Evaluation of time courses of agreement between minutely obtained transcutaneous blood gas data and the gold standard arterial data from spontaneously breathing Asian adults, and various subgroup analyses

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. CONCLUSIONS: Although PtcCO(2) is useful, it cannot completely replace PaCO(2) because PCO(2) occasionally showed large bias. On the other hand, the prediction of PaO(2) using PtcO(2) was unrealistic in Asian adults. PtcCO(2) ≥ 50 mmHg for until 12 min can be used as a screening tool for severe hypercapnia with PaCO(2) > 50 mmHg.