Risks for impaired cerebral autoregulation during cardiopulmonary bypass and postoperative stroke

Abstract

Background: Impaired cerebral autoregulation may predispose patients to cerebral hypoperfusion during cardiopulmonary bypass (CPB). The purpose of this study was to identify risk factors for impaired autoregulation during coronary artery bypass graft, valve surgery with CPB, or both and to evaluate whether near-infrared spectroscopy (NIRS) autoregulation monitoring could be used to identify this condition.

Methods: Two hundred and thirty-four patients were monitored with transcranial Doppler and NIRS. A continuous, moving Pearson's correlation coefficient was calculated between mean arterial pressure (MAP) and cerebral blood flow (CBF) velocity, and between MAP and NIRS data, to generate the mean velocity index (Mx) and cerebral oximetry index (COx), respectively. Functional autoregulation is indicated by an Mx and COx that approach zero (no correlation between CBF and MAP); impaired autoregulation is indicated by an Mx and COx approaching 1. Impaired autoregulation was defined as an Mx ≥0.40 at all MAPs during CPB.

Results: Twenty per cent of patients demonstrated impaired autoregulation during CPB. Based on multivariate logistic regression analysis, time-averaged COx during CPB, male gender, Pa(CO(2)), CBF velocity, and preoperative aspirin use were independently associated with impaired CBF autoregulation. Perioperative stroke occurred in six of 47 (12.8%) patients with impaired autoregulation compared with five of 187 (2.7%) patients with preserved autoregulation (P=0.011).

Conclusions: Impaired CBF autoregulation occurs in 20% of patients during CPB. Patients with impaired autoregulation are more likely than those with functional autoregulation to have perioperative stroke. Non-invasive monitoring autoregulation may provide an accurate means to predict impaired autoregulation. Clinical trials registration. www.clinicaltrials.gov (NCT00769691).

Figures

Fig 1

Monitoring results from a patient with (a) intact CBF autoregulation and (b) impaired CBF autoregulation during CPB. In a and b, the top graph is MAP, and the middle two graphs are the mean velocity index (Mx) for the right and left brain hemispheres. The bottom graph is the percentage of time during the recording at each 5 mm Hg bin of arterial pressure. When arterial pressure is within the autoregulation range, Mx approaches zero. When arterial pressure is outside the autoregulatory range, Mx increases toward 1 as CBF and arterial pressure become correlated. Using an Mx cut-off of ≥0.40, arterial pressure of the patient shown in (a) approaches the lower limit of autoregulation at around 75 mm Hg, while the upper limit of autoregulation is approached at an MAP of 100 mm Hg. In contrast, the patient in (b) demonstrates impaired autoregulation at all arterial pressure readings.