Transcutaneous CO₂ Measurement in an Adult Long-Term Ventilation (LTV) Service

Background: Transcutaneous CO₂ (TcCO₂) measurement is widely used in the diagnosis and monitoring of ventilatory failure. Robust data on the success rates of measurement is scant. We aimed to discern the factors affecting the success rate of TcCO₂ measurement in a regional LTV service. Methods: Patients undergoing TcCO₂ measurement between October 2019 and January 2022 were identified retrospectively. Notes were analysed for basic demographics, indications for TcCO₂ measurement, measurement outcome, device used (Radiometer TCM5 or Sentec, based on availability), setup (self, carer, or clinician), inpatient or domiciliary study, and number of TcCO₂ measurement attempts occurred. Statistical comparisons were made by Fisher's exact test. Results: We identified 435 recording events on 288 patients, mean age of 53, and 56% were males. A total of 189 (66%) had a neuromuscular disorder (NMD). The commonest indications for TcCO₂ measurement were 'assessing ventilatory failure' (43%) in treatment-naïve patients and 'adequacy of ventilation therapy due to persistent symptoms' (26%) in those established on LTV. Over 80% of our recording events were applied by patients or their carers. Overall, TCM5 devices had statistically higher successful recording rates (197/268, 73.5%) than Sentec (100/165, 60.6%) [p = 0.0056]. In domiciliary studies, TCM5's success rate of 187/253 (73.9%) versus Sentec's 94/154 (61.0%) was significantly better [p = 0.0079]. The success rate of each measurement attempt ranged between 62.9 and 67.0%, with up to three attempts on each subject. Conclusions: Home TcCO₂ is helpful in managing those with respiratory failure. Repeating tests after initial failure of recording is worthwhile. There may be differences in performance across devices which warrants further study.