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Thoralf M. Sundt Jr., Frank W. Sharbrough, Robert E. Anderson and John D. Michenfelder

✓ Ninety-three endarterectomies for carotid stenosis were monitored with cerebral blood flow (CBF) measurements, and 113 with both CBF measurements and a continuous electroencephalogram (EEG). Significant CBF increase occurred only when carotid endarterectomy was for a stenosis greater than 90%. A high correlation between CBF and EEG indicated when a shunt was required. To sustain a normal EEG, the CBF ascertained by the initial slope technique must be 18 ml/100 gm/min at an arterial carbon dioxide tension (PaCO2) of 40 torr. The degree of EEG change below this level during occlusion reflected the severity of reduced blood flow and was reversible with replacement of a shunt. The value and limitations of these monitoring techniques and a concept of ischemic tolerance and critical CBF are discussed.

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John D. Michenfelder, Roy F. Cucchiara and Thoralf M. Sundt Jr.

✓ Because of a suspicion that intraoperative penicillin antibiotics might be causing early postoperative seizures in craniotomy patients, a deliberate effort was initiated in 1987 to avoid these agents in favor of nonpenicillin antibiotics. This permitted a retrospective comparison of the incidence of early postoperative seizures in craniotomy patients who did and who did not receive intraoperative penicillins. Records of patients treated between July 1, 1984, and July 1, 1985, and between July 1, 1987, and July 1, 1988, were reviewed, for a total of 1316 procedures. There were no seizures in the 323 patients who underwent suboccipital craniectomy. However, among the 993 patients receiving supratentorial procedures there were 30 with seizures within the first 6 hours postoperatively, 19 of which were generalized seizures. The incidence of early seizures was 4.7% (20 cases) of the 427 patients given penicillins and only 1.8% (10 cases) of the 566 not given penicillins (p < 0.01). Since patients undergoing surgery for intractable seizures have a high incidence of early postoperative seizures (11 of 92 in this series, or 12%), creation of a subgroup eliminated these from consideration but did not alter the relationship of penicillins to early seizures (p < 0.02). The authors conclude that intraoperative (and early postoperative) penicillin antibiotic administration should be avoided, if possible, in patients undergoing craniotomy for supratentorial pathology.

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Alan A. Artru, Michael Nugent and John D. Michenfelder

✓ A new method for determining rates of cerebrospinal fluid (CSF) production under nonsteady-state conditions, namely, closed recirculatory spinal subarachnoid perfusion, was used to determine the effect of enflurane on the rate of CSF production in dogs. Considerable variability in results was observed such that there was no statistical difference in rates of production among animals that received enflurane 2.2%, enflurane 2.2% and nitrous oxide 60% to 70%, enflurane 3.2% and nitrous oxide 60% to 70%, or nitrous oxide 60% to 70% (controls). Possible sources of variability were sought in additional studies using a modification of the new method, and in an in vitro model. The results were compared to those obtained using an established method for determining rates of CSF production, namely, open ventriculocisternal perfusion. It was concluded that the sources of variability in the closed recirculatory method relate in part to adherence of the fluorescein-conjugated albumin tracer to glass and other surfaces, and to uneven flow and distribution of the tracer in the recirculatory system. When the open ventriculocisternal perfusion method was used, consistent results were obtained, demonstrating that CSF production rate increased significantly in animals that received enflurane. The authors conclude that the new closed recirculatory method is less reliable than the classical open perfusion method.

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Thoralf M. Sundt Jr., Frank W. Sharbrough, Robert E. Anderson and John D. Michenfelder

✓ Ninety-three endarterectomies for carotid stenosis were monitored with cerebral blood flow (CBF) measurements, and 113 with both CBF measurements and a continuous electroencephalogram (EEG). Significant CBF increase occurred only when carotid endarterectomy was for a stenosis greater than 90%. A high correlation between CBF and EEG indicated when a shunt was required. To sustain a normal EEG, the CBF ascertained by the initial slope technique must be 18 ml/100 gm/min at an arterial carbon dioxide tension (PaCO2) of 40 torr. The degree of EEG change below this level during occlusion reflected the severity of reduced blood flow and was reversible with replacement of a shunt. The value and limitations of these monitoring techniques and a concept of ischemic tolerance and critical CBF are discussed.