Week 1 - Basic Clinical Monitoring (Neurologic System) Flashcards
What does an EEG do?
Measures electrical potentials differences in the brain
What brain waves do you expect to see while a patient is awake and stable?
Beta waves (HIGH frequency, LOW amplitude)
What waveform in indicative of ischemia in an EEG
Delta waves
Which anesthetic agents decrease EEG waves more? IV or Inhalation anesthetics
Inhalation anesthetics
How would you describe a burst suppression EEG pattern?
Alternating high voltage, mixed frequency, and slow wave activity lasting several seconds
What is unilateral burst suppression indicative of?
Ischemia, brain injury
Why is burst suppression an ideal waveform to have during types of neurosurgery?
It decreases CMRO2, it’s neuro protective
Ex - Carotid endartectomy
What does NIRS measure and how?
Cerebral oxygenation, utilizes Beer-Lambert law
Can detect decrease in CBF in relation to CMRO2
Normal is 60-75%
What artery is monitored most commonly when using a Transcranial Doppler Ultrasonography?
Middle cerebral artery
How does Transcranial Doppler Ultrasonography work?
Emits ultrasound waves to detect hypo/hyper perfusion in the brain
What is a contraindication for a Jugular Bulb Oxygen Venous Saturation sample?
Neck or C spine injury, trauma, coagulopathy
What is an evoked potential and what is the purpose of monitoring them?
Electrical potentials triggered by a stimulus
* can be useful to monitor integrity of neural structures
What level on a BIS monitor is generally associated with adequate anesthesia?
40-60
What does the COVERABCD mnemonic stand for?
Circulation/Color
Oxygen/Oxygen analyzer
Ventilation/Vaporizer
Endotracheal Tube
Review monitors/equipment
Airway
Breathing
Circulation
Drugs
The adult brain comprises of ______ to _____ percent of body weight, but requires ________ to _______ of cardiac output.
2-3% of body weight. Requires 15-20% of cardiac output.
What is the most important goal of clinical monitoring of the CNS?
Identify and rapidly treat ischemia
Does the brain emit electrical waves?
NO, EEG works by measuring DIFFERENCES in electrical potentials in different regions of the brain.
Components of an EEG
Frequency - rate of or duration between impulses
Amplitude - peak to peak measurements in a vertical plane measured in mV
Morphology - Shape
4 common brainwaves and 2 subgroups
Common - alpha, beta, delta, and theta
Sub - gamma - higher order activity, problem solving/analytical thinking
mu - represents synchronous firing at rest
What is the sign of irreversible damage on an EEG?
Electrical standstill
What waveform gives off the most frequency?
Gamma > 40
When would you see theta waves?
Light sleep
What does a TCD (transcranial doppler) measure?
Cerebral blood flow velocities, hypo/hyper perfusion
By what method can cerebral metabolism be measured?
Microdialysis
Which inhalation agents in high doses will you see diffuse delta and theta waveforms?
Desflurane, Isoflurane, and Sevoflurane
When inducing a patient with etomidate or propofol, what EEG pattern suggests the loss of consciousness?
Increased frequency and decreased amplitude of delta waves
General anesthesia has what effect on brainwaves seen on an EEG?
Reduction in high frequency waves, and an increase in low frequency amplitudes. (Decrease frequency, Increase amplitude)
A greater than ______ % decrease in cerebral oxygen saturation can be indicative of ________ during carotid endarterectomy (removing plaque disposed in the carotid arteries)
20%, ischemia
What is a specific limitation associated with TCD (transcranial doppler) monitoring?
Individuals with a thicker temporal bone will impede the doppler waves.
The jugular bulb receives blood drainage from?
Both the left and right cerebral hemispheres. (70% ipsilateral, 30% contralateral)
If ICP is maintained at a normal range (7-15 mmHg), an SjvO2 between ____ and _____ has been found as a good predictor of positive outcomes for traumatic brain injury.
55-75%
A ________ decrease in amplitude or a _________ increase in latency (time necessary for EP to be measured in the brain) is suggestive of _________ ___________
50%, 10%, cerebral ischemia
3 things that can cause reductions in brainwaves
changes in CBF, O2, and glucose delivery.
Which inhaled anesthetic should not be used in epilepsy?
Sevoflurane, potentiates this
Etomidate can cause ________ on induction
Myoclonus (twitching of the muscles)
Propofol offers a __________ __________ ___ ____________ than most IV anesthetics
deeper level of sedation
What 2 IV drugs can produce burst suppression in the brain?
Propofol and Etomidate. These are the only two IV drugs that will do this
With non-depolarizing NMBA, you can expect 4 full twitches with a blockade of less than ____________
65-70% (or less)
3 full twitches = 75%
2 full twitches = 80 %
1 full twitch = 90%
0 twitches = at least 95%
With an increase in ischemia or hypoxia, ______ waves begin to disappear, and there is an appearance of low amplitude ________ waves.
beta, delta
The majority of anesthetic agents ________ neuronal activity and _________ EEG waveforms
inhibit, depress
_______ of cerebral blood flow is venous
70%
What is the purpose of monitoring EP’s intraoperatively?
To guide the surgical strategy and to act as a warning of neurological deficits to prevent irreversible ischemia.
Which peripheral nerves are stimulated most commonly in regard to SSEP monitoring?
Lower extremity –> Posterior tibial, backup – (peroneal nerve located in the popliteal fossa)
Upper extremity –> Median nerve (placed at erbs point, 2-3 cm above clavicle) , backup – (Ulnar nerve)
What are contraindications for motor evoked potentials monitoring?
Patients with pacemakers, spinal or bladder stimulators, epilepsy, metallic foreign body, or a previous craniotomy.
What is the purpose of motor evoked potentials?
They monitor the functional integrity of the motor tracts, particularly in the corticospinal tract.
They use electrical or magnetic stimuli to accomplish this.
Disadvantages to magnetic motor evoked potential monitoring?
Magnetic stimulation produces intense heat, this needs to dissipate at safe levels, causing prolonged procedures.
Magnetic stimulation can also produce high intensity noise, so ear protection is recommended.
What 2 things should be done to produce the best results when using brainstem auditory evoked potential monitoring?
- Place the transducer after the head is positioned, this reduces the likelihood of causing abrasive injury to the ear canal
- Ensure that the auditory canal is free of any build up of cerumen or fluid.
What test is used to assess auditory hair cell function?
Otoacoustic emissions (OAEs)
(Not an EP)
What is the purpose of an electrocochleography (ECochG)?
Used to evaluate or verify blood supply to the cochlea
What is the purpose of brainstem auditory evoked potentials? (BAEP’s)
Used to monitor the entire auditory pathway from the distal auditory nerve to the midbrain, inadvertently allowing monitoring of basic brainstem functions.
