RE5: Chapter 18: Clinical Monitoring III Flashcards
What is ICP directly r/t?
Intrathoracic pressure and changes dramatically with coughing or increased intrathoracic pressures.
What is a normal ICP range?
1-15 mmHg
A jugular venous oxygenation (SjvO2) that ranges between ____% to ___% has been found to be a reasonable predictor of positive outcomes for traumatic brain injury.
55% to 75%
What is an electrogencephalogram (EEG)?
A measurement of differences in electrical potentials in groups of neurons between brain regions rather than the brain emitting electrical waves.
It measures how “awake” or metabolically active the brain is during surgery.
What are the basic parameters of an EEG?
Frequency
Amplitude
Shape
Time
What are the 4 common types of brainwaves noted on an EEG?
Alpha
Beta
Delta
Theta
What are common variants or subgroups of waves noted during specific activities?
Gamma
My
Lambda
What types of waves are typically seen with high order activity such as problem solving or analytical thinking?
Gamma waves
The amplitude of the mu wave is about _____ that of the beta wave and is seen more frequently over the motor areas of the brain.
1/2
What types of waves occur in the awake patient and are usually present when staring, reading, or looking at objects for long periods?
Lambda waves
During the awake state, describe the type of waves commonly seen.
High-frequency and low-amplitude beta waves
What can cause depression of EEG activity?
Reduction in cerebral blood flow, oxygen or glucose delivery
With increased ischemia or hypoxia, what waves start to disappear and what waves start to appear?
Beta waves start to disappear and low-amplitude delta waves start to appear on the EEG.
True or False. The EEG can provide information about the cerebral cortex fxn, sub cortical brain, spinal cord and the cranial/peripheral nerves.
FALSE. EEG only provides information about the cerebral cortex function!
What effects do etomidate and propofol cause on the EEG?
They increase the frequency and decrease the amplitude of beta waves. This beta-rhythm EEG correlates with the patient losing consciousness.
Is myoclonus caused by etomidate seen on EEG?
No. EEG frequency decreases as serum levels rise, leading to burst suppression.
What is burst suppression?
An alternated high-frequency activity with 0.5 to several-second periods of electrical suppression.
When is burst suppression typically seen?
With a decrease in cerebral circulation and oxygenation as well as with hypothermia, particularly during CPB.
Why is burst suppression sometimes desirable?
To reduce cerebral oxygen requirements and provide neuroprotective properties. This may be desirable during manipulation of the brain tissues.
What anesthetics can cause burst suppression?
Etomidate
Propofol
Inhalation agents
What is unilateral burst suppression usually indicative of?
Ischemia or injury to the brain
What are CSA and DSA?
Compressed spectral array
Density spectral array
These methods further analyze the EEG
What is the Fourier analysis?
Compressed view of EEG waveforms presented in a 2 or 3 dimensional graph
How does GA affect EEG?
Reduction in high frequency waves and an increase in low-frequency amplitudes
What are the two major variables preventing exact correlation between EEG and anesthetic depth?
- Combination of many different drugs and dosages affecting the EEG in different ways
- Environmental factors and manipulation of the brain intraoperatively
What is the BIS?
Bispectral index monitor. It assesses anesthetic depth based on EEG electrical signals and processes them displaying a number from 0 (no brain activity) to 100 (awake).
What BIS values suggest adequate general anesthesia for surgery?
40-60
What device is the intraoperative gold standard for EEG monitoring?
16- to 32-channel analog EEG monitored by an experienced tech
What is NIRS?
Near-infrared spectroscopy
It is a noninvasive physiologic interpretation of oxygenation by evaluating the transmission and absorption of infrared light in the Hgb in brain tissue in real time.
What three things can NIRS evaluate during anesthesia?
Oxygenation
Blood volume
Motor function monitoring
What are evoked potentials?
Electrical potentials that are measured in response to some type of stimulus.