Capnography

[Off Label]

Off Label can you please explain why you feel that nasal ETCO2 is not a diagnostic tool in the non intubated patient, but that it is in the intubated patient.

because it samples the gas via an airway that varies significantly from patient to patient. That airway variation affects the value that you're reading to the extent that the values become unreliable for diagnostic determinations.

In the intubated patient, the airway is reliably established and the sample is consistently taken from an unobstructed source which eliminates most if not all sample error. So, airway obstruction (diagnostic) acute fall in cardiac output (diagnostic), hypermetabolic states (diagnostic) as well as hypoventilation (monitoring), extubation (monitoring), mainstem intubation (monitoring) etc. are reliable.

Nasal sampling, by and large, is for monitoring purposes only... that is for presence or absence of a patent airway with respiratory effort and respiratory rate.

[rock_shoes]

because it samples the gas via an airway that varies significantly from patient to patient. That airway variation affects the value that you're reading to the extent that the values become unreliable for diagnostic determinations.

In the intubated patient, the airway is reliably established and the sample is consistently taken from an unobstructed source which eliminates most if not all sample error. So, airway obstruction (diagnostic) acute fall in cardiac output (diagnostic), hypermetabolic states (diagnostic) as well as hypoventilation (monitoring), extubation (monitoring), mainstem intubation (monitoring) etc. are reliable.

Nasal sampling, by and large, is for monitoring purposes only... that is for presence or absence of a patent airway with respiratory effort and respiratory rate.

The problems you mention are why it isn't reliable for absolute values. It's still useful for establishing a waveform, respiratory pattern, and even trending. If a patient's anatomy results in a false low for example, it will consistently do that. That means changes in values over time will still tell you if EtCO2 is increasing or decreasing. If you want actual blood values do an ABG.

[Spock]

These comments are great and prove that the folks that post on the City are really smart.  Off label may not realize the difference in the types of capnography and may not have the advantage of the sophisticated technology available today.  If I do a sedation case in the operating room, I have the patient on oxygen via a simple face mask and attach my ETCO2 tubing to the mask.  This gives me an indication of the patients respiratory pattern but the number is always low and has no real value other than tell me a quick glance that the patient is breathing.  You may ask why I don't just look at the patient and that is a good question.  I am frequently distracted by other things in the OR (the surgeon wants the table moved or some other BS) or the lights have been dimmed because of the procedure and I can't see the patient.  

The capnography we use in our ambulances around here use micro stream technology and the quantitative values given have true meaning.  Capnography is one more tool in your tool box and is just as important as your BP cuff, pulse oximeter and EKG monitor.  

Tube or not, ETCO2 is important for every patient with respiratory compromise.

May the tube be with you.

Spock

[1EMT-P]

When I first started in EMS we didn't have ETCO2 or Pulse Ox. I use both regularly in the field because they give me additional information. Micro stream technology is a wonderful tool!