Evoked Potentials during Cardiac and Major Vascular Operations

Monitoring cardiac and ascending aortic procedures

Although cardiac and aortic operations have been successfully performed for more than 60 years, the risk of neurologic complications remains high. In particular, the rate of stroke with cardiac operations continues to be significant in the 1%-5% range. Similarly, the risk of stroke with aortic operations remains in the range of 7%-10% despite many years of improving techniques. Because of this persistently high risk, the use of intra-operative neurophysiologic monitoring (IONM) has the potential of improving outcomes. This chapter provides an overview of cardiac/aortic arch procedures from the neurophysiologic standpoint and discusses the roles of different monitoring modalities in detecting injury.

Analyses of the temperature and pH effects on the complexation of magnesium and calcium in human blood plasma: an approach using artificial neural networks

The temperature and pH effects on the equilibrium of a blood plasma model have been studied on the basis of artificial neural networks. The proposed blood plasma was modeled considering two important metals, calcium and magnesium, and six ligands, namely, alanate, carbonate, citrate, glycinate, histidinate and succinate. A large data set has been used to simulate different concentrations of magnesium and calcium as a function of temperature and pH and these data were used for training the neural network. The proposed model allowed different types of analyses, such as the effects of pH on calcium and magnesium concentrations, the competition between calcium and magnesium for ligands and the effects of temperature on calcium and magnesium concentrations. The model developed was also used to predict how the variation of calcium concentration can affect magnesium concentrations. A comparison of neural network predictions against experimental data produced errors of about 3%. Moreover, in agreement with experimental measurements (Wang et al. in Arch. Pathol. 126:947-950, 2002; Heining et al. in Scand. J. Clin. Lab. Invest. 43:709-714, 1983), the artificial neural network predicted that calcium and magnesium concentrations decrease when pH increases. Similarly, the magnesium concentrations are less sensitive than calcium concentrations to pH changes. It is also found that both calcium and magnesium concentrations decrease when the temperature increases. Finally, the theoretical model also predicted that an increase of calcium concentrations will lead to an increase of magnesium concentration almost at the same rate. These results suggest that artificial neural networks can be efficiently applied as a complementary tool for studying metal ion complexation, with especial attention to the blood plasma analysis.

Perioperative multimodality neuromonitoring: an overview

Neurologic damage after cardiac surgery remains an important cause of postoperative morbidity. In addition to a wide variety of procedural risks, patient-specific factors such as the presence of extracranial or intracranial atherosclerotic disease, either alone or together, have a fundamental impact on the risk of brain injury developing after cardiovascular surgery. A variety of neurophysiologic monitoring techniques have been used during cardiovascular surgery in hopes of averting neurologic injury. In this issue of Seminars, the strengths and weaknesses of each are discussed by a group of highly experienced clinical investigators. The ultrasound techniques of epiaortic scanning and continuous transcranial Doppler insonation of large intracranial arteries can alter perfusion management and surgical habits to markedly decrease the delivery of atherosclerotic, lipoidal, and gaseous microemboli to the brain and other vital organs. Cerebral hypoperfusion from unrecognized cerebral venous obstruction, inadequate mean arterial pressure, or hypocapnic cerebral alkalosis can be identified by transcranial near-infrared spectroscopy, electroencephalogram, and sensory evoked potentials. Compromise of spinal cord perfusion during the repair of thoracoabdominal aneurysms may be identified and corrected with the guidance provided by transcranial electric motor-evoked potentials. Quantitative electroencephalogram and auditory evoked potential indices also appear beneficial in producing objective measures of the hypnotic component of anesthesia. These neuromonitoring methods, particularly when used in concert, can improve overall patient outcome and reduce hospital length of stay.