Capnography to Augment ED Procedural Sedation
August 2010
Capnography to Augment ED Procedural Sedation
Search Strategy: You quickly (< 1 minute) conduct a PUBMED search for three terms “procedural sedation” (523 citations), “emergency medicine” (51223 citations), and “capnography” (1195 citations) and then combine the three searches yielding 11 citations which contain the references below. To reproduce this search strategy see http://tinyurl.com/2vl594a. An alternative search strategy using two additional MESH headings can be found at http://tinyurl.com/23osuk7.
As you polish off the documentation on your last five patients, the nurse for the closed femur fracture in Room 26 asks if you are ready for the pending reduction. Orthopedic surgery is patiently waiting and the nurse has the ketamine and Propofol that you requested at the bedside. Informed consent is obtained and as you pause for the Joint Commission recommended pre-procedural “time-out” to mark the correct extremity for reduction and ensure that optimal patient safety conditions have been attained for this particular case – you note a problem. The patient is not on capnography to monitor expiratory carbon dioxide (CO2) levels. As per the Washington University-Barnes Jewish Hospital-St. Louis Children’s Hospital Stop-the-Line policy, you conscientiously halt the procedure before any sedation is administered and ask the nurse why capnography has not been initiated. You are told that the ED’s only functional CO2 detector is now broken (the other two have been missing for months).
You have three choices now. Postpone the urgent reduction until the capnometer can be found, defer the reduction to the operating room setting where capnometry is available, or proceed with procedural sedation without the benefit of CO2 monitoring. As you contemplate the options, you search the evidence to support capnometry for ED-based procedural sedation.
PICO Question
Population: Emergency Department patients requiring procedural sedation
Intervention: End-tidal CO2 monitoring + routine procedural sedation care
Comparison: Routine procedural sedation care
Outcome: Hypoxia, bradycardia, respiratory depression with intervention, hypotension, sedation-related mortality
Years
Second years: End-tidal carbon dioxide monitoring during procedural sedation, Acad Emerg Med 2002; 9: 275-280. (http://pmid.us/11927449)
Articles
Article 1: Microstream Capnography Improves Patient Monitoring During Moderate Sedation: A Randomized, Controlled Trial, Pediatrics 2006;117:e1170-e1178
ANSWER KEY
Article 2: End-tidal Carbon Dioxide Monitoring during Procedural Sedation, Acad Emerg 2002; 9:275-80
ANSWER KEY
Article 3: Does End-tidal Carbon Dioxide Monitoring Detect Respiratory Events Prior to Current Sedation Monitoring Practices, Acad Emerg Med 2006; 13:500-504
ANSWER KEY
Article 4: Does End Tidal CO2 Monitoring During Emergency Department Procedural Sedation and Analgesia With Propofol Decrease the Incidence of Hypoxic Events? A Randomized, Controlled Trial, Ann Emerg Med 2010; 55:258-264
ANSWER KEY
Bottom Line
Providing sedation and analgesia during painful procedures is the standard of care in 21st Century Emergency Medicine. Procedural sedation/Analgesia (PSA) is the technique of administering sedatives or dissociative agents, with or without analgesics, to induce a state that allows the patient to tolerate unpleasant procedures while maintaining cardiorespiratory function. Potential complications of PSA include hypoventilation, aspiration, and respiratory failure with hypoxic brain injury. Fortunately, EM-based PSA adverse events are rare (Peña1999 , Pitetti 2003), and serious events are exceedingly rare. Nonetheless, the Joint Commission has increasingly focused on the safety of PSA in a variety of operative and non-operative settings.
ETCO2 monitoring may seem like expensive technology looking for a medical application. After all, if a tree falls in the forest, but nobody is there to hear it – does it make a noise? Similarly, if hypoventilation or transient hypoxia occur without detectable sequelae, does it have sufficient clinical importance to merit the time & expense to bring capnography to your ED?
Capnography is the non-invasive measurement of the partial pressure of carbon dioxide in exhaled breath and a capnometer displays the numeric value for ETCO2. Because hypoventilation always precedes hypoxia during PSA, either due to airway obstruction or diminished respiratory drive, ETCO2 monitoring provides an early warning signal permitting time to intervene before the onset of hypoxia. Capnography was developed in the 1940’s and was first described by Dr. Art Sanders in the emergency medicine literature in the 1980’s. Some have hypothesized a role of ETCO2 monitoring to rapidly assess gastroenteritis or chemical-weapons related acidosis, non-invasive positive pressure ventilation success, pulmonary embolism risk stratification or to confirm endotracheal tube positioning during transports. Observational data have suggested that monitoring of ETCO2 during ED PSA detects respiratory depression significantly faster than pulse oximetry alone (Miner 2002, Burton 2006, Deitch 2008), but randomized trials have not previously been performed. While the ACEP Clinical Policy for PSA suggests one “consider capnometry to provide additional information regarding early identification of hypoventilation,” Anesthesiology guidelines for non-Anesthesiologists suggest “…monitoring of exhaled carbon dioxide should be considered for all patients receiving deep sedation and for patients whose ventilation cannot be directly observed during moderate sedation.” In anesthesia, ETCO2 monitoring has been standard of care in the operating room for over 25 years. The current study provides the first objective evidence in ED settings that ETCO2 monitoring may improve patient safety during PSA.
One-third of patients at one urban academic ED undergoing Propofol procedural sedation experience a hypoxic event (oxygen saturation £ 93%) and Capnostream 20™ ETCO2 monitoring significantly predicts the development of hypoxia with a Number Needed to Treat (NNT) of 6 and up to 4-minutes advanced notice compared with pulse oximetry or clinical observation alone.
| Table | ||||
|---|---|---|---|---|
| Capnography (%) | No Capnography (%) | Absolute Risk Reduction (95% CI) | NNT (95% CI) | |
| Hypoxia | 17/68 (2%) | 27/64 (42%) | 17% | 6 (3-91) |
| No Hypoxia | 51/68 (75%) | 37/64 (58%) |
The investigators do not provide significant demographic descriptors for their patient population such as the proportion with known or suspected obstructive sleep apnea or measurements of co-morbid illness burden, acute illness severity or hospital length-of-stay. Furthermore, in a tight-economy with increasing declarations for fiscal constraint, ED leaders recognize that the Capnostream 20™ retails at $4950 per unit raising the following questions
- What is the value of detecting a respiratory event up to 4-minutes before clinical intuition or oximetry monitoring will currently provide?
- What is the Patient Oriented Outcome that Matters (POEM) of a 20-second episode of hypoxia?
- How much would a lawsuit cost if a preventable PSA-related brain injury, or death, occurred while NOT using ETCO2 monitoring?
Healthy skepticism dictates that the worldly-wise, physician-scientist be neither the first nor the last to adopt a new diagnostic/therapeutic innovation. Pro and con arguments can and have been forwarded to support and refute ETCO2 monitoring. This is a single trial that does not demonstrate any patient-oriented outcomes. Yet, EBM encourages physician-scientists to use all appropriate data sources to inform best practices. The weight of observational data and this single controlled trial suggest a theoretical benefit for ED PSA patients, which further trials and cost-benefit analyses will hopefully elucidate. In the meantime, your charge nurse locates a functional capnography unit and you proceed with your reduction uneventfully.