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A Pilot Study on the Clinical Significance of Cerebrovascular Autoregulation Monitoring during Non-Cardiac Anaesthesia

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Id: ACTRN12613000825752

Organisation Name: Liverpool Hospital, South West Sydney Local Health District

Overal Status: Completed

Start Date: 01/04/2014

Brief Summary: This study is a prospective, single centre, observational pilot study examining the clinical relevance and outcomes of changes in cerebral vascular autoregulation during general anaesthesia in patients presenting for non-cardiac surgery. Primary outcome is post-operative quality of recovery, and secondary outcomes are patient mortality and major morbidity.
This study is a sub-study of a larger, multicenter study on the effect of depth of anaesthesia on patient outcomes (BALANCED study).

Recent animal and human studies have investigated indices of cerebrovascular autoregulation (CVAR), including the tissue oxygenation index (TOx), cerebral oximetry index, haemoglobin volume index, and pressure reactivity index. These indices are derived from measuring different surrogates of cerebral blood volume or cerebral blood flow, and calculating a moving correlation coefficient between the surrogate and mean arterial pressure.

Specifically, the TOx index measures cerebral tissue oxygenation using non-invasive near infrared spectroscopy (NIRS) as a surrogate of cerebral blood flow and correlation with mean arterial pressure (MAP). Thus, a TOx index can reflect CVAR changes in blood vessel diameter to maintain a constant cerebral blood flow despite changes in systemic arterial blood pressure. The TOx index is thus a novel measure of adequacy of cerebral perfusion.

We hypothesise that patients who have impairment in CVAR may be exposed to episodes of cerebral ischaemia resulting in end organ dysfunction. In a number of prospective observational studies recruiting cardiac surgical patients undergoing cardiopulmonary bypass, impaired autoregulation has been associated with cerebral injury, stroke and acute kidney injury. These studies have also defined a threshold level of MAP when autoregulation is lost, as well as a range of MAP when autoregulation is optimised.

However, our understanding of this association is incomplete. This study will improve this understanding in a non-cardiac surgical population who are at higher risk of complications after anaesthesia. Elderly patients greater than or equal to 60 years old admitted for major non-cardiac surgery will be monitored using NIRS to derive a real-time TOx index. We will prospectively measure patient outcomes including post-operative quality of recovery, symptoms and signs of major organ dysfunction, and mortality. Statistical analysis will be performed to determine the strength of association between patient outcomes and episodes of cerebral ischaemia as detected by TOx.

This study will also provide essential data to help design a future randomised clinical trial. We would plan an interventional arm using the TOx index and the optimal autoregulation MAP value, as goal-directed therapy to minimise the time that patients are exposed to potential cerebral ischaemia.

  • Australia
  • Post-operative recovery, mortality, and morbidity from major surgery
  • cerebrovascular autoregulation

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