The effect of vasopressor therapy on cerebral oxygen delivery
Surgery may require patients to be placed in an upright position, which can result in hypotension and risk of inadequate blood flow to the brain. Vasopressor therapy is commonly used to elevate blood pressure, in the belief that cerebral perfusion will be maintained. However we have found that phenylephrine, a commonly used vasopressor agent, can decrease cerebral oxygen saturation despite having a favourable haemodynamic effect. Our current project aims to study the effects of clinically used vasopressor agents in patients undergoing "beachchair" shoulder surgery. Their effect on the circulation will be assessed using intraoperative transthoracic echocardiography, which correlates with changes in cerebral perfusion, by measurement of middle cerebral arterial velocity and cerebral oxygen saturation. By using an integrative approach, the systemic effects of vasopressor therapy will be discerned from effects within the cerebral circulation. Further in vitro studies will involve the study of the pharmacological responses of isolated cerebral vessels to individual drugs.