Evaluation of a non-invasive method of assessing opioid induced respiratory depression.
Pattinson KT., Bowes M., Wise RG., Parkes MJ., Morrell MJ.
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 (CO(2)) 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 CO(2) challenge, were similar; group mean (SD), pneumotachograph 13.9 (3.5) l x min(-1) x kPa(-1), RIP 14.3 (2.9) l x min(-1) x kPa(-1). Bland-Altmann analysis showed the variation between these two methods was +/- 5 l x min(-1) x kPa(-1) (2 SD). Second, we confirmed that the venturi mask is suitable for delivering CO(2) 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 CO(2).