Cognitive impairment is a common consequence of cardiac surgery using cardiopulmonary bypass and embolisation of particulate and gaseous debris is believed to be the most important cause. Using a new generation of transcranial Doppler (TCD) ultrasonography the aim was to quantify gaseous and solid cerebral microemboli during different cardiac surgical procedures and to relate this to cerebral abnormalities identified using magnetic resonance imaging techniques. A substantial reduction in microembolic load was demonstrated with avoidance of cardiopulmonary bypass (CPB). The majority of microemboli detected during cardiac surgical procedure~ were gaseous and use of CPB was associated with a significantly higher proportion of solid microemboli - regarded as potentially more harmful. Reduction or elimination of aortic m~ipulation resulted in a significant reduction in intraoperative cerebral microembolisation with the potential for reduction of postoperative cerebral injury. Microemboli are not' only restricted to the intraoperative period and could be detected postoperatively following aortic valve replacement. Use ofa mechanical prosthesis is associated with significant increases in solid and gaseous microemboli. Functional magnetic resonance imaging (FMRI) performed serially in patients pre- and postoperatively demonstrated a significant overall reduction in taskassociated activation in the postoperative period. However, increased activation in certain regions of interest suggested a compensatory mechanism or adaptive change that may contribute to functional recovery after cerebral injury from microemboli. Then comparing off-pump and on-pump surgery, there was a significant reduction in prefrontal cerebral activation in patients undergoing on-pump surgery but preservation of cerebral activity following off-pump surgery. These changes in activation correlate with intraoperative microembolic load and were persistent at longer-term follow-up. Magnetic resonance spectroscopy of the frontal white matter showed no significant reductions in N-acetyl aspartate (NAA) levels - a marker of neuronal integrity. This was reassuring indicating that neuroaxonal damage is an unlikely explanation of the functional cerebral changes observed with FMRI. Careful assessment and further understanding of the pathophysiology of postoperative neurological injury would allow the development of targeted neuroprotective strategies aiming to reduce the rate and severity of this important complication
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:487140 |
| Date | January 2006 |
| Creators | Abu-Omar, Yasir |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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