Should we use criteria or eyeballing to reject post-interruption tracings?

During the analysis of interrupter resistance (R(int))-measurements, most authors reject post-interruption tracings based on the shape of the pressure-time and flow-time curves. However, objective criteria for rejection are lacking. We aimed to formulate explicit rejection criteria that correspond to eyeballing the curve pattern (daily practice), in order to simplify the analysis. Inter-observer agreement within and between both methods was studied. Results obtained with the developed rejection criteria were compared to those of current practice (eyeballing) using 54 measurements (807 interruptions) of children with severe neurological impairment. Inter-observer agreement on rejection was similar using the criteria or eyeballing (85.6% vs. 82.8%). Using the criteria, more individual interruptions were rejected (43.4% vs. 29.8% using eyeballing), while discarding total measurements (<5 remaining interruptions) was similar (9.2% vs. 7.4% using eyeballing). Results using only the criteria for pressure-time curves were comparable to eyeballing. Outcome values were comparable between any of the used rejection methods and not rejecting at all. In this first detailed study on rejection of post-interruption tracings, explicit rejection criteria were developed. None of the rejection methods influenced the outcome value relevantly. However, rejection criteria can contribute to the standardization of the R(int) technique and simplify decision-making in daily practice.