Reduced multimodal physiological signal complexity during neurointensive care is associated with delayed cerebral ischaemia and worse functional outcome in aneurysmal subarachnoid haemorrhage: a single-centre retrospective study

Background Autonomic dysfunction and reduced signal complexity (SC) may occur after aneurysmal subarachnoid haemorrhage (aSAH) and reflect impaired physiological adaptability. However, the relationships with cerebral physiology, delayed cerebral ischaemia (DCI), and long-term functional outcome remain incompletely understood. This study explores heart rate variability (HRV), baroreflex sensitivity (BRS), and systemic and cerebral SC in aSAH patients during neurointensive care (NIC). Methods This observational, single-centre cohort study included 690 aSAH patients with intracranial pressure (ICP) monitoring during the first 10 days post-ictus, treated at Uppsala University Hospital, Sweden (2008–2024). HRV, BRS, and multiscale entropy derived SC of each of heart rate (HR), mean arterial pressure (MAP), ICP, ICP pulse amplitude (AMP), and cerebral perfusion pressure (CPP) were analysed using high-frequency monitoring data. Associations with NIC physiology (ICP, CPP, pressure reactivity index [PRx]), DCI, and 12-month Glasgow Outcome Scale-Extended (GOSE) were assessed using multivariable logistic regression, two-variable outcome heatmaps, and Spearman's correlations. DCI was defined as new focal neurological deficits or declining consciousness after exclusion of other aetiologies. Results In multivariable regression adjusted for demographic, clinical, radiological, and physiological predictors, reduced SC of each of HR, MAP, ICP, AMP, and CPP independently correlated with worse functional outcome, while reduced cerebral SC (of ICP, AMP, and CPP) the first 3 days post-ictus was independently associated with DCI. Reduced SC generally correlated with higher ICP, lower CPP, and higher PRx. Reduced SC combined with high ICP and PRx and low CPP was particularly associated with poor recovery in outcome heatmaps. Conclusion Reduced SC was independently associated with DCI and worse functional outcome after aSAH. SC may serve as a prognostic marker and a bedside indicator of DCI and vulnerability to secondary insults, with potential to guide more individualised NIC. Prospective, multi-centre studies are needed to validate these findings.