Flow-through versus sidestream capnometry for detection of end tidal carbon dioxide in the sedated patient.
BACKGROUND
End tidal carbon dioxide (ETCO(2)) in non-intubated patients can be monitored using either sidestream or flow-through capnometry [Yamamori et al., J Clin Monit Comput 22(3):209-220, 2008]. The hypothesis of this validation study is that, flow-through capnometry will yield a more accurate estimate of ETCO(2) than sidestream capnometry when evaluated in a bench study during low tidal volumes and high oxygen administration via nasal cannula. Secondarily, when ETCO(2) from each is compared to arterial CO(2) (PaCO(2)) during a study in which healthy, non-intubated volunteers are tested under normocapnic, hypocapnic and hypercapnic conditions, the flow-through capnometer will resemble PaCO(2) more closely than the sidestream capnometer. This will be especially true during periods of lower minute ventilation and high oxygen flow rates via mask in non-intubated, remifentanil sedated, healthy volunteers whose physiologic deadspace is small.


METHODS
The performance of a flow-through (cap-ONE, Nihon Kohden, Tokyo, Japan) and a sidestream (Microcap Smart CapnoLine Plus, Oridion Inc., Needham, MA) capnometer were compared in a bench study and a volunteer trial. A bench study evaluated ETCO(2) accuracy using waveforms generated via mechanical lungs during low tidal volumes and high oxygen flow rates. A volunteer study compared the ETCO(2) for each capnometer against PaCO(2) during sedation in which 8 l O(2) was delivered via mask rather than the nasal cannula.


RESULTS
In the bench study, the flow-through capnometer gave slightly higher values of ETCO(2) during high-flow oxygen and no discernable differences during variable tidal volumes. Bland and Altman plots comparing ETCO(2) to PaCO(2) showed essentially equal performance between the two capnometers in the volunteers.


CONCLUSIONS
Within a wide limit of agreement between the volunteer and bench study, flow-through and sidestream capnometry performed equally well during bench testing and in non-intubated, sedated patients.
Sakata
Derek J
DJ
Department of Anesthesiology, University of Utah, 30 North 1900 East, 3C444 SOM, Salt Lake City, UT 84132, USA. derek.sakata@hsc.utah.edu
Matsubara
Isao
I
Gopalakrishnan
Nishant A
NA
Westenskow
Dwayne R
DR
White
Julia L
JL
Yamamori
Shinji
S
Egan
Talmage D
TD
Pace
Nathan L
NL
D000293:Adolescent; D000328:Adult; D019296:Capnography / Q000295:instrumentation / Q000379:methods*; D002245:Carbon Dioxide / Q000378:metabolism*; D003199:Computer Systems; D045853:Exhalation / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D016857:Hypocapnia / Q000378:metabolism; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods; D010100:Oxygen / Q000378:metabolism; D010880:Piperidines / Q000494:pharmacology; D000077208:Remifentanil; D014474:Unconsciousness / Q000378:metabolism*; D055815:Young Adult
D006993:Hypnotics and Sedatives; D010880:Piperidines; D002245:Carbon Dioxide; D000077208:Remifentanil; D010100:Oxygen