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Principles I > neurological and level of consciousness monitoring > Flashcards

neurological and level of consciousness monitoring Flashcards

1
Q

what is beneficial of EEG monitoring?

A

detects decreases in perfusion and ultimately ischemia based on reductions in electrical brain activity
*CBF leading to electrical failure is higher than that needed to maintain cell integrity so EEG can pick up on problems before cell integrity is compromised

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2
Q

how does drop in CBF affect EEG results?

A
  • CBF averages 50 but can vary regionally from 30-300 ml/100gm/min
  • CBF
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3
Q

how does drops in CPP affect EEG results?

A

-CPP

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4
Q

what other factors affect EEG results?

A
  • hypothermia
  • tumors
  • anesthesia
  • crucial to maintain same level of anesthesia throughout the surgical procedure
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5
Q

describe EEG monitoring

A
  • monitors electrical signals of the cerebral cortex
  • limited usefulness (no skilled staff, unreliable)
  • 10-20 electrodes on scalp provide electrical signal
  • used during carotid, heart surgery, neurosurgery to assess and monitor cerebral functioning
  • accuracy questioned in prior brain damage
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6
Q

how can EEG reading easily be misinterpreted?

A
  • readings can be misinterpreted since hypothermia, hypercapnia, electrolyte imbalance, volatile anesthetics, all resemble ischemic changes
  • ischemic changes diminish EEG signal by decreasing amplitude and increasing latency
  • focal vs. global changes can be determined by evaluating symmetry of signals
  • anesthesia affects brain symmetrically
  • ischemia affects brain focally and asymmetrically
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7
Q

describe EEG alpha frequency band

A
  • 8-12 Hz
  • major rhythm seen in normal resting relaxed, awake adults
  • attenuates in eye opening and mental exertion
  • moderate sedation
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8
Q

describe EEG beta frequency band

A
  • 13-40 Hz
  • fast activity
  • awake,alert
  • eyes open
  • concentrating
  • anxious or busy thinking
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9
Q

describe EEG theta frequency band

A
  • 4-7 Hz
  • slow activity
  • considered abnormal in awake adults
  • can indicate encephalopathy and subcortical lesions
  • normal in young children
  • general anesthesia
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10
Q

describe EEG delta frequency band

A
  • 1-3 Hz
  • slowest frequency and highest amplitude
  • subcortical lesions, encephalopathy, hydrocephalus
  • normal in babies
  • deep anesthesia
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11
Q

how do barbiturates and benzodiazepines affect EEG?

A

accentuate frequency, then decrease it

*used with seizures

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12
Q

how do opioids affect EEG?

A

slow frequency (increased latency) and increased amplitude

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13
Q

how do inhalation anesthetics affect EEG?

A

both frequency and amplitude are attenuated (decreased) (latency increased)

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14
Q

what is an isoelectric state?

A

flat line EEG associated with anesthesia indicative of decreased metabolic oxygen demands and neuroprotective qualities

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15
Q

define explicit (conscious) memory

A

conscious recall or remembering of previous experiences

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16
Q

define implicit (unconscious) memory

A

movement and ability to respond to commands w/o conscious recall of events
*awareness w/o recall

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17
Q

define awareness

A
  • also known as “recall”

- consciousness (explicit memory) under general anesthesia with subsequent recall of the experienced events

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18
Q

define awake paralysis

A

paralysis of unanesthetized patients occurring when patients are given NMB prior to anesthesia (out of sequence, mislabeling)

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19
Q

what is the anesthetist’s goal?

A

to create balanced anesthesia with hypnosis, immobility, and analgesia

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20
Q

what are the chances of awareness?

A

1 in 14,000

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21
Q

what are risks for awareness?

A
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22
Q

what are the three primary reasons for awareness?

A
  • light anesthesia: inattentive to pt. anesthetic needs (busy with unexpected difficult intubation or low volatile agent) or unable to tolerate therapeutic dose (trauma, pregnancy, hemodynamic instability)
  • pt. requires an increased level of anesthetic (opioids, ETOH, amphetamines, cocaine users)
  • anesthetic delivery problem (vaporizer not calibrated; machine malfunction; non-functioning IV line)
23
Q

what are signs or light anesthesia and possible awareness/recall?

A
  • minor pt. movement
  • tearing and sweating (sympathetic NS outflow)
  • autonomic nervous system changes (tachycardia, HTN, increased RR and depth if SV)
  • none are reliable indicators
  • may dose benzo if “light”
24
Q

what drugs can mask signs of awareness?

A
  • amphetamines, beta blockers, and calcium channel blockers all mask physiological responses to light anesthesia
  • high levels of Vit. C shown to possibly interfere with desired anesthetic effect
  • NMB prevent movement during inadequate anesthesia (watch autonomic NS for increasing HR, BP and tearing or sweating)
25
Q

how can the risk of awareness be reduced?

A
  • pre-medicate with amnestic drug (benzo, scopolamine for less change in hemodynamics)
  • volatile anesthetic at > 0.7 MAC using end-tidal agent level not set level to determine MAC
  • develop awareness policy and educate staff
  • informed consent for high risk patients
  • prompt maintenance/repair of anesthesia equipment
  • counseling for those experiencing awareness
  • use multiple monitors to monitor awareness
26
Q

what measures can be taken to prevent awareness?

A
  • inform patients where anesthesia may be deliberately “light” about risk of awareness (open-heart; trauma; C-section, etc.)
  • avoid complete neuromuscular blockade unless required
  • use adequate concentrations of inhalation/IV agents
  • re-dose induction agent during difficult intubations
  • reverse NMB before discontinuing N2O
  • consider use of amnestic agents like Versed (esp. when anesthesia “light”)
27
Q

how should awareness claims be evaluated?

A
  • speak to pt. and obtain details of event
  • do not deny or downplay event- sympathize
  • 5 questions
    1. what was the last thing you remember before you went to sleep?
    2. what is the first thing you remember after you operation?
    3. can you remember anything in between?
    4. can you remember if you had any dreams during your procedure?
    5. what was the worst thing about your procedure?
  • offer counseling or psychological support
28
Q

describe PSArray

A

patient state analyzer array
-based on patient state index (PSI- quantitative EEG index assessing LOC during sedation or anesthesia)
-proprietary algorithm
-high-resolution 4 channel EEG analysis
+power, frequency, and phase
+analyzes anterior and posterior and bilateral regions of brain
+generates a value

29
Q

what is the optimal range of sedation/anesthesia levels on the PSA array?

A

PSI values b/w 25-50 (green)
-> 50, light hypnotic state, may signal emergence (yellow)
-

30
Q

describe bispectral index system (BIS) monitoring

A

analysis of raw EEG data to derive a formula-driven numerical value indicative of LOC

  • amount of slow wave content (beta ratio)
  • amount of bicoherence of all frequency pairs
  • amount of burst suppression present (EEG slows to random burst of electrical activity) (ratio)
    assumption: slow EEG activity = deep anesthesia
  • insensitive to specific anesthetic or sedative agent
  • allows anesthetist to titrate the anesthetic level
31
Q

what are the benefits of BIS?

A

allows anesthetist to titrate the anesthetic level

  • utilizes less drug to achieve hypnotic state (save $)
  • rapid emergence and recovery from general anesthesia
32
Q

describe BIS indication of awareness

A
  • BIS ranges 0-100 representing LOC
  • electrical impedance and artifact filters
  • general anesthesia is a BIS reading b/w 40-60
  • BIS value of 0 represents flat line EEG
  • BIS value > 70 associated with an increased probability of recall
  • *do not rely on a single monitor to assess awareness
33
Q

what should the signal quality index (SQI) be for BIS to be accurate?

A

90 or above

make sure nothing is affecting signal, sweating? stickers on good?

34
Q

what anesthetic drugs increase BIS value?

A
  • ketamine
  • ephedrine
  • etomidate (excitatory response, myoclonus)
35
Q

what are BIS use for non-awareness reasons?

A
  • reduce hypnotic drug use increasing cost savings
  • more efficient delivery of anesthesia
  • achieve 35-55% faster wake up and extubations
  • improve quality of post-anesthesia recovery
  • reduction in incidence of PONV (less gas use)
  • reduce PACU length of stay, faster discharges
  • pts. more sensitive to hemodynamic effects of anesthesia (elderly population)
  • precise titration of anesthetic (trauma cases requiring reduced levels)
  • monitor sub-clinical seizure activity in ECT
36
Q

what are some arguments against BIS?

A
  • hypothermia can alter BIS value
  • shivering and use of warming blankets alter signal
  • unipolar cautery interferes and interrupts BIS signals
  • ketamine and N2O increase BIS value
  • head trauma may interfere with signal
  • pt. position significantly affects values
  • BIS monitors analyze cortical electrical activity using a sensor on the forehead; memory is considered a biochemical function occurring in the hippocampus
37
Q

describe evoke potentials

A
  • electrical signals produced in response to various stimuli by the nervous system
  • neuronal pathway dysfunction can be identified by various changes to the evoked potential
  • latency, amplitude and site of stimulus are all terms used to describe evoked potentials
  • used especially with neuro and spinal cases
  • send an evoke potential to see if there is a response to stimuli
38
Q

what are the four types of evoked potentials?

A
  • somatosensory (SSEP)
  • motor (MEP)
  • auditory (BAEP)
  • visual (VEP)
39
Q

what are the effects of anesthetics on evoke potential monitoring?

A
  • general anesthetics inhibit neurotransmission of impulses
  • volatile anesthetics produce a dose-dependent increase in SSEP latency and decrease in amplitude (slows down)
  • IV anesthetics affect SSEP
40
Q

describe motor evoked potentials (MEP)

A
  • assess corticospinal tracts that are not monitored by SSEP
  • generally inaccurate, less utilized
  • stimulus above surgical site via transcranial or direct stimulation of spinal cord
  • electrical potentials measured below the surgical site by monitoring nerve or muscle potentials
  • NMB agents interfere with signal
  • anesthesia affects transcranial > direct spinal
  • MEP usefulness is still under discussion
  • EMG monitors motor response to nerve stimulation
  • used to assess facial nerve integrity (facial surgery)
  • avoid NMB when this monitor utilized
41
Q

describe sensory evoked potentials (SSEP)

A
  • assess the integrity of sensory pathway- dorsal column of spinal cord
  • stimulation of peripheral nerve sends electrical signal to brain where electrodes sense response (median/ulnar nerves of arms; posterior tibial nerve of legs)
  • receiving electrodes on scalp near spinal cord
  • damage to pathway will display a decreased signal amplitude and an increased latency
  • volatile agent b/w 0.5-0.7 MAC is optimal (keep low)
42
Q

describe brainstem auditory evoked potentials (BAEP)

A

clicking sends auditory nerve sensory signal

-indicated for surgery in the posterior fossa to assess integrity of CN #8

43
Q

describe cerebral oximetry

A
  • near infrared spectroscopy (NIRS) technology
  • non pulsatile blood (venous blood O2 only)
  • like pulse ox, hgb absorbs light frequencies
  • oxyhgb and deoxyhgb absorb at different frequencies
  • probe on scalp, reflectors capture reflected light in both deep and superficial structures
  • regional sat 25% of baseline indicate possible reduction in cerebral O2
44
Q

what is a reduction in cerebral O2 associated with?

A

-poor neurological outcomes

45
Q

how should a drop in cerebral O2 be treated?

A
  • increase cerebral perfusion pressure > 60 mmHg

- decrease ICP

46
Q

what are indications of cerebral oximetry use?

A
  • cardiac surgery
  • carotid endarterectomy
  • cerebral autoregulation
  • beach chair positions
  • evidence is weak since looking at superficial and not circle of willis
  • not a standard of care
47
Q

what are two key factors to keep adequate cerebral oxygenation?

A
  • maintain perfusion with acceptable BP

- maintain ETCO2 greater than 40 mmHg

48
Q

describe Guedel’s Stage I of anesthesia

A
  • analgesia
  • disorientation
  • no substantial changes in respiration, HR, pupillary activity, reflexes, or muscle tone
49
Q

describe Guedel’s Stage II of anesthesia

A
  • delirium, agitation, and excitement
  • respiration: irregular, breath holding/apnea, gasping
  • reflexes: hyperactive
  • muscle tone: hyperactive; often thrashing extremities
  • during emergence; do not pull ETT or chords will clamp shut!
50
Q

describe Guedel’s Stage III, plane 1

A
  • respirations: regular, nearly normal volume and rate
  • reflexes: eyelid and pharyngeal reflexes eliminated
  • muscle tone: normal to slightly reduced skeletal muscle tone
51
Q

describe Guedel’s Stage III, plane 2

A
  • respirations: regular, volume reduced, and rate increased as anesthetic deepens
  • reflexes: laryngeal reflex eliminated
  • muscle tone: progressively reduced as anesthetic deepens
52
Q

describe Guedel’s Stage III, plane 3

A
  • respirations: regular; volume markedly reduced, rate fast; may not be detectable with common anesthetic techniques but physiologic capacity for respiration with stimulation remains
  • reflexes: carinal reflex eliminated (if cough when ETT hits carina, know you’re in plane 2 or lighter)
  • muscle tone: onset of intercostal muscle paralysis
53
Q

describe Guedel’s Stage III, plane 4

A
  • respirations: intercostal muscle paralysis complete; physiologic capacity for respiration rapidly eliminated as anesthesia continues to deepen
  • reflexes: absent
  • muscle tone: complete intercostal muscle paralysis
54
Q

describe Guedel’s Stage IV

A
  • medullary paralysis (Moribund)
  • progressive CV collapse
  • too deep!!

Principles I (18 decks)

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