Is continuous transcutaneous monitoring of P CO2(Tc P CO2) over 8 h reliable in adults?

Abstract

Monitoring of non-invasive ventilation (NIV) in a non-intensive care unit (non-ICU) setting requires a method of evaluating nocturnal P aCO2, such as transcutaneous CO2monitoring (Tc P CO2). However, changing the probe site after 4 h and recalibrating (as recommended) is time-consuming and impractical. Continuous (8-h) Tc P CO2monitoring at a lower electrode temperature (43°C) in this setting has never been formally studied.Patients under intermittent NIV were studied (n=28, aged 69±9 years, P aO2: 71±13 mmHg, P aCO2: 49±9 mmHg). After calibration and stabilization of TcP CO2(Radiometer®Tina TCM3 capnograph), arterial blood gases (ABG) were measured and compared with transcutaneous readings. In 10 patients who underwent continuous 8-h Tc P CO2recording, ABGs were also measured after 4 and 8 h.The correlation between Tc P CO2and P aCO2was highly significant (r2=0·92, P<0·0001). Mean (Tc P CO2–P aCO2) gradient (bias) was: −2·8±3·8 mmHg; limits of agreement were: (−10·4; +4·8 mmHg). Tc P CO2–P aCO2gradient was lowest (i.e. within-bias±2 mmHg) between 40 and 54 mmHg, increasing below and above these values. Over 8 h, no significant drift of the Tc P CO2signal occurred (ANOVA). No discomfort or skin lesion was noted.In conclusion, with an electrode temperature of 43°C, 8-h continuous monitoring of Tc P CO2was well tolerated, without any local side-effects or significant drift of Tc P CO2signal; when compared to previous reports, lowering the electrode temperature did not decrease performance for CO2monitoring.