Atypical upswing at initial part of phase III in capnograms due to technical cause

We sporadically experienced three paediatric cases of atypical upswing at the initial part of phase III in the capnograms via side‐stream capnometer immediately following endotracheal intubation and mechanical ventilation. No fault was found in the monitor or anaesthetic system including breathing circuits, carbon dioxide ( CO 2 ) sampling tube, water trap, and unidirectional valves. The upsurge of CO 2 disappeared with increasing the respiratory rate; however, it reappeared with decreasing the respiratory rate and vice versa. We experimentally reproduced the phenomenon of overshooting CO 2 measurement after the luer lock connection of the sample gas line at the water trap had been unscrewed a little bit.