RESUMO
BACKGROUND: Capnometry detects hypoventilation earlier than pulse oximetry while supplemental oxygen is being administered. We compared the end-tidal CO2 (PETCO2 ) measured using a newly developed oxygen nasal cannula with a CO2-sampling port and the PaCO2 in extubated subjects after abdominal surgery. We also investigated whether the difference between PaCO2 and PETCO2 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, PETCO2 , and PaCO2 were measured after 30 min of oxygen supplementation. PETCO2 was continuously measured during rest, during breathing with the mouth consciously closed, and during deep breathing with the mouth closed. The difference between PETCO2 and PaCO2 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 PETCO2 compared with PaCO2 , 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. PETCO2 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 PETCO2 and PaCO2 , as compared with other breathing patterns. CONCLUSIONS: PETCO2 measurements under deep breathing with mouth closed with a capnometry-type oxygen cannula improved the prediction of the absolute value of PaCO2 in extubated post-abdominal surgical subjects without respiratory dysfunction.
