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Intraoperative Monitoring During Extracorporeal Circulation

  • U. Ruberti
  • M. Cenzato
  • A. Ducati
  • E. Fava
  • A. Landi
  • P. Giorgetti
  • R. Trazzi
Chapter

Abstract

Modern anesthesiology has allowed surgeons to extend surgical treament to areas once considered beyond approach. The technique of cardiopulmonary bypass, associated with hypothermia, makes it possible to maintain a patient in extreme conditions; i.e., the patient is kept alive for the whole duration of a surgical procedure, with the heart at a standstill, with the lungs not breathing, and with a mean arterial blood pressure of 40 mmHg or below. The conditions necessary for heart surgery are allowed by hypothermia which lowers the metabolism of the body to facilitate survival in these conditions. This is particularly important for the central nervous system, where a temperature of 20–25 °C can effectively compensate for the reduction of blood pressure and prevent neural damage. On the other hand, it has been reported2,5,10 that hypothermia may in itself cause neurologic injury. This view, however, is not shared by all authors. An adequate balance is required between hypothermia (a factor offering some protection) and hypotension (a potentially dangerous factor). Neural function should therefore be monitored to verify whether, at specific levels of body temperature and of mean arterial pressure, the ability to respond to external stimuli is preserved. Evoked potentials (EPs) have been useful and reliable for this purpose. Within the central nervous system, the structure most sensitive to ischemia is the cortex. For this reason, the study of the cortical somatosensory response appears to be the best approach to the problem. In the literature a few studies are reported 1,7,9 concerning evoked potential monitoring during cardiopulmonary bypass. These papers mainly describe subcortical and early cortical responses, the brainstem auditory evoked potential (BAEP) and the short latency somatosensory evoked potential (SSEP). It appeared that a detailed study of the entire cortical evoked potential, including late waves, might help early identification of cortical dysfunction. Cortical SEPs are made up of a primary component, the N 20–P 25 complex, and late waves. The N 20–P 25 complex (often called simply N 20) is related to the arrival of the afferent sensory volley at the primary somatosensory cortex. All the later components are of cortical origin. The sensitivity of the primary component to anesthetic drugs is less than the sensitivity of later components, as these are mediated by a multisynaptic pathway. Our experience with intraoperative SEP monitoring during carotid surgery indicated that a change affecting late waves was the first sign of cortical ischemia, seen well before either prolongation of the N 20 latency or reduction of the SEP primary complex. In this study we tried to define the limits of EP changes seen when both body temperature (T) and blood pressure (BP) were modified in parallel.

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References

  1. 1.
    Aren C, Badr G, Feddersen K, Radegran K (1985) Somatosensory evoked potentials and cerebral metabolism during cardiopulmonary bypass with special reference to hypotension induced by prostacyclin infusion. J Thorac Cardiovasc Surg 90: 73–79PubMedGoogle Scholar
  2. 2.
    Brunberg JA, Reilly EL, Doty DB (1974) Central nervous system consequences in infants of cardiac surgery using deep hypothermia and circulatory arrest. Circulation [Suppl] 11: 60–68Google Scholar
  3. 3.
    Coles JG, Taylor MJ, Pearce JM, Lowry NJ, Stewart DJ, Trusler GA, Williams WG (1984) Cerebral monitoring of somatosensory evoked potentials during profoundly hypothermic circulatory arrest. Circulation 70: 196–202Google Scholar
  4. 4.
    Colon EJ, de Weerd AW (1986) Long-latency somatosensory evoked potentials. J Clin Neurophysiol 3: 279–296PubMedCrossRefGoogle Scholar
  5. 5.
    Egerton N, Egerton WS, Kay JH (1963) Neurologic changes following profound hypothermia. Ann Surg 157: 366–374PubMedCentralPubMedCrossRefGoogle Scholar
  6. 6.
    Grundy BL (1982) Monitoring of sensory evoked potentials during neurosurgical operations: methods and applications. Neurosurgery 11: 556–575PubMedCrossRefGoogle Scholar
  7. 7.
    Hume AL, Durkin MA (1986) Central and spinal somatosensory conduction times during hypothermic cardiopulmonary bypass and some observations on the effects of Fentanyl and Isoflurane anesthesia. Electroencephalogr Clin Neurophysiol 65: 46–58PubMedCrossRefGoogle Scholar
  8. 8.
    Kopf GS, Hume AL, Durkin MA, Hammond GL, Hashim SW, Geha AS (1985) Measurement of central somatosensory conduction time in patients undergoing cardiopulmonary bypass: an index of neurologic function. Am J Surg 149: 445–448PubMedCrossRefGoogle Scholar
  9. 9.
    Markand OM, Warren CH, Moorthy SS, Stoelting RK, King RD (1984) Monitoring of multimodality evoked potentials during open heart surgery under hypothermia. Electroencephalogr Clin Neurophysiol 59: 432–440PubMedCrossRefGoogle Scholar
  10. 10.
    Wright JS, Hicks RG, Newman DC (1979) Deep hypothermia arrest: observations on later development in children. J Thorac Cardiovasc Surg 77: 466468Google Scholar

Copyright information

© Springer-Verlag Wien 1988

Authors and Affiliations

  • U. Ruberti
    • 1
  • M. Cenzato
    • 2
  • A. Ducati
    • 2
  • E. Fava
    • 3
  • A. Landi
    • 2
  • P. Giorgetti
    • 1
  • R. Trazzi
    • 4
  1. 1.Institutes of General and Cardiovascular SurgeryUniversity of MilanoItaly
  2. 2.NeurosurgeryUniversity of MilanoItaly
  3. 3.II Chair of AnesthesiologyUniversity of MilanoItaly
  4. 4.CNR Institute of Muscle Physiology, c/oUniversity of MilanoItaly

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