The positioning above produced the following wave form:
Due to the patient's mouth breathing, the cannula was then repositioned.
And the new wave form:
Thanks to bdmedic for submitting.
February 25, 2007 - Cannula Positioning
Today I had an elderly patient with CHF. The initial end tidal was 8, but quickly jumped to 30 when I repositioned the cannula because the patient was a mouth breather. I put a non rebreather on and the number went down to 20. Several times during the call, the numbers moved, and each time when I repositioned the device the numbers came back to near 30.
(The other day I heard a medic patch in with a patient with stable vital signs but an ETCO2 of 9. Positioning of the cannula was probably the issue.)
The point of all this is that positioning the cannula is very important if your reading doesn’t seem right. It can be affected by a patient’s unique anatomy, by the patient’s method and manner of breathing and by their anxiousness during transport, which can shift the cannula position. (The position will affect not only the ETCO2 number but the RR number.) This patient had an initial RR of 48, which gradually came down to 38 due to some NTG SL, which seemed to help the breathing. The ETCO2 rose to 32, and settled there, which I was happy with considering. I stayed alert to make certain the RR wasn’t declining due to the patient growing more tired. Her effort in breathing seemed a bit more relaxed.
This all goes along with what I wrote below about normal values. You can't just always accept the numbers at face value and compare them to traditional norms.
February 20, 2007 - Normal Values
The normal values for ETCO2 are listed at 35-45 mm Hg. I have read that they are really 33-43 due to the possible gradient between arterial Co2 and ETCo2. What is normal anyway? Normal HR is 60-80, Bp 110/70-130/80. It all depends on the person obviously. But as I don't get too concerned with a HR of 88 or a BP of 140/90, I think you have to take the same approach with ETCO2. Most of my patients have ETCO2 in the 28-35 range, it seems. It is an emergency situation and usually they are a little short of breath -- that accounts for it. Sometimes the 02 dilutes it a little. I guess all I'm saying is normal is different for everyone to a point, and that in the emergency setting, it is not uncommon to have many people outside the normal range. I am most concerned with extreme readings that are trending worse.
Check out this letter exchange in the March Respiratory Care concerning the accuracy of the nasal ETCO2 cannulas. It brings up some concerns I have had about the accuracy of the nasal cannula versus the intubated filterline.