Respiratory monitoring is important after surgery to prevent pulmonary complications. End-tidal carbon dioxide (Petco2) measurement by capnometry is an indirect and noninvasive measurement of Pco2 in blood and is accepted and recognized in critical care.


To determine the correlation and level of agreement between Petco2 and Paco2 in spontaneously breathing children after cardiac surgery and to determine whether Petco2 measured by using tidal volume (Vt-Petco2) or vital capacity (VC-Petco2) shows more or less significant correlation with Paco2.


Vt-Petco2 and VC-Petco2 by capnometry and Paco2 by blood gas analysis were measured once a day after tracheal extubation. The determination coefficient and degree of bias between the methods were assessed in children with and without supplemental oxygen.


A total of 172 Vt-Petco2, VC-Petco2, and Paco2 values from 48 children were analyzed. The overall coefficients of determination were 0.84 (P < .001) for Vt-Petco2 and Paco2 and 0.62 (P = .02) for VC-Petco2 and Paco2. The mean gradient for Paco2 to Petco2 in all groups increased with the increase in supplemental oxygen; the gradient was significantly larger in the groups given 2 to 5 L of oxygen per minute.


In spontaneously breathing children, Vt-Petco2 provided a more accurate estimate of Paco2 than did VC-Petco2, especially in children given little or no supplemental oxygen. The difference between the methods was significantly larger in the groups given 2 to 5 L of oxygen per minute.

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