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TitleA Practical Appr. to Neurophysiologic Intraop. Monitoring - A. Husain (Demos, 2008) WW
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Table of Contents
                            Title Page
Table of Contents
Basic Principles
	1. Introduction to Operating Room
	2. Basic Neurophysiologic Intraoperative Monitoring Techniques
	3. Remote Monitoring
	4. Anesthetic Considerations
	5. Billing, Ethical, and Legal Issues
	6. Buyer's Guide to Monitoring Equipment
Clinical Methods
	7. Vertebral Column Surgery
	8. Spinal Cord Surgery
	9. Lumbosacral Surgery
	10. Tethered Cord Surgery
	11. Selective Dorsal Rhizotomy
	12. Peripheral Nerve Surgery
	13. Cerebellopontine Angle Surgery: Microvascular Decompression
	14. Cerebellopontine Angle Surgery: Tumor
	15. Thoracic Aortic Surgery
	16. Carotid Surgery
	17. Epilepsy Surgery
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Document Text Contents
Page 2

A Practical Approach to

Intraoperative Monitoring

Husain 00 1/17/08 11:50 AM Page i

Page 169

tion of direct muscle activation as twitches by
the anesthesiologist, underestimating the
degree of pharmacologic neuromuscular
blockade. Muscles from the cranial, cervical,
and lumbosacral myotomes have different
susceptibilities to the effects of neuromuscular
blocking agents. In addition, chronically com-
pressed nerves may have enhanced sensitivity
to the effects of neuromuscular blockade. For
these reasons, neuromuscular transmission
should be monitored using repetitive nerve
stimulation from a muscle belonging to the
appropriate myotome for the nerves or roots
considered at risk from surgery.


Intraoperative EMG can be monitored in
the presence of up to 75% neuromuscular
blockade. This is defined as a CMAP response
amplitude to a single supramaximal stimulus
that is more than 25% of its baseline (pre-
anesthesia) value. In practice, it is rare to set
up and test patients prior to induction of anes-
thesia. It is more usual to monitor neuromus-
cular transmission in anesthetized patients
using repetitive nerve stimulation. Less than

75% neuromuscular blockade corresponds to
a decrement of less than 100% over four suc-
cessive supramaximal repetitive nerve stimu-
lations (10) (Figure 9.7). It is easy to monitor
repetitive nerve stimulation from the tibialis
anterior muscles during lumbar spine surgery
because this muscle is routinely used for EMG
monitoring during these cases anyway. The
deep peroneal nerve can be stimulated tran-
scutaneously using needle or surface elec-
trodes at the fibula head. Most EMG
machines used for intraoperative monitoring
will come with repetitive nerve stimulation
software. As long as four CMAP responses
are identifiable from supramaximal repetitive
nerve stimulation at 2 Hz, the degree of neu-
romuscular blockade is sufficiently low to
allow EMG monitoring. (Figure 9.8B and C)
Less than four identifiable CMAP responses
indicates pharmacologic neuromuscular
blockade exceeding 75%, which might lower
the sensitivity of EMG monitoring for the
detection of intraoperative nerve root injury
(Figure 9.8A). The surgeon should be kept
apprised of this and may order reversal of
neuromuscular blockade if it occurs during a
critical phase of surgery.

148 • SECTION I I : Cl in ica l Methods

FIGURE 9.7 Relationship between repetitive nerve stimulation (train of four) and degree of neuromuscu-
lar blockade. Less than 75% neuromuscular blockade is required for EMG monitoring, which corresponds
to less than 25% twitch height and the presence of four twitches on train-of-four repetitive nerve stimula-
tion. [© The Board of Management and Trustees of the British Journal of Anesthesia. Reproduced by per-
mission of Oxford University Press/British Journal of Anesthesia. Viby-Mogensen (10).]

Husain 09 1/17/08 12:00 PM Page 148

Page 170

CHAPTER 9: Lumbosacra l Surger y • 149

FIGURE 9.8 Supramaximal repetitive nerve sur-
face stimulation of the right peroneal nerve at 2
Hz, with CMAP recordings made from needle elec-
trodes within the right tibialis anterior muscle. A.
Early during surgery, only one CMAP response is
visible, indicating greater than 90% pharmacologic
neuromuscular blockade and precluding adequate
EMG monitoring. B and C. Later during surgery,
four CMAP responses are clearly visible; there is
less than 75% pharmacologic neurologic blockade,
which safe for EMG monitoring. The time base
shown is 10 ms/div and the display sensitivity is 0.5



Husain 09 1/17/08 12:00 PM Page 149

Page 337

ultraviolet (UV) protection, 16
upper limb derivations (SEP), 100–101, 101
urethral sphincter function monitoring, 161–162,


vagus nerve, 262, 264
vascular surgeries, 276–277
vascular tumors, 215t. See also tumors of the

cerebellopontine angle
vecuronium, 130
ventilation during anesthesia, 57
ventral posterolateral (VPL) nucleus, 118
vertebral column surgery, 95–116

anatomy of vertebral column in, 95
anesthesia for, 112–113
anterior cervical discotomy and fusion as, 98
anterior spinal release as, 98
baseline readings for, 113
clinical features of disorders in, 97
cortical potentials for, 100–104
decussation and, 100–104, 101
distal nerve disturbances in, 110
electroencephalography (EEG) in, 101
evoked potentials (EP) in, 95
feedback rapidity in, 100
interpretation and warning criteria in,

108–111, 109
lower limb derivations (SEP) for, 101–104,

102, 103, 104t
monitoring techniques in, 99
motor evoked potentials (MEPs) in, 96–115,
muscle potentials in, 106–107, 107, 108
pathologic EP decrements in, 110, 113, 114
peripheral potentials in, 105
posterior decompression as, 99
posterior spinal fusion (SPF) as, 98
preparation, procedure, postprocedure for,

proximal nerve or plexus disturbances in, 110

radiculopathy in, 110
scoliosis in, 96–98
signal-to-noise ratio (SNR), 99–101, 101
somatosensory evoked potentials (SEPs) in,

spinal cord anatomy in, 96
spinal cord blood supply in, 96
spinal cord compromise in, 110–111, 111
spinal potentials in, 105
subcortical potentials in, 104–105
surgical feedback tracing, 113
systemic factors affecting, 109
technical factors affecting, 109–110
transcranial electric stimulation (TES) and,

106–107, 107, 108
upper limb derivations (SEP) for, 100–101,

vertical resolution, 85–86
video-EEG, 287, 289
Viking NIOM stimulator, 106
virtual network computing (VNC), 52
virtual private networks (VPNs), for remote

monitoring, 48–49, 49, 51, 52
voltage-divider rule, amplification, 81, 81

Wada test, 296
Web servers, remote monitoring and, 53–54
widespread anteriorly maximum rhythmic activity

(WAR) in, 272
widespread persistent slow waves (WPS), 272,

Windows-based remote monitoring systems,

45–46, 46, 47
wrist, median neuropathy (carpal tunnel syndrome)

at, 188, 189

X-ray machines, 11, 16

Z-meters, 177

316 ¥ Index

Husain 18 Index 1/17/08 12:09 PM Page 316

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