EEG And ICP Monitoring Flashcards
How much energy does the cerebrum require?
3-5 ml O2/min/100g tissue
Normal Cerebral Blood Flow is ___.
50 ml/min/100 g tissue 750 ml/min for brain Delivers 150 ml O2/min
O2 extraction from cerebral blood flow is:
35-50%
What is the equation for Cerebral Perfusion Pressure (CPP)?
CPP = MAP - ICP
Cerebral blood flow is:
- Tightly regulated except post-trauma
Cerebral blood flow stays around ____, as long as MAP is between _____ mm Hg.
50 ml/100g/min , 50-100
CBF is reduced by
- Head injury 2. Intracranial hypertension 3. Hypotension 4. Hyperventilation 5. Vasospasm
Ways of directly monitoring ICP:
- Ventricular catheters 2. Subdural/subarachnoid bolts 3. Epidural transducers 4. Intraparenchymal fiber optic devices
What is the Monroe-Kellie hypothesis:
The skull is a fixed volume. If one or more of these components increases, ICP rises: - Blood - CSF - Brain
ICP determined by:
- Brain mass (80%) - Blood flow (10%) - CSF volume (10%)
ICP monitoring physical set up
- Connection of device to transducer 2. Watertight fluid interface 3. Deformation of transducer membrane converted to electrical pulsations and amplified and displayed as a waverform
Zeroing of ICP Monitors requires:
- Zeroing to room air - Catheter tip transducers only zeroed prior to insertion - External transducers can be zeroed anytime
Indication for ICP monitoring:
-GCS < 8 (or higher if CT of concern {Hematoma, Edema, Contussion, etc}) -Normal CT with GCS 40 2. Posturing 3. SBP < 90 mm Hg -Sedation precluding clinical assessment
ICP monitoring is useful in:
- Head injury 2. Poor grade SAH 3. Intracerebral hematoma 4. Meningitis 5. Stroke 6. Allows calculation of CPP 7. Info on intracerebral compliance
ICP Values:
Normal: 7-15 mm Hg Abnormal: > 20 mm Hg If > 25 mm Hg, aggressive management indicated
High ICP:
will cause internal or external herniation of the brain, distortion and pressure on cranial nerves and vital neurological centers
When ICP is elevated cerebral perfusion will be:
Impeded and operating conditions difficult or impossible
When brain volume increases
loss of CSF and reduction of venous blood volume act to compensate
Subdural hematoma can lead to:
Tentorial herniation
Hemorrhage can lead to:
Subfalcine herniation
Devices to measure ICP:
What is the Gold Standard of ICP measuring?
Intraventricular drain and transducer b/c you can control ICP by CSF drainage and zero externally
What are the contraindications of intraventricular drain and transducer?
- Bleeding
- Blockage
- Infection risk
- Insertion difficulties
Which ventricle is the intraventricular catheter placed?
Lateral ventricle (frontal horn)
What are the positive points of the intraparenchymal pressure monitor?
- Lower infection risk
- Less risk of hermorrage
- Excellent metrological properties (less drift)
What are the negatives to a intraparenchymal pressure monitor?
- Underestimate very high ICP
- Drift a problem after several days
What are the contraindications of intraparenchymal pressure monitors?
- Intracranial infection
- Coagulopathies
- Severe skull fractures
- Conditions where CFS drainage is necessary
Phase 1 of the ICP Waveform:
P1: Percussion wave (arterial pulsation)
Phase 2 of ICP waveform:
P2: Rebound wave (Intracranial compliance)
Phase 3 of ICP waveform:
P3: Dichrotic wave (venous pulsations)
ICP Management: Decrease brain water w/
- hyperosmolar diuretics (Mannitol w/ intact BBB 0.25 - 1 g/kg)
- Loop diuretics (Lasix)
- Corticosteroids
ICP Management: Reduce CSF Volume by:
- Drainage (Ventricular, lumbar subarachnoid, head elevation)
Auto regulation is impaired by:
- Inhalational anesthetics
- Direct acting vasodilators (Adenosine, Prostacyclin, Ca++ Channel blockers, NTG, Nitroprusside)
Transcranial Doppler (TCD) Ultrasonography:
- Allows CBF velocity measurement (continuous or intermittent)
- Most usefule for vasospasm post subarachnoid hemorrhage
- Vasospasm: increased flow velocity
- Ratio of ICA:MCA flow allows monitoring independent of rising ICP
Continuous Electroencephalogram (EEG) Monitoring:
The summation and recording of postsynaptic potentials from the pyramidal cells of the cerebral cortex; reflects metabolic activity of the brain
EEG is a tracing:
Of voltage fluctuations versus time recorded from electrodes placed over scalp in specific array; represent fluctuating dendritic potentials from superficial cortical layers;
Disadvantages of EEG:
- Required Amplification
- Deep parts of the brain are not well sampled
- Detects cortical dysfunction but rarely discloses its etiology
- Relatively low sensitivty and specificty
- Subject to electrical and physiological artifacts
- Influenced by state of alertness, hypoglycemia, drugs
- Small or deep lesions might not produce an EEG abnormality
- Limited time sampling and spatial sampling
Placement of EEG Electrodes:
- Usually 21 or more
- Spaced at 10 or 20% of distances btwn specified anatomic landmarks
- Odd # of electrodes over left, even over right
Indication for EEG:
- Craniotomy for cerebral aneurysm clipping when a temporary clip is used
- Carotid Endarterectomy (under GA)
- Cardiopulmonary bypass
- Extra cranial-intracranial bypass procedures
- Pharmacologic depression of brain for “cerebral protection”
EEG Waveforms: Beta
13 - 30 Hz; Awake and alert (short and frequent)
EEG Waveforms: Alpha
8-13 Hz; closed eyes, relaxed (Tall and frequent)
EEG Waveforms: Theta
4-7 Hz Tall and infrequent (GA)
EEG Waveforms: Delta
0-4 Hz, Deep sleep, deep sedation (Very tall and very infrequent)
EEG Artifacts
- Eye-induced artifacts (includes eye blinks and eye mvmt)
- Gloss kinetic artifacts
- Poor grounding
- IV drips
- Body mvmt
- EKG artifact
EEG Monitors: Continuous Electroencephalography
- BIS algorithm
- Snap
- State entropy/Respone entropy (Datex-Ohmeda algorithm)
- SEDLine monitor (Patient state analyzer)
- A-Line AEP Monitor/2 (EEG plus AEP) and Cerebral State Monitor (EEG Only)
- EEG and Auditory Evoked Potentials
- Narcotrend (EEG Monitor)
The EEG is NOT
A predictor of mvmt under GA
EEG Monitoring: Activation
High frequency, Low voltage; Light Anesthesia, Surgical stimulation
EEG Monitoring: Depression
Low frequency, high voltage; Deep anesthesia, cerebral compromise
Agents That Activate
- Subanesthetic inhalationals
- Low dose barbiturates/benzodiazepines
- Small doses of etomidate
- N2O
- Ketamine
- Mild hypercapnia
- Stimulation (surgical)
- Early hypoxia
Agents That Depress
- 1-2 MAC gases
- Barbiturates/propofol/etomidate
- Narcotics- dose dependent
- Hypocapnia
- Hypothermia
- Late hypoxia
