CAPNOMETER TRANSPORT DELAY - MEASUREMENT AND CLINICAL IMPLICATIONS

The sidestream capnogram is delayed behind real time by transport dela y (TD; time to aspirate gas through the sampling tubing) and by the dy namic response (DR) of the measurement cuvette. In six capnometers, we measured TD and DR by plunging the end of the sample tubing into a fl ask containing CO2 and then digitally analyzing the capnogram. TD rang ed from 0.6 to 5.0 s and accounted for 89% or more of the total respon se time (TD + DR) of the capnometer. TD was generally not reported in the manufacturers' specifications, TD was further prolonged by low asp iration rates or by sampling tube extensions. During a series of quick breaths after endotracheal intubation, long TD can delay the appearan ce of CO2 and result in a false diagnosis of esophageal intubation. Al so, long TD can prolong DR, which can result in underestimation of end -tidal PCO2 during rapid ventilation in pediatric anesthesia.