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Evaluation of a non‐invasive method of assessing opioid induced respiratory depression

Opioid induced respiratory depression is potentially fatal. The aim of this study was to validate a monitoring system that could be used to assess respiratory depression in postoperative patients. The hypercapnic ventilatory response was estimated non‐invasively in 12 volunteers. In two steps, we tested a system which delivered carbon dioxide (CO2) challenges through a venturi mask, measuring changes in ventilation with an uncalibrated respiratory inductance plethysmograph (RIP). RIP and pneumotachograph measurements of ventilation, taken at the same time during a CO2 challenge, were similar; group mean (SD), pneumotachograph 13.9 (3.5) l.min−1.kPa−1, RIP 14.3 (2.9) l.min−1.kPa−1. Bland–Altmann analysis showed the variation between these two methods was ± 5 l.min−1.kPa−1 (2 SD). Second, we confirmed that the venturi mask is suitable for delivering CO2 challenges. Despite the variability in RIP measurements, a simple multimodal respiratory monitoring system could be developed that incorporates clinical observation and non‐invasive measurement of the ventilatory response to CO2.