Duration and magnitude of blood pressure below cerebral autoregulation threshold during cardiopulmonary bypass is associated with major morbidity and operative mortality

Abstract

Objectives: Optimizing blood pressure using near-infrared spectroscopy monitoring has been suggested to ensure organ perfusion during cardiac surgery. Near-infrared spectroscopy is a reliable surrogate for cerebral blood flow in clinical cerebral autoregulation monitoring and might provide an earlier warning of malperfusion than indicators of cerebral ischemia. We hypothesized that blood pressure below the limits of cerebral autoregulation during cardiopulmonary bypass would be associated with major morbidity and operative mortality after cardiac surgery.

Methods: Autoregulation was monitored during cardiopulmonary bypass in 450 patients undergoing coronary artery bypass grafting and/or valve surgery. A continuous, moving Pearson's correlation coefficient was calculated between the arterial pressure and low-frequency near-infrared spectroscopy signals and displayed continuously during surgery using a laptop computer. The area under the curve of the product of the duration and magnitude of blood pressure below the limits of autoregulation was compared between patients with and without major morbidity (eg, stroke, renal failure, mechanical lung ventilation >48 hours, inotrope use >24 hours, or intra-aortic balloon pump insertion) or operative mortality.

Results: Of the 450 patients, 83 experienced major morbidity or operative mortality. The area under the curve of the product of the duration and magnitude of blood pressure below the limits of autoregulation was independently associated with major morbidity or operative mortality after cardiac surgery (odds ratio, 1.36; 95% confidence interval, 1.08-1.71; P = .008).

Conclusions: Blood pressure management during cardiopulmonary bypass using physiologic endpoints such as cerebral autoregulation monitoring might provide a method of optimizing organ perfusion and improving patient outcomes from cardiac surgery.

Trial registration: ClinicalTrials.gov NCT00981474.

Keywords: CABG; CBF; COx; CPB; MAP; MMOM; NIRS; cardiopulmonary bypass; cerebral blood flow; cerebral oximetry index; coronary artery bypass grafting; major morbidity and operative mortality; mean arterial pressure; near-infrared spectroscopy; rScO(2); regional cerebral oxygen saturation.

FIGURE 1

Cerebral oximetry index (COx) monitoring results during cardiopulmonary bypass. Top channel, Mean arterial blood pressure (ABP) and left (l) and right (r) regional cerebral oxygen saturation (rScO₂). Middle 2 channels, Right and left COx results are shown. Bottom channel, the percentage of time spent at each 5-mm Hg bin. COx represents the value for the Pearson’s correlation coefficient between the low-frequency changes in rScO₂ and mean arterial pressure. In the example shown, the lower limit of autoregulation, defined as the mean arterial pressure at which COx increased from <0.3 to ≥0.3 was 75 mm Hg. Similar displays of COx shown continuously during surgery on a laptop computer enabled clinicians to assess the blood pressure associated with preserved cerebral autoregulation.