BACKGROUNDVariable rate intravenous insulin infusions (VRIIIs) are widely used to treat elevated blood glucose (BG) in adult inpatients who are severely ill and/or will miss more than one meal. VRIIIs can cause serious harm to the patient if used incorrectly. Recent safety initiatives have embraced the Resilient Health Care (RHC) approach to safety by understanding how VRIIIs are expected to be used (Work as Imagined, 'WAI') and how it is actually used in everyday clinical care (Work as Done, 'WAD').OBJECTIVESTo systematically compare WAI and WAD and analyse adaptations used in situ to develop a model explaining VRIII use.METHODSA qualitative observational study video-recording healthcare practitioners using VRIII. The video data were transcribed and inductively coded to develop a hierarchical task analysis (HTA) to represent WAD. This HTA was compared with a HTA previously developed to represent WAI. The comparison output was used to develop a model of VRIII use.RESULTSWhile many of the tasks in the WAD HTA were aligned with the tasks presented in the WAI HTA, some important ones did not. When misalignment was observed, permanent adaptations (e.g. signing as a witness for a changed VRIII's rate without independently verifying whether the new rate was appropriate) and temporary workarounds (e.g. not administering intermediate-acting insulin analogues although the intermediate-acting insulin prescription was not suspended) were the most frequently observed adaptations. The comparison between WAI and WAD assisted in developing a model of VRIII use. The model shed light on strategies used to imagine everyday work (e.g. incident reports, VRIII guidelines), how everyday work was accomplished (e.g. context-dependent adaptations) and how these contributed to both successful and unsuccessful outcomes.CONCLUSIONSThis study provided in-depth understanding of the tasks required while using VRIIIs, and responses and adaptations needed to achieve safer care in a complex environment.