Neuro Monitoring Flashcards
detects decreases in perfusion and ultimately ischemia based on reductions in electrical brain activity
EEG
CBF average
50 mL/100 gm/min but can vary regionally from 30-300 mL/100 gm/min
CBF < 25 mL/100 gm/min =
slowing of EEG
CBF ≈ 15-20 mL/100 gm/min =
isoelectric EEG (internal cell)
CBF < 10 mL/100 gm/min =
↓ cell integrity, irreversible injury
CPP of this will show EEG changes
CPP < 50 torr
CPP of this shows ↓ cell integrity, irreversible damage
CPP < 25 tor
what does an EEG monitor?
electrical signals of the cerebral cortex
Readings of EEG can be misinterpreted with what 4 pathologies?
hypothermia,
hypercapnia,
electrolyte imbalance,
volatile anesthetic agents resemble ischemic ∆s
affects brain focally and asymmetrically
ischemia
affects brain symmetrically
anesthesia
Major rhythm seen in normal
resting relaxed awake adults. stops in eye
opening and mental exertion.
alpha 8-12 htz
Fast activity, alert, eyes open,
concentrating, anxious or busy thinking.
Beta - 13-40 Hz
Slow activity, considered abnormal
in awake adults. Can indicate encephalopathy,
subcortical lesions, Normal in young children.
Theta - 4-7 Hz
slowest frequency and highest
amplitude. Subcortical lesions and
encephalopathy, hydrocephalus. Normal in babies.
Delta - 1-3 Hz
Anesthetic effects on EEG Barbiturates and Benzodiazepines
accentuate frequency then
decrease it.
Opioids Anesthetic effects on EEG
slow frequency, increase amplitude
Inhalation anesthetics effects on EEG
both frequency and amplitude are reduced
flat line EEG associated with anesthesia
indicative of decreased metabolic oxygen demands and neuroprotective qualities.
Isoelectric state:
conscious recall or
remembering exact events of previous experiences
Explicit (conscious) memory
movement and ability
to respond to commands without specific conscious
recall of events (some call awareness w/o recall)
Implicit (unconscious) memory
also known as “recall” is defined as a
consciousness(explicit memory) under general
anesthesia with subsequent recall of the experienced
events
awareness
paralysis of un-anesthetized patients
occurring when patients are given NMB prior to
anesthesia (out of sequence, mislabeling)
Awake paralysis
risk factors for awareness
< 60 y.o., ASA 1-2, female, elective surgery
3 primary reasons for awareness?
- light anesthesia
- pt requires an increased level of anesthetic
- anesthetic delivery problems
Signs of “Light” Anesthesia and possible
awareness/recall [none reliable]
• Minor patient movement • Tearing and sweating • Autonomic nervous system changes –Tachycardia –Hypertension –Increased respiratory rate and depth if spontaneous respiration
drugs that Mask physiological responses to light anesthesia
–Amphetamines
–Beta blockers
–Calcium channel blockers
-NMB
what vitamin interferes with anesthesia levels?
vit C
Reducing the Risks of Awareness Claims
- premedicate with amnestic drugs - benzo, scopalamine
- MAC >.7 monitoring expired
Quantitative EEG index assessing level of
consciousness during sedation or anesthesia
Patient State Analyzer Array PSArray
what regions of brain does PSArray monitor?
Analyzes anterior and posterior and bilateral
regions of the brain
Analysis of raw EEG data to derive a formula-driven
numerical value indicative of level of consciousness
BIS
3 things BIS takes into account?
–Amount of slow wave content (beta ratio)
–Amount of bicoherence of all frequency pairs
–Amount of burst suppression present (ratio)
General anesthesia is a BIS reading of
40-60
BIS value of 0 represents
flat line EEG
BIS value >
70 is associated with
increased probability of
recall
Arguments against relying on BIS
hypothermia shivering unipolar cautery ketamine and N2O head trauma patient position
Electrical signals produced in response to
various stimuli by the nervous system to monitor neuronal pathway
Evoked Potentials
4 types of evoked potentials
somatosensory (SSEP), motor
MEP), auditory (BAEP), and visual (VEP
how t general anesthetics affect Evoked Potential Monitoring
inhibit neurotransmission of impulses
produce a dose-dependent increase
in SSEP latency and decrease in amplitude
volatiles
IV anesthetics affect SSEP ___ inhaled anesthetics
less than
meds that increase SSEP amplitude
Etomidate and Ketamine
have little to no affect on SSEP amplitude
opioids
nitrous affect on SSEP amplitude?
60% decreased SSEP, but had no effect on latency
decrease SSEP
reduction in blood flow
Assesses corticospinal tracts that are not monitored by SSEP
Motor Evoked Potentials (MEP)
Monitors motor response to nerve stimulation.
EMG
Damage to the sensory pathway will display a
decreased
signal amplitude and an increased latency
optimal MAC?
0.5-0.7 MAC
valuable indicators of depth of anesthesia.
The rate, rhythm, and muscles used for respiration
explain ether eye signs
The gaze becomes disconjugate during stage II and becomes congruent again when stage III is entered.
No substantive changes in respiration, heart
rate, pupillary activity, reflexes or muscle
tone.
Stage I: Analgesia and Disorientation
Respiration: irregular, breath holding/apnea,
gasping.
Reflexes: hyperactive.
Muscle Tone: hyperactive, often thrashing
extremities.
Stage II: Delirium, Agitation, and Excitement
Medullary Paralysis (Moribund) Progressive cardiovascular collapse
stage IV
