ETCO2 and Monitoring Sedated Patients
The January 2007 issue of the Annals of Emergency Medicine has a number of articles about sedation, most notably a fine article by capnography seer Baruch Krauss called Capnography for Procedural Sedation and Analgesia in the Emergency Department. It is an excellent discussion of the utilty, literature and history of capnography to monitor for adverse respiratory events.
Also in the January issue is a study, Capnography and depth of sedation during propofol sedation in children, which again shows capnography"detects most airway and respiratory events leading to intervention before clinical examination or pulse oximetry."
Research Advances in Procedural Sedation and Analgesia by Dr. Steven Green, is an editorial from the same issue of Annals of Emergency Medicine.
Here are two brief excerpts:
"It now seems beyond reasonable dispute that most sedation-related airway and respiratory adverse events begin with abnormalities in ventilation that are detectable by capnography and then only latter evolve into the typical clinical manifestations of respiratory depression, apnea, or airway obstruction. Oxygen desaturation is often the last sign of complication. particuarly when supplemental oxygen has been administered..."
"The evidence suggests that supplemental oxygen cannot be considered mandatory during procedural sedation and analgesia and that the peril of disabling the warning capacity of pulse oximetry with this prophylaxis is real. Many readers will have already seen the obvious solution: the addition of capnography. Capnography accurately monitors ventilatory status regardless of supplemental oxygen administration and thus can serve as early warning for ventilatory compromise regardless of oxygen preference."
Microstream capnography improves patient monitoring during moderate sedation: a randomized, controlled trial.
Pediatrics. 2006 Jun;117(6):e1170-8.
CONCLUSIONS: The results of this controlled effectiveness trial support routine use of microstream capnography to detect alveolar hypoventilation and reduce hypoxemia during procedural sedation in children. In addition, capnography allowed early detection of arterial oxygen desaturation because of alveolar hypoventilation in the presence of supplemental oxygen. The current standard of care for monitoring all patients receiving sedation relies overtly on pulse oximetry, which does not measure ventilation. Most medical societies and regulatory organizations consider moderate sedation to be safe but also acknowledge serious associated risks, including suboptimal ventilation, airway obstruction, apnea, hypoxemia, hypoxia, and cardiopulmonary arrest. The results of this controlled trial suggest that microstream capnography improves the current standard of care for monitoring sedated children by allowing early detection of respiratory compromise, prompting intervention to minimize hypoxemia. Integrating capnography into patient monitoring protocols may ultimately improve the safety of nonintubated patients receiving moderate sedation.
Bottom Line for EMS:
Capnography provides early warning of respiratory compromise.
Supplemental oxygen impairs detection of hypoventilation by pulse oximetry.
Chest. 2004 Nov;126(5):1552-8.
CONCLUSION: Hypoventilation can be detected reliably by pulse oximetry only when patients breathe room air. In patients with spontaneous ventilation, supplemental oxygen often masked the ability to detect abnormalities in respiratory function in the PACU. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilatory abnormalities, but only in the absence of supplemental inspired oxygen.
Bottom Line for EMS:
Without capnography, supplemental 02 can obscure impending respiratory problems.
Does end-tidal carbon dioxide monitoring detect respiratory events prior to current sedation monitoring practices?
Burton JH, Harrah JD, Germann CA, Dillon DC. Acad Emerg Med. 2006 May;13(5):500-4.
This was a study of 60 patients undergoing sedation. There were abnormal findings in 36 encounters. 17 patients had acute respiratory events (apnea or hypoventilation). ETCO2 documented changes in 14 acute events before changes in SP02 or observed changes in respiratory rate.
“End-tidal carbon dioxide monitoring of patients undergoing PSA detected many clinically significant acute respiratory events before standard ED monitoring practice did so. The majority of acute respiratory events noted in this trial occurred before changes in SP02 or observed hypoventilation and apnea.”
Bottom Line for EMS: All sedated patients should receive ETCO2 monitoring instead of pulse oximetry alone.