Background: Usual clinical practice for arterial blood gas analysis (BGA) in conscious patients involves a one-time arterial puncture to be performed after a resting period of 20-30 min. The aim of this study was to evaluate the use of transcutaneous BGA for estimating this gold standard arterial BGA. Methods: Spontaneously breathing Asian adults (healthy volunteers and respiratory patients) were enrolled (n = 295). Transcutaneous PO 2 (PtcO 2) and PCO 2 (PtcCO 2) were monitored using a transcutaneous monitor (TCM4, Radiometer Medical AsP, Denmark) with sensors placed on the chest, forearm, earlobe or forehead. Transcutaneous BGA at 1-min intervals was compared with arterial BGA at 30 min. Reasonable steps to find severe hypercapnia with PaCO 2 > 50 mmHg were evaluated. Results: Sensors on the chest and forearm were equally preferred and used because of small biases (n = 272). The average PCO 2 bias was close to 0 mmHg at 4 min, and was almost constant (4-5 mmHg) with PtcCO 2 being higher than PaCO 2 at ≥8 min. The limit of agreement for PCO 2 narrowed over time: ± 13.6 mmHg at 4 min, ± 7.5 mmHg at 12-13 min, and ± 6.3 mmHg at 30 min. The limit of agreement for PO 2 also narrowed over time (± 23.1 mmHg at 30 min). Subgroup analyses showed that the PaCO 2 and PaO 2 levels, gender, and younger age significantly affected the biases. All hypercapnia subjects with PaCO 2 > 50 mmHg (n = 13) showed PtcCO 2 ≥ 50 mmHg for until 12 min.
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