The risk factors for and the frequency and outcomes of subsyndromal delirium among patients who have undergone cardiac surgery: a protocol for systematic review and meta-analysis

INTRODUCTION: Several key symptoms must be present for the accurate diagnosis of patients with postoperative cardiac delirium. Some patients present with symptoms of delirium but do not meet the diagnostic criteria for delirium; such individuals are considered to have having subsyndromal delirium (SSD). SSD is associated with misdiagnosis and poor outcomes. However, to date, no systematic review (SR) has examined the frequency of, risk factors for, and outcomes of SSD among adults who have undergone cardiac surgery. METHODS AND ANALYSIS: The aim of this SR is to identify those studies that have explored SSD after cardiac surgery. MeSH and free entry terms associated with “subsyndromal delirium” and “subclinical delirium” will be used to search for relevant studies. The PubMed, Web of Science, OVID, Cochrane Library, CINAHL, EMBASE, PsycINFO, China National Knowledge Infrastructure, Wanfang data, VIP database and SinoMed will be searched from inception to the date of retrieval without any restrictions. The primary outcomes will be the frequency of SSD, the risk factors for SSD, and the outcomes of SSD. Analyses will be performed using STATA V.16.0, and descriptive analyses will be performed if the data are not suitable for meta-analysis (ie, data with significant heterogeneity or from different comparisons). ETHICS AND DISSEMINATION: The SR will examine the frequency of, risk factors for and outcomes of SSD in adults who have undergone cardiac surgery. The results will provide guidance for the identification of knowledge gaps in this field, and areas for further research will be highlighted. The review protocol will be submitted for publication in peer-reviewed journals for dissemination of the findings. Individual patient data will not be included in this protocol, so ethical approval will not be needed. PROSPERO REGISTRATION NUMBER: CRD42022379211.