Fig. 3. Example of the effect of remifentanil staircase infusion against the background of a constant propofol infusion. (A ) Target plasma remifentanil concentration (TCP). (B ) Bispectral index. (C ) Measured inspired ventilation (Vi). Note that ventilation quickly reaches apneic values after the initiation of the remifentanil infusion. Next, breathing remains irregular with reduced breathing frequency and periods of cyclic breathing. To get an indication of the sequential breathing pattern, the breaths are connected by a gray line . (D ) Measured end-tidal carbon dioxide concentration (PETCO2).