A clinical appraisal of the adequacy of brain circulation during anaesthesia (with particular reference to carotid thromboendarterectomy)

Perioperative stroke. Part I: General surgery, carotid artery disease, and carotid endarterectomy

Although stroke, defined as a focal neurological deficit lasting more than 24 hr, is uncommon in the perioperative period, its associated mortality and long-term disability are high. No large-scale data are available to identify the importance of recognized risk factors for stroke in the perioperative period. A review of the literature shows that the incidence and mechanism of its occurrence are influenced by the presence of cardiovascular disease and the type of surgery. The most common cause of perioperative stroke is embolism. In non-cardiac surgery, the incidence of perioperative stroke is higher among the elderly. Properly administered, controlled hypotension is associated with minimal risk of stroke. Cerebral vasospasm may be the cause of focal cerebral ischaemia in eclamptic patients, and the aggressive treatment of hypertension may exacerbate the neurological damage. The risk of stroke associated with carotid endarterectomy is closely related to the preoperative neurological presentation, and the experience of the surgical/anaesthetic team. Symptomatic cerebrovascular disease, acute stroke, asymptomatic carotid lesions, preoperative assessment of risk, local and general anaesthesia, cerebral protection and monitoring during carotid endarterectomy are discussed with reference to reducing the risk of perioperative stroke. Adequate monitoring and protection have minimized the risk of ischaemia from carotid clamping, and the major mechanism of stroke is embolization.

Relationship between hemispheric cerebral blood flow, central conduction time, and clinical grade in aneurysmal subarachnoid hemorrhage

The relationship between central conduction time (CCT) and hemispheric cerebral blood flow (CBF) has been examined in 20 patients presenting with subarachnoid hemorrhage. A total of 63 combined CCT/CBF recordings were performed at various times throughout the hospital course of these patients, and the findings were correlated to clinical status. The initial-slope index of the CBF (CBF isi) was found to correlate well with clinical grade, and a gradation in flow was noted between the different neurological grades. Patients in Grades I and II (Hunt and Hess classification) had the highest flows (mean CBF isi = 47.2 +/- 8.1); Grade III patients had intermediate flows (mean CBF isi = 39.6 +/- 7.8); and Grade IV patients had the lowest flows (mean CBF isi = 32.0 +/- 6.4). While CCT tended to become increasingly prolonged with worsening grade, a significant difference could not be demonstrated between Grade I, II, and III patients. Only when Grade IV status was reached was the CCT significantly prolonged. When CBF isi and CCT were examined, a threshold relationship was noted between CBF isi and CCT prolongation. At flow values above 30, little change was noted in CCT, and CCT remained in the normal range. However, at flow values below 30, CCT became increasingly prolonged as blood flow diminished. The degree of CCT prolongation appeared to be directly proportional to the degree of blood flow diminution at flows below threshold.

Correlation of continuous electroencephalograms with cerebral blood flow measurements during carotid endarterectomy

During an 11-month period, 81 endarterectomies under a carefully controlled level of general anesthesia were monitored with continuous electroencephalograms (EEG) and intermittent regional cerebral blood flow (CBF) measurements. There was a high correlation between the CBF (milliliter per 100 gm per minute) during carotid occlusion and alterations in the EEG: no EEG change was seen with the flow above 30 ml/100 gm brain per minute, major changes were not seen with a flow between 18 and 30 ml, and changes invariably occurred with a flow below 17 ml. The degree of EEG change reflected the severity of flow reduction but was always reversible with the placement of a shunt. The EEG at the termination of the surgery corresponded with the patient's neurological state in that all EEG tracings were normal or unchanged as compared to the preoperative tracing and no neurological worsening occurred in any patients studied. The EEG is a valuable monitoring technique that indicates when a shunt is required and informs the surgeon of the state of cerebral function not only during occlusion but also throughout the entire operative procedure.