tidal CO2 [etco2]). A capnograph is a CO2 monitor that displays a number and a waveform. The CO2 waveform or capnogram displays changes in the CO2 concentration during the respiratory cycle.
Technology
Most capnography technology is built on infrared radiation techniques. These techniques are based on the fact that CO2 molecules absorb infrared radiation at a very specific wavelength (4.26 μm), with the amount of radiation absorbed having a close to exponential relation to the CO2 concentration present in the breath sample. Detecting these changes in infrared radiation levels, using appropriate photodetectors sensitive in this spectral region, allows for the calculation of the CO2
Emergency Medicine Studies on Capnography Use in Procedural Sedation and Analgesia
Research on the use of capnography for ED procedural sedation and analgesia has shown that capnography can frequently identify respiratory depression and airway complications before clinical observation.
The first ED study investigating the use of capnography for procedural sedation and analgesia was reported by Wright7 in 1991. He studied the use of noninvasive oxygenation monitoring with pulse oximetry and noninvasive ventilation monitoring with capnography in a convenience sample of 27 adult
Physiology
The capnogram, corresponding to a single tidal breath, has been described as having 4 phases (ascending phase, alveolar plateau, inspiratory limb, dead space ventilation) in which each of these phases has conventionally been approximated as a straight line.2, 13 Thus, the capnogram of a subject with normal lung function, irrespective of age, has been described as rectangular or trapezoidal. At the start of exhalation, the concentration of CO2 is initially zero (phase I) as the airway dead space
Capnographic Assessment of Ventilatory Patterns During Procedural Sedation and Analgesia
Capnography is the only single monitoring modality that provides airway, breathing, and circulation assessment.6 The presence of a normal waveform denotes that the airway is patent and that the patient is breathing. Normal etco2 (35 to 45 mm Hg), in the absence of obstructive lung disease, reflects adequate perfusion. Unlike pulse oximetry, the capnogram remains stable during patient motion and is reliable in low-perfusion states. Capnography is the earliest indicator of airway or respiratory
Conclusion
Capnography is a useful diagnostic monitoring tool for airway, breathing, and circulation assessment and rapid capnogram identification of procedural sedation and analgesia-related airway and respiratory adverse events. Further research is needed to better understand the clinical significance of changes in etco2 levels during procedural sedation and analgesia.
References (48)
- et al.
Procedural sedation and analgesia in children
Lancet.
(2006) Conscious sedation in the emergency department: the value of capnography and pulse oximetry
Ann Emerg Med.
(1992)- et al.
Expiratory carbon dioxide concentration curve: a test of pulmonary function
Dis Chest
(1962) - et al.
Utility of the expiratory capnogram in the assessment of bronchospasm
Ann Emerg Med.
(1996) - et al.
Comparison of arterial-end-tidal Pco2 difference and dead space/tidal volume ratio in respiratory failure
Chest
(1987) - et al.
Utility of monitoring capnography, pulse oximetry, and vital signs in the detection of airway mishaps: a hyperoxemic animal model
Am J Emerg Med.
(1998) - et al.
Automated graphic assessment of respiratory activity is superior to pulse oximetry and visual assessment for the detection of early respiratory depression during therapeutic upper endoscopy
Gastrointest Endosc.
(2002) - et al.
Perioperative hypoxia: the clinical spectrum and current oxygen monitoring methodology
Anesthesiol Clin North Am.
(2001) - et al.
An Atlas of Capnography
(1975) Capnometry and capnography: the anesthesia disaster early warning system
Semin Anesth.
(1986)
Capnography as a rapid assessment and triage tool for chemical terrorism
Pediatr Emerg Med.
The value of end-tidal CO2 monitoring when comparing three methods of procedural sedation for children undergoing painful procedures in the emergency department
Pediatr Emerg Care
End-tidal carbon dioxide monitoring during procedural sedation
Acad Emerg Med.
Bispectral EEG analysis of patients undergoing procedural sedation in the emergency department
Acad Emerg Med.
Randomized clinical trial of propofol versus methohexital for procedural sedation during fracture and dislocation reduction in the emergency department
Acad Emerg Med.
Does end-tidal carbon dioxide monitoring detect respiratory events prior to current sedation monitoring practices?
Acad Emerg Med.
Single-breath analysis of carbon dioxide concentration records
J Appl Physiol.
A Quick Guide to Capnography and Its Use in Differential Diagnosis
Mastering Infrared Capnography
Intraoperative events diagnosed by expired carbon dioxide monitoring in children
Can Anaesth Soc J.
Early detection of inadvertent oesophageal intubation: pulse oximetry vs. capnography
Acta Anaesthesiol Scand.
Comparison of end-tidal carbon dioxide, oxygen saturation and clinical signs for the detection of oesophageal intubation
Can J Anaesth.
Cited by (132)
Are respiratory rate counters really so bad? Throwing the baby out with the bath water
2019, EClinicalMedicineCapnography Detection Using Nasal Cannula Is Superior to Modified Nasal Hood in an Open Airway System: A Randomized Controlled Trial
2019, Journal of Oral and Maxillofacial SurgeryCitation Excerpt :The ASA first mandated the use of capnography for all operating room general anesthetics in 1999. After that time, there was a great deal of interest in exploring the technology's use for monitoring in procedural sedation and analgesia in gastroenterology endoscopy suites, emergency departments, and, to a lesser extent, OMS offices.1,2,5-25 Most of the primary literature on the topic was focused on the question of whether capnography provided a benefit over visual monitoring and pulse oximetry alone.
Procedural sedation and analgesia practices in the emergency centre
2019, African Journal of Emergency MedicineCitation Excerpt :Basic requirement for procedural sedation include; a high flow oxygen source, suction apparatus, airway management equipment, three-lead electrocardiography (ECG), pulse oximetry, non-invasive blood pressure (NIBP) monitoring, intravenous (IV) access, a defibrillator, appropriate drugs for resuscitation (including reversal agents) and adequate staffing [15]. Although capnography is useful [16,17], its current use is not routine [18,19]. Selection of the appropriate choice of drugs for procedural sedation is dependent on the type of procedure (non-painful procedures requiring immobilization, low-pain high anxiety procedures or highly painful procedures) as well as current patient physiology [5,15,20].
Supervising editor: Richard M. Levitan, MD
Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article, that might create any potential conflict of interest. The authors have stated that no such relationships exist. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement.
Available online January 12, 2007.
Reprints not available from the authors.
- 1
Dr. Krauss is a consultant for Oridion Medical, a capnography company, and holds 2 patents in the area of capnography.