A capnograph device includes a carbon dioxide measurement component (20) configured to measure respiratory carbon dioxide level, and an electronic processor (30) programmed to generate a capnogram signal (40) and compute an end-tidal carbon dioxide (etCO2) signal (50) by performing a sliding window maximum operation (42, 44) on the capnograph signal. In some embodiments the sliding window maximum operation employs a sliding time window (W) whose duration (Tw) is at least 30 seconds. A smoothing filter may be applied to the capnograph signal before performing the sliding window maximum operation, and/or a smoothing filter (52) may be applied after the sliding window maximum operation to produce a smoothed etCO2 signal (54). The capnograph device may be a sidestream capnograph device (10) or a mainstream capnograph device.
