Association of postoperative delirium with haemodynamic determinants of cerebral perfusion pressure during cardiac surgery: a retrospective cohort study.

Abstract

Delirium is common after cardiac surgery, and an important factor could be cerebral perfusion. As cerebral perfusion pressure (CPP) is determined by the difference between mean arterial pressure (MAP) and central venous pressure (CVP), which are modifiable factors, understanding their relationship with delirium is essential. In a retrospective cohort study, patients undergoing cardiac surgery were assessed for delirium using the Confusion Assessment Method for the ICU. Haemodynamic exposures were calculated as time spent in narrow ranges: 14 MAP ranges in increments of 5 mm Hg (45-115), 10 CVP ranges in increments of 2 mm Hg (0-20), and 70 joint MAP/CVP ranges. Separate regression models estimated odds ratios for each range (or predefined zones of adjacent ranges), adjusted for covariates and multiple comparisons. Simulations estimated the effect of redistributing MAP/CVP exposures. In 1759 patients, 345 (19.6%) developed delirium. In predefined zones that grouped MAP and CVP ranges, delirium was associated with time spent in the cerebral hypoperfusion zone (adjusted odds ratio 1.02, 95% confidence interval 1.00-1.03, P=0.04). Simulated reductions of time in zones of cerebral hypoperfusion and hyperperfusion reduced delirium, particularly in patients with prolonged exposures to these zones. There were also associations between delirium and time in individual haemodynamic ranges of high CVP/low MAP (hypoperfusion) and high MAP/low CVP (hyperperfusion). Delirium was associated with a zone of low cerebral perfusion pressure in adjusted models and individual ranges of low and high cerebral perfusion pressures. Trials to assess whether optimising cerebral perfusion reduces delirium are needed but may require large enrolment or prognostic enrichment.