How reliable is capnography?
- Thread starter willtcam
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In terms of sensitivity or specificity?
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That's sensitivity
The reason I ask is because in the real world, the accuracy of a capnograph depends on several factors, probably the most important of which is the patient exhaling a true full tidal volume breath. If they are breathing rapidly as people often do when they are in pain or anxious, you may not be getting a true "end tidal" waveform. The morphology can vary too, based on whether they are breathing solely out of their mouth or nose
All things being equal and working they way they are expected to, I think capnography is generally very reliable. But like any clinical tool, it is imperfect, and I think that like many assessment tools, it is probably more specific than it is sensitive. In other words, if you see a well-formed shark fin waveform, it is probably better evidence for the actual presence of bronchoconstriction (specificity) than lack of a shark fin is evidence of a lack of bronchoconstriction (sensitivity). Similar to the way that presence of ST elevation is generally reliable evidence for myocardial ischemia, whereas lack of ST elevation can't rule out myocardial ischemia.
Why do you ask?
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Disagreement on if a albuterol treatment would have been beneficial or not. Patient was an elderly lady with CHF, COPD that had been without her oxygen for an unknown amount of time. Patient complained of just shortness of breath but was very anxious and breathing about 50 Bpm. Patient's room air was low 70's but rose to patients normal (90%) within about 7 minutes on a nasal cannula. Patients lung sounds were clear and etco2 was 23-26 and wave form was normal. Patient was tachycardia around 130.
Gurby
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Cannula seems real bad for an O2 sat in the 70s breathing 50/min. Rather not sit around for 7 minutes waiting for it to come up.
TransportJockey
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Why are you giving albuterol to a patient with no indication for it?
SpecialK
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You don't need ETCO2 to tell you if somebody should be given salbutamol.
Salbutamol is a bronchodilator used to treat bronchoconstriction, thus do diagnose bronchoconstriction all you need is a stethoscope (provided you know where to listen and what for).
Salbutamol is a bronchodilator used to treat bronchoconstriction, thus do diagnose bronchoconstriction all you need is a stethoscope (provided you know where to listen and what for).