Transcutaneous carbon dioxide measurements in anesthetized apneic patients with BMI > 35 kg/m²

Transcutaneous carbon dioxide measurement (TcCO₂) offers the ability to continuously and non-invasively monitor carbon dioxide (CO₂) tensions when end-tidal monitoring is not possible. The accuracy of TcCO₂ has not been established in anesthetized apneic patients with obesity. In this secondary publication, we present a methods comparison analysis of TcCO₂ with the gold standard arterial PCO₂, in adult patients with body mass index (BMI) > 35kg/m² who were randomized to receive high flow or low flow nasal oxygenation during post-induction apnea. Agreement between PaCO₂ and TcCO₂ 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/m². The mean (SD) PaCO₂ 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 PaCO₂ and TcCO₂ measures. For a short period of apnea, TcCO₂ showed inadequate agreement with PaCO₂ in patients with BMI > 35 kg/m². These techniques require comparison in a larger population, with more frequent sampling and over a longer timeframe, before TcCO₂ can be confidently recommended in this setting.