Reduced cerebral blood flow (CBF) has been proposed as a mechanism or exacerbating factor in major cerebral complications of surgery and anaesthesia including delirium, post-operative cognitive dysfunction, and stroke. It is currently unclear whether vasopressor agents cause a decrease or increase CBF when used to elevate blood pressure (BP). Vasopressor agents have been recently reported to reduce cerebral oxygenation measured by near-infrared spectroscopy, as well as increase in middle cerebral artery velocity using transcranial Doppler, which may reflect in decreased CBF due to cerebral vasoconstriction. However, both these methods have inherent inaccuracies as it does not measure CBF directly. This knowledge is critical for the safe management of patients during general anaesthesia (GA) for surgery and the acute management of patients with or at risk of brain injury.
This study will compare the effects on brain blood flow of two commonly used vasopressors, norepinephrine and phenylephrine, while patients are undergoing general anaesthesia. The investigators will use an improved method of measurement, Doppler ultrasound of the internal carotid artery, which measures both blood vessel diameter and velocity in real time to assess blood flow more accurately. The aim is to determine if one vasopressor better maintains brain blood flow.
Understanding the effect on CBF during vasopressor infusion during GA is particularly important. The findings may provide clinically significant guidance on selecting a vasopressor which both maintains blood pressure and brain blood flow. This may potentially reduce the incidence of cerebral complications after anaesthesia and surgery and translate to improvement in patient outcome following surgery and anaesthesia.
Dr Chen Chen, Dr Douglas Campbell, Auckland City Hospital, New Zealand, Associate Professor James Fisher, Dr Mickey Fan, University of Auckland, New Zealand.
The project was awarded $A17,255 through the ANZCA research grants program for 2022.