Thinks to twitter buddies @keeweedoc and @paramedickiwi for inspiring me to write this.
Cardiac arrest is one of the more common indications for endotracheal intubation, indeed for many health professionals, like paramedics in jurisdictions without prehospital RSI, it may be essentially the only indication. Over the last few years, the use of continuous, or waveform end-tidal CO2 monitoring has pretty much become ubiquitous, both inside the hospital and out. I think you would struggle to find an ambulance in a first world country that doesn’t have a defibrillator capable of waveform ETCO2.
ETCO2 is now considered a standard of care both for confirming correct ET tube placement, and for guiding ventilation to appropriate ETCO2 targets once intubated. But there is still some doubt amongst practitioners as to the utility of ETCO2 in confirming tracheal intubation in cardiac arrest.
I was taught many years ago by an intensivist (who I have a great deal of respect for, I must add) that there is no role for ETCO2 in confirming tube placement in cardiac arrest. Yes, ETCO2 can be used once the tube is in to assess the adequacy of chest compressions and to prognosticate, but the ETCO2 will be too low for it to reliably tell you if you have but the tube in the right hole. The theory is that in a low cardiac output state, so little CO2 will be delivered to the lungs that you will get lots of false negatives and pull out tubes that were in the trachea to begin with. Other (unreliable) methods of tube confirmation are advocated, like auscultation and (o)esophageal intubation detectors (EIDs, eerily similar to IEDs, which you shouldn’t use to confirm intubation).
Over the last couple of years though, the teaching has changed. Large-ish studies have shown that in fact ETCO2 can be used to confirm tube placement in cardiac arrest and of course NAP4 has shown that not using ETCO2 can lead to disastrous outcomes. This has changed my practice and even led me to demand change in a hospital that I worked in and get a defibrillator capable of ETCO2 measurement brought to every cardiac arrest. But the myth is still out there. I’ve attached a reference to a letter in Anaesthesia from last year (I’m very much a believer in level 5 evidence) which, I think, will render the myth well and truly busted after reading. Its by arguably 2 of the biggest names in anaesthesia and ICU, Tim Cook and Jerry Nolan. It’s superbly written, with quotes like;
“When intubation is undertaken within 30 min of cardiac arrest, failure to detect exhaled CO2 using wave- form capnography during CPR indicates that oesophageal intubation is very likely. ”
“In the better of the two studies supporting the use of capnography in cardiac arrest, there was 100% sensitivity and 100% specificity in identifying correct tracheal tube placement among 246 cardiac arrest patients (including four oesophageal tube placements) ”
“In the setting of CPR, all caregivers should assume a flat capnograph is due to a misplaced or blocked tube. The message is simple: do not assume that failure to detect CO2 is because of cardiac arrest. ”
I couldn’t have put it better myself.
Cook, T. M. and Nolan, J. P. (2011), Use of capnography to confirm correct tracheal intubation during cardiac arrest. Anaesthesia, 66: 1183–1184. doi: 10.1111/j.1365-2044.2011.06964.x