PMID- 16167223
OWN - NLM
STAT- MEDLINE
DCOM- 20060119
LR  - 20181113
IS  - 1387-1307 (Print)
IS  - 1387-1307 (Linking)
VI  - 19
IP  - 1-2
DP  - 2005 Apr
TI  - Cerebral monitoring in the operating room and the intensive care unit - an 
      introductory for the clinician and a guide for the novice wanting to open a 
      window to the brain. Part II: Sensory-evoked potentials (SSEP, AEP, VEP).
PG  - 77-168
AB  - An evoked potential differs from the EEG mainly in two ways: 1. The EEG is a 
      random, continuous signal, which arises from the ongoing activity of the outer 
      layers of the cortex. An evoked potential is the brain's response to a repetitive 
      stimulus along a specific nerve pathway. 2.EEG signals range from 10-200 
      milliVolt (mV). Evoked potentials are smaller in amplitude (1-5-20 microVolt 
      requiring precise electrode positioning and special techniques (signal averaging) 
      to extract the specific response from the underlying EEG "noise". The technique 
      of signal averaging, as originally described by Dawson in 1954 [69J, has been 
      further developed in computer processing. The technique is now used by applying a 
      stimulus repeatedly--preferably at randomized intervals--and to record the evoked 
      response over the corresponding area of the brain, averaging out mathematically 
      the change over the number of stimuli. Rationale for the use of EPs in the OR and 
      the ICU. Evoked potentials (EPs) serve the following major purposes: 1. 
      Monitoring of the functional integrity of neural structures that may be at risk 
      during, for instance, ECC (extracorporeal circulation) or endarterectomy 
      indicating cerebral hypoxia. 2. Monitoring of the effects of anesthetic agents 
      and other centrally active drugs, which, besides the cortex, affect deeper 
      neuronal structures. 3. Orthopedic cases where the spinal cord is at risk such as 
      Harrington rod insertion and removal. 4. Clamping of the abdominal aortic artery 
      during aneurysmectomy resulting in a potential damage of the lower parts of the 
      spinal cord. 5. Clipping of an intracerebral aneurysm, which may be impeding 
      blood flow to vital cerebral textures. 6. An indicator of cerebral hypoxia when 
      the blood pressure is deliberately lowered. 7. Operation on peripheral nerves and 
      nerve roots to identify early trauma. 8. Monitoring the cerebral function during 
      controlled hypothermia when the EEG becomes flat. 9. Monitoring of the 
      pathophysiological conditions after severe head trauma and the effects of 
      therapy. 10. An intraoperative warning device of unsuspected awareness during 
      light anesthesia when movement is abolished by muscle relaxants and 
      cardiovascular responses are modified by vasoactive drugs. In case of the latter 
      the stimulus is a small electrical potential applied to the skin of the hand. 
      Thereafter, the stimulus travels along the specific nervous pathways inducing (= 
      generating) potential activation at various sites. The generation of potential 
      changes at various sites along the pathway is an index for the integrity of the 
      nerve. Thus, the evoked potential can be considered a neurophysiological response 
      (usually of the cortex) to impulses originating from some externally stimulated 
      sensory nerve. They provide a physiological measure of the functional integrity 
      of the sensory nerve pathway, which can be used as a clinical diagnostic tool as 
      well as for intraoperative monitoring. The evoked potential usually is recorded 
      from the specific cortical area corresponding to the stimulus input. The 
      classification of evoked potentials. Stimulating a sensory nervous pathway 
      induces evoked potentials. If the auditory nerve is stimulated by "clicks" from 
      headphones, it is called the auditory evoked potential (AEP). The early part of 
      the AEP waveform (less than 10 msec) is called the Brainstem Auditory Evoked 
      Potential (BAEP) since it reflects the passing of the impulse through the 
      brainstem. If a nerve on the arm or the leg is stimulated by a small electrical 
      current applied to the overlying skin, it is called the Somatosensory Evoked 
      Potential (SSEP). If, however, the retina is stimulated by means of flicker light 
      or a sudden change in a checkerboard pattern, the evoked potential thus recorded 
      over the corresponding cortical area is called the Visual Evoked Potential (VEP). 
      Evoked potentials are used both as a diagnostic tool and as a monitoring 
      technique. As diagnostic tests, evoked potentials are useful to evaluate 
      neurologic disorders such as: a) multiple sclerosis, b) acoustic nerve tumors, 
      and c) optic neuritis. As a monitoring modality, evoked potentials are used 
      during all surgical procedures, which might compromise part of the brain or the 
      spinal cord.
FAU - Freye, Enno
AU  - Freye E
AD  - Clinics of Vascular Surgery and Renal Transplantation, 
      Heinrich-Heine-University-Dusseldorf, Deichstrasse 3a, 41468 Neuss-Uedesheim, 
      Germany. enno.freye@uni-duesseldorf.de
LA  - eng
PT  - Journal Article
PL  - Netherlands
TA  - J Clin Monit Comput
JT  - Journal of clinical monitoring and computing
JID - 9806357
SB  - IM
MH  - Brain/*physiopathology/surgery
MH  - *Evoked Potentials, Auditory
MH  - *Evoked Potentials, Somatosensory
MH  - *Evoked Potentials, Visual
MH  - Humans
MH  - *Intensive Care Units
MH  - Monitoring, Physiologic/instrumentation/*methods
MH  - *Operating Rooms
EDAT- 2005/09/17 09:00
MHDA- 2006/01/20 09:00
CRDT- 2005/09/17 09:00
PHST- 2005/09/17 09:00 [pubmed]
PHST- 2006/01/20 09:00 [medline]
PHST- 2005/09/17 09:00 [entrez]
AID - 10.1007/s10877-005-0713-y [doi]
PST - ppublish
SO  - J Clin Monit Comput. 2005 Apr;19(1-2):77-168. doi: 10.1007/s10877-005-0713-y.