The Effects of Anesthesia on Cerebral Perfusion in Patients With High Blood Pressure

High blood pressure is a serious and common health problem. This disease affects 1 billion people all over the world and responsible for 7,1 million deaths. Trials involving more than 1 million people state that stroke incidence rises as blood pressure rises. The effects of high blood pressure on cerebral perfusion is not well realized. Intraoperative blood pressure management of patients with high blood pressure is not well known. And it is still not clear how autoregulation of cerebral perfusion is affected by high blood pressure.

Systemic arterial pressure changes have little effect on cerebral perfusion. This is regulated by changes of precapillary resistance. When systemic arterial blood pressure drops, it is regulated by vasodilatation of arteriolar smooth muscles. And when systemic blood pressure rises, it is regulated by vasoconstriction of arterioles. Cerebral perfusion is well preserved between 50-125 mmHg changes of mean arterial blood pressure (MAP). Patients with high blood pressure have higher ranges. Patients with chronic high blood pressure can better tolerate higher blood pressures. But even physiologic drops of systemic blood pressure can cause ischemia.

Anesthetic drugs have variable effects on cerebral blood flow and physiology. The drugs used with anesthetic drugs, the noxious stimulus of surgery, intracranial compliance, blood pressure, and carbon dioxide pressure can all alter and complicate these effects. Anesthetic drugs must be selected carefully in patients with high blood pressure. It is still investigated whether, management of blood pressure under anesthesia, should be individualized.

For patients with high blood pressure, some neuromonitorization technics have been evaluated to prevent neurologic complications under anesthesia. But there is not a technic, which is considered as a gold standard. Cerebral blood pressure has been studied by, nitrous oxide method, krypton uptake method, and xenon injection methods previously. Near-infrared spectroscopy (NIRS) is the best monitorization technic of intracranial pressure (ICP), cerebral blood flow (CBF), and cerebral metabolism. But it can not be applied to all patients. Recently, it is possible to measure blood flow of cerebrum with transcranial Doppler ultrasound in anesthesia practice.

In this trial, the investigators aim to evaluate cerebral perfusion of hypertensive patients with transcranial Doppler during lumbar disc surgery to optimize the blood pressure under anesthesia.

To best of our knowledge, there is no trial evaluating cerebral perfusion of hypertensive patients with transcranial Doppler ultrasound.