End tidal CO2 and procedural sedation

One hundred and thirty-two adults underwent propofol sedation in the emergency department and were randomised into a group in which treating physicians had access to the capnography and a blinded group in which they did not. All patients received supplemental oxygen (3 L/minute) and opioids greater than 30 minutes before. Propofol was dosed at 1.0 mg/kg, followed by 0.5 mg/kg as needed.

Hypoxia (defined as SpO2 less than 93%) was observed in 17 of 68 (25%) subjects with capnography and 27 of 64 (42%) with blinded capnography (p=.035; difference 17%; 95% confidence interval 1.3% to 33%). Capnography identified all cases of hypoxia before onset (sensitivity 100%; specificity 64%), with the median time from capnographic evidence of respiratory depression to hypoxia 60 seconds (range 5 to 240 seconds).

The journal comments: ‘this study provides compelling evidence that capnography can aid in the detection of respiratory depression and reduce hypoxia during procedural sedation.’

However in an accompanying article outlining a pro-con debate for introducing capnography as standard practice in ED procedural sedation, the point is made that the safety benefit purported in this and similar studies is decreased hypoxemia, according to thresholds ranging from 90% to 95%, lasting from 5 to 15 seconds. In the clinical context, many of these events are self-limiting or resolve with minimal interventions such as airway repositioning or supplemental oxygen, and other more clinically relevant outcomes are rarely examined (perhaps due to the rarity of genuinely adverse events in ED procedural sedation by emergency physicians).

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 Mar;55(3):258-64