Journal of neurosurgical anesthesiology
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J Neurosurg Anesthesiol · Jul 1998
The effect of sevoflurane on myogenic motor-evoked potentials induced by single and paired transcranial electrical stimulation of the motor cortex during nitrous oxide/ketamine/fentanyl anesthesia.
To overcome anesthetic-induced depression of myogenic motor-evoked potentials (MEPs), several techniques of stimulation using paired pulses or trains of pulses are used. This study investigated the effect of sevoflurane on myogenic MEPs induced by single and paired transcranial electrical stimulation of the motor cortex. Nine patients undergoing elective spinal surgery were anesthetized with fentanyl-N2O-ketamine. ⋯ The success rate of MEP recording during the administration of sevoflurane was greater after paired stimulation than after single stimulation, and percentage MEP amplitude (percentage of the control value after single stimulation but before sevoflurane) after paired stimulation was significantly higher than after single stimulation before and during the administration of 0.25 MAC and 0.5 MAC sevoflurane. The success rate of MEP recording and MEP amplitude after paired stimulation decreased in a dose-dependent manner during the administration of sevoflurane. These results suggest that although facilitation by the second stimulus was considerable, paired stimuli are still not sufficient to overcome the depressant effects of sevoflurane in clinically used concentrations.
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J Neurosurg Anesthesiol · Apr 1998
Case ReportsA case of shock subsequent to treatment of intracranial hypertension by mannitol injection combined with hyperventilation.
This report describes a sudden decrease in blood pressure after conservative treatment of acute intracranial hypertension. A 63-year-old woman with acute hydrocephalus after undergoing clipping of an aneurysm of the right supracerebellar artery developed increased intracranial pressure, necessitating surgical management. On the operating table, the patient developed Cushing's reflex. ⋯ Fifteen minutes later, a sudden and prolonged suppression of circulation was observed (blood pressure 65/35-85/40 mmHg, heart rate 90-100 beats/min). Postoperatively, computed tomography of the head showed compression of the brain stem. We believe that this patient's blood pressure decrease was related to a sudden reduction of intracranial pressure and that mannitol injection was principally responsible for this occurrence.
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J Neurosurg Anesthesiol · Apr 1998
Clinical TrialCerebral CO2 vasoreactivity evaluation with and without changes in intrathoracic pressure in comatose patients.
It is well established that cerebral blood flow (CBF) is sensitive to variations in arterial PCO2 (PaCO2) and can be influenced by changes in jugular venous return due to elevated intrathoracic pressure. Therefore, we compared cerebral CO2 vasoreactivity when PaCO2 was altered either by changing inspired PCO2 or tidal volume. In addition, we sought to determine if noninvasive transcranial Doppler ultrasonography can be used instead of invasive CBF measurement to determine cerebral CO2 vasoreactivity. ⋯ When compared with CBF by jugular thermodilution, the rates of sensitivity and specificity of transcranial Doppler ultrasonography to detect impaired cerebral CO2 vasoreactivity were 69% and 65%, respectively. In conclusion, the reduction of PaCO2 from 40 to 25 mmHg by modifying either tidal volume or inspired PCO2 resulted in similar effects on cerebral, pulmonary, and systemic circulations. Cerebral CO2 vasoreactivity is of prognostic value in brain-injured patients when determined using CBF but may be misleading when evaluated using velocities measured by transcranial Doppler ultrasonography.
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J Neurosurg Anesthesiol · Apr 1998
The upper limit of cerebral blood flow autoregulation in acute intracranial hypertension.
The present series of experiments was performed to investigate the influence of acute intracranial hypertension on the upper limit (UL) of cerebral blood flow (CBF) autoregulation. Three groups of eight rats each--one with normal intracranial pressure (ICP) (2 mmHg), one with ICP = 30 mmHg, and one with ICP = 50 mmHg--were investigated. Intracranial hypertension was maintained by continuous infusion of lactated Ringer's solution into the cisterna magna, where the pressure was used as ICP. ⋯ At normal ICP the UL was found at a CPP of 141 +/-2 mmHg, at ICP = 30 mmHg the UL was 103+/-5 mmHg, and at ICP = 50 mmHg the UL was found at 88+/-7 mmHg. This shift of the UL was more pronounced than the shift of the lower limit (LL) of the CBF autoregulation found previously. We conclude that intracranial hypertension is followed by both a shift toward lower CPP values and a narrowing of the autoregulated interval between the LL and the UL.
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J Neurosurg Anesthesiol · Jan 1998
Effect of hemorrhage on cerebral microcirculation during normal and high cerebrospinal fluid pressure in pigs.
Studies on cerebral blood flow during hypotension and high intracranial pressure are scarce. Accordingly, this study examines the effects of increased cerebrospinal fluid (CSF) pressure on the cerebral circulatory response to hemorrhage. Measurements of cerebral microcirculation with laser Doppler flowmetry was performed in 12 pentobarbital-anesthetized pigs during hemorrhage, with and without high CSF pressure. ⋯ During high CSF pressure, the cerebral perfusion pressure was 23 mmHg and the laser Doppler signal was 52+/-29% of baseline. Bleeding of 15% of blood volume reduced the laser Doppler signal to 0 (equal to postmortem values) in three pigs, and bleeding of 25% of the blood volume reduced the laser Doppler signal to 0 in seven of eight pigs. Consequently, a blood loss that is of minor importance for the cerebral microcirculation in the normal state may be deleterious to the circulation when combined with high CSF pressure.