Polysubstance use (PSU), particularly opioid-involved and stimulant-involved PSU, is a growing issue in the USA. PSU increases the risk of negative health consequences, including infectious diseases, worsening physical and mental health conditions, and overdose-related deaths. These consequences occur in the context of varying health risk behaviours, substance-related preferences, and treatment engagements among people with PSU. To inform improvements in prevention, harm reduction, and substance use disorder (SUD) treatment, additional research is needed to comprehensively understand the current context and drivers of PSU preferences, motivations, and behaviours.

Herein, we describe the protocol for a prospective cohort study designed to capture detailed patterns, profiles, and trajectories of PSU, with the aim of comprehensively examining the drivers of PSU behaviours and SUD treatment utilisation. Adults (ages 18–75; n=400) who engage in PSU will be recruited from healthcare institutions, an established participant database maintained by an adjacent SUD research team, and online advertisements. Study assessments will capture dynamic patterns, choice preferences, and motivators of PSU via behavioural economic (BE) measures, detailed Timeline Follow-Back (TLFB) interviews, and self-administered surveys. The assessment timeline will include a baseline survey and TLFB interview, weekly TLFB interviews for 4 weeks post-baseline, and follow-up surveys and TLFB interviews at 4-, 8-, and 12-months post-baseline.

The study is funded through the National Institutes of Health Helping to End Addiction Long-term (HEAL) initiative and was approved by the University of Michigan Medical Institutional Review Board. Findings will be disseminated to academic, clinical, and community partners through the Michigan Innovations in Addiction Care through Research and Education programme. Results from this study will inform actionable and practical insights relevant to the delivery of personalised care in the context of PSU.

Peripheral arterial disease (PAD) commonly coexists with chronic kidney disease (CKD). Patients with symptomatic PAD often require endovascular revascularisation to relieve pain or salvage limbs. However, the iodinated intra-arterial contrast routinely used in these procedures is nephrotoxic, placing patients with CKD at increased risk of acute kidney injury (AKI) and long-term renal decline. Carbon dioxide (CO₂) delivered via automated injection is a potential alternative imaging contrast medium. This trial will evaluate whether using CO₂ instead of iodinated contrast reduces the risk of AKI and short-term renal function decline in this high-risk group.

This is a multicentre, open-label, prospective randomised controlled trial across six secondary-care National Health Service (NHS) vascular surgery centres. A total of 174 patients with PAD and CKD undergoing endovascular intervention will be randomised 1:1 to receive iodinated contrast (standard of care) or CO₂ via automated injector (Angiodroid). All perioperative care will follow local NHS protocols.

The primary outcome is log serum creatinine at 2, 30 and 90 days postprocedure. Key secondary outcomes include: incidence and severity of AKI within 48 hours postprocedure, major adverse kidney events (death, dialysis or >25% estimated glomerular filtration rate decline) by 90 days, inpatient length of stay, procedural pain, quality of life, procedural success, reinterventions, acceptability and feasibility (patient/practitioner questionnaires) of using CO₂, and cost-effectiveness (healthcare resource use analysis). A mixed-methods process evaluation will be undertaken with patients and clinicians.

The trial has been approved by an NHS ethical review committee (24/WA/0332) and patients have been involved in trial design. Findings will be disseminated to participants, clinicians and the wider public through patient groups, lay summaries, social media, conferences, peer-reviewed journals and NHS policy channels.

ISRCTN23564393.