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Purpose of Review: This review will examine the recent literature on anesthesia and monitoring techniques in relation to cerebral autoregulation. We will discuss the effect of physiologic and pharmacological factors on cerebral autoregulation alongside its clinical relevance with the help of new evidence., Recent Findings: Intravenous anesthesia, such as combination of propofol and remifentanil, provides best preservation of autoregulation. Among inhaled agents sevoflurane appears to preserve autoregulation at all doses, whereas with other agents autoregulation is impaired in a dose-related manner., Summary: Intraoperative cerebral autoregulation monitoring is an important consideration for the patients with neurologic disease. Transcranial Doppler based static autoregulation measurements appears to be the most robust bedside method for this purpose.

We have examined the cerebrovascular response to carbon dioxide during normotension, sodium nitroprusside (SNP)-induced hypotension and high dose isoflurane-induced hypotension in 10 patients who received a standardized general anaesthetic. Carbon dioxide reactivity was determined by varying PaCO2 between 3.0 and 8.0 kPa and recording simultaneously blood flow velocity from the middle cerebral artery (vmca). The paired vmca-PaCO2 data were analysed using linear regression to determine carbon dioxide reactivity. During hypotension, both high-dose isoflurane and SNP reduced significantly mean absolute (from 17.4 (SEM 2.3) to 13.0 (1.7) and 8.8 (1.3) cm s-1 kPa-1, respectively; P < 0.05) and relative (from 32.5 (3.8) to 23.6 (2.0) and 15.5 (1.3)% kPa-1, respectively; P < 0.05) cerebrovascular reactivity to carbon dioxide. This reduction was greater during SNP-induced hypotension (P < 0.05). We conclude that cerebrovascular reactivity to carbon dioxide was attenuated during isoflurane and SNP-induced hypotension, and that it was better preserved during isoflurane-induced hypotension.

Monitoring of brainstem auditory evoked potentials (BAEP) during neurological surgery can provide useful information. However, in order to interpret intraoperative BAEP changes, it is necessary to delineate the influence of anesthesia, including inhalation agents. In this study, we examined the influence of isoflurane and isoflurane-nitrous oxide anesthesia on BAEP in ten healthy volunteers during normothermic, normocapnic, and normotensive conditions. Isoflurane significantly increased the latencies of peaks III, IV, and V at all end-tidal concentrations studied (1.0%, 1.5%, and 2.0%). Addition of 50% nitrous oxide did not influence these findings. The increase in latencies with isoflurane anesthesia, however, was nonlinear and appeared to plateau after 1.5%. We suggest that during isoflurane anesthesia, an intraoperative increase in peak V latency beyond 1.0 msec is best explained by factors other than direct effects of isoflurane.

Intraoperative monitoring of sensory-evoked potential has been found to be useful in many areas, particularly during scoliosis surgery and neurovascular surgery. However, it remains a complicated technique, devoid of simple interpretation and as such cannot be considered a routine clinical monitor except in large centres with special expertise. Increase in utilization must await improvement in technique and development of strict criteria for interpretation.

The authors measured resting ventilation, the ventilatory response to added CO2, the VD/VT ratio, the rate of carbon dioxide output, and arterial PCO2 in four healthy volunteers, awake and anesthetized with, in order (I) enflurane 0.4 MAC with nitrous oxide 70 per cent, (II) enflurane 1.1 MAC with nitrous oxide 70 per cent, and (III) enflurane 1.1 MAC alone. Enflurane 1.1 MAC reduced ventilation and the response to added CO2 markedly, increased the VD/VT radio, reduced rate of CO2 output, and elevated values of PaCO2 from 41 +/- 1 to 65 +/- 3 mmHg (mean +/- SEM). Enflurane 1.1 MAC with nitrous oxide 70 per cent had similar effects. Enflurane 1.1 MAC with nitrous oxide 70 per cent had similar effects. Enflurane 0.4 MAC with nitrous oxide 70 per cent caused much smaller changes in each measured respiratory variable, increasing PaCO2 values to only 49 +/- 1 mmHg. The results indicate that enflurane 1.1 MAC alone is too potent a depressant of alveolar ventilation to permit spontaneous breathing, but that the "equi-anesthetic" enflurane 0.4 MAC with nitrous oxide 70 per cent may not be. The magnitude of the beneficial respiratory effects of substituting nitrous oxide for an equivalent amount of vapor is substantially greater with enflurane than with either halothane or isoflurane.

Moyamoya disease is a rare neurovascular condition that affects both children and adults. Increasingly these patients present for surgical management to improve the cerebral circulation since medical therapy is essentially ineffective. Because of the precarious cerebral circulation, these patients represent an anaesthetic challenge. In this report we review the pathophysiology of moyamoya disease, summarize our experience with seven patients and discuss the anaesthetic management.