Transcutaneous carbon dioxide measurements in anesthetized apneic patients with BMI > 35 kg/m.

Transcutaneous carbon dioxide measurement (TcCO) offers the ability to continuously and non-invasively monitor carbon dioxide (CO) tensions when end-tidal monitoring is not possible. The accuracy of TcCO has not been established in anesthetized apneic patients with obesity. In this secondary publication, we present a methods comparison analysis of TcCO with the gold standard arterial PCO, in adult patients with body mass index (BMI) > 35kg/m who were randomized to receive high flow or low flow nasal oxygenation during post-induction apnea. Agreement between PaCO and TcCO at baseline, the start of apnea and the end of apnea were assessed using a non-parametric difference plot. Forty-two participants had a median (IQR) BMI of 52 (40-58.5) kg/m. The mean (SD) PaCO was 33.9 (4.0) mmHg at baseline and 51.4 (7.5) mmHg at the end of apnea. The bias was the greatest at the end of apnea median (95% CI, 95% limits of agreement) 1.90 mmHg (-2.64 to 6.44, -7.10 to 22.90). Findings did not suggest significant systematic differences between the PaCO and TcCO measures. For a short period of apnea, TcCO showed inadequate agreement with PaCO in patients with BMI > 35 kg/m. These techniques require comparison in a larger population, with more frequent sampling and over a longer timeframe, before TcCO can be confidently recommended in this setting.