Deep Breathing Improves End-Tidal Carbon Dioxide Monitoring of an Oxygen Nasal Cannula-Based Capnometry Device in Subjects Extubated After Abdominal Surgery.

Background: Capnometry detects hypoventilation earlier than pulse oximetry while supplemental oxygen is being administered. We compared the end-tidal CO (P ) measured using a newly developed oxygen nasal cannula with a CO-sampling port and the P in extubated subjects after abdominal surgery. We also investigated whether the difference between P and P is affected by resting, by spontaneous breathing with the mouth consciously closed, and by deep breathing with the mouth closed.

Methods: Adult post-abdominal surgery subjects admitted to the ICU were enrolled. After extubation, oxygen was supplied at 4 L/min using a capnometry-type oxygen cannula. The breathing frequency, P , and P were measured after 30 min of oxygen supplementation. P was continuously measured during rest, during breathing with the mouth consciously closed, and during deep breathing with the mouth closed. The difference between P and P during various breathing patterns was analyzed using the Bland-Altman method.

Results: Twenty subjects were included. The bias ± SD (limits of agreement) for breathing frequency measured by capnometry compared with those obtained by direct measurement was 0.4 ± 3.6 (-6.7 to 7.4). In P compared with P , the biases (limits of agreement) were 14.8 ± 8.2 (-1.3 to 30.9) at rest, 10.2 ± 6.4 (-2.3 to 22.7) with the mouth closed, and 7.7 ± 5.6 (-3.2 to 18.6) for deep breathing with the mouth closed. P determined using the capnometry device yielded unreliable and widely ranging values under various breathing patterns. However, deep breathing with the mouth closed decreased the difference between P and P , as compared with other breathing patterns.

Conclusions: P measurements under deep breathing with mouth closed with a capnometry-type oxygen cannula improved the prediction of the absolute value of P in extubated post-abdominal surgical subjects without respiratory dysfunction.