Pre-apneic capnography waveform abnormalities during procedural sedation and analgesia
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ORIGINAL RESEARCH
Pre‑apneic capnography waveform abnormalities during procedural sedation and analgesia Aaron Conway1,2,6 · Peter Collins2 · Kristina Chang2 · Sebastian Mafeld3 · Joanna Sutherland4 · James Fingleton5 · Matteo Parotto3,7 Received: 7 June 2019 / Accepted: 22 September 2019 © Springer Nature B.V. 2019
Abstract Capnography monitoring is recommended for use during procedural sedation. This study examined associations between capnography waveform abnormalities and the onset of apnea. Capnography waveforms from a sample of 102 participants undergoing moderate procedural sedation with bolus doses of midazolam and fentanyl were analyzed using a mixed effects Cox model. Patients were at increased risk of apnea (classified as end-tidal carbon dioxide concentration of zero) while demonstrating a capnography waveform abnormality classified as hypopnea (more than 10% increase or decrease from baseline end-tidal carbon dioxide concentration) (Hazard Ratio 2.14; 95% CI 1.75 to 2.62). Risk of apnea was not increased during capnography waveform abnormalities classified as bradypnea (capnography-derived respiratory rate less than 8 breaths/min) (Hazard Ratio 0.64; 95% CI 0.33 to 1.25). These estimates were similar when apneic episodes were defined as only those that lasted more than 20 s duration. Deciphering which capnography waveform abnormalities should promote intervention (and therefore alarms to signal the event to clinicians) from those that do not is an essential step towards successful implementation of this technology into practice. Our results indicate that using information about the history of previous capnography waveform abnormalities may be a promising solution to assist prediction of apneic episodes. Keywords Conscious sedation · Capnography · Respiratory depression
1 Introduction
* Aaron Conway [email protected] 1
Lawrence S. Bloomberg Faculty of Nursing, University of Toronto, Toronto, Canada
2
Peter Munk Cardiac Centre, University Health Network, Toronto, Canada
3
Toronto General Hospital, University Health Network, Toronto, Canada
4
Department of Anaesthesia, Coffs Harbour Health Campus, Coffs Harbour, Australia
5
Medical Research Institute of New Zealand, Wellington, New Zealand
6
School of Nursing, Queensland University of Technology, Brisbane, Australia
7
Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada
The use of capnography for respiratory monitoring during procedural sedation and analgesia is recommended in guidance produced by anesthesiologist professional organisations for anesthesia in Canada, the United States and Europe [1–3]. Capnography waveforms display carbon dioxide ( CO2 ) concentrations in expired breath over time to show changes throughout the respiratory cycle. Abnormal capnography waveforms assist in the detection and diagnosis of specific conditions, such as partial airway obstruction and apnea. For example, significantly decreased capnography waveform amplitude (i.e. the height of the waveform
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