Introduction <p>Surgery is a complex intervention, so it is important to establish standards for both the standard and ‘novel’ procedures in randomized controlled trials (RCTs) that demonstrate that interventions are delivered as intended to fully understand and explain trial results. This study set out to identify and agree the key steps of a surgical intervention to be tested in the ‘near infrared fluorescent imaging in thyroid surgery’ (NIFTy) RCT to inform development of the surgical protocol, and trial materials.</p> Method <p>Qualitative case studies of surgeries were undertaken prior to undertaking an RCT to evaluate the potential of a device to reduce post-surgical hypoparathyroidism. Each case study involved non-participant observation, video capture of total and completion thyroidectomies, and interviews with surgeons. A typology of operative steps was constructed. Two surveys were undertaken (1) to identify current practice around parathyroid identification; and (2) to determine surgeon views on the surgical steps. An international expert panel of six clinicians met to review findings and agree on the surgical steps (mandatory/optional) for operations in the RCT, including timing for use of fluorescence and the data items to be collected.</p> Results <p>Ten case studies were undertaken. Video, observation and interview data found differences in surgical approach were driven only by pathology. A typology detailing the surgical steps and points where imaging could be used was developed. Sixty-four surgeons responded to survey 1; three-quarters always looked for parathyroid glands when operating. Forty surgeons responded to survey 2; capsular dissection of the thyroid lobe, preservation of parathyroid pedicle, and clinical assessment were important for parathyroid preservation. The expert panel agreed the key surgical components. These informed key data collection in NIFTy. Two specific surgical steps were strongly recommended and three mandated.</p> Conclusion <p>Qualitative research in the operating theatre, prior to RCT allowed the identification of key components of the surgical intervention. The surveys and expert panel provided certainty about the acceptability of the surgical protocol and identified the core data to collect to evidence surgical decision making prior to embarking on the RCT. This qualitative process achieved clinical buy-in, improved trial conduct and allowed full explanation of the subsequent trial results.</p> Trial registration <p>ISRCTN59074092.&#xa0;Registration date: 07/03/2022.</p>