Official reprint from UpToDate®
www.uptodate.com ©2016 UpToDate®

Neuromonitoring in surgery and anesthesia

Antoun Koht, MD
Tod B Sloan, MD, MBA, PhD
Laura B Hemmer, MD
Section Editors
Jeffrey J Pasternak, MD
Jeremy M Shefner, MD, PhD
Deputy Editor
Marianna Crowley, MD


Electrophysiologic monitoring, or neuromonitoring, is used during surgery to assess the functional integrity of the brain, brain stem, spinal cord, or peripheral nerves. The goal of monitoring is to alert the surgeon and anesthesiologist to impending injury in order to allow modification of management in time to prevent permanent damage. In some cases, neuromonitoring is used to map areas of the nervous system in order to guide management.

Neuromonitoring can include the recording of spontaneous activity (eg, electroencephalogram and spontaneous electromyogram) or evoked response to stimulus (eg, somatosensory evoked potentials, motor evoked potentials, and brainstem auditory evoked potentials). Frequently, multiple techniques are used together in order to increase the utility of monitoring and to overcome limitations of individual techniques [1,2].

Neuromonitoring has become common during many surgical procedures, often replacing intraoperative wake-up testing. Neuromonitoring is performed by a specialized team with specific expertise in the technique that is used. In most instances, no "standard of care" exists for intraoperative neuromonitoring, and techniques are chosen by the surgeon and monitoring team in order to assess or protect structures at risk (table 1).

This topic will present an overview of neuromonitoring techniques, the effects of anesthetic agents on recorded signals, and the strategy for responding to electrophysiological changes.


Electroencephalography (EEG), electromyography (EMG), somatosensory evoked potentials (SSEPs), brainstem auditory evoked potentials (BAEPs), and motor evoked potentials (MEPs) are electrophysiologic monitoring techniques that are commonly used in the operating room to improve surgical decision-making and possibly reduce neurologic complications in both adult and pediatric patients [3-23].


Subscribers log in here

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information or to purchase a personal subscription, click below on the option that best describes you:
Literature review current through: Sep 2016. | This topic last updated: Aug 29, 2016.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2016 UpToDate, Inc.
  1. Weinzierl MR, Reinacher P, Gilsbach JM, Rohde V. Combined motor and somatosensory evoked potentials for intraoperative monitoring: intra- and postoperative data in a series of 69 operations. Neurosurg Rev 2007; 30:109.
  2. Lall RR, Lall RR, Hauptman JS, et al. Intraoperative neurophysiological monitoring in spine surgery: indications, efficacy, and role of the preoperative checklist. Neurosurg Focus 2012; 33:E10.
  3. Jameson LC, Sloan TB. Monitoring of the brain and spinal cord. Anesthesiol Clin 2006; 24:777.
  4. Barkley GL, Baumgartner C. MEG and EEG in epilepsy. J Clin Neurophysiol 2003; 20:163.
  5. Bootin ML. Deep brain stimulation: overview and update. J Clin Monit Comput 2006; 20:341.
  6. Cioni B, Meglio M, Rossi GF. Intraoperative motor evoked potentials monitoring in spinal neurosurgery. Arch Ital Biol 1999; 137:115.
  7. Deletis V. Intraoperative neurophysiology and methodologies used to monitor the functional integrity of the motor system. In: Neurophysiology in Neurosurgery, Deletis V, Shils JL (Eds), Academic Press, New York 2002. p.25.
  8. Harper CM, Daube JR. Facial nerve electromyography and other cranial nerve monitoring. J Clin Neurophysiol 1998; 15:206.
  9. Harper CM. Intraoperative cranial nerve monitoring. Muscle Nerve 2004; 29:339.
  10. Kothbauer KF, Novak K. Intraoperative monitoring for tethered cord surgery: an update. Neurosurg Focus 2004; 16:E8.
  11. Leppanen RE. Intraoperative applications of the H-reflex and F-response: a tutorial. J Clin Monit Comput 2006; 20:267.
  12. López JR. The use of evoked potentials in intraoperative neurophysiologic monitoring. Phys Med Rehabil Clin N Am 2004; 15:63.
  13. Misiaszek JE. The H-reflex as a tool in neurophysiology: its limitations and uses in understanding nervous system function. Muscle Nerve 2003; 28:144.
  14. Sala F, Krzan MJ, Deletis V. Intraoperative neurophysiological monitoring in pediatric neurosurgery: why, when, how? Childs Nerv Syst 2002; 18:264.
  15. Sala F, Lanteri P, Bricolo A. Motor evoked potential monitoring for spinal cord and brain stem surgery. Adv Tech Stand Neurosurg 2004; 29:133.
  16. Shils JL, Tagliati M, Alterman RL. Neurophysiological monitoring during neurosurgery for movement disorders. In: Neurophysiology in neurosurgery, Deletis V, Shils JL (Eds), Academic Press, Boston 2002. p.405.
  17. Holland NR. Intraoperative electromyography. J Clin Neurophysiol 2002; 19:444.
  18. Macdonald DB. Intraoperative motor evoked potential monitoring: overview and update. J Clin Monit Comput 2006; 20:347.
  19. Leppanen RE. Intraoperative monitoring of segmental spinal nerve root function with free-run and electrically-triggered electromyography and spinal cord function with reflexes and F-responses. A position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput 2005; 19:437.
  20. Deletis V, Sala F. Intraoperative neurophysiological monitoring of the spinal cord during spinal cord and spine surgery: a review focus on the corticospinal tracts. Clin Neurophysiol 2008; 119:248.
  21. Deletis V, Sala F. The role of intraoperative neurophysiology in the protection or documentation of surgically induced injury to the spinal cord. Ann N Y Acad Sci 2001; 939:137.
  22. Macdonald DB, Skinner S, Shils J, et al. Intraoperative motor evoked potential monitoring - a position statement by the American Society of Neurophysiological Monitoring. Clin Neurophysiol 2013; 124:2291.
  23. Holdefer RN, MacDonald DB, Skinner SA. Somatosensory and motor evoked potentials as biomarkers for post-operative neurological status. Clin Neurophysiol 2015; 126:857.
  24. Jameson LC, Janik DJ, Sloan TB. Electrophysiologic monitoring in neurosurgery. Anesthesiol Clin 2007; 25:605.
  25. Sloan MA. Prevention of ischemic neurologic injury with intraoperative monitoring of selected cardiovascular and cerebrovascular procedures: roles of electroencephalography, somatosensory evoked potentials, transcranial Doppler, and near-infrared spectroscopy. Neurol Clin 2006; 24:631.
  26. Holland NR. Subcortical strokes from intracranial aneurysm surgery: implications for intraoperative neuromonitoring. J Clin Neurophysiol 1998; 15:439.
  27. Toleikis JR. Electromyography. In: Monitoring the Nervous System for Anesthesiologists and Other Health Care Professionals, Koht A, Sloan TB, Toleikis JR (Eds), Springer, New York 2012. p.137.
  28. López JR. Neurophysiologic intraoperative monitoring of the oculomotor, trochlear, and abducens nerves. J Clin Neurophysiol 2011; 28:543.
  29. Hamilton DK, Smith JS, Sansur CA, et al. Rates of new neurological deficit associated with spine surgery based on 108,419 procedures: a report of the scoliosis research society morbidity and mortality committee. Spine (Phila Pa 1976) 2011; 36:1218.
  30. Maertens de Noordhout A, Born JD, Hans P, et al. Intraoperative localisation of the primary motor cortex using single electrical stimuli. J Neurol Neurosurg Psychiatry 1996; 60:442.
  31. Morota N, Deletis V, Epstein FJ, et al. Brain stem mapping: neurophysiological localization of motor nuclei on the floor of the fourth ventricle. Neurosurgery 1995; 37:922.
  32. Morota N, Deletis V, Lee M, Epstein FJ. Functional anatomic relationship between brain-stem tumors and cranial motor nuclei. Neurosurgery 1996; 39:787.
  33. Kumar A, Bhattacharya A, Makhija N. Evoked potential monitoring in anaesthesia and analgesia. Anaesthesia 2000; 55:225.
  34. Toleikis JR, American Society of Neurophysiological Monitoring. Intraoperative monitoring using somatosensory evoked potentials. A position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput 2005; 19:241.
  35. Banoub M, Tetzlaff JE, Schubert A. Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring. Anesthesiology 2003; 99:716.
  36. Cruccu G, Aminoff MJ, Curio G, et al. Recommendations for the clinical use of somatosensory-evoked potentials. Clin Neurophysiol 2008; 119:1705.
  37. Legatt AD. Mechanisms of intraoperative brainstem auditory evoked potential changes. J Clin Neurophysiol 2002; 19:396.
  38. Simon MV. Neurophysiologic intraoperative monitoring of the vestibulocochlear nerve. J Clin Neurophysiol 2011; 28:566.
  39. Kim HN, Kim YH, Park IY, et al. Variability of the surgical anatomy of the neurovascular complex of the cerebellopontine angle. Ann Otol Rhinol Laryngol 1990; 99:288.
  40. Nadol JB Jr, Levine R, Ojemann RG, et al. Preservation of hearing in surgical removal of acoustic neuromas of the internal auditory canal and cerebellar pontine angle. Laryngoscope 1987; 97:1287.
  41. Thirumala PD, Habeych ME, Crammond DJ, Balzer JR. Neurophysiologic intraoperative monitoring of olfactory and optic nerves. J Clin Neurophysiol 2011; 28:538.
  42. Chi OZ, Field C. Effects of isoflurane on visual evoked potentials in humans. Anesthesiology 1986; 65:328.
  43. Sasaki T, Itakura T, Suzuki K, et al. Intraoperative monitoring of visual evoked potential: introduction of a clinically useful method. J Neurosurg 2010; 112:273.
  44. Kodama K, Goto T, Sato A, et al. Standard and limitation of intraoperative monitoring of the visual evoked potential. Acta Neurochir (Wien) 2010; 152:643.
  45. Wright JE, Arden G, Jones BR. Continuous monitoring of the visually evoked response during intra-orbital surgery. Trans Ophthalmol Soc U K 1973; 93:311.
  46. MacDonald DB, Al-Enazi M, Al-Zayed Z. Vertebral Column Surgery. In: A Practical Approach to Neurophysiologic Intraoperative Monitoring, Husain AM (Ed), Demos Medical Publishing, New York 2008. p.95.
  47. Tamkus A, Rice K. The incidence of bite injuries associated with transcranial motor-evoked potential monitoring. Anesth Analg 2012; 115:663.
  48. Deiner SG, Kwatra SG, Lin HM, Weisz DJ. Patient characteristics and anesthetic technique are additive but not synergistic predictors of successful motor evoked potential monitoring. Anesth Analg 2010; 111:421.
  49. Chen X, Sterio D, Ming X, et al. Success rate of motor evoked potentials for intraoperative neurophysiologic monitoring: effects of age, lesion location, and preoperative neurologic deficits. J Clin Neurophysiol 2007; 24:281.
  50. Sloan TB, Janik D, Jameson L. Multimodality monitoring of the central nervous system using motor-evoked potentials. Curr Opin Anaesthesiol 2008; 21:560.
  51. Leis AA, Zhou HH, Mehta M, et al. Behavior of the H-reflex in humans following mechanical perturbation or injury to rostral spinal cord. Muscle Nerve 1996; 19:1373.
  52. Feyissa AM, Tummala S. Intraoperative neurophysiologic monitoring with Hoffmann reflex during thoracic spine surgery. J Clin Neurosci 2015; 22:990.
  53. Peterson DO, Drummond JC, Todd MM. Effects of halothane, enflurane, isoflurane, and nitrous oxide on somatosensory evoked potentials in humans. Anesthesiology 1986; 65:35.
  54. McPherson RW, Mahla M, Johnson R, Traystman RJ. Effects of enflurane, isoflurane, and nitrous oxide on somatosensory evoked potentials during fentanyl anesthesia. Anesthesiology 1985; 62:626.
  55. Pathak KS, Amaddio MD, Scoles PV, et al. Effects of halothane, enflurane, and isoflurane in nitrous oxide on multilevel somatosensory evoked potentials. Anesthesiology 1989; 70:207.
  56. Vaugha DJ, Thornton C, Wright DR, et al. Effects of different concentrations of sevoflurane and desflurane on subcortical somatosensory evoked responses in anaesthetized, non-stimulated patients. Br J Anaesth 2001; 86:59.
  57. Jäntti V, Sloan T. Anesthesia and intraoperative electroencephalographic monitoring. In: Intraoperative Monitoring of Neural Function, Handbook of Clinical Neurophysiology, Nuwer M. (Ed), Elsevier, New York 2008. p.77.
  58. Sloan TB, Toleikis JR, Toleikis SC, Koht A. Intraoperative neurophysiological monitoring during spine surgery with total intravenous anesthesia or balanced anesthesia with 3% desflurane. J Clin Monit Comput 2015; 29:77.
  59. Hemmer LB, Zeeni C, Bebawy JF, et al. The incidence of unacceptable movement with motor evoked potentials during craniotomy for aneurysm clipping. World Neurosurg 2014; 81:99.
  60. Manninen PH, Lam AM, Nicholas JF. The effects of isoflurane and isoflurane-nitrous oxide anesthesia on brainstem auditory evoked potentials in humans. Anesth Analg 1985; 64:43.
  61. Kalkman CJ, Drummond JC, Ribberink AA, et al. Effects of propofol, etomidate, midazolam, and fentanyl on motor evoked responses to transcranial electrical or magnetic stimulation in humans. Anesthesiology 1992; 76:502.
  62. Logginidou HG, Li BH, Li DP, et al. Propofol suppresses the cortical somatosensory evoked potential in rats. Anesth Analg 2003; 97:1784.
  63. Luo LL, Zhou LX, Wang J, et al. Effects of propofol on the minimum alveolar concentration of sevoflurane for immobility at skin incision in adult patients. J Clin Anesth 2010; 22:527.
  64. Drummond JC, Todd MM, U HS. The effect of high dose sodium thiopental on brain stem auditory and median nerve somatosensory evoked responses in humans. Anesthesiology 1985; 63:249.
  65. Shimoji K, Kano T, Nakashima H, Shimizu H. The effects of thiamylal sodium on electrical activities of the central and peripheral nervous systems in man. Anesthesiology 1974; 40:234.
  66. Ganes T, Lundar T. The effect of thiopentone on somatosensory evoked responses and EEGs in comatose patients. J Neurol Neurosurg Psychiatry 1983; 46:509.
  67. Glassman SD, Shields CB, Linden RD, et al. Anesthetic effects on motor evoked potentials in dogs. Spine (Phila Pa 1976) 1993; 18:1083.
  68. Koht A, Schütz W, Schmidt G, et al. Effects of etomidate, midazolam, and thiopental on median nerve somatosensory evoked potentials and the additive effects of fentanyl and nitrous oxide. Anesth Analg 1988; 67:435.
  69. Schubert A, Licina MG, Lineberry PJ. The effect of ketamine on human somatosensory evoked potentials and its modification by nitrous oxide. Anesthesiology 1990; 72:33.
  70. Kano T, Shimoji K. The effects of ketamine and neuroleptanalgesia on the evoked electrospinogram and electromyogram in man. Anesthesiology 1974; 40:241.
  71. Sloan TB, Ronai AK, Toleikis JR, Koht A. Improvement of intraoperative somatosensory evoked potentials by etomidate. Anesth Analg 1988; 67:582.
  72. Bala E, Sessler DI, Nair DR, et al. Motor and somatosensory evoked potentials are well maintained in patients given dexmedetomidine during spine surgery. Anesthesiology 2008; 109:417.
  73. Mahmoud M, Sadhasivam S, Salisbury S, et al. Susceptibility of transcranial electric motor-evoked potentials to varying targeted blood levels of dexmedetomidine during spine surgery. Anesthesiology 2010; 112:1364.
  74. Tobias JD, Goble TJ, Bates G, et al. Effects of dexmedetomidine on intraoperative motor and somatosensory evoked potential monitoring during spinal surgery in adolescents. Paediatr Anaesth 2008; 18:1082.
  75. Rozet I, Metzner J, Brown M, et al. Dexmedetomidine Does Not Affect Evoked Potentials During Spine Surgery. Anesth Analg 2015; 121:492.
  76. MacDonald DB, Janusz M. An approach to intraoperative neurophysiologic monitoring of thoracoabdominal aneurysm surgery. J Clin Neurophysiol 2002; 19:43.
  77. Pathak KS, Brown RH, Cascorbi HF, Nash CL Jr. Effects of fentanyl and morphine on intraoperative somatosensory cortical-evoked potentials. Anesth Analg 1984; 63:833.
  78. Schubert A, Drummond JC, Peterson DO, Saidman LJ. The effect of high-dose fentanyl on human median nerve somatosensory-evoked responses. Can J Anaesth 1987; 34:35.
  79. Schubert A, Licina MG, Glaze GM, Paranandi L. Systemic lidocaine and human somatosensory-evoked potentials during sufentanil-isoflurane anaesthesia. Can J Anaesth 1992; 39:569.
  80. Chaves-Vischer V, Brustowicz R, Helmers SL. The effect of intravenous lidocaine on intraoperative somatosensory evoked potentials during scoliosis surgery. Anesth Analg 1996; 83:1122.
  81. Sloan TB, Mongan P, Lyda C, Koht A. Lidocaine infusion adjunct to total intravenous anesthesia reduces the total dose of propofol during intraoperative neurophysiological monitoring. J Clin Monit Comput 2014; 28:139.
  82. Kalkman CJ, Drummond JC, Kennelly NA, et al. Intraoperative monitoring of tibialis anterior muscle motor evoked responses to transcranial electrical stimulation during partial neuromuscular blockade. Anesth Analg 1992; 75:584.
  83. Sloan TB. Anesthetics and the brain. Anesthesiol Clin North America 2002; 20:265.
  84. Brodkey JS, Richards DE, Blasingame JP, Nulsen FE. Reversible spinal cord trauma in cats. Additive effects of direct pressure and ischemia. J Neurosurg 1972; 37:591.
  85. Dolan EJ, Transfeldt EE, Tator CH, et al. The effect of spinal distraction on regional spinal cord blood flow in cats. J Neurosurg 1980; 53:756.
  86. Gregory PC, McGeorge AP, Fitch W, et al. Effects of hemorrhagic hypotension on the cerebral circulation. II. Electrocortical function. Stroke 1979; 10:719.
  87. Haghighi SS, Keller BP, Oro JJ, Gibbs SR. Motor-evoked potential changes during hypoxic hypoxia. Surg Neurol 1993; 39:399.
  88. Grundy BL, Jannetta PJ, Procopio PT, et al. Intraoperative monitoring of brain-stem auditory evoked potentials. J Neurosurg 1982; 57:674.
  89. Kitahata LM, Taub A, Sato I. Hyperventilation and spinal reflexes. Anesthesiology 1969; 31:321.
  90. Nakagawa Y, Ohtsuka K, Tsuru M, Nakamura N. Effects of mild hypercapnia on somatosensory evoked potentials in experimental cerebral ischemia. Stroke 1984; 15:275.
  91. CLOWES GH Jr, KRETCHMER HE, McBURNEY RW, SIMEONE FA. The electro-encephalogram in the evaluation of the effects of anesthetic agents and carbon dioxide accumulation during surgery. Ann Surg 1953; 138:558.
  92. Oro J, Haghighi SS. Effects of altering core body temperature on somatosensory and motor evoked potentials in rats. Spine (Phila Pa 1976) 1992; 17:498.
  93. Jacobs MJ, Meylaerts SA, de Haan P, et al. Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair. J Vasc Surg 1999; 29:48.
  94. Sueda T, Okada K, Watari M, et al. Evaluation of motor- and sensory-evoked potentials for spinal cord monitoring during thoracoabdominal aortic aneurysm surgery. Jpn J Thorac Cardiovasc Surg 2000; 48:60.
  95. Meylaerts SA, Jacobs MJ, van Iterson V, et al. Comparison of transcranial motor evoked potentials and somatosensory evoked potentials during thoracoabdominal aortic aneurysm repair. Ann Surg 1999; 230:742.
  96. Seyal M, Mull B. Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord. J Clin Neurophysiol 2002; 19:409.
  97. Nagao S, Roccaforte P, Moody RA. The effects of isovolemic hemodilution and reinfusion of packed erythrocytes on somatosensory and visual evoked potentials. J Surg Res 1978; 25:530.