Comparison of the Effect of Norepinephrine and Dopamine on Cerebral Haemodynamics in Severely Brain Injured Patients Using Transcranial Doppler

Abstract

Severe brain injury is a major cause of death and disability. It constitutes a substantial proportion of Intensive Care Unit (ICU) admissions, and is a heterogeneous disease in terms of cause, pathology, severity and prognosis, that poses diagnostic and therapeutic challenges. The brain is highly vulnerable to the effect of hypotension, which is an important risk factor for cerebral ischemia, that is known as secondary neuronal injures. In neurocritically ill patients, it is desirable to maintain MAP or CPP within a narrow range because the autoregulation may be impaired at the site of injury. Hypotension may worsen ischemic damage in marginally perfused tissue and may trigger cerebral vasodilation and intracranial hypertension. A poor outcome is predicted with low CBF values due to low BP in the first few hours after brain injury. Episodes of high ICP, hypoxia, hypotension and reduced CPP are important factors that reduce CBF and oxygen delivery. Cerebral ischemia happens if compensation by increased oxygen extraction is incomplete. So monitoring of cerebral ischemic episodes is important. Secondary cerebral ischemic episodes vary in the depth and duration even may last for few minutes. Monitoring of physiologic functions is an important element of patient care in the ICU. Cardiovascular and pulmonary functions can be continuously monitored in ICU; however, the development of continuous monitoring of cerebrovascular function has lagged behind. Bedside measurement of CBF is a cumbersome task and requires expensive techniques that are not available in the ICU setting. The routine use of invasive imaging modalities for oxygenation and CBF using contrast agents and isotopes in neurointensive care is inaccurate, which require transfer of critically ill patients to specialized facilities. In addition, they only allow isolated estimations which will miss transient secondary episodes. Monitors that allow a real-time estimation of cerebral pathophysiological parameters have evolved which include the continuous measurement of ICP, CPP, and the indirect estimation of global cerebral oxygenation by measuring SjO2 using jugular venous oximetry. Transcranial Doppler ultrasonography was introduced by Aaslid and colleagues in 1982 as a non-invasive technique for monitoring FV in the basal cerebral