Predicting the limits of cerebral autoregulation during cardiopulmonary bypass

Abstract

Background: Mean arterial blood pressure (MAP) targets are empirically chosen during cardiopulmonary bypass (CPB). We have previously shown that near-infrared spectroscopy (NIRS) can be used clinically for monitoring cerebral blood flow autoregulation. The hypothesis of this study was that real-time autoregulation monitoring using NIRS-based methods is more accurate for delineating the MAP at the lower limit of autoregulation (LLA) during CPB than empiric determinations based on age, preoperative history, and preoperative blood pressure.

Methods: Two hundred thirty-two patients undergoing coronary artery bypass graft and/or valve surgery with CPB underwent transcranial Doppler monitoring of the middle cerebral arteries and NIRS monitoring. A continuous, moving Pearson correlation coefficient was calculated between MAP and cerebral blood flow velocity and between MAP and NIRS data to generate mean velocity index and cerebral oximeter index. When autoregulated, there is no correlation between cerebral blood flow and MAP (i.e., mean velocity and cerebral oximetry indices approach 0); when MAP is below the LLA, mean velocity and cerebral oximetry indices approach 1. The LLA was defined as the MAP at which mean velocity index increased with declining MAP to ≥ 0.4. Linear regression was performed to assess the relation between preoperative systolic blood pressure, MAP, MAP in 10% decrements from baseline, and average cerebral oximetry index with MAP at the LLA.

Results: The MAP at the LLA was 66 mm Hg (95% prediction interval, 43 to 90 mm Hg) for the 225 patients in which this limit was observed. There was no relationship between preoperative MAP and the LLA (P = 0.829) after adjusting for age, gender, prior stroke, diabetes, and hypertension, but a cerebral oximetry index value of >0.5 was associated with the LLA (P = 0.022). The LLA could be identified with cerebral oximetry index in 219 (94.4%) patients. The mean difference in the LLA for mean velocity index versus cerebral oximetry index was -0.2 ± 10.2 mm Hg (95% CI, -1.5 to 1.2 mm Hg). Preoperative systolic blood pressure was associated with a higher LLA (P = 0.046) but only for those with systolic blood pressure ≤ 160 mm Hg.

Conclusions: There is a wide range of MAP at the LLA in patients during CPB, making estimation of this target difficult. Real-time monitoring of autoregulation with cerebral oximetry index may provide a more rational means for individualizing MAP during CPB.

Conflict of interest statement

See Disclosures at end of article for Author Conflicts of Interest.

Disclosures:

Name: Brijen Joshi, MD

Contribution: This author helped conduct the study, analyze the data, and write the manuscript.

Attestation: Brijen Joshi has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Brijen Joshi reported no conflicts of interest.

Name: Masahiro Ono, MD

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Masahiro Ono has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Masahiro Ono reported no conflicts of interest

Name: Charles Brown, MD

Contribution: This author helped conduct the study, analyze the data, and write the manuscript.

Attestation: Charles Brown has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Charles Brown reported no conflicts of interest.

Name: Kenneth Brady, MD

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: Kenneth Brady has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Kenneth Brady consulted for Somanetics, received royalties from Somanetics, and received research funding from Somanetics Ken Brady has consulted for Somanetics, Inc. in a relationship that was managed by the committee for outside interests at the Johns Hopkins University School of Medicine.

Name: R. Blaine Easley, MD

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: R. Blaine Easley has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: R. Blaine Easley reported no conflicts of interest.

Name: Gayane Yenokyan, PhD

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Gayane Yenokyan has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Gayane Yenokyan reported no conflicts of interest.

Name: Rebecca F. Gottesman, MD, PhD

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: Rebecca F. Gottesman reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Rebecca F. Gottesman reported no conflicts of interest.

Name: Charles W. Hogue, MD

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Charles W. Hogue has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts: Charles W. Hogue received research funding from Somanetics and consulted for Ornim.

Figures

Figure 1

Number of subjects versus the mean arterial blood pressure at the lower limit of cerebral blood flow autoregulation during cardiopulmonary bypass based on the transcranial Doppler-determined mean velocity index.

Figure 2

Mean arterial blood pressure (MAP) at the lower limit of cerebral blood flow autoregulation for men and women based on age for patients with and without a history of diabetes, hypertension, or stroke. The error bars are the 95% confidence intervals. The LLA was defined as the MAP associated with an increase in the mean velocity index to ≥ 0.4 (see Methods section in the text). The MAP at the LLA tended to be higher for men than women (p=0.081).