High cognitive load in nurses is a common problem in the intensive care unit (ICU). However, it remains unclear what different types of cognitive load the ICU nurses have experienced during the implementation of delirium interventions.To describe the characteristics and explore the effect of implementing a delirium intervention on the cognitive load of nurses working in the ICU.A cluster-randomized controlled clinical trial was conducted. Six ICUs were randomized in a 1:1 ratio, and eligible nurses from these units provided either a delirium bundle intervention in addition to usual care (27 nurses) or usual care alone. An instrument was used to measure different types of cognitive load (MDT-CL), assessing intrinsic, extraneous and germane cognitive load. The repeated measures analysis of variance was used to detect between-group differences.Among these nurses, significant between-group differences were identified in terms of their overall (P < 0.001), intrinsic (P < 0.001) and extraneous (P < 0.001) cognitive load. There was no significant change observed in the germane cognitive load (P = 0.489) in the delirium intervention group.It is important to understand how the implementation of a delirium intervention affects different types of cognitive load in nurses, in order that tailored strategies can be applied to reduce cognitive load in ICU nurses.© 2023 John Wiley & Sons Australia, Ltd.