[Cerebral monitoring]

Several studies have shown that most anaesthesia-related critical incidents are due to human error. There is evidence that cerebral monitoring procedures may be of value for an early detection of cerebral hypoxia or ischaemia. Monitoring of central nervous physiology includes both evaluation of systemic parameters like arterial blood pressure, arterial PO2, PCO2, and temperature, and more specific parameters for the assessment of central nervous system function and intracranial haemodynamics. It has been suggested that parameters from the processed EEG may be used as an indicator for depth of anaesthesia. Even though anaesthetic-induced EEG alterations are unspecific, depth of anaesthesia may be assessed quantitatively by combined monitoring of general parameters and processed EEG. Interpretation of the EEG signals has to take into account that critical events like hypoxia or cerebral ischaemia results in EEG patterns similar to those seen under deep anaesthesia. Sensory evoked potentials are frequently used to monitor specific neural pathways that are at risk during surgery. Different pathways may be tested using different trigger modalities (somatosensory, auditory, visual). Changes in latencies and amplitudes of primary components may indicate impaired conduction in the pathway monitored. For operations in which monitoring of evoked responses is indicated, the anaesthetic technique should have minimal impact on latencies and amplitudes. In patients, cerebral blood flow can be monitored only at discrete time intervals. In contrast, non-invasive transcranial Doppler sonography may provide continuous information on intracranial haemodynamics. Relative changes in cerebral blood flow velocity have been shown to correlate closely to changes in cerebral blood flow. Cerebral perfusion pressure can be calculated by monitoring of intracranial pressure in patients with compromised intracranial compliance.