QEEG changes during cardiopulmonary bypass: relationship to postoperative neuropsychological function

Monitoring the Electroencephalogram During Bypass Procedures

Electroencephalographic monitoring has been performed since the early days of cardiopulmonary bypass. Despite this long experience, the technology has never been widely used for cardiac operations. This review examines the reasons for the limited use and describes technological advances that may alter this pattern.

Electroencephalography as a tool for assessment of brain ischemic alterations after open heart operations

Cardiac surgery is commonly associated with brain ischemia. Few studies addressed brain electric activity changes after on-pump operations. Eyes closed EEG was performed in 22 patients (mean age: 45.2 ± 11.2) before and two weeks after valve replacement. Spouses of patients were invited to participate as controls. Generalized increase of beta power most prominent in beta-1 band was an unambiguous pathological sign of postoperative cortex dysfunction, probably, manifesting due to gamma-activity slowing (“beta buzz” symptom). Generalized postoperative increase of delta-1 mean frequency along with increase of slow-wave activity in right posterior region may be hypothesized to be a consequence of intraoperative ischemia as well. At the same time, significant changes of alpha activity were observed in both patient and control groups, and, therefore, may be considered as physiological. Unexpectedly, controls showed prominent increase of electric activity in left temporal region whereas patients were deficient in left hemisphere activity in comparison with controls at postoperative followup. Further research is needed in order to determine the true neurological meaning of the EEG findings after on-pump operations.

Antithrombin-heparin covalent complex reduces microemboli during cardiopulmonary bypass in a pig model

Transcranial Doppler-detected high-intensity transient signals (HITS) during cardiopulmonary bypass (CPB) surgery have been associated with postoperative neurocognitive dysfunction, suggesting microemboli in the brain could be a contributing factor. HITS occur despite administration of unfractionated heparin (UFH). This study was done to determine whether antithrombin-heparin covalent complex (ATH), a more potent anticoagulant than heparin, can reduce HITS during CPB. In a pig CPB model, ATH, UFH, or UFH + antithrombin (AT) was intravenously administered to female Yorkshire pigs after sternotomy. Twenty minutes later, hypothermic CPB was initiated and continued for 1.25 hours, then normothermia was re-established for 45 minutes. Protamine sulfate was given to neutralize the anticoagulants, and pigs were allowed to recover. HITS were monitored using an arterial flow probe placed over the carotid artery. Compared with UFH (300 or 1000 U/kg), ATH reduced the number of HITS during CPB in a dose-dependent manner. AT (3 mg/kg) + UFH (300 U/kg) resulted in an intermediate HITS rate between UFH and ATH (2 mg/kg in terms of AT). Examination of brain sections for emboli formation confirmed that, similar to HITS, number of thrombi decreased in direct proportion to ATH dosage. These results support the hypotheses that the majority of HITS represent thromboemboli and that ATH reduces emboli formation during CPB.

New developments in cerebral monitoring

In past years, cerebral monitoring was mostly focused around global cerebral perfusion and metabolism monitoring, with the use of transcranial Doppler recordings, jugular bulb oximetry and near-infrared spectroscopy. Most of the recently introduced cerebral monitoring modalities, such as brain tissue partial oxygen tension monitoring and cerebral microdialysis, offer new opportunities by providing regional information on the specific brain area in which the probe is inserted. Ideally, these probes should be inserted in that area of the brain that is most vulnerable to ischaemia, but that may be salvageable with appropriate therapy. In this case, the combination of global and regional cerebral monitoring might offer the best information on which to base patient management. Also, the introduction of more clinically useful, functional neuroimaging techniques may be a valuable adjunct to future neurological critical care management.

La neuro-anesthésie assistée par l’électroencéphalogramme

The electrophysiology can be considered as one of the most reliable assessment of the nervous system function during anaesthesia. For instance, the electroencephalogram (EEG) can be relatively easily simplified and adapted to the current practice of the neuro-anaesthesia or neuro-intensive medicine. Since approximately 10 years, some extremely simplified devices have been introduced, but they allowed only inaccurate assessment because of their too global analysis of the brain function. The monitoring of the true digitised EEG, based on a simplified brain mapping montage combined to the analysis in the frequency and the time domains corresponds to a new investigation tool: the simplified EEG or sEEG, which can be included in our usual monitors or anaesthesia and intensive care machines. This new sort of monitoring could give us valuable information about, first, the control of the peroperative consciousness and the nociceptive or not afferent inputs due to surgical stimulations, and, second, the detection of several particular physiopathologic states during neuro-anaesthesia (brain ischaemia, non-convulsive epilepsy, cerebral protection em leader ). These different theoretical and practical topics are reviewed to try to define the possible preliminary rules of the use of the sEEG.