Hypotension-Induced Changes in Cerebral Function During Cardiac Surgery

Abstract

HypotensionInduced Changes in Cerebral Function During Cardiac Surgery• In a series of 75 patients undergoing cardiac operations with the assistance of cardiopulmonary bypass (CPB), 15 patients were subjected to relatively large hypotensive stresses during CPB as measured by the depth and duration of the fall in cerebral perfusion pressure. Of these 15 patients, eight manifested cerebral dysfunction postoperatively ranging from temporary exacerbation of pre-existing focal neurological deficits to irreversible coma. In each of these eight cases, EEG disturbances which first appeared at the time of hypotensive episodes during CPB persisted postoperatively and correlated with the nature and evolution of the clinical deficit. In two of the patients who did not regain consciousness postoperatively, neuropathological studies revealed bilateral laminar cortical necrosis, primarily involving cerebral cortex in one case and cerebellar cortex in the other, with accentuation in arterial border zones. Of seven other patients who suffered comparable exposures to hypotension during CPB, none evidenced cerebral dysfunction postoperatively. The most important determinants of this selective vulnerability to low extracorporeal perfusion pressure appeared to be the "reperfusion" pressure established after the hypotensive episode, postoperative blood pressure and cardiac output, and brain temperature at the time of the hypotension. Advanced age and history of cerebrovascular insufficiency were the greatest risk factors among patient variables. Despite these advances, however, postoperative neurological morbidity remains a frequent sequel to operations involving cardiopulmonary bypass (CPB). Numerous studies have incriminated pump-generated microemboli as a major factor in these neurological sequelae 2 -3 while other reports have emphasized the role of adverse situational aspects of recovery such as lack of sleep and sensory deprivation. Additional Key Words -5Other investigators who correlated histological evidence of ischemic anoxia following CPB with extracorporeal perfusion pressure have suggested that hypotension during CPB may also contribute to CNS dysfunction following cardiac surgery. "10 However, in none of these studies was the intraoperative blood pressure recorded continuously and, in the only one in which the EEG was monitored during bypass, 9 the EEG findings were not discussed. Thus, there was no direct evidence that low perfusion pressures were responsible for the ischemia which produced the lesions in these studies.From the Departments of Neurosciences, Surgery and Anesthesiology, University of California, San Diego, La Jolla, California 92037.More direct evidence was provided in a preliminary study in which six of seven patients having severe hypotensive episodes during CPB developed irreversible or slowly resolving EEG abnormalities during the episodes which later correlated with clinical or pathological evidence of cerebral damage. 11Although the important role of intraoperative hypotension in the neur...

Central nervous system complications of open heart surgery.

“…Some cases of prolonged encephalopathy or unexplained coma may be due to relative hypotension in patients with defective autoregulation. 15 Other causes of brain dysfunction after open heart surgery must be considered. Both Halothane and Ethrane may produce alterations in neuronal microtubules 16 and thereby alter axonal transport.…”

Monitoring of cerebral perfusion during anesthesia by time-compressed Fourier analysis of the electroencephalogram.

“…7 "' Ultrastructural characterizations of parenchymal response following ischemic insults induced by the clip model have been reported, 10 …”

Neurophysiological Monitoring in the Intensive Care Unit

“…Pathogenesis may relate to hypotension, air emboli, or pump-generated emboli [14,15]. Cerebral hypoperfusion can occur during CPB surgery, which results in postoperative neurological deficits, and seizures.…”

“…Cerebral hypoperfusion can occur during CPB surgery, which results in postoperative neurological deficits, and seizures. EEG has been demonstrated to indicate cerebral ischemia related to this procedure, and electrographical seizure activity without clinical manifestations has been identified during CPB surgery [15]. The reliability of EEG has been used in the ICU as an indicator of cerebral ischemia [2].…”