Relative cerebral hyperperfusion during cardiopulmonary bypass is associated with risk for postoperative delirium: a cross-sectional cohort study

Abstract

Background: Our objective was to evaluate if changes in on-pump cerebral blood flow, relative to the pre-bypass baseline, are associated with the risk for postoperative delirium (POD) following cardiac surgery.

Methods: In 47 consecutive adult patients, right middle cerebral artery blood flow velocity (MCAV) was assessed using transcranial Doppler sonography. Individual values, measured during cardiopulmonary bypass (CPB), were normalized to the pre-bypass baseline value and termed MCAV_rel. An MCAV_rel > 100% was defined as cerebral hyperperfusion. Prevalence of POD was assessed using the Confusion Assessment Method for the Intensive Care Unit.

Results: Overall prevalence of POD was 27%. In the subgroup without POD, 32% of patients had experienced relative cerebral hyperperfusion during CPB, compared to 67% in the subgroup with POD (p < 0.05). The mean averaged MCAV_rel was 90 (±21) % in the no-POD group vs. 112 (±32) % in the POD group (p < 0.05), and patients developing delirium experienced cerebral hyperperfusion during CPB for about 39 (±35) min, compared to 6 (±11) min in the group without POD (p < 0.001). In a subcohort with pre-bypass baseline MCAV (MCAV_bas) below the median MCAV_bas of the whole cohort, prevalence of POD was 17% when MCAV_rel during CPB was kept below 100%, but increased to 53% when these patients actually experienced relative cerebral hyperperfusion.

Conclusions: Our results suggest a critical role for cerebral hyperperfusion in the pathogenesis of POD following on-pump open-heart surgery, recommending a more individualized hemodynamic management, especially in the population at risk.

Keywords: Cardiac surgery; Cardiopulmonary bypass; Cerebral blood flow; Delirium; Transcranial Doppler sonography.

Fig. 1

Relative blood flow velocity in middle cerebral artery during cardiopulmonary bypass. Blood flow velocity in the right middle cerebral artery (MCAV) was measured using transcranial Doppler sonography. Individual values, assessed during cardiopulmonary bypass (CPB) every 10 min, were normalized to the baseline value obtained before cannulation of the aorta and was termed MCAV_rel. Cerebral hyperperfusion was defined as relative MCAV > 100%. a Mean averaged MCAV_rel values for the no-POD group and the POD group, respectively. b Duration of cerebral hyperperfusion periods during CPB in the no-POD group and the POD group, respectively.Mean ± SD (boxes) and minimum and maximum (whiskers); n = 32 (no delirium) and n = 12 (delirium); unpaired, two-tailed Student’s t-test (b); * p < 0.05, *** p < 0.005

Fig. 2

Individual relative blood flow velocities in middle cerebral artery during cardiopulmonary bypass. Blood flow velocity in the right middle cerebral artery (MCAV) was measured using transcranial Doppler sonography. Individual values, assessed during cardiopulmonary bypass (CPB) every 10 min, were normalized to the baseline value obtained before cannulation of the aorta and was termed MCAV_rel. The figure shows the relative cerebral blood flow velocities in right MCA during CPB (solid lines, plotted on left Y axis), together with the corresponding mean arterial blood pressure (MAP) values (dashed lines, plotted on right Y axis), from two representative patients over the time. MCAV of patient no. 27, which developed no delirium, was below his individual baseline value almost the whole time during CPB. By contrast, the MCAV of patient no. 26, developing POD, was above his baseline at any time point, with peak values exceeding 160%. Note that MAP was kept within a range between 50 and 90 mmHg almost all the time in both patients

Fig. 3

Significance of age and baseline blood flow velocity in middle cerebral artery for cerebral hyperperfusion during cardiopulmonary bypass. Blood flow velocity in the right middle cerebral artery (MCAV) was measured using transcranial Doppler sonography before cardiopulmonary bypass (CPB) and was termed MCAV_bas. a Comparison of the patients’ baseline MCAV values (in cm/s), assessed before beginning of CPB, between the no-POD group and the POD group. b Association of the patients’ age with their measured MCAV_bas values, with elderly patients having a reduced baseline blood flow velocity (Pearson product-moment correlation). The dashed curved lines indicate the confidence band. r = Pearson product-moment correlation coefficient, CI = confidence interval; mean ± SD (boxes) and minimum and maximum (whiskers); n = 32 (no delirium) and n = 12 (delirium); unpaired, two-tailed Student’s t-test (a); ** p < 0.01, *** p < 0.005