Introduction A cSDH is an encapsulated collection of fluid and blood degradation products in the subdural space. It is increasingly common, affecting older people and those living with frailty. Currently, no guidance exists to define optimal care from onset of symptoms through to recovery. This paper presents the first consensus-built recommendations for best practice in the care of cSDH, co-designed to support each stage of the patient pathway. Methods Guideline development was led by a multidisciplinary Steering Committee with representation from diverse clinical groups, professional associations, patients, and carers. Literature searching to identify relevant evidence was guided by core clinical questions formulated through facilitated discussion with specially convened working groups. A modified Delphi exercise was undertaken to build consensus on draft statements for inclusion in the guideline using survey methodology and an in-person meeting. The proposed guideline was subsequently endorsed by the Society for British Neurological Surgeons, Neuroanaesthesia and Critical Care Society, Association of Anaesthetists, British Association of Neuroscience Nurses, British Geriatric Society, and Centre for Perioperative Care. Results We identified that high quality evidence was generally lacking in the literature, although randomised controlled trial (RCT) data were available to inform specific recommendations on aspects of surgical technique and use of corticosteroids. The final guideline represents the outcome of synthesising the available evidence as well as consensus-built expert opinion and patient involvement. The guideline comprises 67 recommendations across 8 major themes, covering: presentation and diagnosis, neurosurgical triage and shared decision-making, non-operative management, perioperative management (including of anticoagulation), timing of surgery, intraoperative care, postoperative care, rehabilitation and recovery. Conclusions We present the first multidisciplinary guideline for the care of patients with cSDH. The recommendations reflect a paradigm shift in the care of cSDH, recognising and formalising the need for multidisciplinary and collaborative clinical management and communication and decision-making with patients delivered effectively across secondary and tertiary care.

WT has received speakers fees or sat on advisory boards for: Alexion, Portola, Sobi, Pfizer, Bayer, NovoNordisk, Ablynx, Daiichi Sankyo, Takeda, and Sanofi. PH is supported by Homerton College and the Health Foundations grant to the University of Cambridge for The Healthcare Improvement Studies Institute (THIS Institute). THIS Institute is supported by the Health Foundation, an independent charity committed to bringing about better health and health care for people in the UK. NRE is supported by a Stroke Association Senior Clinical Lectureship [SA-SCL-MED-22\100006]. JB reports consulting fees with Synchron. VFJN is supported by a NIHR Rosetrees Trust Advanced Fellowship NIHR302544, which is funded in partnership by the NIHR and Rosetrees Trust. The views expressed are those of the author(s) and not necessarily those of the NIHR, Rosetrees Trust or the Department of Health and Social Care. TB is funded by the NIHR Global Health Research Group on Acquired Brain and Spine Injury using UK international development funding from the UK Government to support global health research. The views expressed in this publication are those of the author(s) and not necessarily those of the NIHR or the UK government. AJJ is supported by the National Institute for Health Research (NIHR) HealthTech Research Centre in Brain Injury based at Cambridge University Hospitals NHS Foundation Trust. The views are those of the authors and not neces- sarily those of the NHS, the NIHR, or the Department of Health. ODM is supported by an NIHR Academic Clinical Fellowship. KS receives funding from UKRI, NIHR and the Royal Osteoporosis Society for research not related to the current work. JU declares speaker fees and funding from: Bayer, Daiichi-Sankyo, Octapharma. DKM is supported by the TBI-REPORTER Project, which is supported by a multi-funder consortium consisting of: UK Research and Innovation; National institute for Health and Care Research; UK Department of Health and Social Care; UK Ministry of Defence, and Alzheimers Research UK AA is supported by the THIS Institute: THIS Institute is supported by the Health Foundation (Grant/Award Number: RHZF/001 - RG88620), an independent charity committed to bringing about better health and health care for people in the UK. JPC is supported by the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. IM holds the position of Director of Centre for Research & Improvement, Royal College of Anaesthetists. IM is supported by Grant funding from NIHR and charities for research into perioperative care of older people. AK has been previously supported by NIHR (Dex-CSDH trial). FE is a Topic Adviser for NG 232.

This project was funded by the Association of Anaesthetists (WKR0-2021-0014) and the Addenbrookes charitable trust (ACT - #900268). The modified Delphi exercise and Mary Dixon-Woods contribution was supported by The Health Foundations grant to the THIS institute. The Health Foundation is an independent charity committed to bringing about better health and health care for people in the UK.

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