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Estimation of arterial carbon dioxide by end‐tidal and transcutaneous P CO 2 measurements in ventilated children
Author(s) -
Sivan Yakov,
Eldadah Maher K.,
Cheah Teikee,
Newth Christopher J. L.
Publication year - 1992
Publication title -
pediatric pulmonology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.866
H-Index - 106
eISSN - 1099-0496
pISSN - 8755-6863
DOI - 10.1002/ppul.1950120305
Subject(s) - medicine , perfusion , nuclear medicine , carbon dioxide , mechanical ventilation , cardiology , anesthesia , ecology , biology
Simultaneous measurements of arterial, end‐tidal, and transcutaneous carbon dioxide (Pa CO 2, Pet CO 2, Ptc CO 2, respectively) were obtained in 134 children receiving mechanical ventilation (ages, 2 days to 16 years; mean, 2.5 years). The mean ± SD Pet CO 2± bias (Pa CO 2− Pet CO 2) was 3.4 ± 6.6 mmHg. When the Pet CO 2bias was plotted against the Pa O 2/P AO 2ratio, a change in the scatter was obvious at about 0.3. The Pet CO 2bias for patients with Pa O 2/P AO 2under 0.3 was 7.8 ± 7.3 mmHg compared to 0 ± 3.4 in patients with Pa O 2/P AO 2above 0.3 ( P < 0.001). Pet CO 2differed significantly from Pa CO 2( P < 0.001) only for patients with Pa O 2/P AO 2under 0.3. The slope (Pa CO 2versus Pet CO 2) for these patients was 1.59, while the slope for patients with Pa O 2/P AO 2above 0.3 coincided with the line of identity (1.00). The mean ± SD Ptc CO 2bias (Pa CO 2− Ptc CO 2) was − 1.3 ± 7.2 mmHg. Skin perfusion was recorded at the area close to the transcutaneous CO 2 monitor electrode and was defined as normal when capillary refill was below 3 seconds. The Ptc CO 2bias for patients with normal skin perfusion was −0.2 ± 5.4 mmHg ( P = 0.73) compared to −4.1 ± 9.9 for patients with decreased skin perfusion ( P = 0.01). The slope of Ptc CO 2against Pa CO 2was closer to identity in patients with normal skin perfusion (1.17) than in patients where it was decreased (slope, 1.40). We suggest that Pa CO 2estimation by both Pet CO 2and Ptc CO 2is sufficiently precise and reliable for clinical use in critically ill children. Certain limitations stem from the nature of the techniques. Measurement of alveolar to arterial O 2 ratio may improve the precision of Pa CO 2estimation by capnography; assessment of skin perfusion is important in order to increase the accuracy of the transcutaneous method, especially in critically ill children.